Astrophysics
New submissions
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New submissions for Wed, 1 Jul 09
- [1] arXiv:0906.5346 [ps, pdf, other]
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Title: Confirming a Population of Hot-Dust Dominated, Star Forming Ultraluminous Galaxies at High-RedshiftAuthors: C.M. Casey (1), S.C. Chapman (1), R.J. Beswick (2), A.D. Biggs (3), A.W. Blain (4), L.J. Hainline (5), R.J. Ivison (6), T. Muxlow (2), I. Smail (7) ((1) IoA Cambridge, (2) Jodrell Bank/Manchester, (3) ESO, (4) Caltech, (5) Maryland, (6) Edinburgh, (7) Durham)Comments: 9 pages, 6 figures; accepted for publication in MNRASSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We identify eight z>1 radio sources undetected at 850um but robustly detected at 70um, confirming that they represent ultraluminous infrared galaxies (ULIRGs) with hotter dust temperatures (T_dust=52+-10 K) than Submillimetre Galaxies (SMGs) at similar luminosities and redshifts. These galaxies share many properties with SMGs: ultra-violet (UV) spectra consistent with starbursts, high stellar masses and radio luminosities. We can attribute their radio emission to star formation since high-resolution MERLIN radio maps show extended emission regions (with half light radii of 2-3kpc), which are unlikely to be generated by AGN activity. These observations provide the first direct confirmation of hot, dusty ULIRGs which are missed by current submillimetre surveys. They have significant implications for future observations from the Herschel Space Observatory and SCUBA2, which will select high redshift luminous galaxies with less selection biases.
- [2] arXiv:0906.5348 [ps, pdf, other]
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Title: The Dark Disk of the Milky WayComments: 11 pages, 6 figures, 1 table; submitted to ApJSubjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter in disk-like configurations that co-rotate with the galaxy. This phenomenon has potentially dramatic consequences for dark matter detection experiments. We utilize focused, high-resolution simulations of accretion events onto disks designed to be Galaxy analogues, and compare the resultant disks to the morphological and kinematic properties of the Milky Way's thick disk in order to bracket the range of co-rotating accreted dark matter. We find that the Milky Way's merger history must have been unusually quiescent compared to median LCDM expectations and therefore its dark disk must be relatively small: the fraction of accreted dark disk material near the Sun is about 20% of the host halo density or smaller and the co-rotating dark matter fraction near the Sun, defined as particles moving with a rotational velocity lag less than 50 km/s, is enhanced by about 30% or less compared to a standard halo model. Such a dark disk could contribute dominantly to the low energy (of order keV for a dark matter particle with mass 100 GeV) nuclear recoil event rate of direct dectection experiments, but it will not change the likelihood of detection significantly. These dark disks provide testable predictions of weakly-interacting massive particle dark matter models and should be considered in detailed comparisons to experimental data. Our findings suggest that the dark disk of the Milky Way may provide a detectable signal for indirect detection experiments, contributing up to about 25% of the dark matter self-annihilation signal in the direction of the center of the Galaxy, lending the signal a noticeably oblate morphology.
- [3] arXiv:0906.5349 [ps, pdf, other]
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Title: Empirical Estimate of Lyman-alpha Escape Fraction in a Statistical Sample of Lyman-alpha EmittersAuthors: Hakim Atek (1), Daniel Kunth (1), Daniel Schaerer (2), Matthew Hayes (2), Jean-Michel Deharveng (3), Goran Ostlin (4), J. Miguel Mas-Hesse (5) ((1) IAP, (2) Observatoire de Geneve, (3) LAM, (4) OKC Stockholm, (5) CSIC-INTA)Comments: 4 pages, 2 figures, submitted to Astronomy and AstrophysicsSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The Lyman-alpha (Lya) recombination line is a fundamental tool for galaxy evolution studies and modern observational cosmology. However, subsequent interpretations are still prone to a number of uncertainties. Besides numerical efforts, empirical data are urgently needed. We empirically estimate the Lyman-alpha escape fraction fesc(Lya) in a statistically significant sample of z ~ 0 - 0.3 galaxies in order to calibrate high-redshift Lyman-alpha observations. An optical spectroscopic follow-up of a sub-sample of 24 Lyman-alpha emitters (LAEs) detected by GALEX at z ~ 0.2-0.3, combined with a UV-optical sample of local starbursts, both with matched apertures, allow us to quantify the dust extinction through Balmer lines, and to estimate the Lyman-alpha escape fraction from the Halpha flux corrected for extinction and the recombination theory. The global escape fraction of Lyman-alpha radiation spans nearly the entire range of values, from 0.5 to 100 %, and fesc(Lya) clearly decreases with increasing nebular dust extinction E(B-V). Several objects show fesc(Lya) greater than fesc(continuum) which may be an observational evidence for clumpy ISM geometry, or for an aspherical ISM. Selection biases and aperture size effects may still exist between z ~ 0.2-0.3 LAEs and local starbursts, which may explain the difference observed for fesc(Lya).
- [4] arXiv:0906.5350 [ps, pdf, other]
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Title: The Palomar Transient Factory: System Overview, Performance and First ResultsAuthors: N.M. Law, S.R. Kulkarni, R.G. Dekany, E.O. Ofek, R.M. Quimby, P.E. Nugent, J. Surace, C.C. Grillmair, J.S. Bloom, M.M. Kasliwal, L. Bildsten, T. Brown, S.B. Cenko, D. Ciardi, E. Croner, S.G. Djorgovski, J.C. van Eyken, A.V. Filippenko, D.B. Fox, A. Gal-Yam, D. Hale, N. Hamam, G. Helou, J.R. Henning, D.A. Howell, J. Jacobsen, R. Laher, S. Mattingly, D. McKenna, A. Pickles, D. Poznanski, G. Rahmer, A. Rau, W. Rosing, M. Shara, R. Smith, D. Starr, M. Sullivan, V. Velur, R.S. Walters, J. ZolkowerComments: 12 pages, 11 figures, 3 tables, submitted to PASPSubjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The Palomar Transient Factory (PTF) is a fully-automated, wide-field survey aimed at a systematic exploration of the optical transient sky. The transient survey is performed using a new 8.1 square degree camera installed on the 48-inch Samuel Oschin telescope at Palomar Observatory; colors and light curves for detected transients are obtained with the automated Palomar 60-inch telescope. PTF uses eighty percent of the 1.2-m and fifty percent of the 1.5-m telescope time. With an exposure of 60-s the survey reaches a depth of approximately 21.3 in g' and 20.6 in R (5 sigma, median seeing). Four major experiments are planned for the five-year project: 1) a 5-day cadence supernova search; 2) a rapid transient search with cadences between 90 seconds and 1 day; 3) a search for eclipsing binaries and transiting planets in Orion; and 4) a 3-pi sr deep H-alpha survey. PTF provides automatic, realtime transient classification and follow up, as well as a database including every source detected in each frame. This paper summarizes the PTF project, including several months of on-sky performance tests of the new survey camera, the observing plans and the data reduction strategy. We conclude by detailing the first 51 PTF optical transient detections, found in commissioning data.
- [5] arXiv:0906.5351 [ps, pdf, other]
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Title: Shrinking the Braneworld: Black Hole in a Globular ClusterSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
Large extra dimensions have been proposed as a possible solution to the hierarchy problem in physics. One of the suggested models, the RS2 braneworld model, makes a prediction that black holes evaporate by Hawking radiation on a short timescale that depends on the black hole mass and on the asymptotic radius of curvature of the extra dimensions. Thus the size of the extra dimensions can be constrained by astrophysical observations. Here we point out that the black hole, recently discovered in a globular cluster in galaxy NGC 4472, places the strongest constraint on the maximum size of the extra dimensions, L < 0.003 mm. This black hole has the virtues of old age and relatively small mass. The derived upper limit is within an order of magnitude of the absolute limit afforded by astrophysical observations of black holes.
- [6] arXiv:0906.5352 [ps, pdf, other]
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Title: Viscous and Resistive Effects on the MRI with a Net Toroidal FieldComments: 29 pages (preprint format), 7 figures; submitted to ApJSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
Resistivity and viscosity have a significant role in establishing the energy levels in turbulence driven by the magnetorotational instability (MRI) in local astrophysical disk models. This study uses the Athena code to characterize the effects of a constant shear viscosity \nu and Ohmic resistivity \eta in unstratified shearing box simulations with a net toroidal magnetic flux. A previous study of shearing boxes with zero net magnetic field performed with the ZEUS code found that turbulence dies out for values of the magnetic Prandtl number, P_m = \nu/\eta, below P_m \sim 1; for P_m \gtrsim 1, time- and volume-averaged stress levels increase with P_m. We repeat these experiments with Athena and obtain consistent results. Next, the influence of viscosity and resistivity on the toroidal field MRI is investigated both for linear growth and for fully-developed turbulence. In the linear regime, a sufficiently large \nu or \eta can prevent MRI growth; P_m itself has little direct influence on growth from linear perturbations. By applying a range of values for \nu and \eta to an initial state consisting of fully developed turbulence in the presence of a background toroidal field, we investigate their effects in the fully nonlinear system. Here, increased viscosity enhances the turbulence, and the turbulence decays only if the resistivity is above a critical value; turbulence can be sustained even when P_m < 1, in contrast to the zero net field model. While we find preliminary evidence that the stress converges to a small range of values when \nu and \eta become small enough, the influence of dissipation terms on MRI-driven turbulence for relatively large \eta and \nu is significant, independent of field geometry.
- [7] arXiv:0906.5353 [ps, pdf, other]
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Title: Simulations of structure formation in interacting dark energy cosmologiesAuthors: Marco Baldi (ITP, Heidelberg & MPA, Garching)Comments: to appear in the proceedings volume of the GGI Dark Energy Conference, Florence, Italy, March 2009Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The evidence in favor of a dark energy component dominating the Universe, and driving its presently accelerated expansion, has progressively grown during the last decade of cosmological observations. If this dark energy is given by a dynamic scalar field, it may also have a direct interaction with other matter fields in the Universe, in particular with cold dark matter. Such interaction would imprint new features on the cosmological background evolution as well as on the growth of cosmic structure, like an additional long-range fifth-force between massive particles, or a variation in time of the dark matter particle mass. We review here the implementation of these new physical effects in the N-body code GADGET-2, and we discuss the outcomes of a series of high-resolution N-body simulations for a selected family of interacting dark energy models, as already presented in Baldi et al. [20]. We interestingly find, in contrast with previous claims, that the inner overdensity of dark matter halos decreases in these models with respect to LCDM, and consistently halo concentrations show a progressive reduction for increasing couplings. Furthermore, the coupling induces a bias in the overdensities of cold dark matter and baryons that determines a decrease of the halo baryon fraction below its cosmological value. These results go in the direction of alleviating tensions between astrophysical observations and the predictions of the LCDM model on small scales, thereby opening new room for coupled dark energy models as an alternative to the cosmological constant.
- [8] arXiv:0906.5354 [ps, pdf, other]
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Title: Gödel-type universes in f(R) gravityComments: 5 pagesSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The f(R) gravity theories provide an alternative way to explain the current cosmic acceleration without a dark energy matter component. If gravity is governed by a f(R) theory a number of issues should be reexamined in this framework, including the violation of causality problem. We examine the question as to whether the f(R) gravity theories permit space-times in which the causality is violated. We show that the field equations of these f(R) gravity theories do not exclude solutions with breakdown of causality for a physically well-motivated perfect-fluid matter content. We demonstrate that every perfect fluid solution of generic $f(R)$ gravity satisfying the stability conditions is necessarily isometric to the G\"{o}del geometry, generalizing therefore a theorem on G\"{o}del-type models, which has been established in the context of general relativity. We also derive an expression for the critical radius $r_c$ (beyond which the causality is violated) which makes apparent that the violation of causality depends on both the f(R) gravity theory and the matter content. We concretely take a recent f(R) gravity theory that is free from singularities of the Ricci scalar and is cosmological viable, and show that this theory accommodates both non-causal and causal G\"{o}del-type solutions.
- [9] arXiv:0906.5355 [ps, pdf, other]
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Title: Exploring the Optical Transient Sky with the Palomar Transient FactoryAuthors: Arne Rau (1,2), Shrinivas R. Kulkarni (2), Nicholas M. Law (2), Joshua S. Bloom (3), David Ciardi (2), George S. Djorgovski (2), Derek B. Fox (4), Avishay Gal-Yam (5), Carl C. Grillmair (2), Mansi M. Kasliwal (2), Peter E. Nugent (6), Eran O. Ofek (2), Robert M. Quimby (2), William T. Reach (2), Michael Shara (7), Lars Bildsten (8), S. Bradley Cenko (3), Andrew J. Drake (2), Alexei V. Filippenko (3), David J. Helfand (9), George Helou (2), D. Andrew Howell (8,10), Dovi Poznanski (3), Mark Sullivan (11) ((1) MPE, (2) Caltech, (3) UC Berkeley, (4) Pennstate, (5) Weizman, (6) LBLN, (7) AMNH, (8) UC Santa Barbara, (9) Columbia, (10) LCOGT, (11) Oxford)Comments: 15 pages, 6 figures, submitted to PASPSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
The Palomar Transient Factory (PTF) is a wide-field experiment designed to investigate the optical transient and variable sky on time scales from minutes to years. PTF uses the CFH12k mosaic camera, with a field of view of 7.9 deg^2 and a plate scale of 1 asec/pixel, mounted on the the Palomar Observatory 48-inch Samuel Oschin Telescope. The PTF operation strategy is devised to probe the existing gaps in the transient phase space and to search for theoretically predicted, but not yet detected, phenomena, such as fallback supernovae, macronovae, .Ia supernovae and the orphan afterglows of gamma-ray bursts. PTF will also discover many new members of known source classes, from cataclysmic variables in their various avatars to supernovae and active galactic nuclei, and will provide important insights into understanding galactic dynamics (through RR Lyrae stars) and the Solar system (asteroids and near-Earth objects). The lessons that can be learned from PTF will be essential for the preparation of future large synoptic sky surveys like the Large Synoptic Survey Telescope. In this paper we present the scientific motivation for PTF and describe in detail the goals and expectations for this experiment.
- [10] arXiv:0906.5357 [ps, pdf, other]
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Title: Mergers and Bulge Formation in Lambda-CDM: Which Mergers Matter?Authors: Philip F. Hopkins (1), Kevin Bundy (1), Darren Croton (2), Lars Hernquist (3), Dusan Keres (3), Sadegh Khochfar (4), Kyle Stewart (5), Andrew Wetzel (1), Joshua D. Younger (3) ((1) Berkeley, (2) Swinburne, (3) CfA, (4) MPE, (5) Irvine)Comments: 18 figures, 25 pages. Submitted to MNRASSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
We use a suite of semi-empirical models to predict galaxy merger rates and contributions to bulge growth as functions of merger mass, redshift, and mass ratio. The models use empirical halo occupation constraints to identify mergers, together with high-resolution simulations to quantify how mergers with different properties contribute to the bulge population. We find good agreement with a variety of observational constraints, and provide fitting functions for merger rates and contributions to bulge growth. We identify several robust conclusions. (1) Major mergers dominate formation and assembly of L* bulges and the spheroid mass density, minor mergers contribute ~30%. (2) This is mass-dependent: bulge formation is dominated by more minor mergers in lower-mass systems. At higher masses, bulges form in major mergers near L*, but subsequently assemble in minor mergers. (3) The minor/major contribution is also morphology-dependent: higher B/T systems form in more major mergers, lower B/T systems form in situ from minor mergers. (4) Low-mass galaxies, being gas-rich, require more major mergers to reach the same B/T as high-mass systems. (5) Absolute merger rates increase with galaxy mass. (6) Predicted rates agree well with observations, but suggest that some morphology-selected samples include contamination from minor mergers. (7) Predicted rates agree with integrated growth in bulge mass with cosmic time, but with factor ~2 uncertainty - half the bulge mass density could come from non-mergers. We consider ~1000 model variations and quantify resulting uncertainties. Conclusions regarding the major/minor contribution to bulge growth are very robust, absolute merger rates have systematic factor ~2 uncertainties.
- [11] arXiv:0906.5358 [ps, pdf, other]
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Title: The Disruption of Giant Molecular Clouds by Radiation Pressure and the Efficiency of Star Formation in GalaxiesComments: 17 pages, 5 figures, submitted to ApJSubjects: Galaxy Astrophysics (astro-ph.GA)
Star formation is slow, in the sense that the gas consumption time is much longer than the dynamical time. It is also inefficient; essentially all star formation in local galaxies takes place in giant molecular clouds (GMCs), but the fraction of a GMC converted to stars is very small, ~5%. In the most luminous starbursts, the GMC lifetime is shorter than the main sequence lifetime of even the most massive stars, so that supernovae can play no role in GMC disruption. We investigate the disruption of GMCs across a wide range of galaxies, from normal spirals to the densest starbursts; we take into account the effects of HII gas pressure, shocked stellar winds, protostellar jets, and radiation pressure produced by the absorption and scattering of starlight on dust grains. In the Milky Way, we find that a combination of three mechanisms, jets, HII gas pressure, and radiation pressure, disrupts the clouds. In more rapidly star forming galaxies such as ``clump'' galaxies at high-redshift, ultra-luminous infrared galaxies (ULIRGs) and submillimeter galaxies, radiation pressure dominates natal cloud distribution. We predict the presence of 10-20 clusters with masses ~10^7 Msun in local ULIRGs such as Arp 220 and a similar number of clusters with M_* ~ 10^8 Msun in high redshift clump galaxies; submillimeter galaxies will have even more massive clusters. We find that the mass fraction of a GMC that ends up in stars is an increasing function of the gas surface density of a galaxy, reaching ~35% in the most luminous starbursts. Furthermore, the disruption of bubbles by radiation pressure stirs the interstellar medium to velocities of ~10 km/s in normal galaxies and to ~100 km/s in ULIRGs like Arp 220, consistent with observations. Thus, radiation pressure may play a dominant role in the ISM of star-forming galaxies.
- [12] arXiv:0906.5361 [ps, pdf, other]
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Title: Reconstructing WIMP Properties in Direct Detection Experiments Including Galactic Dark Matter Distribution UncertaintiesComments: 4+ pages, 2 figuresSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
We present a new method for determining Weakly Interacting Massive Particle (WIMP) properties in future tonne scale direct detection experiments which accounts for uncertainties in the Milky Way (MW) smooth dark matter distribution. Using synthetic data on the kinematics of MW halo stars matching present samples from the Sloan Digital Sky Survey, complemented by local escape velocity constraints, we demonstrate that the local dark matter density can be constrained to approximately 20% accuracy. For low mass WIMPs, we find that a factor of two error in the assumed local dark matter density leads to a severely biased reconstruction of the WIMP spin-independent cross section that is incorrect at the 15-sigma level. We show that this bias may be overcome by marginalizing over parameters that describe the MW potential, and use this formalism to project the accuracy attainable on WIMP properties in future 1 tonne Xenon detectors. Our method can be readily applied to different detector technologies and extended to more detailed MW halo models.
- [13] arXiv:0906.5364 [ps, pdf, other]
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Title: Luminosity functions of LMXBs in Centaurus A: globular clusters versus the fieldAuthors: R. Voss, M. Gilfanov, G.R. Sivakoff, R.P. Kraft, A. Jordan, S. Raychaudhury, M. Birkinshaw, N.J. Brassington, J.H. Croston, D.A. Evans, W.R. Forman, M.J. Hardcastle, W.E. Harris, C. Jones, A.M. Juett, S.S. Murray, C.L. Sarazin, K.A. Woodley, D.M. WorrallComments: 12 pages, Accepted by ApJSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
We study the X-ray luminosity function (XLF) of low mass X-ray binaries (LMXB) in the nearby early-type galaxy Centaurus A, concentrating primarily on two aspects of binary populations: the XLF behavior at the low luminosity limit and comparison between globular cluster and field sources. The 800 ksec exposure of the deep Chandra VLP program allows us to reach a limiting luminosity of 8e35 erg/s, about 2-3 times deeper than previous investigations. We confirm the presence of the low luminosity break in the overall LMXB XLF at log(L_X)=37.2-37.6 below which the luminosity distribution follows a constant dN/d(ln L). Separating globular cluster and field sources, we find a statistically significant difference between the two luminosity distributions with a relative underabundance of faint sources in the globular cluster population. This demonstrates that the samples are drawn from distinct parent populations and may disprove the hypothesis that the entire LMXB population in early type galaxies is created dynamically in globular clusters. As a plausible explanation for this difference in the XLFs, we suggest that there is an enhanced fraction of helium accreting systems in globular clusters, which are created in collisions between red giants and neutron stars. Due to the 4 times higher ionization temperature of He, such systems are subject to accretion disk instabilities at approximately 20 times higher mass accretion rate, and therefore are not observed as persistent sources at low luminosities.
- [14] arXiv:0906.5366 [ps, pdf, other]
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Title: Is $w \neq -1$ evidence for a dynamical dark energy equation of state ?Comments: 5 pages, 2 figuresSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Current constraints on the dark energy equation of state parameter, $w$, are expected to be improved by more than one order of magnitude in the next decade. If $|w-1| \gsim 0.01$ around the present time, but the dark energy dynamics is sufficiently slow, it is possible that future constraints will rule out a cosmological constant while being consistent with a time-independent equation of state parameter. In this paper, we show that although models with such behavior can be constructed, they do require significant fine-tuning. Therefore, if the observed acceleration of the Universe is induced by a dark energy component, then finding $w \neq -1$ would, on its own, constitute very strong evidence for a dynamical dark energy equation of state.
- [15] arXiv:0906.5367 [ps, pdf, other]
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Title: Analytical computation of the off-axis Effective Area of grazing incidence X-ray mirrorsComments: 12 pages, 11 figures, accepted for publication in "Astronomy & Astrophysics", section "Instruments, observational techniques, and data processing"Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE)
Focusing mirrors for X-ray telescopes in grazing incidence are characterized in their performances by the imaging quality and by the effective area. Even though the on-axis effective area is assumed in general to characterize the collecting power of an X-ray optic, the telescope capability of imaging extended X-ray sources is also determined by the variation of the effective area with the off-axis angle. The complex task of designing optics for future X-ray telescopes comprises detailed computations of the imaging quality and of the effective area on and off-axis. Due to their apparent complexity, both aspects have been, so far, treated along with ray-tracing routines. Although this approach has been widely exploited and proven as effective, it would be also attractive to regard the same problem from an analytical viewpoint. In this paper we thereby focused on devising out analytical solutions to compute the off-axis effective area of double-reflection X-ray mirrors. We have found useful analytical formulae for the off-axis effective area of a double-reflection mirror in double cone approximation, requiring only a numerical integration and the standard routines to calculate the X-ray coating reflectivity for a given incidence angle. Algebraic expressions are provided for the mirror geometric area, as a function of the off-axis angle. Finally, the results of the analytical computations presented here are also validated by a comparison with the corresponding predictions of a ray-tracing code.
- [16] arXiv:0906.5368 [ps, pdf, other]
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Title: The Infrared Nuclear Emission of Seyfert Galaxies on Parsec Scales: Testing the Clumpy Torus modelsAuthors: Cristina Ramos Almeida, Nancy A. Levenson, Jose Miguel Rodriguez Espinosa, Almudena Alonso Herrero, Andres Asensio Ramos, James T. Radomski, Chris Packham, R. Scott Fisher, Charles M. TelescoComments: 26 pages, 8 figures, 9 tables. Accepted for publication in ApJSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We present subarcsecond resolution mid-infrared (mid-IR) photometry in the wavelength range from 8 to 20 micron of eighteen Seyfert galaxies, reporting high spatial resolution nuclear fluxes for the entire sample. We construct spectral energy distributions (SEDs) that the AGN dominates adding near-IR measurements from the literature at similar angular resolution. The IR SEDs of intermediate-type Seyferts are flatter and present higher 10 to 18 micron ratios than those of Seyfert 2. We fit the individual SEDs with clumpy torus models using the in-house-developed BayesClumpy tool. The models reproduce the high spatial resolution measurements. Regardless of the Seyfert type, even with high spatial resolution data, near- to mid-IR SED fitting poorly constrains the radial extent of the torus. For the Seyfert 2, we find that edge-on geometries are more probable than face-on views, with a number of clouds along equatorial rays of N = 5-15. The 10 micron silicate feature is generally modeled in shallow absorption. For the intermediate-type Seyferts, N and the inclination angle of the torus are lower than those of the Seyfert 2 nuclei, with the silicate feature appearing in weak emission or absent. The columns of material responsible for the X-ray absorption are larger than those inferred from the model fits for most of the galaxies, which is consistent with X-ray absorbing gas being located within the dust sublimation radius whereas the mid-IR flux arises from an area farther from the accretion disc. The fits yield both the bolometric luminosity of the intrinsic AGN and the torus integrated luminosity, from which we derive the reprocessing efficiency of the torus. In the models, the outer radial extent of the torus scales with the AGN luminosity, and we find the tori to be confined to scales less than 5 pc.
- [17] arXiv:0906.5370 [pdf]
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Title: Globular Clusters and Satellite Galaxies: Companions to the Milky WayComments: 3 pages, published in Mercury vol. 38, No. 2, page 24. See this http URL for a full colour version with figuresSubjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Our Milky Way galaxy is host to a number of companions. These companions are gravitationally bound to the Milky Way and are stellar systems in their own right. They include a population of some 30 dwarf satellite galaxies (DSGs) and about 150 globular clusters (GCs). Here we discuss the relationship between GCs and DSGs using an interactive 3D model of the Milky Way.
- [18] arXiv:0906.5377 [ps, pdf, other]
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Title: Galactic C and S Stars as Guidelines for Magellanic Cloud AGB StarsComments: 4 pages, 3 figures. Proceeding of the IAU Symposium 256: The Magellanic System: Stars, Gas, and Galaxies. It is available online at this http URLJournal-ref: 2009, in: The Magellanic System: Stars, Gas, and Galaxies, eds. Jacco Th. van Loon and Joana M. Oliveira, IAUS 256 (CUP), P-4Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
The study of the evolutionary properties of Asymptotic Giant Branch stars still presents unresolved topics. Progress in the theoretical understanding of their evolution is hampered by the difficulty to empirically explain key physical parameters like their luminosity, mass loss rate and chemical abundances. We are performing an analysis of Galactic AGB stars trying to find constraints for these parameters. Our aim is of extending this analysis to the AGB stars of the Magellanic Clouds and of the Dwarf Spheroidal Galaxies using also mid-infrared observations from the Antarctic telescope IRAIT. AGB sources from the Magellanic Clouds will be fundamental in our understanding of the AGB evolution because they are all at a well defined distance (differently from the Galactic AGBs). Moreover, these sources present different values of metallicity: this fact should permit us of examining in a better way their evolutionary properties comparing their behaviour with the one from Galactic sources.
- [19] arXiv:0906.5382 [pdf, other]
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Title: Spontaneous non-steady magnetic reconnection within the solar environmentComments: 29 pages, 10 figuresSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
This work presents a 2.5-dimensional simulation study of the instability of current-sheets located in a medium with a strong density variation along the current layer. The initial force-free configuration is observed to undergo a two-stage evolution consisting of an abrupt regime transition from a slow to a fast reconnection process leading the system to a final chaotic configuration. Yet, the onset of the fast phase is not determined by the presence of any anomalous enhancement in plasma's local resistivity, but rather is the result of a new mechanism discovered in Lapenta (2008)* and captured only when sufficient resolution is present. Hence, the effects of the global resistivity, the global viscosity and the plasma beta on the overall dynamics are considered. This mechanism allowing the transition from slow to fast reconnection provides a simple but effective model of several processes taking place within the solar atmosphere from the high chromosphere up to the low corona. In fact, the understanding of a spontaneous transition to a self-feeding fast reconnection regime as well as its macroscopic evolution is the first and fundamental step to produce realistic models of all those phenomena requiring fast (and high power) triggering events (* Lapenta G. 2008, Phys. Rev. Lett., 100, 235001).
- [20] arXiv:0906.5395 [pdf, other]
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Title: Contribution of Unresolved Point Sources to the Diffuse X-ray Background below 1 keVComments: Accepted for publication in ApJ; 27 pages, 8 figuresSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We present here the analysis of X-rays point sources detected in several observations available in the XMM-Newton public archive. We focused, in particular, on energies below 1 keV, which are of particular relevance to the understanding of the Diffuse X-ray Background. The average field of all the exposures is 0.09 deg^-2. We reached an average flux sensitivity of 5.8x10^-16 erg s^-1 cm^-2 in the soft band (0.5-2.0 keV) and 2.5x10^-16 erg s^-1 cm^-2 in the very soft band (0.4-0.6 keV). In this paper we discuss the logN-logS results, the contribution to the integrated X-ray sky flux, and the properties of the cumulative spectrum from all sources. In particular, we found an excess flux at around 0.5 keV in the composite spectrum of faint sources. The excess seems to be a general property of all the fields observed suggesting an additional class of weak sources is contributing to the X-ray emission at these energies. Combining our results with previous investigations we have also quantified the contribution of the individual components of the diffuse X-ray Background in the 3/4 keV band.
- [21] arXiv:0906.5423 [ps, pdf, other]
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Title: Measuring spin of a supermassive black hole at the Galactic centre -- Implications for a unique spinComments: 5 pages, 3 figures, submitted to MNRAS LETTERSubjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We determine the spin of a supermassive black hole in the context of discseismology by comparing newly detected quasi-periodic oscillations (QPOs) of radio emission in the Galactic centre, Sagittarius A* (Sgr A*), as well as infrared and X-ray emissions with those of the Galactic black holes. We find that the spin parameters of black holes in Sgr A* and in Galactic X-ray sources have a unique value of $\approx 0.44$ which is smaller than the generally accepted value for supermassive black holes, suggesting evidence for the angular momentum extraction of black holes during the growth of supermassive black holes. Our results demonstrate that the spin parameter approaches the equilibrium value where spin-up via accretion is balanced by spin-down via the Blandford-Znajek mechanism regardless of its initial spin. We anticipate that measuring the spin of black holes by using QPOs will open a new window for exploring the evolution of black holes in the Universe.
- [22] arXiv:0906.5424 [ps, pdf, other]
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Title: Carbon abundance in Small Magellanic Cloud planetary nebulae through Advanced Camera for Surveys prism spectroscopy: constraining stellar evolution at low metallicityComments: The Astrophysical Journal, in pressSubjects: Solar and Stellar Astrophysics (astro-ph.SR); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We perform near ultraviolet ACS prism spectroscopy of 11 Small Magellanic Cloud (SMC) planetary nebulae (PNe) with the main aim of deriving the abundance of carbon. The analysis of the ACS spectra provide reliable atomic carbon abundances for all but a couple of our targets; ionic C^(2+) abundances are calculated for all target PNe. With the present paper we more than double the number of SMC PNe with known carbon abundances, providing a good database to study the elemental evolution in low- and intermediate-mass stars at low metallicity. We study carbon abundances of Magellanic Cloud PNe in the framework of stellar evolution models and the elemental yields. Constraining SMC and LMC stellar evolutionary models is now possible with the present data, through the comparison of the final yields calculated and the CNO abundances observed. We found that SMC PNe are almost exclusively carbon rich, and that for the most part they have not undergone the hot-bottom burning phase, contrary to half of the studied LMC PNe. The yields from stellar evolutionary models with LMC and SMC metallicities broadly agree with the observations. In particular, evolutionary yields for M$_{\rm to}<3.5 {\rm M}_{\odot}$ well encompass the abundances of round and elliptical PNe in the SMC. We found that the carbon emission lines are major coolants for SMC PNe, more so than in their LMC counterparts, indicating that metallicity has an effect on the physics of PNe, as predicted by Stanghellini et al. (2003).
- [23] arXiv:0906.5434 [ps, pdf, other]
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Title: Observing the Roots of Solar Coronal Heating - in the ChromosphereComments: 14 pages, 5 figures, accepted for publication in ApJ lettersSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
The Sun's corona is millions of degrees hotter than its 5,000 K photosphere. This heating enigma is typically addressed by invoking the deposition at coronal heights of non-thermal energy generated by the interplay between convection and magnetic field near the photosphere. However, it remains unclear how and where coronal heating occurs and how the corona is filled with hot plasma. We show that energy deposition at coronal heights cannot be the only source of coronal heating, by revealing a significant coronal mass supply mechanism that is driven from below, in the chromosphere. We quantify the asymmetry of spectral lines observed with Hinode and SOHO and identify faint but ubiquitous upflows with velocities that are similar (50-100 km/s) across a wide range of magnetic field configurations and for temperatures from 100,000 to several million degrees. These upflows are spatio-temporally correlated with and have similar upward velocities as recently discovered, cool (10,000 K) chromospheric jets or (type II) spicules. We find these upflows to be pervasive and universal. Order of magnitude estimates constrained by conservation of mass and observed emission measures indicate that the mass supplied by these spicules can play a significant role in supplying the corona with hot plasma. The properties of these events are incompatible with coronal loop models that only include nanoflares at coronal heights. Our results suggest that a significant part of the heating and energizing of the corona occurs at chromospheric heights, in association with chromospheric jets.
- [24] arXiv:0906.5440 [ps, pdf, other]
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Title: GRB Afterglow Polarimetry: Past, Present and FutureAuthors: Stefano Covino (INAF / Brera Astronomical Observatory)Comments: Proceedings of the conference "The coming of age of X-ray polarimetry", Rome, Italy, 27-30 April 2009Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Gamma-ray bursts and their afterglows are thought to be produced by an ultrarelativistic jet. One of the most important open questions is the outflow composition: the energy may be carried out from the central source either as kinetic energy (of baryons and/or pairs), or in electromagnetic form (Poynting flux). While the total observable flux may be indistinguishable in both cases, its polarization properties are expected to differ markedly. The later time evolution of afterglow polarization is also a powerful diagnostic of the jet geometry. Again, with subtle and hardly detectable differences in the output flux, we have distinct polarization predictions.
- [25] arXiv:0906.5441 [ps, pdf, other]
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Title: Sounding stellar cycles with Kepler - I. Strategy for selecting targetsComments: accepted for publication in MNRASSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
The long-term monitoring and high photometric precision of the Kepler satellite will provide a unique opportunity to sound the stellar cycles of many solar-type stars using asteroseismology. This can be achieved by studying periodic changes in the amplitudes and frequencies of the oscillation modes observed in these stars. By comparing these measurements with conventional ground-based chromospheric activity indices, we can improve our understanding of the relationship between chromospheric changes and those taking place deep in the interior throughout the stellar activity cycle. In addition, asteroseismic measurements of the convection zone depth and differential rotation may help us determine whether stellar cycles are driven at the top or at the base of the convection zone. In this paper, we analyze the precision that will be possible using Kepler to measure stellar cycles, convection zone depths, and differential rotation. Based on this analysis, we describe a strategy for selecting specific targets to be observed by the Kepler Asteroseismic Investigation for the full length of the mission, to optimize their suitability for probing stellar cycles in a wide variety of solar-type stars.
- [26] arXiv:0906.5442 [ps, pdf, other]
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Title: Exomoon simulationsComments: 5 pages, 2 figures with 9 figure panels, accepted by EM&PSubjects: Earth and Planetary Astrophysics (astro-ph.EP)
We introduce and describe our newly developed code that simulates light curves and radial velocity curves for arbitrary transiting exoplanets with a satellite. The most important feature of the program is the calculation of radial velocity curves and the Rossiter-McLaughlin effect in such systems. We discuss the possibilities for detecting the exomoons taking the abilities of Extremely Large Telescopes into account. We show that satellites may be detected also by their RM effect in the future, probably using less accurate measurements than promised by the current instrumental developments. Thus, RM effect will be an important observational tool in the exploration of exomoons.
- [27] arXiv:0906.5444 [ps, pdf, other]
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Title: Molecular Gas Disk Structures around AGNsComments: 15 pages, 12 figures, accepted by Astrophysical JournalSubjects: Galaxy Astrophysics (astro-ph.GA)
We present new high resolution numerical simulations of the ISM in a central R ~32 parsecs region around a supermassive black hole at a galactic center. Three-dimensional hydrodynamic modeling of the ISM (Wada & Norman 2002) with the nuclear starburst now includes tracking of the formation of molecular hydrogen out of the neutral hydrogen phase. In a quasi equilibrium state, mass fraction of H2 is about 0.4 (total H2 mass is ~1.5 10^6 Msun) of the total gas mass for the uniform far UV (FUV) with G_0 = 10. The gas forms an inhomogeneous disk, whose scale-height becomes larger in the outer region. H2 forms a thin nuclear disk in the inner ~ 5 pc, which is surrounded by molecular clouds swelled up toward h < 10 pc. The velocity field of the disk is highly turbulent in the torus region, whose velocity dispersion is ~ 20 km/s on average. Average supernova rate (SNR) of ~ 5 10^-5/yr is large enough to energize these structures. Gas column densities toward the nucleus larger than 10^22 cm^-2 are observed if the viewing angle is smaller than \theta_v ~ 50 deg from the edge-on. However, the column densities are distributed over almost two orders of magnitude around the average for any given viewing angle due to the clumpy nature of the torus. For a stronger FUV (G_0 =100), the total H2 mass in an equillibrium is only slightly smaller (~ 0.35). Finally the morphology and kinematics of the circumnuclear molecular gas disks emerging from our models is similar to that revealed by recent near infrared observations using VLTI/Keck.
- [28] arXiv:0906.5448 [ps, pdf, other]
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Title: Performance of the Camera of the MAGIC II TelescopeAuthors: D. Borla Tridon, F. Goebel, D. Fink, W. Haberer, J. Hose, C.C. Hsu, T. Jogler, R. Mirzoyan, R. Orito, O. Reimann, P. Sawallisch, J. Schlammer, T. Schweizer, B. Steinke, M. Teshima, for the MAGIC CollaborationComments: 4 pages, to be presented at 31st ICRC 2009Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)
MAGIC comprises two 17m diameter IACTs to be operated in stereo mode. Currently we are commissioning the second telescope, MAGIC II. The camera of the second telescope has been equipped with 1039 pixels of 0.1-degree diameter. Always seven pixels are grouped in a hexagonal configuration to form a cluster. This modular design allows easier control and maintenance of the camera. The pixel sensors are high quantum efficiency photomultiplier tubes (PMTs) from Hamamatsu (superbialkali type, QE ~ 32% at the peak wavelength) that we operate at rather low gain of 30 k. This allows us to also perform extended observations under moderate moonlight. The system of two MAGIC telescopes will at least double the sensitivity compared to MAGIC I and also will allow us to lower the energy threshold.Here we will report the performances of the Camera of the second MAGIC telescope.
- [29] arXiv:0906.5449 [ps, pdf, other]
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Title: New extended atomic data in cool star model atmospheres - Using Kurucz's new iron data in MAFAGS-OS modelsComments: 5 pages, 6 figures, to be publishged on A&A LettersSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
Context. Cool star model atmospheres are a common tool for the investigation of stellar masses, ages and elemental abundance composition. Theoretical atmospheric models strongly depend on the atomic data used when calculating them. Aims. We present the changes in flux and temperature stratification when changing from iron data computed by R.L. Kurucz in the mid 90s to the Kurucz 2009 iron computations. Methods. MAFAGS-OS opacity sampling atmospheres were recomputed with Kurucz 2009 iron atomic data as implemented in the VALD database by Ryabchikova. Temperature stratification and emergent flux distribution of the new version, called MAFAGS-OS9, is compared to the former version and to solar flux measurements. Results. Using the Kurucz line lists converted into the VALD format and new bound-free opacities for Mg i and Al i leads to changes in the solar temperature stratification by not more than 28 K. At the same time, the calculated solar flux distribution shows significantly better agreement between observations and theoretical solar models. These changes in the temperature stratification of the corresponding models are small, but nevertheless of a magnitude that affects stellar parameter determinations and abundance analysis.
- [30] arXiv:0906.5464 [ps, pdf, other]
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Title: Twisted flux tube emergence from the convection zone to the corona II: Later statesComments: 31 pages, 12 figures, accepted in ApJSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
3D simulations of magnetic flux emergence are carried out in a computational domain spanning the upper layers of the convection zone to the lower corona. We use the Oslo Staggered Code to solve the full MHD equations with non-grey and NLTE radiative transfer and thermal conduction along the magnetic field lines. In this paper we concentrate on the later stages of the simulations and study the evolution of the structure of the rising flux in the upper chromosphere and corona, the interaction between the emerging flux and the weak coronal magnetic field initially present, and the associated dynamics.
The flux tube injected at the bottom boundary rises to the photosphere where it largely remains. However, some parts of the flux tube become unstable and expand in patches into the upper chromosphere. The flux rapidly expands towards the corona, pushing the coronal and transition region material aside, lifting and maintaining the transition region at heights greater than 5 Mm above the photosphere for extensive periods of time. The pre-existing magnetic field in the corona and transition region is perturbed by the incoming flux and reoriented by a series of high Joule heating events. Low density structures form in the corona while at later times a high density filamentary structure appears in the lower part of the expanding flux. The dynamics of these and other structures is discussed. While Joule heating due to the expanding flux is episodic, it increases in relative strength as fresh magnetic field rises and becomes energetically important in the upper chromosphere and corona at later times. Chromospheric, transition region and coronal lines are computed and their response to the perturbation caused by the expanding emerging flux is discussed. - [31] arXiv:0906.5476 [pdf]
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Title: Cassini/VIMS hyperspectral observations of the HUYGENS landing site on TitanAuthors: S. Rodriguez (AIM), S. Le Mouélic (LPGN), C. Sotin (LPGN), H. Clénet (DTP), R. N. Clark, B. Buratti (JPL), R. H. Brown (LPL), T. B. Mccord, P. D. Nicholson, K. H. Baines (JPL)Journal-ref: Planetary and Space Science 54 (2006) 1510-1523Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Titan is one of the primary scientific objectives of the NASA ESA ASI Cassini Huygens mission. Scattering by haze particles in Titan's atmosphere and numerous methane absorptions dramatically veil Titan's surface in the visible range, though it can be studied more easily in some narrow infrared windows. The Visual and Infrared Mapping Spectrometer (VIMS) instrument onboard the Cassini spacecraft successfully imaged its surface in the atmospheric windows, taking hyperspectral images in the range 0.4 5.2 ?m. On 26 October (TA flyby) and 13 December 2004 (TB flyby), the Cassini Huygens mission flew over Titan at an altitude lower than 1200 km at closest approach. We report here on the analysis of VIMS images of the Huygens landing site acquired at TA and TB, with a spatial resolution ranging from 16 to14.4 km/pixel. The pure atmospheric backscattering component is corrected by using both an empirical method and a first-order theoretical model. Both approaches provide consistent results. After the removal of scattering, ratio images reveal subtle surface heterogeneities. A particularly contrasted structure appears in ratio images involving the 1.59 and 2.03 ?m images north of the Huygens landing site. Although pure water ice cannot be the only component exposed at Titan's surface, this area is consistent with a local enrichment in exposed water ice and seems to be consistent with DISR/Huygens images and spectra interpretations. The images show also a morphological structure that can be interpreted as a 150 km diameter impact crater with a central peak.
- [32] arXiv:0906.5480 [ps, pdf, other]
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Title: VLT optical observations of the isolated neutron star RX J0420.0-5022Authors: R. P. Mignani (UCL-MSSL), C. Motch (CNRS, Universite' de Strasbourg, Observatoire Astronomique), F. Haberl (MPE), S. Zane (UCL-MSSL), R. Turolla (University of Padua), A. Schwope (Astrophysikalisches Institut Potsdam)Comments: 9 pages, 9 postscript figures, accepted for publication in Astronomy & AstrophysicsSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
X-ray observations performed with ROSAT led to the discovery of 7 radio-silent isolated neutron stars (INSs) which are detected only through the relatively dim and purely thermal X-ray emission from the cooling star surface. A few of these INSs (a.k.a. X-ray Dim INSs, or XDINSs) have been also detected at optical wavelengths where they seem to feature thermal spectra. Optical studies of XDINSs thus play a crucial role in mapping the temperature distribution on the neutron star surface and in investigating the existence of an atmosphere around the neutron star. The aim of this work is to investigate the optical identification of the XDINS RX J0420.0-5022, tentatively proposed by Haberl et al. (2004) based on VLT observations. We re-analysed the original observations of Haberl et al. to assess the detection significance of the proposed counterpart and we performed deeper VLT observations aiming at a higher confidence detection. With a ~2 sigma detection significance and a re-computed flux of B=27.52+/-0.61, we can not rule out that the proposed counterpart was spurious and produced by the halo of a very bright nearby star. While we could not detect the proposed counterpart in our deeper VLT observations, we found evidence for a marginally significant (~3.9 sigma) detection of a similarly faint object (B= 27.5+/-0.3), ~ 0.5" north of it and coincident with the updated Chandra position of RX J0420.0-5022. Interestingly, the angular separation is consistent with the upper limit on the RX J0420.0-5022 proper motion (Motch et al. 2009), which suggests that we might have actually detected the Haberl et al. proposed counterpart. From the flux of the putative RX J0420.0-5022 counterpart we can rule out a > 7 optical excess with respect to the extrapolation of the XMM-Newton spectrum.
- [33] arXiv:0906.5487 [ps, pdf, other]
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Title: Fluorescence emission induced by extensive air showers in dependence on atmospheric conditionsComments: Submitted to the 31th ICRC, Lodz, Poland, 2009Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
Charged particles of extensive air showers (EAS), mainly electrons and positrons, initiate the emission of fluorescence light in the Earth's atmosphere. This light provides a calorimetric measurement of the energy of cosmic rays. For reconstructing the primary energy from an observed light track of an EAS, the fluorescence yield in air has to be known in dependence on atmospheric conditions, like air temperature, pressure, and humidity. Several experiments on fluorescence emission have published various sets of data covering different parts of the dependence of the fluorescence yield on atmospheric conditions. Using a compilation of published measurements, a calculation of the fluorescence yield in dependence on altitude is presented. The fluorescence calculation is applied to simulated air showers and different atmospheric profiles to estimate the influence of the atmospheric conditions on the reconstructed shower parameters.
- [34] arXiv:0906.5493 [ps, pdf, other]
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Title: Accretion disks around massive stars: Hydrodynamic structure, stability and dust sublimationComments: 23 pages, 8 figures, accepted by ApJ, For full version see this http URLSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
We investigate the structure of accretion disks around massive protostar applying steady state models of thin disks. The thin disk equations are solved with proper opacities for dust and gas taking into account the huge temperature variation along the disk. We explore a wide parameter range concerning stellar mass, accretion rate, and viscosity parameter \alpha . The most essential finding is a very high temperature of the inner disk. For e.g. a 10 M_sun protostar and an accretion rate of 10^-4 M_sun/yr, the disk midplane temperature may reach almost 10^5 K. The disk luminosity in this case is about 10^4 L_sun and, thus, potentially higher than that of a massive protostar. We motivate our disk model with similarly hot disks around compact stars. We calculate a dust sublimation radius by turbulent disk self-heating of more than 10AU, a radius, which is 3 times larger than caused by stellar irradiation. We discuss implications of this result on the flashlight effect and the consequences for the radiation pressure of the central star. In difference to disks around low mass protostars our models suggest rather high values for the disk turbulence parameter \alpha close to unity. However, disk stability to fragmentation due to thermal effects and gravitational instability would require a lower \alpha value. For \alpha = 0.1 we find stable disks out to 80AU. Essentially, our model allows to compare the outer disk to some of the observed massive protostellar disk sources, and from that, extrapolate on the disk structure close to the star which is yet impossible to observe.
- [35] arXiv:0906.5495 [ps, pdf, other]
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Title: Interferometric imaging of carbon monoxide in comet C/1995 O1 (Hale-Bopp): evidence for a strong rotating jetAuthors: D. Bockelée-Morvan, F. Henry, N. Biver, J. Boissier, P. Colom, J. Crovisier, D. Despois, R. Moreno, J. WinkComments: 20 pages, 26 figures. Accepted for publication in Astronomy & AstrophysicsSubjects: Earth and Planetary Astrophysics (astro-ph.EP)
Observations of the CO J(1-0) 115 GHz and J(2-1) 230 GHz lines in comet C/1995 O1 (Hale-Bopp) were performed with the IRAM Plateau de Bure interferometer on 11 March, 1997. The observations were conducted in both single-dish (ON-OFF) and interferometric modes with 0.13 km s-1 spectral resolution. Images of CO emission with 1.7 to 3" angular resolution were obtained. The ON-OFF and interferometric spectra show a velocity shift with sinusoidal time variations related to the Hale-Bopp nucleus rotation of 11.35 h. The peak position of the CO images moves perpendicularly to the spin axis direction in the plane of the sky. This suggests the presence of a CO jet, which is active night and day at about the same extent, and is spiralling with nucleus rotation. The high quality of the data allows us to constrain the characteristics of this CO jet. We have developed a 3-D model to interpret the temporal evolution of CO spectra and maps. The CO coma is represented as the combination of an isotropic distribution and a spiralling gas jet, both of nucleus origin. Spectra and visibilities (the direct output of interferometric data) analysis shows that the CO jet comprises ~40% the total CO production and is located at a latitude ~20 degrees North on the nucleus surface. Our inability to reproduce all observational characteristics shows that the real structure of the CO coma is more complex than assumed, especially in the first thousand kilometres from the nucleus. The presence of another moving CO structure, faint but compact and possibly created by an outburst, is identified.
- [36] arXiv:0906.5497 [ps, pdf, other]
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Title: Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger ObservatoryAuthors: The Pierre Auger CollaborationSubjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.
- [37] arXiv:0906.5503 [ps, pdf, other]
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Title: Search for an extended emission around blazars with the MAGIC telescopeComments: Contribution to the 31st ICRC, Lodz, Poland, July 2009Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
Very high energy gamma rays coming from extra-galactic sources can interact with intergalactic radiation fields. This process may result in electromagnetic cascades with the following cycle: the production of electron-positron pairs and then secondary gamma-rays due to inverse Compton scattering. Since electrons and positrons will be scattered in the intergalactic magnetic field, under certain conditions their radiation may be redirected towards the observer. Thus one can anticipate that the secondary gamma-ray emission may produce an apparent extended halo around the source.
MAGIC is an Imaging Atmospheric Cerenkov Telescope located on Canary island of La Palma at Roque de los Muchachos Observatory (2200 m.a.s.l). Various source sizes and extended emission profiles within $1^\circ$ diameter have been studied by using dedicated Monte Carlo simulations for the MAGIC telescope. We present results of the study of a possible extended emission for Mrk 421 and Mrk501 done with the MAGIC telescope. - [38] arXiv:0906.5507 [ps, pdf, other]
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Title: M-Band Spectra of Dust Embedded Sources at the Galactic CenterComments: 23 pages, 9 figures, Accepted for publication in ApJSubjects: Galaxy Astrophysics (astro-ph.GA)
The goal of the present paper is to investigate the circumstellar material around the brightest dust-enshrouded sources in the central stellar cluster of the Milky Way. Observations have been carried out at the European Southern Observatory's Very Large Telescope on Paranal, Chile. We have used the long wavelength (LWS3) low resolution (LR) spectroscopic mode of the ISAAC camera at the VLT in the spectral range of the M filter from 4.4micron to 5.1micron. The use of a slit width of 0.6" implied a spectral resolution of R=l/Dl=800 (Dv=375 km/s). These observations resulted in M-band spectra of 15 bright sources in the central stellar cluster of the Milky Way. In addition to gaseous 12^CO (4.666 micron) and 13^CO (4.77 micron) vibration-rotational absorptions, we detect a strong absorption due to a mixture of polar and apolar CO ice (centered at 4.675 micron). In the shorter wavelength absorption wing there is an absorption feature due to XCN at 4.62 micron. The XCN absorption is strongest toward the M2 supergiant IRS7. We find that the extinctions due to material traced by the CO ice and the CO gas absorptions may be of comparable importance. Using the spectra of IRS2L and IRS16C we perform a first order correction of the line of sight absorption due to CO-ice and 13^CO gas. In combination with published hydrogen number density estimates from sub-mm CO(7-6) and FIR [OI] line data we obtain gas masses of the circumstellar shells of the order of 10^-3 and 10^-2 solar masses. This implies that in future spectra taken at high spectral and angular resolution the bright and dust embedded Galactic Center sources should show a substantial line absorption due to source intrinsic absorption.
- [39] arXiv:0906.5511 [ps, pdf, other]
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Title: Oscillation Phenomena in the disk around the massive black hole Sagittarius A*Comments: 5 pages, 3 figures, submitted to MN LetterSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
We report the detection of radio QPOs with structure changes using the Very Long Baseline Array (VLBA) at 43 GHz.
We found conspicuous patterned changes of the structure with P = 16.8, 22.2, 31.4, & 56.4 min, roughly in a 3:4:6:10 ratio. The first two periods show a rotating one-arm structure, while the P = 31.4 min shows a rotating 3-arm structure, as if viewed edge-on. At the central 50 microasec the P = 56.4 min period shows a double amplitude variation of those in its surroundings.
Spatial distributions of the oscillation periods suggest that the disk of SgrA* is roughly edge-on, rotating around an axis with PA = -10 degree. Presumably, the observed VLBI images of SgrA* remain several features of the black hole accretion disk of SgrA* in spite of being obscured and broadened by scattering of surrounding plasma. - [40] arXiv:0906.5516 [ps, pdf, other]
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Title: A high-order Godunov scheme for global 3D MHD accretion disks simulations. I. The linear growth regime of the magneto-rotational instabilitySubjects: Earth and Planetary Astrophysics (astro-ph.EP)
We employ the PLUTO code for computational astrophysics to assess and compare the validity of different numerical algorithms on simulations of the magneto-rotational instability in 3D accretion disks. In particular we stress on the importance of using a consistent upwind reconstruction of the electro-motive force (EMF) when using the constrained transport (CT) method to avoid the onset of numerical instabilities. We show that the electro-motive force (EMF) reconstruction in the classical constrained transport (CT) method for Godunov schemes drives a numerical instability. The well-studied linear growth of magneto-rotational instability (MRI) is used as a benchmark for an inter-code comparison of PLUTO and ZeusMP. We reproduce the analytical results for linear MRI growth in 3D global MHD simulations and present a robust and accurate Godunov code which can be used for 3D accretion disk simulations in curvilinear coordinate systems.
- [41] arXiv:0906.5520 [ps, pdf, other]
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Title: Constraining the orbit of the possible companion to Beta Pictoris: New deep imaging observationsAuthors: Anne-Marie Lagrange (LAOG), Markus Kasper (ESO), Anthony Boccaletti (LESIA), Gaël Chauvin (LAOG), Damien Gratadour (LESIA), Thierry Fusco, David Ehrenreich (LAOG), Daniel Apai (STSci), David Mouillet (LAOG), Daniel Rouan (LESIA)Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
We recently reported on the detection of a possible planetary-mass companion to Beta Pictoris at a projected separation of 8 AU from the star, using data taken in November 2003 with NaCo, the adaptive-optics system installed on the Very Large Telescope UT4. Eventhough no second epoch detection was available, there are strong arguments to favor a gravitationally bound companion rather than a background object. If confirmed and located at a physical separation of 8 AU, this young (~1500 K) massive Jovian companion (~8 Mjup) would be the closest planet to its star ever imaged, could be formed via core-accretion, and could explain most of the dust disk properties. Our goal was to return to Beta Pic five years later to obtain a second-epoch observation of the companion or, in case of a non-detection, constrain its orbit. Deep adaptive-optics L'-band direct images of Beta Pic and Ks-band Four-Quadrant-Phase-Mask (4QPM) coronagraph images were recorded with NaCo in January and February 2009. We also use 4QPM data taken in November 2004. No point-like signal with the brightness of the companion candidate (apparent magnitudes L'=11.2 or Ks~12.5$) is detected at projected distances down to 6.5 AU from the star in the 2009 data. As expected, the non-detection does not allow to rule out a background object; however, we show that it is consistent with the orbital motion of a bound companion getting closer to the star between 2003 and 2009. We place strong constraints on the possible orbits of the companion and discuss future observing prospects.
- [42] arXiv:0906.5524 [ps, pdf, other]
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Title: Vertical structure of debris discsAuthors: Philippe ThebaultComments: accepted for publication in Astronomy and Astrophysics (full abstract in the pdf file)Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
The vertical thickness of debris discs is often used as a measure of these systems' dynamical excitation and as clues to the presence of hidden massive perturbers such as planetary embryos. However, this argument could be flawed because the observed dust should be naturally placed on inclined orbits by the combined effect of radiation pressure and mutual collisions. We critically reinvestigate this issue and numerically estimate what the "natural" vertical thickness of a collisionally evolving disc is, in the absence of any additional perturbing body. We use a deterministic collisional code, following the dynamical evolution of a population of indestructible test grains suffering mutual inelastic impacts. Grain differential sizes as well as the effect of radiation pressure are taken into account. We find that, under the coupled effect of radiation pressure and collisions, grains naturally acquire inclinations of a few degrees. The disc is stratified with respect to grain sizes, with the smallest grains having the largest vertical dispersion and the bigger ones clustered closer to the midplane. Debris discs should have a minimum "natural" observed aspect ratio $h_{min}\sim 0.04\pm0.02$ at visible to mid-IR wavelengths where the flux is dominated by the smallest bound grains. These values are comparable to the estimated thicknesses of many vertically resolved debris discs, as is illustrated with the specific example of AU Mic. For all systems with $h \sim h_{min}$, the presence (or absence) of embedded perturbing bodies cannot be inferred from the vertical dispersion of the disc
- [43] arXiv:0906.5539 [ps, pdf, other]
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Title: Lithium and magnetic fields in giants. HD 232862 : a magnetic and lithium-rich giant starAuthors: A. Lèbre, A. Palacios, J. D. do Nascimento Jr, R. Konstantinova-Antova, D. Kolev, M. Aurière, P. de Laverny, J. R. De MedeirosComments: 11 pages, 9 figures ; accepted by Astronomy and AstrophysicsSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
We report the detection of an unusually high lithium content in HD 232862, a field giant classified as a G8II star, and hosting a magnetic field. With the spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected high resolution and high signal-to-noise spectra of three giants : HD 232862, KU Peg and HD 21018. From spectral synthesis we have inferred stellar parameters and measured lithium abundances that we have compared to predictions from evolutionary models. We have also analysed Stokes V signatures, looking for a magnetic field on these giants. HD 232862, presents a very high abundance of lithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically value expected at this spectral type and for this luminosity class (i.e, G8II). The evolutionary stage of HD 232862 has been precised, and it suggests a mass in the lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0 solar mass, at the bottom of the Red Giant Branch. Besides, a time variable Stokes V signature has been detected in the data of HD 232862 and KU Peg, pointing to the presence of a magnetic field at the surface of these two rapidly rotating active stars.
- [44] arXiv:0906.5544 [ps, pdf, other]
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Title: The fraction of Compton-thick sources in an INTEGRAL complete AGN sampleComments: 8 pages, accepted for publication on MNRAS main journalSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
We study the NH distribution in a complete sample of 88 AGN selected in the 20-40 keV band from INTEGRAL/IBIS observations. We find that the fraction of absorbed (NH > 10^{22} cm^2) sources is 43% while the Compton thick AGN comprise 7% of the sample. While these estimates are fully compatible with previous soft gamma-ray surveys, they would appear to be in contrast with results reported by Risaliti et al. (1999) using an optically selected sample. This apparent difference can be explained as being due to a selection bias caused by the reduction in high energy flux in Compton thick objects rendering them invisible at our sensitivity limit. Taking this into account we estimate that the fraction of highly absorbed sources is actually in close agreement with the optically selected sample. Furthermore we show that the measured fraction of absorbed sources in our sample decreases from 80% to about 20-30% as a function of redshift with all Compton thick AGN having z < 0.015. If we limit our analysis to this distance and compare only the type 2 objects in our sample with the Risaliti et al. objects below this redshift value, we find a perfect match to their NH distribution. We conclude that in the low redshift bin we are seeing almost the entire AGN population, from unabsorbed to at least mildly Compton thick objects, while in the total sample we lose the heavily absorbed 'counterparts' of distant and therefore dim sources with little or no absorption. Taking therefore this low z bin as the only one able to provide the 'true' distribution of absorption in type 1 and 2 AGN, we estimate the fraction of Compton thick objects to be >24%.
- [45] arXiv:0906.5574 [ps, pdf, other]
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Title: Detection of very-high-energy gamma-ray emission from the vicinity of PSR B1706-44 with H.E.S.SAuthors: S. Hoppe, E. de Oña-Wilhemi, B. Khélifi, R.C.G. Chaves, O.C. de Jager, C. Stegmann, R. Terrier, for the H.E.S.S. CollaborationComments: 4 pages, 2 figures, submitted to ICRC Proceedings on 15 May 2009Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)
The high spin-down luminosity pulsar PSR B1706-44 together with the adjacent supernova remnant candidate G 343.1-2.3 have been observed by H.E.S.S. in dedicated observations in 2007. A new source of very-high-energy (VHE; E > 100 GeV) gamma-ray emission was detected in these observations with its centroid at RA(J2000) = 17h08m10s and Dec(J2000) = -44d21', with a statistical error of 3 arcmin on each axis (HESS J1708-443). The VHE gamma-ray source is significantly more extended than the H.E.S.S. point spread function, with an intrinsic Gaussian width of 0.29 +/- 0.04 deg. Its energy spectrum can be described by a power law with a photon index Gamma = 2.0 +/- 0.1 (stat) +/- 0.2 (sys). The integral flux measured between 1-10 TeV is ~17% of the Crab Nebula flux in the same energy range.
- [46] arXiv:0906.5582 [ps, pdf, other]
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Title: Analysis of the Swift Gamma-Ray Bursts durationComments: NANJING GAMMA-RAY BURST CONFERENCE 2008Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 seconds. There are, however, some indications for the existence of a third type of burst. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for gamma-ray bursts. Therefore it is worth to reanalyze the durations and their distribution and also the classification of GRBs. Using The First BAT Catalog the maximum likelihood estimation was used to analyzed the duration distribution of GRBs. The three log-normal fit is significantly (99.54 % probability) better than the two for the duration distribution. Monte-Carlo simulations also confirm this probability (99.2 %).
- [47] arXiv:0906.5594 [ps, pdf, other]
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Title: The Anticipated Supernova Associated with GRB090618Comments: 10 pages, 2 FiguresSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We use the cannonball model of gamma ray bursts (GRBs) and public data from the first day of observations of GRB 090618 to predict its X-ray and optical lightcurves until very late times, and, in particular, the emergence of a photometric and spectroscopic signature of an SN akin to SN1998bw in its optical afterglow with an anticipated peak brightness of magnitude 23 in the R band around July 10, 2009, if extinction in the host galaxy can be neglected.
- [48] arXiv:0906.5605 [pdf, other]
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Title: Spin-orbit misalignment in the HD80606 planetary systemAuthors: F. Pont, G. Hebrard, J.M. Irwin, F. Bouchy, C. Moutou, D. Ehrenreich, T. Guillot, S. Aigrain, et alComments: accepted for Publication in Astronomy & Astrophysics, submitted 11 May 2009Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
We recently reported the photometric and spectroscopic detection of the primary transit of the 111-day-period, eccentric extra-solar planet HD80606 b, at Observatoire de Haute-Provence, France (Moutou et al. 2009). The whole egress of the primary transit and a section of its central part were observed, allowing the measurement of the planetary radius, and evidence for a spin-orbit misalignment through the observation of the Rossiter-McLaughlin anomaly. The ingress having not been observed for this long-duration transit, uncertainties remained in the parameters of the system. We present here a refined, combined analysis of our photometric and spectroscopic data, together with further published radial velocities, ground-based photometry, and Spitzer photometry around the secondary eclipse, as well as new photometric measurements of HD 80606 acquired at Mount Hopkins, Arizona, just before the beginning of the primary transit. Although the transit is not detected in those new data, they provide an upper limit for the transit duration, which narrows down the possible behaviour of the Rossiter-McLaughlin anomaly in the unobserved part of the transit. We analyse the whole data with a Bayesian approach using a Markov-chain Monte Carlo integration on all available information. We find R_p = 0.98 +- 0.03 R_Jup for the planetary radius, and a total primary transit duration of 11.9 +- 1.3 hours from first to fourth contact. Our analysis reinforces the hypothesis of spin-orbit misalignment in this system (alignment excluded at >95 % level), with a positive projected angle between the planetary orbital axis and the stellar rotation (median solution lambda ~ 50 degrees). As HD80606 is a component of a binary system, the peculiar orbit of its planet could result from a Kozai mechanism.
- [49] arXiv:0906.5610 [ps, pdf, other]
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Title: A Joint GMRT/X-ray study of galaxy groupsAuthors: E. O'Sullivan, S. Giacintucci, J. M. Vrtilek, S. Raychaudhury, R. Athreya, T. Venturi, L. P. DavidComments: 5 pages, 3 figures, Oral contribution to the Conference "The Low Frequency Radio Universe", ASP Conference Series, Eds. D.J. Saikia, D. Green, Y. Gupta and T. VenturiSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We present results from combined low-frequency radio and X-ray studies of nearby galaxy groups. We consider two main areas: firstly, the evolutionary process from spiral-dominated, HI-rich groups to elliptical-dominated systems with hot, X-ray emitting gas halos; secondly, the mechanism of AGN feedback which appears to balance radiative cooling of the hot halos of evolved groups. The combination of radio and X-ray observations provides a powerful tool for these studies, allowing examination of gas in both hot and cool phases, and of the effects of shock heating and AGN outbursts. Low-frequency radio data are effective in detecting older and less energetic electron populations and are therefore vital for the determination of the energetics and history of such events. We present results from our ongoing study of Stephan's Quintet, a spiral-rich group in which tidal interactions and shock heating appear to be transforming HI in the galaxies into a diffuse X-ray emitting halo, and show examples of AGN feedback from our sample of elliptical-dominated groups, where multi-band low-frequency radio data have proved particularly useful.
Cross-lists for Wed, 1 Jul 09
- [50] arXiv:0905.3632 (cross-list from hep-th) [ps, pdf, other]
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Title: Identification of All Dark Matter as Black HolesAuthors: Paul H. FramptonComments: History of baryons discussedSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
For the universe I use dimensionless entropy $S/k = \ln \Omega$ for which the most convenient unit is the googol ($10^{100}$) and identify all dark matter as black holes whereupon the present entropy is about a thousand googols. While the energy of the universe has been established to be about 0.04 baryons, 0.24 dark matter and 0.72 dark energy, the cosmological entropy is almost entirely, about $(1 - 10^{-15})$, from black holes and only $10^{-15}$ from everything else. This identification of all dark matter as black holes is natural in statistical mechanics. Cosmological history of dark matter is discussed.
- [51] arXiv:0906.0957 (cross-list from hep-ph) [ps, pdf, other]
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Title: Selecting a Model of Supersymmetry Breaking MediationComments: 38 pages, 11 figures. Version 2: refs added, Sec. 6.3 changedSubjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Experiment (hep-ex)
We study the problem of selecting between different mechanisms of supersymmetry breaking in the Minimal Supersymmetric Standard Model using current data. We evaluate the Bayesian evidence of four supersymmetry breaking scenarios: mSUGRA, mGMSB, mAMSB and moduli mediation. The results show a strong dependence on the dark matter assumption. Using the inferred cosmological relic density as an upper bound, minimal anomaly mediation is at least moderately favoured over the CMSSM. Our fits also indicate that evidence for a positive sign of the mu parameter is moderate at best. We present constraints on the anomaly and gauge mediated parameter spaces and some previously unexplored aspects of the dark matter phenomenology of the moduli mediation scenario. We use sparticle searches, indirect observables and dark matter observables in the global fit and quantify robustness with respect to prior choice. We quantify how much information is contained within each constraint.
- [52] arXiv:0906.4909 (cross-list from nucl-th) [ps, pdf, other]
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Title: Symmetry coefficients and incompressibility of clusterized supernova matterComments: 9 pages + 12 figuresSubjects: Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)
The symmetry energy coefficients, incompressibility, and single-particle and isovector potentials of clusterized dilute nuclear matter are calculated at different temperatures employing the $S$-matrix approach to the evaluation of the equation of state. Calculations have been extended to understand the aforesaid properties of homogeneous and clusterized supernova matter in the subnuclear density region. Comparison of the results in the $S$-matrix and mean-field approach reveals some subtle differences in the density and temperature region we explore.
- [53] arXiv:0906.5069 (cross-list from hep-th) [ps, pdf, other]
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Title: Caustic avoidance in Horava-Lifshitz gravityAuthors: Shinji MukohyamaComments: 17 pagesSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
There are at least four versions of Horava-Lishitz gravity in the literature. We consider the version without the detailed balance condition with the projectability condition and address one aspect of the theory: avoidance of caustics for constant time hypersurfaces. We show that caustics cannot form with codimension one in the absence of matter source if lambda deviates from 1 near would-be caustics via RG flow. We argue that inclusion of matter source will not change the conclusion. We also argue that caustics with codimension higher than one will not form because of repulsive gravity generated by nonlinear higher curvature terms. Finally, we discuss implications to the recently proposed scenario of ``dark matter as integration constant''.
- [54] arXiv:0906.5078 (cross-list from gr-qc) [ps, pdf, other]
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Title: Vacuum pressure, dark energy and dark matterComments: 6 pages, 0 figures, LaTeX, minor improvementsSubjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
It has been argued that the correct, i.e. positive, sign of quantum vacuum energy density, or more properly, negative sign of quantum vacuum pressure, requires not a very large number, e.g. ~100, of additional, undiscovered fundamental bosonic particle species, absent in the standard model. Interpretation of the new particle species in terms of dark matter ones permits to qualitatively, and even quantitatively, connect all the three concepts given in the title.
- [55] arXiv:0906.5135 (cross-list from hep-th) [ps, pdf, other]
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Title: Quintessence and phantom dark energy from ghost D-branesComments: 7 pages, 2 figuresSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
We present a novel dark energy candidate, based upon the existence and dynamics of Ghost D-branes in a warped compactification of type IIB string theory. Gp-branes cancel the combined BPS sectors of the Dp-branes, while they preserve the same supersymmetries. We show that this scenario can naturally lead to either quintessence or phantom-like behaviors, depending on the form of the involved potentials and brane tension.
Replacements for Wed, 1 Jul 09
- [56] arXiv:0809.2053 (replaced) [ps, pdf, other]
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Title: Extended Palatini action for general relativity and the natural emergence of the cosmological constantAuthors: Eran RosenthalComments: in the revised version the original scalar matter action is replaced with a general matter actionSubjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)
- [57] arXiv:0810.4561 (replaced) [ps, pdf, other]
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Title: Observational $5-20\mu$m Interstellar Extinction Curves Toward Star-Forming Regions Derived from Spitzer IRS SpectraAuthors: M. K. McClureComments: Submitted to ApJ Letters, 5 pages, 4 figures, 1 table. Revised version published in ApJ Letters, with 5 pages, 3 figures, and 2 tables. Empirical extinction curves are available as online-only from ApJJournal-ref: 2009ApJ...693L..81MSubjects: Astrophysics (astro-ph)
- [58] arXiv:0811.0041 (replaced) [ps, pdf, other]
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Title: Quark-Novae, cosmic reionization, and early r-process element productionAuthors: R. Ouyed (U. Calgary), R. E. Pudritz (McMaster U.), P. Jaikumar (IMSc, Chennai & Argonne (PHY))Comments: Accepted for publication in the Astrophysical Journal. 9 journal pages, 2 figures. This version includes more discussion, 3 new appendices and extended literatureSubjects: Astrophysics (astro-ph); Nuclear Theory (nucl-th)
- [59] arXiv:0811.1219 (replaced) [ps, pdf, other]
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Title: The growth of supermassive black holes in pseudo-bulges, classical bulges and elliptical galaxiesComments: 7 pages, 2 figures, accepted for publication in MNRAS main journal after implementing referee's suggestions; results essentially unchanged; main change is to take into account intrinsic scatter in black hole relationsSubjects: Astrophysics (astro-ph)
- [60] arXiv:0811.1991 (replaced) [ps, pdf, other]
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Title: The cosmology dependence of weak lensing cluster countsComments: 4 pages, 2 figures. Accepted for publication in ApJL. Figure 1 modified, unchanged conclusionsJournal-ref: Astrophysical Journal Letters, Volume 698, Issue 1, L33-L36, June 2009Subjects: Astrophysics (astro-ph)
- [61] arXiv:0811.2532 (replaced) [ps, pdf, other]
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Title: Arecibo Pulsar Survey Using ALFA. III. Probing Radio Pulsar Intermittency and TransientsAuthors: J. S. Deneva, J. M. Cordes, M. A. McLaughlin, D. J. Nice, D. R. Lorimer, F. Crawford, N. D. R. Bhat, F. Camilo, D. J. Champion, P. C. C. Freire, S. Edel, V. I. Kondratiev, J. W. T. Hessels, F. A. Jenet, L. Kasian, V. M. Kaspi, M. Kramer, P. Lazarus, J. van Leeuwen, S. M. Ransom, I. H. Stairs, B. W. Stappers, A. Brazier, A. Venkataraman, J. A. ZollwegSubjects: Astrophysics (astro-ph)
- [62] arXiv:0811.3441 (replaced) [pdf, other]
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Title: Helioseismic data inclusion in solar dynamo modelsAuthors: Andrés Muñoz-Jaramillo (1), Dibyendu Nandy (2), Petrus C. H. Martens (3) ((1) Montana State University, (2) Indian Institute for Science Education and Research-Kolkata, (3) Harvard-Smithsonian Center for Astrophysics)Journal-ref: Astrophys.J.698:461-478,2009Subjects: Astrophysics (astro-ph)
- [63] arXiv:0812.4248 (replaced) [ps, pdf, other]
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Title: Mass Ejection by Strange Star Mergers and Observational ImplicationsAuthors: A. Bauswein (1), H.-Th. Janka (1), R. Oechslin (1), G. Pagliara (2), I. Sagert (3), J. Schaffner-Bielich (2), M.M. Hohle (4,5), R. Neuhaeuser (4) ((1) MPI Astrophysik, Garching; (2) Inst. Theor. Physik, Univ. Heidelberg; (3) Inst. Theor. Physik, Goethe Univ. Frankfurt; (4) Astrophysik. Inst., Univ. Jena; (5) MPI Extraterr. Physik, Garching)Comments: 5 pages, 2 eps figures; referee comments included, accepted by Phys. Rev. LettSubjects: Astrophysics (astro-ph)
- [64] arXiv:0901.4334 (replaced) [ps, pdf, other]
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Title: Small Angular Scale Measurements of the CMB Temperature Power Spectrum from QUaDAuthors: QUaD collaboration: R. B. Friedman, P. Ade, J. Bock, M. Bowden, M. L. Brown, G. Cahill, P. G. Castro, S. Church, T. Culverhouse, K. Ganga, W. K. Gear, S. Gupta, J. Hinderks, J. Kovac, A. E. Lange, E. Leitch, S. J. Melhuish, Y. Memari, J. A. Murphy, A. Orlando, C. O' Sullivan, L. Piccirillo, C. Pryke, N. Rajguru, B. Rusholme, R. Schwarz, A. N. Taylor, K. L. Thompson, A. H. Turner, E. Y. S. Wu, M. ZemcovComments: 5 pages, 5 figures, updated beam model, full data release available online (see text), accepted to ApJLSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [65] arXiv:0902.3237 (replaced) [ps, pdf, other]
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Title: The Clustering of MgII Absorption Systems at z=0.5 and Detection of Cold Gas in Massive HalosAuthors: Jean-Rene Gauthier (1), Hsiao-Wen Chen (1), Jeremy L. Tinker (1,2) ((1) KICP/UChicago, (2) BCCP UC Berkeley)Comments: 15 pages, 7 figures, Accepted by ApJSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [66] arXiv:0903.1216 (replaced) [ps, pdf, other]
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Title: Integral field spectroscopy with SINFONI of VVDS galaxies. I. Galaxy dynamics and mass assembly at 1.2 < z < 1.6Authors: B. Epinat, T. Contini, O. Le Fevre, D. Vergani, B. Garilli, P. Amram, J. Queyrel, L. Tasca, L. TresseComments: 23 pages, 22 figures, accepted for publication in A&ASubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [67] arXiv:0903.1303 (replaced) [ps, pdf, other]
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Title: Time Delays of Strings in D-particle Backgrounds and Vacuum Refractive IndicesComments: RevTex4, 10 pages, 3 eps.figures incorporated, amended discussion on Lorentz symmetry (section I), and on gamma-ray phenomenology, based on version to appear in Phys. Lett. BSubjects: High Energy Physics - Theory (hep-th); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
- [68] arXiv:0903.2753 (replaced) [ps, pdf, other]
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Title: Classifying and avoiding singularities in the alternative gravity dark energy modelsComments: 21 pages, 12 figures, published version in PRDJournal-ref: Phys.Rev.D79:124007,2009Subjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
- [69] arXiv:0903.2805 (replaced) [ps, pdf, other]
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Title: Genetic Algorithms and Supernovae Type Ia AnalysisComments: Added 1 figure. Final, published versionJournal-ref: JCAP05(2009)006Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
- [70] arXiv:0903.4925 (replaced) [ps, pdf, other]
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Title: Lyman-alpha transfer in primordial hydrogen recombinationComments: 16 pages, 7 figures, matches PRD accepted version. Fixed bug in numerical transport code, resulting in slightly reduced effect on recombination historySubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [71] arXiv:0904.2092 (replaced) [ps, pdf, other]
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Title: Vacuum structure for scalar cosmological perturbations in Modified Gravity ModelsComments: 17 pages, 1 figure, uses RevTeX, references addedJournal-ref: JCAP 06, 034 (2009)Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
- [72] arXiv:0904.3704 (replaced) [ps, pdf, other]
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Title: Analytical solution for light propagation in Schwarzschild field having an accuracy of 1 micro-arcsecondComments: 24 pages, 2 figures, Report for GAIA astrometric missionSubjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Galaxy Astrophysics (astro-ph.GA)
- [73] arXiv:0905.3169 (replaced) [ps, pdf, other]
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Title: Turbulent Motions and Shocks Waves in Galaxy Clusters simulated with AMRComments: Accepted for publication in A&A. 12 pages, 11 color figures - 2 additional figures respect to v.1, and updated bibliography. The paper with full quality figures is available at this http URLSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)
- [74] arXiv:0906.1187 (replaced) [ps, pdf, other]
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Title: Probing Gravitino Dark Matter with PAMELA and FermiComments: 21 pages, 6 figures. Typos correctedSubjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
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