Download or read book A Search for Discrete X Ray Spectral Features in a Sample of Bright Gamma Ray Burst Afterglows written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We present uniform, detailed spectral analyses of gamma-ray burst (GRB) X-ray afterglows observed with ASCA, Beppo-SAX, Chandra, and XMM-Newton, and critically evaluate the statistical significances of X-ray emission and absorption features in these spectra. The sample consists of 21 X-ray afterglow observations up to and including that of GRB040106 with spectra of sufficient statistical quality to allow meaningful line searches, chosen here somewhat arbitrarily to be detections with more than 100 total (source plus background) counts. This sample includes all nine X-ray afterglows with published claims of line detections. Moderate resolution spectra are available for 16 of the 21 sources, and for the remaining five the Chandra transmission grating spectrometers obtained high-resolution data. All of the data are available from the public archive. We test a simple hypothesis in which the observed spectra are produced by a power-law continuum model modified by photoelectric absorption by neutral material both in our Galaxy and possibly also local to the burst. As a sample, these afterglow spectra are consistent with this relatively simple model. However, since the [chi][sup 2] statistic is not sensitive to weak and/or localized fluctuations, we have performed Monte Carlo simulations to search for discrete features and to estimate their significances. Our analysis shows that there are four afterglows (GRB011211, GRB030227, GRB021004, and GRB040106) with line-like features that are significant at the 3 [sigma] level. We cautiously note that, in two cases, the features are associated with an unusual background feature; in the other two, the fractional magnitudes of the lines are small, and comparable to the expected level of systematic uncertainty in the spectral response. In addition, none of the statistically significant features are seen in more than one detector or spectral order where available. We conclude that, to date, no credible X-ray line feature has been detected in a GRB afterglow. Finally, in a majority of cases, we find no evidence for significant absorbing columns local to the GRB host galaxy, implying there is little evidence from X-ray observations that GRB preferentially explode in high-density environments.
Download or read book Gamma Ray Bursts written by Gilbert Vedrenne and published by Springer Science & Business Media. This book was released on 2009-03-20 with total page 613 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since their discovery was first announced in 1973, gamma-ray bursts (GRBs) have been among the most fascination objects in the universe. While the initial mystery has gone, the fascination continues, sustained by the close connection linking GRBs with some of the most fundamental topics in modern astrophysics and cosmology. Both authors have been active in GRB observations for over two decades and have produced an outstanding account on both the history and the perspectives of GRB research.
Download or read book Gamma ray Bursts and Compact X ray Binaries written by Neil Gehrels and published by . This book was released on 2007 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book X ray Spectral Properties of gamma ray Bursts written by and published by . This book was released on 1997 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: The authors summarize the spectral characteristics of a sample of 22 bright gamma-ray bursts detected with the gamma-ray burst sensors aboard the satellite Ginga. This instrument employed a proportional and scintillation counter to provide sensitivity to photons in the 2--400 keV range, providing a unique opportunity to characterize the largely unexplored X-ray properties of gamma-ray bursts. The photon spectra of the Ginga bursts are well described by a low energy slope, a bend energy, and a high energy slope. In the energy range where they can be compared, this result is consistent with burst spectral analyses obtained from the BATSE experiment aboard the Compton Observatory. However, below 20 keV they find evidence for a positive spectral number index in approximately 40% of their burst sample, with some evidence for a strong rolloff at lower energies in a few events. They find that the distribution of spectral bend energies extends below 10 keV. The observed ratio of energy emitted in the X-rays relative to the gamma-rays can be much larger than a few percent and, in fact, is sometimes larger than unity. The average for their sample is 24%.
Download or read book Prompt Observations of Gamma ray Burst Afterglows with ROTSE III written by Eli S. Rykoff and published by . This book was released on 2005 with total page 418 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Gamma ray Bursts written by Chryssa Kouveliotou and published by Cambridge University Press. This book was released on 2012-11-22 with total page 361 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive graduate-level review of GRB astrophysics and its history, featuring the latest research by an international team of experts.
Download or read book Toward an Understanding of the Progenitors of Gamma Ray Bursts written by Joshua S. Bloom and published by Universal-Publishers. This book was released on 2002 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: The various possibilities for the origin ("progenitors") of gamma-ray bursts (GRBs) manifest in differing observable properties. Through deep spectroscopic and high-resolution imaging observations of some GRB hosts, I demonstrate that well-localized long-duration GRBs are connected with otherwise normal star-forming galaxies at moderate redshifts of order unity. Using high-mass binary stellar population synthesis models, I quantify the expected spatial extent around galaxies of coalescing neutron stars, one of the leading contenders for GRB progenitors. I then test this scenario by examining the offset distribution of GRBs about their apparent hosts making extensive use of ground-based optical data from Keck and Palomar and space-based imaging from the Hubble Space Telescope. The offset distribution appears to be inconsistent with the coalescing neutron star binary hypothesis (and, similarly, black-hole--neutron star coalescences); instead, the distribution is statistically consistent with a population of progenitors that closely traces the ultra-violet light of galaxies. This is naturally explained by bursts which originate from the collapse of massive stars ``collapsars''). This claim is further supported by the unambiguous detections of intermediate-time (approximately three weeks after the bursts) emission ``bumps'' which appear substantially more red than the afterglows themselves. I claim that these bumps could originate from supernovae that occur at approximately the same time as the associated GRB; if true, GRB 980326 and GRB 011121 provide strong observational evidence connecting cosmological GRBs to high-redshift supernovae and implicate massive stars as the progenitors of at least some long-duration GRBs.
Download or read book Gamma ray Bursts written by Cheng Ho and published by Cambridge University Press. This book was released on 1992-03-12 with total page 532 pages. Available in PDF, EPUB and Kindle. Book excerpt: Summarizes the current understanding of Astronomical gamma-ray bursts, short-lived flashes of high-energy radiation, which have eluded even a basic explanation for over twenty years, and describes directions for future research.
Download or read book A Study of the Temporal and Spectral Characteristics of Gamma Ray Bursts written by Jay Preston Norris and published by . This book was released on 1983 with total page 570 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Probing Extragalactic Dust Through Gamma ray Burst Afterglows written by Sunlin Liang and published by . This book was released on 2010 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gamma-Ray Bursts (GRBs) are the most powerful explosions in the universe and a very interesting phenomenon in themselves. The gamma-rays and the X-ray flashes (XRFs) are the manifestations of the most violent, cataclysmic explosions in the Universe. GRBs are followed by so-called afterglow emission detected in lower energy bands and on longer timescales, e.g. Xray, UV, optical, near-infrared, radio emissions from a few hundred seconds to a few months. The following thesis does not deal with the GRB phenomenon itself but it is studying their environment and host galaxies through optical spectroscopy and using them as light sources In the distant universe. This thesis is divided into six parts. The first chapter of the thesis discusses the importance of dust on exploring the host galaxies of GRBs. In the second chapter, we present a detailed study on the obscuration and reddening by dust in GRB host galaxies. We propose a novel approach - "Drude" model to derive the GRB host extinction law. We also present the general dust extinction models and explain why our "Drude" model is more favorable. With the template extinction laws all self-contained, and the capability of revealing extinction laws differing from the conventional ones, it is shown that this is a powerful approach in modeling the afterglow SEDs to derive GRB host extinction. In the third chapter, we select GRB070802 at z= 2.45 (which shows clear evidence for the 2175Å extinction bump) and GRB050904 at z= 6.29, the 3rd most distant GRB observed to date and fit their afterglow spectra to determine the extinction of their host galaxies, with an emphasis on the 2175Å extinction feature at high redshifts. We find that their extinction curves differ substantially from that of the Milky Way, the Small and Large Magellanic Clouds, the 2175Å extinction feature appears to be also present in GRB050904 at z=6.29. In the fourth and fifth chapter, we present a study of the dust properties for a large sample (33 objects) of long-GRB host galaxies at z [lesser than] 2.0 and another large sample (27 objects) at z [greater than] 2.0, respectively. From the derived strength of the far-UV extinction rise, strength of the 2175Å extinction, the total-to selective extinction ratio RV , host galaxy visual extinction AV , dust composition and the mass weighted mean dust sizes of all 60 GRBs, we find no evidence of evolution of the dust properties (extinction, sizes and abundance) on redshifts. The thesis ends with summary, outlook and the references.
Download or read book Gamma Ray Bursts written by R. Marc Kippen and published by American Institute of Physics. This book was released on 2000-10-06 with total page 936 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reflects the current state of the growing field of gamma-ray burst research and the remarkable progress brought about by recent multiwavelength observations. A full range of topics related to modern burst research is covered, including new observational results, ongoing archival analyses, theoretical modeling, and current/future instrumentation.
Download or read book Searching for the Long Duration Gamma Ray Burst Progenitor written by Robert Allan Mesler III and published by Springer. This book was released on 2014-05-28 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nominated as an outstanding thesis by the Department of Physics and Astronomy of the University of New Mexico, this thesis seeks to identify the gamma-ray burst (GRB) progenitor. GRBs are extragalactic explosions that briefly outshine entire galaxies, but the mechanism that can release that much energy over a 100 second burst is still a mystery. The leading candidate for the GRB progenitor is currently a massive star which collapses to form a black hole–accretion disk system that powers the GRB. GRB afterglows, however, do not always show the expected behavior of a relativistic blast wave interacting with the stellar wind that such a progenitor should have produced before its collapse./pppIn this book, the author uses the Zeus-MP astrophysical hydrodynamics code to model the environment around a stellar progenitor prior to the burst. He then develops a new semi-analytic MHD and emission model to produce light curves for GRBs encountering these realistic density profiles. The work ultimately shows that the circumburst medium surrounding a GRB at the time of the explosion is much more complex than a pure wind, and that observed afterglows are entirely consistent with a large subset of proposed stellar progenitors.
Download or read book Gamma Ray Bursts written by Cheryl Pauline Hurkett and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Study of the Temporal and Spectral Characteristics of Gamma Ray Bursts written by Jay Preston Norris and published by . This book was released on 1983 with total page 514 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Spectral Properties of Gamma ray Bursts Observed by the Burst and Transient Source Experiment written by Lyle A. Ford and published by . This book was released on 1996 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Optical Flashes from Internal Pairs Formed in Gamma ray Burst Afterglows written by and published by . This book was released on 2015 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV-TeV photons. For gamma-ray burst (GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts ($R\lt 10$) lasting for up to one hundred seconds. As a result, the number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.
Download or read book Investigating Gamma ray Burst Afterglows Using Optical UV and X ray Observations from Swift written by and published by . This book was released on 2010 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt:
