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Author: Publisher: ISBN: Category : Languages : en Pages : 8
Book Description
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%.
Author: Publisher: ISBN: Category : Languages : en Pages : 8
Book Description
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%.
Author: Juri Poutanen Publisher: ISBN: Category : Nature Languages : en Pages : 468
Book Description
Annotation Papers from a February 1999 workshop discuss unresolved issues regarding prompt emission of gamma-ray bursts (GRBs). Themes are temporal properties, spectral properties, central engine and radiative mechanisms, spatial distribution, luminosity function, cosmological effects, and future missions. Specific topics include radiation from relativistic strongly magnetized outflows, quasi-thermal comptonization and GRBs, and cosmological signatures in temporal and spectral characteristics of GRBs. The volume lacks a subject index. The editors are affiliated with the Stockholm Observatory. Annotation c. Book News, Inc., Portland, OR (booknews.com)
Author: Cheng Ho Publisher: Cambridge University Press ISBN: 9780521414494 Category : Nature Languages : en Pages : 532
Book Description
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.
Author: Gilbert Vedrenne Publisher: Springer Science & Business Media ISBN: 354039088X Category : Science Languages : en Pages : 613
Book Description
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.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
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.
Author: Joshua S. Bloom Publisher: Universal-Publishers ISBN: 1581121695 Category : Science Languages : en Pages : 198
Book Description
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.
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Author: Lyle A. Ford
Author: Jay Preston Norris
Author: Juri Poutanen
Author: Cheng Ho
Author: Gilbert Vedrenne
Author: Paz Beniamini
Author: Neil Gehrels
Author: 
Author: Joshua S. Bloom