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Title: On the Intermediate Subgroup of the Gamma-Ray Bursts in the Swift Database

Abstract

A sample of 286 gamma-ray bursts, detected by Swift satellite, is studied statistically by the {chi}{sup 2} test and the Student t-test, respectively. The short and long subgroups are well detected in the Swift data. But no intermediate subgroup is seen. The non-detection of this subgroup in the Swift database can be explained, once it is assumed that in the BATSE database the short and the intermediate subgroups form a common subclass.

Authors:
;  [1]
  1. Astronomical Institute of the Charles University, V Holesovickach 2, Prague (Czech Republic)
Publication Date:
OSTI Identifier:
21255172
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1085; Journal Issue: 1; Conference: 4. international meeting on high energy gamma-ray astronomy, Heidelberg (Germany), 7-11 Jul 2008; Other Information: DOI: 10.1063/1.3076763; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; 99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; COSMIC GAMMA BURSTS; GAMMA ASTRONOMY; SATELLITES

Citation Formats

Huja, David, and Meszaros, Attila. On the Intermediate Subgroup of the Gamma-Ray Bursts in the Swift Database. United States: N. p., 2008. Web. doi:10.1063/1.3076763.
Huja, David, & Meszaros, Attila. On the Intermediate Subgroup of the Gamma-Ray Bursts in the Swift Database. United States. doi:10.1063/1.3076763.
Huja, David, and Meszaros, Attila. Wed . "On the Intermediate Subgroup of the Gamma-Ray Bursts in the Swift Database". United States. doi:10.1063/1.3076763.
@article{osti_21255172,
title = {On the Intermediate Subgroup of the Gamma-Ray Bursts in the Swift Database},
author = {Huja, David and Meszaros, Attila},
abstractNote = {A sample of 286 gamma-ray bursts, detected by Swift satellite, is studied statistically by the {chi}{sup 2} test and the Student t-test, respectively. The short and long subgroups are well detected in the Swift data. But no intermediate subgroup is seen. The non-detection of this subgroup in the Swift database can be explained, once it is assumed that in the BATSE database the short and the intermediate subgroups form a common subclass.},
doi = {10.1063/1.3076763},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1085,
place = {United States},
year = {Wed Dec 24 00:00:00 EST 2008},
month = {Wed Dec 24 00:00:00 EST 2008}
}
  • We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowingmore » us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.« less
  • We jointly analyze the gamma-ray burst (GRB) data observed with Burst Alert Telescope (BAT) and X-ray Telescope on board the Swift mission to present a global view on the internal energy dissipation processes in GRBs, including precursors, prompt gamma-ray emission, extended soft gamma-ray emission, and late X-ray flares. The Bayesian block method is utilized to analyze the BAT light curves to identify various emission episodes. Our results suggest that these emission components likely share the same physical origin, which is the repeated activation of the GRB central engine. What we observe in the gamma-ray band may be a small partmore » of more extended underlying activities. The precursor emission, which is detected in about 10% of Swift GRBs, is preferably detected in those GRBs that have a massive star core-collapse origin. The soft extended emission tail, on the other hand, is preferably detected in those GRBs that have a compact star merger origin. Bright X-ray emission is detected during the BAT quiescent phases prior to subsequent gamma-ray peaks, implying that X-ray emission may be detectable prior the BAT trigger time. Future GRB alert instruments with soft X-ray capability are essential for revealing the early stages of GRB central engine activities, and shedding light on jet composition and the jet launching mechanism in GRBs.« less
  • Compact binary system mergers are expected to generate gravitational radiation detectable by ground-based interferometers. A subset of these, the merger of a neutron star with another neutron star or a black hole, are also the most popular model for the production of short gamma-ray bursts (GRBs). The Swift Burst Alert Telescope (BAT) and the Fermi Gamma-ray Burst Monitor (GBM) trigger on short GRBs (SGRBs) at rates that reflect their relative sky exposures, with the BAT detecting 10 per year compared to about 45 for GBM. We examine the SGRB populations detected by Swift BAT and Fermi GBM. We find thatmore » the Swift BAT triggers on weaker SGRBs than Fermi GBM, providing they occur close to the center of the BAT field of view, and that the Fermi GBM SGRB detection threshold remains flatter across its field of view. Overall, these effects combine to give the instruments the same average sensitivity, and account for the SGRBs that trigger one instrument but not the other. We do not find any evidence that the BAT and GBM are detecting significantly different populations of SGRBs. Both instruments can detect untriggered SGRBs using ground searches seeded with time and position. The detection of SGRBs below the on-board triggering sensitivities of Swift BAT and Fermi GBM increases the possibility of detecting and localizing the electromagnetic counterparts of gravitational wave (GW) events seen by the new generation of GW detectors.« less
  • With its rapid response, Swift has revealed plenty of unexpected properties of gamma-ray bursts (GRBs). With an abundance of observations, our current understanding is only limited by the complexity of early X-ray light curves. In this work, based on the public Swift data of 150 well-monitored GRBs with measured redshifts, we find some interesting global features in the rest-frame X-ray light curves. The distinct spectral behaviors between the prompt emission and the afterglow emission imply dissimilar radiation scenarios. Interestingly, an unforeseen plateau is exhibited in the prompt X-ray light curves despite the presence of complex spikes, which might indicate themore » presence of a steady central engine. In particular, the seemingly continuous evolution with a single power law from the prompt to the afterglow of most GRBs might place strong constraints on the theoretical models.« less
  • X-ray flares of gamma-ray bursts (GRBs) are usually observed in the soft X-ray range and the spectral coverage is limited. In this paper, we present an analysis of 32 GRB X-ray flares that are simultaneously observed by both Burst Alert Telescope and X-Ray Telescope on board the Swift mission, so that a joint spectral analysis with a wider spectral coverage is possible. Our results show that the joint spectra of 19 flares are fitted with the absorbed single power law or the Band function models. More interestingly, the joint spectra of the other 13 X-ray flares are fitted with themore » absorbed single power-law model plus a blackbody component. Phenomenally, the observed spectra of these 13 flares are analogous to several GRBs with a thermal component, but only with a much lower temperature of kT = 1 ∼ 3 keV. Assuming that the thermal emission is the photosphere emission of the GRB fireball, we derive the fireball properties of the 13 flares that have redshift measurements, such as the bulk Lorentz factor Γ{sub ph} of the outflow. The derived Γ{sub ph} range from 50 to 150 and a relation of Γ{sub ph} to the thermal emission luminosity is found. It is consistent with the Γ{sub 0} – L {sub iso} relations that are derived for the prompt gamma-ray emission. We discuss the physical implications of these results within the content of jet composition and the radiation mechanism of GRBs and X-ray flares.« less