Gamma-ray burst energetics in the Swift ERA

Daniel Kocevski, Nathaniel Butler

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

We examine the rest-frame energetics of 76 gamma-ray bursts (GRBs) with known redshift that were detected by the Swift spacecraft and monitored by the satellite's X-Ray Telescope (XRT). Using the bolometric fluence values estimated by Butler and coworkers and the last XRT observation for each event, we set a lower limit to their collimation-corrected energy Eγ and find that 68% of our sample is at high enough redshift and/or low enough fluence to accommodate a jet break occurring beyond the last XRT observation and still be consistent with the preSwift Eγ distribution for long GRBs. We find that relatively few of the X-ray light curves for the remaining events show evidence for late-time decay slopes that are consistent with that expected from post-jet break emission. The breaks in the X-ray light curves that do exist tend to be shallower and occur earlier than the breaks previously observed in optical light curves, yielding a Eγ distribution that is far lower than the pre-Swift distribution. If these early X-ray breaks are not due to jet effects, then a small but significant fraction of our sample have lower limits to their collimationcorrected energy that place them well above the pre-Swift Eγ distribution. Either scenario would necessitate a much wider post-Swift Eγ distribution for long cosmological GRBs compared to the narrow standard energy deduced from pre-Swift observations. We note that almost all of the pre-Swift Eγ estimates come from jet breaks detected in the optical whereas our sample is limited entirely to X-ray wavelengths, furthering the suggestion that the assumed achromaticity of jet breaks may not extend to high energies.

Original languageEnglish (US)
Pages (from-to)531-538
Number of pages8
JournalAstrophysical Journal
Volume680
Issue number1
DOIs
StatePublished - Jun 10 2008
Externally publishedYes

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gamma ray bursts
energetics
x rays
light curve
telescopes
energy
fluence
collimation
suggestion
spacecraft
distribution
slopes
wavelength
decay
estimates
wavelengths

Keywords

  • Gamma rays: bursts

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Gamma-ray burst energetics in the Swift ERA. / Kocevski, Daniel; Butler, Nathaniel.

In: Astrophysical Journal, Vol. 680, No. 1, 10.06.2008, p. 531-538.

Research output: Contribution to journalArticle

Kocevski, Daniel ; Butler, Nathaniel. / Gamma-ray burst energetics in the Swift ERA. In: Astrophysical Journal. 2008 ; Vol. 680, No. 1. pp. 531-538.
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