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J/ApJ/787/66     Burst duration measurements for a GRB sample     (Zhang+, 2014)

How long does a burst burst? Zhang B.-B., Zhang B., Murase K., Connaughton V., Briggs M.S. <Astrophys. J., 787, 66 (2014)> =2014ApJ...787...66Z (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays Keywords: gamma-ray burst: general Abstract: Several gamma-ray bursts (GRBs) last much longer (∼hours) in γ-rays than typical long GRBs (∼minutes), and it has recently been proposed that these "ultra-long GRBs" may form a distinct population, probably with a different (e.g., blue supergiant) progenitor than typical GRBs. However, Swift observations suggest that many GRBs have extended central engine activities manifested as flares and internal plateaus in X-rays. We perform a comprehensive study on a large sample of Swift GRBs with X-Ray Telescope observations to investigate GRB central engine activity duration and to determine whether ultra-long GRBs are unusual events. We define burst duration tburst based on both γ-ray and X-ray light curves rather than using γ-ray observations alone. We find that tburstcan be reliably measured in 343 GRBs. Within this "good" sample, 21.9% GRBs have tburst≳103 s and 11.5% GRBs have tburst≳104 s. There is an apparent bimodal distribution of tburst in this sample. However, when we consider an "undetermined" sample (304 GRBs) with tburst possibly falling in the gap between GRB duration T90 and the first X-ray observational time, as well as a selection effect against tburst falling into the first Swift orbital "dead zone" due to observation constraints, the intrinsic underlying tburst distribution is consistent with being a single component distribution. We found that the existing evidence for a separate ultra-long GRB population is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion. We also discuss the theoretical implications of our results. In particular, the central engine activity duration of GRBs is generally much longer than the γ-ray T90 duration and it does not even correlate with T90. It would be premature to make a direct connection between T90 and the size of the progenitor star. Description: In this paper, we perform a comprehensive study of Swift X-ray Telescope (XRT) data, focusing on the long-term central engine activities in the X-ray light curves, to address typically how long a burst lasts, and whether the claimed ultra-long GRBs are special. In order to measure tburst, we use only well-sampled XRT light curves with late-time observations. We select a "good" sample based on the following criteria: (1) the X-ray light curve must have at least six data points, excluding upper limits; (2) the X-ray light curve has at least one steep-to-shallow transitions (with the steeper slope < -3); or (3) if the X-ray light curve has no steep-to-shallow transition, the starting time of XRT observation, TX,0, is smaller than T90. For this latter case, we take T90 as tburst. Our final good sample consists of 343 GRBs. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 24 343 tburst of the Each GRB in Our Good Sample
See also: J/A+A/448/L9 : Position catalogue of Swift XRT afterglows (Moretti+, 2006) J/ApJ/701/824 : Afterglows of short and long-duration GRBs (Nysewander+, 2009) J/MNRAS/397/1177 : Swift-XRT observations of GRBs (Evans+, 2009) J/ApJ/711/495 : Durations of Swift/BAT GRBs (Butler+, 2010) J/ApJ/800/16 : Swift-XRT long GRB durations (Boer+, 2015) J/ApJS/224/20 : 10yr of Swift/XRT obs. of GRBs (Yi+, 2016) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 7 A7 --- GRB GRB identifier (YYMMDDA) 9- 10 A2 --- l_logtburst [≥∼ ] Limit flag on logtburst 11- 15 F5.3 [s] logtburst Log tburst 17- 21 F5.3 [s] e_logtburst ? Uncertainty in logtburst 22- 24 A3 --- n_logtburst [T90 ] Note on logtburst (1)
Note (1): In this case, we take T90 as tburst. T90 measures the duration of the time interval during which 90% of the total observed counts have been detected.
History: From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 26-Jun-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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