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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 24 343 tburst of the Each GRB in Our Good Sample
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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
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Bytes Format Units Label Explanations
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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)
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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.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 26-Jun-2017