J/ApJ/763/15 Fermi GRB analysis. III. T90 distributions (Qin+, 2013)
A comprehensive analysis of Fermi gamma-ray burst data.
III. Energy-dependent T90 distributions of GBM GRBs and instrumental selection
effect on duration classification.
Qin Y., Liang E.-W., Liang Y.-F., Yi S.-X., Lin L., Zhang B.-B., Zhang J.,
Lu H.-J., Lu R.-J., Lu L.-Z., Zhang B.
<Astrophys. J., 763, 15 (2013)>
=2013ApJ...763...15Q 2013ApJ...763...15Q
ADC_Keywords: Gamma rays
Keywords: gamma-ray burst: general; methods: statistical
Abstract:
The durations (T90) of 315 gamma-ray bursts (GRBs) detected with
Fermi/GBM (8-1000keV) up to 2011 September are calculated using the
Bayesian Block method. We compare the T90 distributions between this
sample and those derived from previous/current GRB missions. We show
that the T90 distribution of this GRB sample is bimodal, with a
statistical significance level comparable to those derived from the
BeppoSAX/GRBM sample and the Swift/BAT sample, but lower than that
derived from the CGRO/BATSE sample. The short-to-long GRB number ratio
is also much lower than that derived from the BATSE sample, i.e.,
1:6.5 versus 1:3. We measure T90 in several bands, i.e., 8-15,
15-25, 25-50, 50-100, 100-350, and 350-1000keV, to investigate the
energy-dependence effect of the bimodal T90distribution. It is found
that the bimodal feature is well observed in the 50-100 and 100-350keV
bands, but is only marginally acceptable in the 25-50keV and
350-1000keV bands. The hypothesis of bimodality is confidently
rejected in the 8-15 and 15-25keV bands. The T90distributions in
these bands are roughly consistent with those observed by missions
with similar energy bands. The parameter T90 as a function of energy
follows {overline}{T}90∝E-0.20±0.02 for long GRBs.
Considering the erratic X-ray and optical flares, the duration of a
burst would be even longer for most GRBs. Our results, together with
the observed extended emission of some short GRBs, indicate that the
central engine activity timescale would be much longer than T90 for
both long and short GRBs and the observed bimodal T90 distribution
may be due to an instrumental selection effect.
Description:
We include all 315 GRBs detected by the GBM, as reported by the GBM
team in GCN circulars up to 2011 September. We download the data from
the Fermi Archive available at
ftp://legacy.gsfc.nasa.gov/fermi/data/gbm/bursts/
The time-tagged event (TTE) data have excellent time resolution of 2us.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 101 315 Derived Fermi/GBM T90 in different energy bands
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See also:
IX/20 : The Fourth BATSE Burst Revised Catalog (Paciesas+ 1999)
J/ApJS/211/13 : The second Fermi/GBM GRB catalog (4yr) (von Kienlin+, 2014)
J/MNRAS/431/3608 : BeppoSAX/GRBM and Fermi/GBM long GRBs (Dichiara+, 2013)
J/ApJS/207/39 : IPN supplement to the Fermi GBM (Hurley+, 2013)
J/ApJ/756/112 : Fermi/GBM GRB time-resolved spectral analysis (Lu+, 2012)
J/ApJ/754/121 : GRBs from Fermi/GBM and LAT (The Fermi Team, 2012)
J/ApJS/199/18 : The Fermi GBM catalog (Paciesas+, 2012)
J/ApJS/195/2 : The second Swift BAT GRB catalog (BAT2) (Sakamoto+, 2011)
J/A+A/525/A53 : GBM parameters for detected FERMI bursts (Guetta+, 2011)
J/ApJS/180/192 : BeppoSAX/GRBM γ-ray Burst Catalog (Frontera+, 2009)
http://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html : Fermi GBM burst
catalog
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- ID Fermi/GBM GRB identifier (YYMMDDNNN)
11- 17 A7 --- GRB GRB name (YYMMDDA)
19- 24 F6.2 s T8-15 [0.4/262.5]? T90 time in 8-15keV band
26- 29 F4.2 s e_T8-15 [0.2/2.3]? Uncertainty in 8-15keV
31- 36 F6.2 s T15-25 [0.3/273.2]? T90 time in the 15-25keV band
38- 41 F4.2 s e_T15-25 [0.1/2]? Uncertainty in 15-25keV band
43- 48 F6.2 s T25-50 [0.3/256.5]? T90 time in the 25-50keV band
50- 53 F4.2 s e_T25-50 [0.09/1.6]? Uncertainty in 25-50keV band
55- 60 F6.2 s T50-100 [0.2/215.5]? T90 time in the 50-100keV band
62- 65 F4.2 s e_T50-100 [0.1/1.6]? Uncertainty in 50-100keV band
67- 72 F6.2 s T100-350 [0.1/252.6]? T90 time in the 100-350keV band
74- 77 F4.2 s e_T100-350 [0.05/1.9]? Uncertainty in 100-350keV band
79- 84 F6.2 s T350-1000 [0.1/281]? T90 time in the 350-1000keV band
86- 89 F4.2 s e_T350-1000 [0.1/2.1]? Uncertainty in 350-1000keV band
91- 96 F6.2 s T8-1000 [0.1/261.2]? T90 time in the 8-1000keV band
98-101 F4.2 s e_T8-1000 [0.05/1.6]? Uncertainty in 8-1000keV band
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History:
From electronic version of the journal
References:
Zhang et al. Paper I. 2011ApJ...730..141Z 2011ApJ...730..141Z
Lu et al. Paper II. 2012ApJ...756..112L 2012ApJ...756..112L Cat. J/ApJ/756/112
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 09-Oct-2014