J/ApJ/811/93 Fermi/GBM GRB minimum timescales (Golkhou+, 2015)
The energy dependence of GRB minimum variability timescales.
Golkhou V.Z., Butler N.R., Littlejohns O.M.
<Astrophys. J., 811, 93 (2015)>
=2015ApJ...811...93G 2015ApJ...811...93G (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays ; Redshifts
Keywords: gamma-ray burst: general; gamma-rays: general; methods: statistical
Abstract:
We constrain the minimum variability timescales for 938 gamma-ray
bursts (GRBs) observed by the Fermi/Gamma-ray Burst Monitor instrument
prior to 2012 July 11. The tightest constraints on progenitor radii
derived from these timescales are obtained from light curves in the
hardest energy channel. In the softer bands --or from measurements of
the same GRBs in the hard X-rays from Swift-- we show that variability
timescales tend to be a factor of two to three longer. Applying a
survival analysis to account for detections and upper limits, we find
median minimum timescale in the rest frame for long-duration and
short-duration GRBs of 45 and 10ms, respectively. Less than 10% of
GRBs show evidence for variability on timescales below 2ms. These
shortest timescales require Lorentz factors ≳400 and imply typical
emission radii R∼1x1014cm for long-duration GRBs and R∼3x1013cm
for short-duration GRBs. We discuss implications for the GRB fireball
model and investigate whether or not GRB minimum timescales evolve
with cosmic time.
Description:
We consider 949 GRBs published in the second Fermi/GBM GRB catalog
(von Kienlin et al. 2014, J/ApJS/211/13), spanning the first four
years of the Fermi mission (between 2008 July 14 and 2012 July 11,
inclusive).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 97 938 GRB minimum timescales
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See also:
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/ApJ/763/15 : Fermi GRB analysis. III. T90 distributions (Qin+, 2013)
J/ApJ/748/134 : Variability components in BATSE GRB LCs (Gao+, 2012)
J/ApJ/756/112 : Fermi/GBM GRB time-resolved spectral analysis (Lu+, 2012)
J/A+A/525/A53 : GBM parameters for detected FERMI bursts (Guetta+, 2011)
J/ApJ/722/520 : Gamma-ray light curves of Fermi blazars (Abdo+, 2010)
J/ApJ/711/495 : Durations of Swift/BAT GRBs (Butler+, 2010)
J/MNRAS/268/305 : Variability of optically selected quasars (Hook+ 1994)
http://www.mpe.mpg.de/~jcg/grbgen.html : GRBs compilation
http://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html : Fermi
GBM burst online catalog
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- Trigger Trigger ID
11- 17 A7 --- GRB GRB Name
19- 19 A1 --- f_dtmin Upper limit flag on dtmin
21- 26 F6.3 s dtmin [0.002/32.3] Minimum variability timescale
28- 32 F5.3 s e_dtmin [0.001/3]? Uncertainty on dtmin
34- 39 F6.3 s dtSN [0.001/20] Shortest measurable timescale
41- 45 F5.3 s e_dtSN [0.001/2] Uncertainty on dtSN
47- 53 F7.3 s T90 [0.04/604.5] Duration time;
central 90% of gamma-ray counts
55- 60 F6.3 s e_T90 [0.03/35.4] Uncertainty on T90
62- 69 F8.3 s T100b [-257.1/58] Estimated event start
71- 77 F7.3 s T100e [-0.3/608.6] Estimated event stop
79- 82 F4.2 --- sigXtmin [0.05/1.9] Haar-Structure Function;
minimum variability timescale
84- 87 F4.2 --- sigXtSN [0.03/1] Haar-Structure Function;
shortest measurable timescale
89- 94 F6.4 --- z [0.1/8.1]? Redshift
97- 97 I1 --- r_z [1/2]? Redshift Reference (1)
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Note (1): Redshift reference as follows:
1 = Butler et al. (2007ApJ...671..656B 2007ApJ...671..656B, 2010, J/ApJ/711/495 and references
therein), Butler 2013AstRv...8a.103B 2013AstRv...8a.103B
2 = Taken from http://www.mpe.mpg.de/~jcg/grbgen.html
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 14-Jan-2016