J/ApJ/787/90 Gamma-ray bursts minimum timescales (Golkhou+, 2014)
Uncovering the intrinsic variability of gamma-ray bursts.
Golkhou V.Z., Butler N.R.
<Astrophys. J., 787, 90 (2014)>
=2014ApJ...787...90G 2014ApJ...787...90G (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays ; Redshifts ; Models
Keywords: gamma-ray burst: general - methods: data analysis -
methods: statistical
Abstract:
We develop a robust technique to determine the minimum variability
timescale for gamma-ray burst (GRB) light curves, utilizing Haar
wavelets. Our approach averages over the data for a given GRB,
providing an aggregate measure of signal variation while also
retaining sensitivity to narrow pulses within complicated time series.
In contrast to previous studies using wavelets, which simply define
the minimum timescale in reference to the measurement noise floor, our
approach identifies the signature of temporally smooth features in the
wavelet scaleogram and then additionally identifies a break in the
scaleogram on longer timescales as a signature of a true, temporally
unsmooth light curve feature or features. We apply our technique to
the large sample of Swift GRB gamma-ray light curves and for the first
time - due to the presence of a large number of GRBs with measured
redshift - determine the distribution of minimum variability timescales
in the source frame. We find a median minimum timescale for
long-duration GRBs in the source frame of Δtmin=0.5 s, with
the shortest timescale found being on the order of 10 ms. This short
timescale suggests a compact central engine (3x103 km). We discuss
further implications for the GRB fireball model and present a
tantalizing correlation between the minimum timescale and redshift,
which may in part be due to cosmological time dilation.
Description:
We analyze the Swift data set up until 2013 October 27, which consists
of 744 GRBs, 251 with measured redshifts. We only consider those GRBs
with total light curve S/N≥10, leaving 517 GRBs. Of these, we are
able to confirm the presence of a linear rise phase in σX,Δt
on short timescales for 281 GRBs. We quote upper-limit values for the
remainder. Most (256) of the bursts in this compiled subsample are
long-duration (T90>3 s) GRBs. In the compiled subsample, 98 GRBs
have measured redshift. The temporal specifications of all 517 GRBs
discussed here are determined using fully automatic software.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 95 481 GRB Minimum Timescales
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See also:
J/ApJ/711/495 : Durations of Swift/BAT GRBs (Butler+, 2010)
J/ApJS/209/20 : Swift GRB catalog with X-ray data (Grupe+, 2013)
J/ApJ/811/93 : Fermi/GBM GRB minimum timescales (Golkhou+, 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 Gamma-ray burst identifier (GRB YYMMDDA
in Simbad)
9- 14 F6.2 s Deltmin ? Minimum timescale in observer frame (1)
16- 21 F6.3 s e_Deltmin ? Uncertainty in Deltmin
23- 28 F6.3 s Deltsnr Shortest timescale with a net
σX,Δt over Poisson level (1)
30- 35 F6.3 s e_Deltsnr Uncertainty in Deltsnr
37- 42 F6.2 s T90 GRB duration (2)
44- 48 F5.2 s e_T90 Uncertainty in T90 (2)
50- 55 F6.2 s TR45 Robust duration estimate (2)
57- 61 F5.3 s e_TR45 Uncertainty in TR45 (2)
63- 67 F5.3 --- sigXtmin ? Fractional flux variation level
(σX,Δt) at Deltmin
69- 73 F5.3 --- sigXtsnr Fractional flux variation level
(σX,Δt) at Deltsnr
75- 82 F8.4 --- chi2 Model χ2/ν
84- 88 F5.1 --- S/N Signal-to-Noise ratio (2)
90- 95 F6.4 --- z ? Redshift (2)
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Note (1): Bursts where linear phases in σX,Δt could not be fitted
by a model with confidence level >90%, are considered to yield upper
limits Δtmin≤Δtsnr.
Note (2): From the Butler et al. (2007ApJ...671..656B 2007ApJ...671..656B) catalog (see also
Butler et al. 2010, J/ApJ/711/495; Butler 2013AstRv...8a.103B 2013AstRv...8a.103B).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 27-Jun-2017