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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 (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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 95 481 GRB Minimum Timescales
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
Bytes Format Units Label Explanations
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)
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) catalog (see also Butler et al. 2010, J/ApJ/711/495; Butler 2013AstRv...8a.103B).
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 27-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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