Temporal Properties of Precursors, Main Peaks, and Extended Emissions of Short GRBs in the Third Swift/BAT GRB Catalog

Abstract

A comprehensive study is given to short gamma-ray bursts (sGRBs) in the third Swift Burst Alert Telescope (BAT) GRB Catalog from 2004 December to 2019 July. We examine in detail the temporal properties of the three components in the prompt gamma-ray emission phase, including precursors, main peaks, and extended emissions (EEs). We investigate the similarity of the main peaks between one-component and two-component sGRBs. It is found that there is no substantial difference among their main peaks. Importantly, comparisons are made between in the single-peaked sGRBs and the double-peaked sGRBs. It is found that our results for main peaks in Swift/BAT sGRBs are essentially consistent with those in the Compton Gamma Ray Observatory Burst And Transient Source Experiment (BATSE) ones recently found in our Paper I. Interestingly, we suspect, besides the newly found MODE I/II evolution forms of pulses in BATSE sGRBs in Paper I, that there would have been more evolution modes of pulses across differently adjacent energy channels in view of the Swift/BAT observations. We further inspect the correlation of the main peaks with either the precursors or the EEs. We find that the main peaks tend to last longer than the precursors but shorter than the EEs. Moreover, we verify the power-law correlations related with peak fluxes of the three components, strongly suggesting that they are produced from the similar central-engine activities. In particular, we compare the temporal properties of GRB 170817A with other sGRBs with EE and find no obvious differences between them.

Overall Spectral Properties of Prompt Emissions with Diverse Segments in Swift/BAT Short Gamma-ray Bursts

“…The mask-weighted light curve data of the sGRBs with a 8-ms resolution are taken from the Swift website (Lien et al 2016) 2 . Note that all light curves of the selected 26 Swift/BAT sGRBs can be well fitted by the empirical Kocevski-Ryde-Liang (KRL) function that has been popularly used in literatures (e.g., Kocevski et al 2003;Zhang & Qin 2005;Li et al , 2021. Fig.…”

“…From 2004 December to 2019 July, Swift/BAT had detected 124 sGRBs, of which 26 sGRBs have been selected for this study, including 12 single-peaked sGRBs (SPs), 5 double-peaked sGRBs (DPs), 7 sGRBs with precursor (Pre+sGRBs), and 2 sGRBs with EE (sGRBs+EE). For the DPs, we still divide them into the Mtight types (Mt-DPs) and the M-loose ones (Ml-DPs) as done in our recent works (Li et al , 2021. The criteria that we identify a significant precursor or EE pulse can be referred to our recent paper (Li et al 2021).…”

“…For the DPs, we still divide them into the Mtight types (Mt-DPs) and the M-loose ones (Ml-DPs) as done in our recent works (Li et al , 2021. The criteria that we identify a significant precursor or EE pulse can be referred to our recent paper (Li et al 2021). The standard BAT software (HEADAS 6.26.1) and the latest calibration database (CALDB: 2017-10-16) are used.…”

“…According to the classification criterion of the T 90 duration distribution (Kouveliotou et al 1993), approximately 10% are short GRBs (sGRBs), with a typical duration of T 90 < 2s (Zhang & Choi 2008;Zhang et al 2018). Prompt garmma-ray emissions of GRBs may consist of diverse components, namely precursors, main peaks and extended emissions (EEs), or parts of them, within both long GRBs (lGRBs) and sGRBs (Metzger et al 1974;Koshut et al 1995;Norris & Bonnell 2006;Troja et al 2010;Bernardini et al 2013;Hu et al 2014;Lan et al 2018Lan et al , 2020Zhang et al 2018b;Zhong et al 2019;Zhang et al 2020a;Li et al 2021). The precursor reported first in GRB 720427 is a dim peak occurring before the brightest prompt emission of main peaks (Metzger et al 1974), and the EE as the softer γ-ray emissions usually following the main peaks after a quiescent period is another important component (e.g., Lazzati et al 2001;Connaughton 2002;Burrows et al 2005).…”

“…Then, we examined the temporal properties of the main peaks and the other two components of Swift/BAT sGRBs (Li et al 2021). We adopted a united criterion to search for precursors and EEs as their signals prior and posterior to the main peaks at least S/N > 3 above background (see section 2.2 in Li et al 2021). Unfortunately, no such triplets have been reported in single sGRB to date.…”