Comparing the spectral lag of short and long gamma-ray bursts and its relation with the luminosity

Abstract

We investigated the rest frame spectral lags of two complete samples of bright long (50) and short (6) gamma-ray bursts (GRB) detected by Swift. We analysed the Swift /BAT data through a discrete cross-correlation function (CCF) fitted with an asymmetric Gaussian function to estimate the lag and the associated uncertainty. We find that half of the long GRBs have a positive lag and half a lag consistent with zero. All short GRBs have lags consistent with zero. The distributions of the spectral lags for short and long GRBs have different average values. Limited by the small number of short GRBs, we cannot exclude at more than 2 σ significance level that the two distributions of lags are drawn from the same parent population. If we consider the entire sample of long GRBs, we do not find evidence for a lag-luminosity correlation, rather the lag-luminosity plane appears filled on the left hand side, thus suggesting that the lagluminosity correlation could be a boundary. Short GRBs are consistent with the long ones in the lag-luminosity plane.

Limits on quantum gravity effects from Swift short gamma-ray bursts

“…Short GRBs (S-GRBs) are consistent with negligible spectral lag (Norris et al 2001;Norris & Bonnell 2006;Bernardini et al 2015), while L-GRBs have positive, null or negative lag (Ukwatta et al 2012;Bernardini et al 2015). No clear physical motivation helps one in accounting for the spectral lag contribution in each single case (for possible interpretations of the spectral lag see Dermer 1998;Kocevski & Liang 2003;Ryde 2005;Peng et al 2011;Salmonson 2000;Ioka & Nakamura 2001;Dermer 2004;Shen et al 2005;Lu et al 2006;Guiriec et al 2010Guiriec et al , 2013Mochkovitch et al 2016).…”

“…At variance with previous studies, we considered the largest possible sample of S-GRBs observed by the Swift/Burst Alert Telescope (BAT; Barthelmy et al 2005). This sample provides three main advantages: i) the spectral lag of S-GRBs is negligible; ii) the dispersion of the spectral lag of S-GRBs is much smaller than for L-GRBs (Bernardini et al 2015); iii) the use of a single instrument reduces also the possible systematics that arise when combining data from different instruments (Ellis et al 2008); iv) Swift/BAT enables us to perform the analysis on the largest available sample of S-GRBs with redshift.…”

A simple theory of lags in gamma-ray bursts: Comparison to observations

“…We now fix the two energy bands, 1 [100-150] keV and 2 keV, which were used to obtain the lags in the source frame by Ukwatta et al (2012), Bernardini et al (2015), and Heussaff (2015), and in Fig. 3a we represent the lag as a function of the peak energy of the pulse spectrum.…”

“…Ukwatta et al (2012), Bernardini et al (2015), and Heussaff (2015) recently constructed samples of rest-frame lags for long bursts with known redshift observed with the Swift satellite.…”

“…Moreover spectral lags have been found to correlate with burst luminosity and can be used as distance indicators (Norris et al 2000;Norris 2002). In the present Swift and Fermi era more lags have been obtained in bursts with known distance, which allows the testing of the lag-luminosity relation with larger samples (Ukwatta et al 2010(Ukwatta et al , 2012Bernardini et al 2015;Heussaff 2015) or with better spectral coverage in individual events showing several pulses of different intensities (Zhang 2012;Shenoy et al 2013).…”