Open AccessSoft gamma‐ray repeater giant flares in the BATSE short gamma‐ray burst catalogue: constraints from spectroscopy
Author(s) -
Lazzati Davide,
Ghirlanda Giancarlo,
Ghisellini Gabriele
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society: letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.067
H-Index - 122
eISSN - 1745-3933
pISSN - 1745-3925
DOI - 10.1111/j.1745-3933.2005.00062.x
Subject(s) - physics , astrophysics , flare , black body radiation , light curve , gamma ray burst , spectral line , gamma ray , galaxy , astronomy , radiation , quantum mechanics
The giant flare observed on 2004 December 27 from SGR 1806−20 has revived the idea that a fraction of short (<2 s) gamma‐ray bursts (GRBs) are due to giant flares from soft gamma‐ray repeaters (SGRs) located in nearby galaxies. One of the distinguishing characteristics of these events is the thermal (blackbody) spectrum with temperatures ranging from ∼50 to ∼180 keV, with the highest temperature observed for the initial 0.2‐s spike of the 2004 December 27 event. We have analysed the spectra of a complete sample of short GRBs with peak fluxes greater than 4 photon s −1 cm −2 detected by BATSE. Of the 115 short GRBs so selected, only 76 had sufficient signal‐to‐noise ratio to allow the spectral analysis. We find only three short GRBs with a spectrum well fitted by a blackbody, with 60 ≲ kT ≲ 90 keV , albeit with a considerably longer duration (i.e. ≳1 s) and a more complex light curve than the 2004 December 27 event. This implies a stringent limit on the rate of extragalactic SGR giant flares with spectral properties analogous to the December 27 flare. We conclude that up to 4 per cent of the short GRBs could be associated with giant flares (2σ confidence). This implies that either the distance to SGR 1806−20 is smaller than 15 kpc or the rate of Galactic giant flares is lower than the estimated 0.033 yr −1 .