A search for giant flares from soft gamma-ray repeaters in nearby galaxies in the Konus-WIND short burst sample

Abstract

The knowledge of the rate of soft gamma-ray repeater (SGR) giant flares (GFs) is important for understanding the GF mechanism and the SGR energy budget in the framework of the magnetar model. We estimate the upper limit to the rate using the results of an extensive search for extragalactic SGR GFs among 140 short gamma-ray bursts detected between 1994 and 2010 by Konus-WIND using Interplanetary Network (IPN) localizations and temporal parameters. We show that Konus-WIND and the IPN are capable of detecting GFs with energies of 2.3 × 1046 erg (which is the energy of the GF from SGR 1806-20 assuming a distance of 15 kpc) at distances of up to ∼30 Mpc and GFs with energies of ≲ 1045 erg (which is the energy of the GF from SGR 0526-66) at distances of up to ≈6Mpc. Using a sample of 1896 nearby galaxies, we found that only two bursts, GRB 051103 and GRB 070201, have a low chance coincidence probability between an IPN localization and a nearby galaxy. We found the upper limit to the fraction of GFs among short gamma-ray bursts with fluence above ~5 × 10-7 erg cm-2 to be <8 per cent (95 per cent confidence level). Assuming that the number of active SGRs in nearby galaxies is proportional to their core-collapse supernova rate, we derived the one-sided 95 per cent upper limit to the rate of GFs with energy output similar to the GF from SGR 1806-20 to be (0.6-1.2) × 10-4Q -1.546 yr-1 per SGR, where Q46 is the GF energy output in 1046 erg.