Novel distance indicator for gamma-ray bursts associated with supernovae

¹ Dipartimento di FisicaSapienza Universitá di Roma and ICRA, Piazzale Aldo Moro 5, 00185 Roma, Italy
e-mail: gb.pisani@icranet.org
² ICRANet, Piazza della Repubblica 10, 65122 Pescara, Italy
³ Université de Nice Sophia Antipolis, Grand Chateau Parc Valrose, 06103 Nice Cedex 2, France

Received: 30 November 2012
Accepted: 4 March 2013

Abstract

Context. It has been proposed that the temporal coincidence of a gamma-ray burst (GRB) and a type Ib/c supernova (SN) can be explained with the concept of induced gravitational collapse (IGC), induced by the matter ejected from an SN Ib/c accreting onto a neutron star (NS). The NS is expected to reach the critical mass necessary for it to collapse to a black hole (BH) and emit a GRB. We found a standard luminosity light curve behavior in the late-time X-ray emission of this subclass of GRBs.

Aims. We test if this standard behavior in the luminosity found in this subclass of GRBs can become a redshift estimator of these sources.

Methods. We selected a sample of GRBs that belong to this subclass of IGC GRBs associated to an SN (IGC GRB-SN sources). These sources have an isotropic energy E_iso > 10⁵² erg and their cosmological redshifts are in the range of z = 0.49−1.261. We focused on the corresponding X-ray luminosity light curves.

Results. We find that all GRBs of the sample with measured redshift present a standard luminosity late-time light curve in the 0.3−10 keV rest-frame energy range. We used these results to estimate the GRB redshift of the sample without a measured redshift and found results consistent with other possible redshift indicators.

Conclusions. The standard late-time X-ray luminosity light curve of all GRBs of the sample shows a common physical mechanism in this particular phase of the X-ray emission, possibly related to the creation of the NS from the SN process. This scaling law moreover represents strong evidence of very low or even absent beaming in this late phase of the X-ray afterglow emission process. This could be a fundamental tool for estimating the redshift of GRBs that belong to this subclass of events. We are currently expanding this subclass of GRBs to further verify the universal validity of this new redshift estimation method.