Discovery of the nearby long, soft GRB 100316D with an associated supernova

Abstract

We report the Swift discovery of nearby long, soft gamma-ray burst GRB\n100316D, and the subsequent unveiling of its low redshift host galaxy and\nassociated supernova. We derive the redshift of the event to be z = 0.0591 +/-\n0.0001 and provide accurate astrometry for the GRB-SN. We study the extremely\nunusual prompt emission with time-resolved gamma-ray to X-ray spectroscopy, and\nfind that the spectrum is best modelled with a thermal component in addition to\na synchrotron emission component with a low peak energy. The X-ray light curve\nhas a remarkably shallow decay out to at least 800 s. The host is a bright,\nblue galaxy with a highly disturbed morphology and we use Gemini South, VLT and\nHST observations to measure some of the basic host galaxy properties. We\ncompare and contrast the X-ray emission and host galaxy of GRB 100316D to a\nsubsample of GRB-SNe. GRB 100316D is unlike the majority of GRB-SNe in its\nX-ray evolution, but resembles rather GRB 060218, and we find that these two\nevents have remarkably similar high energy prompt emission properties.\nComparison of the host galaxies of GRB-SNe demonstrates, however, that there is\na great diversity in the environments in which GRB-SNe can be found. GRB\n100316D is an important addition to the currently sparse sample of\nspectroscopically confirmed GRB-SNe, from which a better understanding of long\nGRB progenitors and the GRB--SN connection can be gleaned.\n