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

TL;DR

This paper reports the discovery and detailed analysis of the nearby long, soft gamma-ray burst GRB 100316D, its associated supernova, and host galaxy, providing insights into GRB progenitors and the diversity of their environments.

Contribution

It presents the first detailed characterization of GRB 100316D and its host, revealing unique spectral and environmental properties that expand understanding of GRB-SN connections.

Findings

GRB 100316D is at redshift z=0.0591 with a low-energy thermal spectrum.

The X-ray light curve shows an unusually shallow decay.

The host galaxy is bright, blue, and highly disturbed, differing from typical GRB hosts.

Abstract

We report the Swift discovery of nearby long, soft gamma-ray burst GRB 100316D, and the subsequent unveiling of its low redshift host galaxy and associated supernova. We derive the redshift of the event to be z = 0.0591 +/- 0.0001 and provide accurate astrometry for the GRB-SN. We study the extremely unusual prompt emission with time-resolved gamma-ray to X-ray spectroscopy, and find that the spectrum is best modelled with a thermal component in addition to a synchrotron emission component with a low peak energy. The X-ray light curve has a remarkably shallow decay out to at least 800 s. The host is a bright, blue galaxy with a highly disturbed morphology and we use Gemini South, VLT and HST observations to measure some of the basic host galaxy properties. We compare and contrast the X-ray emission and host galaxy of GRB 100316D to a subsample of GRB-SNe. GRB 100316D is unlike the majority of GRB-SNe in its X-ray evolution, but resembles rather GRB 060218, and we find that these two events have remarkably similar high energy prompt emission properties. Comparison of the host galaxies of GRB-SNe demonstrates, however, that there is a great diversity in the environments in which GRB-SNe can be found. GRB 100316D is an important addition to the currently sparse sample of spectroscopically confirmed GRB-SNe, from which a better understanding of long GRB progenitors and the GRB--SN connection can be gleaned.