GRB 120422A/SN 2012bz: Bridging the gap between low- and high-luminosity gamma-ray bursts

Abstract

Context. At low redshift, a handful of gamma-ray bursts (GRBs) have been discovered with luminosities that are substantially lower (L iso < 10 48.5 erg s -1 ) than the average of more distant ones (L iso > 10 49.5 erg s -1 ). It has been suggested that the properties of several low-luminosity (low-L) GRBs are due to shock break-out, as opposed to the emission from ultrarelativistic jets. This has led to much debate about how the populations are connected. Aims. The burst at redshift z = 0.283 from 2012 April 22 is one of the very few examples of intermediate-L GRBs with a -ray luminosity of L iso 10 49.6-49.9 erg s -1 that have been detected up to now. With the robust detection of its accompanying supernova SN 2012bz, it has the potential to answer important questions on the origin of low-and high-L GRBs and the GRB-SN connection. Methods. We carried out a spectroscopy campaign using medium-and low-resolution spectrographs with 6-10-m class telescopes, which covered a time span of 37.3 days, and a multi-wavelength imaging campaign, which ranged from radio to X-ray energies over a duration of 270 days. Furthermore, we used a tuneable filter that is centred at H to map star-formation in the host and the surrounding galaxies. We used these data to extract and model the properties of different radiation components and fitted the spectral energy distribution to extract the properties of the host galaxy.