Discovery of the broad-lined Type Ic SN 2013cq associated with the very energetic GRB 130427A

TL;DR

This paper reports the discovery of a broad-lined Type Ic supernova, SN 2013cq, associated with the very energetic GRB 130427A at moderate redshift, confirming that high-energy GRBs can be linked to SNe Ic-BL.

Contribution

It provides the first detailed observation of an SN Ic-BL associated with a very energetic GRB at moderate redshift, expanding understanding of GRB-SN connections.

Findings

Detection of SN 2013cq consistent with SN Ic-BL features.

SN 2013cq is slightly fainter than SN 1998bw.

GRB 130427A is among the most energetic GRBs with an associated SN.

Abstract

Long-duration gamma-ray bursts (GRBs) at z < 1 are in most cases found to be accompanied by bright, broad-lined Type Ic supernovae (SNe Ic-BL). The highest-energy GRBs are mostly located at higher redshifts, where the associated SNe are hard to detect observationally. Here we present early and late observations of the optical counterpart of the very energetic GRB 130427A. Despite its moderate redshift z = 0.3399+/-0.0002, GRB 130427A is at the high end of the GRB energy distribution, with an isotropic-equivalent energy release of Eiso ~ 9.6x10^53 erg, more than an order of magnitude more energetic than other GRBs with spectroscopically confirmed SNe. In our dense photometric monitoring, we detect excess flux in the host-subtracted r-band light curve, consistent with what expected from an emerging SN, ~0.2 mag fainter than the prototypical SN 1998bw. A spectrum obtained around the time of the SN peak (16.7 days after the GRB) reveals broad undulations typical of SNe Ic-BL, confirming the presence of a SN, designated SN 2013cq. The spectral shape and early peak time are similar to those of the high expansion velocity SN 2010bh associated with GRB 100316D. Our findings demonstrate that high-energy long-duration GRBs, commonly detected at high redshift, can also be associated with SNe Ic-BL, pointing to a common progenitor mechanism.