10.4m GTC observations of the nearby VHE-detected GRB 190829A/SN 2019oyw

TL;DR

This study presents multi-band photometric and spectroscopic observations of GRB 190829A's afterglow and associated supernova, comparing it with GRB 180728A to explore emission mechanisms and progenitor characteristics.

Contribution

First detailed GTC observations of GRB 190829A's afterglow and supernova, providing insights into emission mechanisms and progenitor properties, and comparing it with a similar GRB.

Findings

Supernova SN 2019oyw is of Type Ic-BL and powered by Ni decay.

Cooling frequency passes between optical and X-ray bands early on.

Prompt emission properties are similar, but spectral differences exist.

Abstract

Aims. GRB 190829A (z = 0.0785), detected by Fermi and Swift with two emission episodes separated by a quiescent gap of ~40 s, was also observed by the H.E.S.S. telescopes at Very-High Energy (VHE). We present the 10.4m GTC observations of the afterglow of GRB 190829A and underlying supernova and compare it against a similar GRB 180728A and discuss the implications on underlying physical mechanisms producing these two GRBs. Methods. We present multi-band photometric data along with spectroscopic follow-up observations taken with the 10.4m GTC telescope. Together with the data from the prompt emission, the 10.4m GTC data are used to understand the emission mechanisms and possible progenitor. Results. A detailed analysis of multi-band data of the afterglow demands cooling frequency to pass between the optical and X-ray bands at early epochs and dominant with underlying SN 2019oyw later on. Conclusions. Prompt emission temporal properties of GRB 190829A and GRB 180728A are similar, however the two pulses seem different in the spectral domain. We found that the supernova (SN) 2019oyw associated with GRB 190829A, powered by Ni decay, is of Type Ic-BL and that the spectroscopic/photometric properties of this SN is consistent with those observed for SN 1998bw but evolved comparatively early.