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

Abstract

Aims. Gamma-ray burst (GRB) 190829A (z = 0.0785) was detected by Fermi and Swift and also at very high energy (VHE) by the High-Energy Stereoscopic System (H.E.S.S.) telescopes. The prompt emission displayed two emission episodes separated by a quiescent gap of ∼40 s. We present the 10.4 m Gran Telescopio Canarias (GTC) observations of the afterglow of GRB 190829A and its underlying supernova. We also compare GRB 190829A to GRB 180728A, a GRB with similar behaviour, 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 10.4 m GTC telescope. Together with the data from the prompt emission, the 10.4 m GTC data are used to understand the emission mechanisms and possible progenitor. Results. A detailed analysis of the multi-band observations of the afterglow requires the cooling frequency to pass between the optical and X-ray bands at early epochs. The afterglow then transitions to the underlying supernova (SN) 2019oyw, which dominates later on. Conclusions. Although the prompt emission temporal properties of GRB 190829A and GRB 180728A are similar, the two pulses are different in the spectral domain. We find that SN 2019oyw associated with GRB 190829A is powered by Ni decay and is a Type Ic-BL SN. The spectroscopic and photometric properties of this SN are consistent with those observed for SN 1998bw, but evolved earlier.

The early afterglow of GRB 190829A

“…Similarly to other nearby long GRBs (e.g. Woosley & Bloom 2006;Cano et al 2017), it was followed by a bright broad-lined Type Ic supernova SN 2019oyw (Hu et al 2021).…”

“…Our model shows a dominant RS component in the UV/optical/nIR range up to ≈1 d after the burst. The underlying FS component begins to emerge several hours after the burst, and might account, at least partially, for the blue excess visible in the optical spectra at 0.3 d (Hu et al 2021).…”

GRB 140102A: Insight into Prompt Spectral Evolution and Early Optical Afterglow Emission

“…This could not be explained by the frequency crossing the X-ray band as the photon index reverses back to the original position after this phase. This unusual emission could be originating due to patchy shells or a refreshed shocks (Chand et al 2020;Hu et al 2021).…”

Gamma-Ray Bursts at TeV Energies: Observational Status

“…The X-ray light curve showed an interesting structure with multiple re-brightening events, most notably significantly increasing in brightness around 1000 s after burst time. Due to the bright nature of this burst, multiple ground based optical observations were made, allowing the identification of the GRB host galaxy [54] and ultimately measuring the GRB redshift at a relatively very local z = 0.0785 ± 0.0005. Although this GRB was very bright, its brightness was largely due to its relative closeness and in fact was of rather low luminosity and had an isotropic energy release of only around 2 × 10 50 erg.…”