Late time observations of GRB080319B: jet break, host galaxy and accompanying supernova

TL;DR

This paper reports late-time multi-wavelength observations of GRB080319B, confirming a jet break, detecting a supernova, and characterizing its faint host galaxy, providing insights into the burst's energy, environment, and relation to low-luminosity GRBs.

Contribution

It presents the first detailed late-time optical and X-ray analysis of GRB080319B, revealing jet collimation, an associated supernova, and a faint host galaxy, expanding understanding of extreme GRB events.

Findings

Achromatic jet break at ~11 days indicating collimated outflow.

Detection of a supernova component in late-time light.

Host galaxy is a faint dwarf with low metallicity.

Abstract

The Swift discovered GRB080319B was by far the most distant source ever observed at naked eye brightness, reaching a peak apparent magnitude of 5.3 at a redshift of z=0.937. We present our late-time optical (HST, Gemini & VLT) and X-ray (Chandra) observations, which confirm that an achromatic break occurred in the power-law afterglow light curve at ~11 days post-burst. This most likely indicates that the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy in the jet E_{jet} \gsim 10^{52} erg. Our observations also show a late-time excess of red light, which is well explained if the GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. The latest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy (r(AB)\approx27.0, rest-frame M_B\approx-17.2). This galaxy is small even by the standards of other GRB hosts, which is suggestive of a low metallicity environment. Intriguingly, the properties of this extreme event - a small host and bright supernova - are entirely typical of the very low-luminosity bursts such as GRB980425 and GRB060218.