GRB 071028B, a burst behind large amounts of dust in an unabsorbed galaxy

TL;DR

This paper presents detailed optical and near-infrared observations of GRB 071028B, revealing its host galaxy's redshift, the afterglow's moderate extinction, and its energetic properties, providing insights into dust effects in gamma-ray burst environments.

Contribution

First detailed multi-band study of GRB 071028B's afterglow and host galaxy, including photometric redshift and extinction analysis, highlighting dust effects in GRB observations.

Findings

Photometric redshift of host galaxy: z = 0.94

Afterglow has moderate extinction with AV(SB) ≈ 0.70 mag

Isotropic energy release: ~1.4 x 10^51 erg

Abstract

We report on the discovery and properties of the fading afterglow and underlying host galaxy of GRB 071028B, thereby facilitating a detailed comparison between these two. Observations were performed with the Gamma-ray Burst Optical and Near-infrared Detector at the 2.2 m telescope on the La Silla Paranal Observatory in Chile. We conducted five observations from 1.9 d to 227.2 d after the trigger and obtained deep images in the g'r'i'z' and JHKs bands. Based on accurate seven-channel photometry covering the optical to near-infrared wavelength range, we derive a photometric redshift of z = 0.94 +0.05 -0.10 for the unabsorbed host galaxy of GRB 071028B. In contrast, we show that the afterglow with an intrinsic extinction of AV(SB) = (0.70 +/- 0.11) mag is moderately absorbed and requires a relatively flat extinction curve. According to the reported Swift/BAT observations, the energetics yield an isotropic energy release of E(gamma,iso.,rest) = (1.4 +2.4 -0.7) x 10^51 erg.