Near-infrared detection and optical follow-up of the GRB990705 afterglow

TL;DR

This paper reports the detection and analysis of the optical and near-infrared afterglow of GRB990705, revealing a steep decay and a high-density environment, along with potential host galaxy identification.

Contribution

First near-infrared and optical follow-up of GRB990705 providing detailed lightcurve and spectral analysis, indicating a high-density environment and possible host galaxy.

Findings

Steep decay in near-infrared lightcurve with alpha ~ 1.7

Evidence of a high-density environment for the GRB

Possible host galaxy detected 5 days post-burst

Abstract

Optical and near-infrared observations of the GRB990705 error box were carried out with ESO telescopes at La Silla and Paranal in Chile and with the NOAO SPIREX 0.6-meter telescope in Antarctica. We detected the counterpart of this GRB in the near-infrared H band and optical V band. The power-law decline of the near-infrared lightcurve is rather steep with a decay index alpha ~ 1.7 in the first hours, and a possible steepening after one day. Broadband spectral analysis of the optical/near-infrared afterglow suggests that this GRB took place in a high density environment. A deep optical image obtained at Antu (VLT-UT1) about 5 days after the GRB trigger shows at the position of the transient an extended object which might be the host galaxy of GRB990705.