The GROND gamma-ray burst sample. I. Overview and statistics

TL;DR

This paper presents a comprehensive overview and statistical analysis of 514 GRB afterglow observations made with GROND over nine years, including new discoveries, redshift measurements, and host galaxy identifications.

Contribution

It provides the first extensive dataset of GROND GRB afterglow measurements, including new detections, redshift estimates, and host galaxy identifications, enhancing understanding of GRB properties.

Findings

81% optical/NIR afterglow detection rate within 30 min for long GRBs

Discovery of 10 new GRB afterglows and one candidate

Identification of the sixth GRB with a 2175 Å dust feature

Abstract

A dedicated gamma-ray burst (GRB) afterglow observing program was performed between 2007 and 2016 with GROND, a seven-channel optical and near-infrared imager at the 2.2m telescope of the Max-Planck Society at ESO/La Silla. In this first of a series of papers, we describe the GRB observing plan, providing first readings of all so far unpublished GRB afterglow measurements and some observing statistics. In total, we observed 514 GRBs with GROND, including 434 Swift-detected GRBs, representing 81\% of the observable Swift sample. For GROND-observations within 30 min of the GRB trigger, the optical/NIR afterglow detection rate is 81\% for long- and 57\% for short-duration GRBs. We report the discovery of ten new GRB afterglows plus one candidate, along with redshift estimates (partly improved) for four GRBs and new host detections for seven GRBs. We identify the (already known) afterglow of GRB 140209A as the sixth GRB exhibiting a 2175 Angstroem dust feature. As a side result, we identified two blazars, with one at a redshift of z=3.8 (in the GRB 131209A field).