# GAMMA RAYS: BURSTS

## Limits on radioactive powered emission associated with a short-hard GRB 070724A in a star-forming galaxy

We present results of an extensive observing campaign of the short- duration, hard spectrum gamma-ray burst (GRB) 070724A, aimed at detecting the radioactively powered emission that might follow from a binary merger or collapse involving compact …

## GRB081028 and its late-time afterglow re-brightening

Swift captured for the first time a smoothly rising X-ray re-brightening of clear non-flaring origin after the steep decay in a long gamma-ray burst (GRB): GRB081028. A rising phase is likely present in all GRBs but is usually hidden by the prompt …

## GRB090426: the environment of a rest-frame 0.35-s gamma-ray burst at a redshift of 2.609

We present the discovery of an absorption-line redshift of z = 2.609 for GRB090426, establishing the first firm lower limit to a redshift for a gamma-ray burst (GRB) with an observed duration of <2s. With a rest-frame burst duration of T$_90z$ = …

## Casting Light on the Anomalous'' Statistics of Mg II Absorbers Toward Gamma-ray Burst Afterglows: The Incidence of Weak Systems

We revisit echelle spectra (spectral resolution R ≈ 40,000) of eight gamma-ray burst (GRB) afterglows to obtain the incidence (dN/dz) of weak intervening Mg II systems at a mean redshift of langzrang = 1.5. We show that dN/dz of systems having …

## Low-resolution Spectroscopy of Gamma-ray Burst Optical Afterglows: Biases in the Swift Sample and Characterization of the Absorbers

We present a sample of 77 optical afterglows (OAs) of Swift detected gamma-ray bursts (GRBs) for which spectroscopic follow-up observations have been secured. Our first objective is to measure the redshifts of the bursts. For the majority (90%) of …

## The Host Galaxies of Swift Dark Gamma-ray Bursts: Observational Constraints on Highly Obscured and Very High Redshift GRBs

In this work, we present the first results of our imaging campaign at Keck Observatory to identify the host galaxies of dark'' gamma-ray bursts (GRBs), events with no detected optical afterglow or with detected optical flux significantly fainter …

## An Imaging and Spectroscopic Study of Four Strong Mg II Absorbers Revealed by GRB 060418

We present results from an imaging and spectroscopic study of four strong Mg II absorbers of W(2796) gsim 1 ̊A revealed by the afterglow of GRB 060418 at z $_GRB$ = 1.491. These absorbers, at z = 0.603, 0.656, 1.107, and z $_GRB$, exhibit large ion …

## The Discovery of Vibrationally Excited H$_2$ in the Molecular Cloud Near GRB 080607

GRB 080607 has provided the first observational signatures of molecular absorption bands toward any galaxy hosting a gamma-ray burst (GRB). Despite the identification of dozens of features as belonging to various atomic and molecular (H$_2$ and CO) …

## GRB 080503: Implications of a Naked Short Gamma-Ray Burst Dominated by Extended Emission

We report on observations of GRB 080503, a short gamma-ray burst (GRB) with very bright extended emission (about 30 times the gamma-ray fluence of the initial spike) in conjunction with a thorough comparison to other short Swift events. In spite of …

## Generalized Tests for Selection Effects in Gamma-Ray Burst High-Energy Correlations

Several correlations among parameters derived from modeling the high- energy properties of gamma-ray bursts (GRBs) have been reported. We show that well known examples of these have common features indicative of strong contamination by selection …