GAMMA RAYS: BURSTS

GRB 011121: A Massive Star Progenitor

Of the cosmological gamma-ray bursts, GRB 011121 has the lowest redshift, z=0.36. More importantly, the multicolor excess in the afterglow detected in the Hubble Space Telescope (HST) light curves is compelling observational evidence of an underlying …

GRB 010222: A Burst within a Starburst

We present millimeter- and submillimeter-wavelength observations and near-infrared K-band imaging toward the bright gamma-ray burst GRB 010222. Over seven different epochs, a constant source was detected with an average flux density of 3.74+/-0.53 …

The Afterglow and the Host Galaxy of the Dark Burst GRB 970828

GRB 970828 was the first well-localized γ-ray burst (GRB) X-ray afterglow for which no optical afterglow was found despite a prompt, deep search down to R$_lim$åisebox-0.5ex 24.5 mag. We report the discovery of a short-lived radio flare within the …

Beaming in Gamma-Ray Bursts: Evidence for a Standard Energy Reservoir

We present a comprehensive sample of all gamma-ray burst (GRB) afterglows with known distances, and we derive their conical opening angles based on observed broadband breaks in their light curves. Within the framework of this conical jet model, we …

Broadband Observations of the Afterglow of GRB 000926: Observing the Effect of Inverse Compton Scattering

GRB 000926 has one of the best-studied afterglows to date, with multiple X-ray observations, as well as extensive multifrequency optical and radio coverage. Broadband afterglow observations, spanning from X-ray to radio frequencies, provide a probe …

GRB 000418: A Hidden Jet Revealed

We report on optical, near-infrared, and centimeter radio observations of GRB 000418 that allow us to follow the evolution of the afterglow from 2 to 200 days after the γ-ray burst (GRB). In modeling these broadband data, we find that an isotropic …

The Redshift and the Ordinary Host Galaxy of GRB 970228

The gamma-ray burst of 1997 February 28 (GRB 970228) ushered in the discovery of the afterglow phenomenon. Despite intense study of the nearby galaxy, however, the nature of this galaxy and the distance to the burst eluded the community. Here we …

Multicolor Observations of the GRB 000926 Afterglow

We present multicolor light curves of the optical afterglow of gamma-ray burst (GRB) 000926. Beginning åisebox-0.5ex 1.5 days after the burst, the light curves of this GRB steepen measurably. The existence of such achromatic breaks is usually taken …

A Jet Model for the Afterglow Emission from GRB 000301C

We present broadband radio observations of the afterglow of GRB 000301C, spanning from 1.4 to 350 GHz for the period of 3-130 days after the burst. These radio data, in addition to measurements in the optical bands, suggest that the afterglow arises …

GRB 991216 Joins the Jet Set: Discovery and Monitoring of Its Optical Afterglow

The optical light curve of the energetic γ-ray burst GRB 991216 is consistent with jetlike behavior in which a power- law decay steepens from t$^-1.22+/-0.04$ at early times to t$^-1.53+/-0.05$ in a gradual transition at around 2 days. The derivation …