HST Observations of GRBs

The fading optical afterglow of GRB 990123, as seen by HST on Days 16, 59 and 380 after the burst.

On these pages we present images, spectra and scientific results from HST observations of a number of gamma-ray bursts.

GRB 011030 This object has been referred to as an X-ray Flasher (XRF) because its spectrum is dominated by X-rays rather than gamma-rays. This suggested that it might be a GRB at very high redshift, or perhaps a new type of Galactic burster because it lies at low galactic latitude. HST images reveal a faint blue galaxy at the location of the GRB, however, implying it is neither of the above, but most likely a close relative of other long, soft GRBs.

GRB 010222 HST WFPC2 images show the optical transient to be located on a compact host, and find that the decay of the transient steepened to a slope of approximately -1.7, far steeper than earlier ground-based imaging had suggested.

GRB 000418 The HST/STIS image reveals a very compact host, with half-light radius of 0."13, immediately under the position of the optical transient. No obvious emission from the OT was still visible, however, at the time of the HST observations, 47 days after outburst.

GRB 000301C In this case HST was on the burst within days (and within about 48 hours of the our submitting the observing form to the Institute). Optical images and UV spectra were obtained. The UV spectrum revealed a break at about 2700 Angstroms, indicative of Lyman limit absorption at a redshift of ~2. The presumed absorbing host galaxy was too faint to be seen in the contemporaneous HST image.

GRB 991208: The host of this GRB is unusually compact -- it is barely resolved by the STIS camera, and must have an intrinsic FWHM < 0."06. The host is seen superposed on a rich field of spiral galaxies -- a group to which it could possibly belong.

GRB 991216: A small faint host is found at the position of the optical transient. A second, apparently separate, faint galaxy is found adjacent to the host. This may explain the presence of two MgI absorption line systems in the VLT spectrum of this object.

GRB 990712: A relatively nearby burst (z=0.4) on a bright galaxy. Observations at two epochs have allowed us to determine the position and magnitude of the GRB. The burst on a bright knot along the main axis of the galaxy. If the burst also produced a supernova, our observations show it must have been at least one magnitude fainter than SN1998bw.

GRB 990510: An elegant burst, whose light curve appears to largely behave as theorists would prefer, although no evidence of a supernova underlying the burst is seen. It is likely that we have now detected its host galaxy, with a magnitude of V~28.

GRB 990123: This extraordinarily powerful burst (visible through a pair of binoculars during the first minute after outburst) will blow away theories of GRB formation from the collapse of stellar mass black holes, unless it was highly beamed. HST observations show a break in the light curve which may be indicative of beaming.

GRB 980326: A deep HST/STIS image taken about 1000 days after outburst reveals a pointlike source at the astrometric position of the GRB. However, it appears too bright to be either the afterglow, or the supernova that some have suspected may account for the odd behavior of this GRB's afterglow about one month after outburst. Is this a 29th magnitude host galaxy?

GRB 970508: HST images show that this burst occured within 0".01 of the center of its very blue host galaxy. Is this GRB associated with a nuclear starburst? An AGN?