HST/STIS observations of GRB 020322

Above: Sum of the two images of the position of GRB 020322 obtained with 8 orbits STIS 50CCD (open) imaging. The circle shows the location of the OT. The field is ~5 arcsec on each side. The image has been drizzled and the pixels shown are one-half the size of the native STIS CCD pixels.

We observed the field of GRB 020322 with STIS in open (50CCD) mode on UT 2000 April 8 and on June 5. The position of the transient with respect to the STIS image was determined by performing relative astrometry using the optical image of the transient from Bloom et al. (GCN 1296). The accuracy of the position translated to the HST image is estimated to be 0.08 arcsec.
We see no evident OT, but at the position of the transient there is an extended 27th magnitude galaxy which is likely to be the host. The sum of the two epochs of observations is displayed above. When subtracting the images from the two epochs no residual signal is detected above 3 sigma near the position of the OT, giving a limiting magnitude of 30.1 mags for any transient.
Based on the ground-based observations of Bloom et al. (GCN 1294), Greiner et al. (GCN 1298), Hjorth et al. (GCN 1300) and Williams et al. (GCN 1307) and the non-detection of the OT in the HST/STIS image we conclude that the late time R-band decay of the OT must be steeper than 2.0. A plot of the light curve is shown below.

We thank J. Bloom and the Caltech GRB group for making their ground based data rapidly public (GCN1296).

This result has appeared as a GCN. Please see the GCN web page for more information on these circulars.

The difference image between the two observations. No significant residual was found near the OT position.

A plot of all the optical data points of GRB 020322 from Bloom et al. (GCN 1294), Greiner et al. (GCN 1298), Hjorth et al. (GCN 1300) and Williams et al. (GCN 1307) and the upper limit from this circular. The upper limits are marked as blue triangles. All the ground based data are recalibrated using the photometry from Henden et al. (GCN 1301). A broken power-law fit is shown as a solid line. The late time slope is 2.0 indicating a lower limit on the late time slope.