TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1518 SUBJECT: GRB 020813 : HST observations DATE: 02/08/22 17:04:55 GMT FROM: Andrew Levan at U.of Leicester A.J. Levan, A.S. Fruchter, I. Burud and J.E. Rhoads (STScI) report for the larger GOSH collaboration: The field containing the optical counterpart of GRB 020813 was imaged by HST using ACS/HRC, ACS/WFC and NICMOS on 17th August beginning at 04:00 UT approximately 98 hours after the burst. The optical counterpart is clearly visible in our images. Using the zeropoints for the filters on ACS/WFC, as given below, we find the magnitude of the counterpart to be: FILTER Z_P(AB) OT MAG(AB) ========================== F435W 25.47 23.20 F606W 26.35 22.71 F814W 25.86 22.33 This is consistent with a spectral slope of beta =-0.8. Comparing to early, 3 hour I Band observations (GCN 1513) gives an approximate slope of ~t^-1.07. Comparing to observations taken after 23 hours (also GCN 1513) indicates a somewhat faster (broken) slope of t^-1.35. The OT appears largely point like, however a PSF subtraction reveals some evidence for a possible 25th magnitude host galaxy underlying the OT. Images of the field of GRB 020813 may be found at http://www.stsci.edu/~fruchter/GRB/020813 Analysis is continuing and further observations are planned.