TITLE: GCN GRB OBSERVATION REPORT NUMBER: 777 SUBJECT: HST/STIS observations of the chaotic environment of GRB 980613 DATE: 00/08/21 20:31:38 GMT FROM: Stephen Holland at IFA, U of Aarhus HST/STIS observations of the chaotic environment of GRB 980613 Stephen Holland, Bjarne Thomsen (University of Aarhus), Jens Hjorth, Johan Fynbo (University of Copenhagen), Michael Andersen (University of Oulu), Gunnlaugur Bjornsson (University of Iceland), Andreas Jaunsen (ESO), Priya Natarajan (University of Cambridge, & Yale), and Nial Tanvir (University of Hertfordshire) We have used the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope to image the environment where GRB 980613 occurred. We obtained 5851 seconds of STIS/CCD images with the 50CCD (clear) aperture and 5936 seconds of images with the F28X50LP (long pass) aperture. This data was taken as part of the Survey of the Host Galaxies of Gamma-Ray Bursts (Holland et al., GCN 698) approximately 799 days after the burst. Combined images are now available at "http://www.ifa.au.dk/~hst/grb_hosts/data/index.html". A comparison with ground-based R-band images of the optical afterglow associated with GRB 980613, taken with from the Nordic Optical Telescope (NOT) (Hjorth et al., GCN 109) suggests that the GRB occurred at X = 1023.95 +/- 1.52, Y = 1068.73 +/- 0.96 on the drizzled 50CCD image. The quoted uncertainties are the uncertainties in the transformation between the NOT and STIS images. They do not reflect the uncertainty in the position of the optical afterglow in the NOT images due to the GRB being superimposed on a fragmented, extended structure (object A in Djorgovski et al., astro-ph/0008029). This systematic uncertainty means that the position of the optical afterglow may be consistent with the position of a blue, compact source at the southeast end of the A complex. This source has a full-width at half-maximum of 0.13 arcsec (the resolution of the drizzled STIS images is 0.089 arcsec), and AB magnitudes of CL = 26.3 +/- 0.1 and LP = 26.2 +/- 0.1 in an aperture of radius 0.25 arcsec. An image of the complex structure where GRB 980613 occurred is available at "http://www.ifa.au.dk/~hst/grb_hosts/data/grb980613cd.gif". There are several extended objects within a few arcseconds of the GRB (Djorgovski et al., astro-ph/0008029). These objects have a wide range of colours, significant substructure, and some of them appear to have extended tails that may be due to tidal interactions. The total diameter of the chaotic environment around GRB 980613 is approximately eight arcseconds. If we assume that all of the structure lies at the same redshift (z = 1.0969, Djorgovski et al., astro-ph/008029), and adopt a cosmology with H0 = 70, Omega_matter = 0.3, and Omega_lambda = 0.7, then this corresponds to a diameter of approximately 65 proper kpc. The total light in this region is CL = 23.0 +/- 0.1, LP = 22.9 +/- 0.2. A detailed analysis of this data is in progress (Hjorth et al., in preparation).