TITLE: GCN GRB OBSERVATION REPORT NUMBER: 733 SUBJECT: GRB000418, HST/STIS Observations DATE: 00/06/29 07:06:01 GMT FROM: Mark R. Metzger at CIT M. Metzger, A. Fruchter, N. Masetti, E. Palazzi, E. Pian, S. Klose, and B. Stecklum report for a larger HST GRB Collaboration: The field of GRB 000418 was observed by the Hubble Space Telescope using the STIS camera in open (50CCD) mode on UT 2000 June 4.17. The position of the transient with respect to the STIS image was made by performing relative astrometry of early infrared images of the transient from the Calar Alto 3.5m (GCN 645) and optical images on Apr 20.9 UT from the Telescopio Nazionale Galileo 3.5m with deep late-time images from Keck (GCN 669). The transient position on the Keck images was then transformed to the STIS image. Near the position of the transient, a compact galaxy with half-light radius of 0.13 arcsec is detected with R = 23.9 +- 0.2 mag (where much of the photometric uncertainty is due to the uncertain spectral energy distribution of the galaxy). The best fit position of the OT is approx 0".08 +- 0".15 arcsec east of the center of this galaxy, which we infer is the likely host. The magnitude measured is within a few tenths of a magnitude of the May 6 Keck measurement (GCN 669), and thus the OT does not likely contribute significant flux to the host in the STIS image. The next nearest galaxies to the transient is a pair approx 2 arcsec southeast of the host and are detected in both the STIS and Keck images at total R magnitude of 26.2 +- 0.3 mag. The pair shows no significant extension toward the host galaxy in either the STIS or Keck images. A reduced image of the STIS field, with transient location indicated, can be obtained at http://www.stsci.edu/~fruchter/GRB/000418. This message may be cited.