GCN Circular 11881
Andrew Fruchter, Kuntal Misra, John Graham (STScI), Andrew Levan (U. Warwick), Nial Tanvir (U. Leicester) and Joshua Bloom (UC Berkeley) report for a larger collaboration: We have observed the field of GRB 110328A / Swift J164449.3+573451 using the WFC3 on the Hubble Space Telescope. We observed in both the near-IR (F160W) and optical (F606W). The observations were performed between 03:00 and 04:00 UT on 4 April 2011. We obtained four dithered exposures of 250s each in F160W. The combined drizzled image has a FWHM of 0.16 arcsec. At the location of the transient we find a nearly pointlike source. Using the two stars in the field which are in both the UCAC3 and 2MASS catalogs for astrometric alignment, we find that the position of this source agrees with that of EVLA (GCN 11854) to within our estimated astrometric error of 0.07 arcsec (340 pc at the distance of the source). In the optical F606W filter we obtained three dithered exposures of 420s each. This combined optical image shows a clearly resolved but compact host galaxy. The nucleus of the galaxy is coincident with the position of the IR source. Using an aperture with a radius of of one arcsecond, we obtain AB magnitudes of 20.75 +/- 0.04 (F160W) and 22.82 +/- 0.02 (F606W) for the central source plus surrounding host galaxy. The astrometric agreement between the HST images and the radio, as well as the observed near-IR variability (GCN 11853) suggest that the transient is associated with the nucleus of this galaxy. Future HST observations should be able to place good constraints on the nuclear variability in both the optical and near-IR, and thus perhaps on the interesting proposal that we are seeing a mini-blazar powered by a tidal disruption event (GCN 11847).