TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1463
SUBJECT: HST Imaging of the Host of GRB 011121
DATE:    02/08/02 19:02:08 GMT
FROM:    Josh Bloom at CIT  <jsb@astro.caltech.edu>

HST Imaging of the Host of GRB 011121

J. S. Bloom (Caltech, Harvard/CfA) and P. A. Price (RSSA, ANU) report:

"Deep late-time images of the field of GRB 011121 were acquired with the
Hubble Space Telescope in from 21 April to 2 May 2002 UT as part of the
large GRB program #9180 (Kulkarni, PI).  Five filters were used---F450W,
F555W, F702W, F814W, F850LP---with a total integration time of 4500 sec
per filter.

The transient afterglow plus intermediate-time bump, suggested elsewhere
as an accompanying supernova (SN) to the GRB (Bloom et al. 2002, Garnavich
et al. 2002), faded beyond detection in each filter. There is no apparent
persistent emission at the burst location aside from diffuse light from
the host galaxy. In Bloom et al. (table 1) we noted the estimated the
contribution of this diffuse light to the total measured flux of the
OT/SN; using the host images as a template for subtraction from earlier
epochs, we confirm those estimations were correct to within the stated
errors; here we provide a direct measurement of the diffuse host flux
contributing to the 0.5" radius aperture PSF photometry: f_nu(host)[F450W,
F555W, F702W, F814W, F850LP] = (0.038 +- 0.048), (0.067 +- 0.034), (0.154
+- 0.035), (0.195 +- 0.067), (0.305 +- 0.184) microJy. These fluxes have
not been corrected for Galactic extinction.

Two rather blue compact knots of emission are detected West of the galaxy
core, near to the OT/SN. Knot #1 is positioned at 0.52"E, 0.01"N and knot
#2 is 0.08"E, 0.28"N relative to the OT/SN location. [For reference, the
OT/SN was 1.99" W, 0.85" N of the star labeled as "B" in figure 1 of Bloom
et al.]. At the redshift of the host (z=0.362; Garnavich et al.)  even the
closest of these knot lies 1.5 kpc in projection from the burst site.

A close-in color image of the host may be found at:
       http://cfa160.harvard.edu/~jsbloom/grb011121

Though we cannot rule out these knots as background galaxies, given the
detection of Hydrogen Balmer-line and [OII] emission in the spectrum of
the larger "host" galaxy, these knots are likely strong pockets of star
formation in the host itself."

This message may be cited.

Paper References:
-----------------
1. Bloom et al., 2002, ApJ Letters, v572, 45-49
2. Garnavich et al., 2002, submitted to ApJ, (astro-ph/0204234)