GCN Circular 702

The Hosts of GRB 980703 and GRB 971214

J. S. Bloom and S. R. Kulkarni report on behalf of the larger
Caltech-NRAO-CARA GRB Collaboration:

"The Hubble Space Telescope (HST) has recently observed the hosts of GRB
971214 and GRB 980703 with STIS as part of the Survey of the Host Galaxies
of Gamma-Ray Bursts (see S. Holland, B. Thomsen, H. Hjorth et al. GCN
#698
Not found
 
 
).  Here we present our data reduction of this public data and relate
the new STIS images to our previously obtained ground-based data and
space-based data.

GRB 980703:
This remains one of the brightest GRB host galaxies at R~22.8 and the
inferred GRB energy release is at the high end of the GRBs energy
distribution. The optical astrometry tie from Bloom et al. (1998,
ApJL 508, 21) revealed the GRB to be nearly coincident with its host
galaxy.

The GRB host was observed for a total of 5264 s with the STIS long-pass
filter (central wavelength ~ 7230 Ang and FWHM 2720 Ang) beginning 12.42
June 2000 UT. The galaxy is compact (though resolved) and has a low
ellipticity (~12%).  The effective seeing of the drizzled image is 85
milliarcsec (FWHM) as measured from a bright star in the image and the
host has a FWHM diameter of 250 milliarcsec.  This is consistent with our
report in Bloom et al. of an unresolved source in 0.5 arcsec seeing on
July 18 (when the host was thought to dominate the total light of the
source).  At a redshift of z=0.966 (Djorgovski et al. ApJL 508, 17, 1998),
this implies a half-light radius of ~1.1 kpc (assuming H_0 = 65 km/s/Mpc,
Omega_0 = 0.3, Omega_lam = 0.7).

For photometric zero-pointing of the HST image, we compared two compact
objects in common to our deep Keck images from 18 July 1998 in V, R, I.  
We find the host galaxy has R = 22.8 +/- 0.3 and I = 22.6 +/- 0.3.  The
error is dominated by the uncertainty in the color correction. These
magnitudes are both within 1-sigma of those predicted for the host galaxy
in Bloom et al. from the light curve data.  We conclude therefore there is
no evidence for the presence of a second light source (e.g. a supernova
component) in the early time light curve.

GRB 971214:
At z=3.418, this burst and its host remains the furthest of GRBs with
spectroscopically confirmed redshifts and also had an implied energy
release at the high end of the GRB energy distribution (Kulkarni et al.
1998, Nature, 393, 35). Using STIS imaging from 13 April 1998 we
previously reported (Odewahn et al. 1998 ApJL, 509, 5) the host as compact
core with an irregular envelope (half-light radius of 1.3 kpc).
Morphologically and in all other observed physical properties the host is
rather typical Lyman break galaxy at comparable redshifts.  Further, we
found a small but significant offset of the GRB from the nucleus of the
galaxy.

The GRB host was observed for 8599s using STIS clear mode beginning 12.21
Jun 2000 UT.  The final image has achieved approximately the same depth as
our previous STIS clear imaging.  A visual comparison of the two epochs
reveals no obvious new or fading component.  Our conclusions about the
nature of the host and its relation to the GRB remain unchanged from
Odewahn et al."

Our final reduced images can be obtained in .fits format at
   http://astro.caltech.edu/~jsb/GRB/Host/

This message may be cited.