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GCN Circular 731

Subject
GRB 990506, HST/STIS Observations of the Host Galaxy
Date
2000-06-27T13:02:28Z (24 years ago)
From
Jens Hjorth at U.Copenhagen <jens@astro.ku.dk>
Stephen Holland, Bjarne Thomsen (University of Aarhus),
Michael Andersen (University of Oulu),
Gunnlaugur Bjornsson (University of Iceland),
Johan Fynbo, Jens Hjorth (University of Copenhagen),
Andreas Jaunsen (University of Oslo),
Priya Natarajan (University of Cambridge, & Yale), and
Nial Tanvir (University of Hertfordshire)

     We have obtained 7856 seconds of STIS images with the 50CCD (clear) 
aperture and 8000 seconds with the F28X50LP (long pass) aperture of the sky 
where the radio afterglow associated with GRB 990506 was detected.  This 
data was taken as part of the Survey of the Host Galaxies of Gamma-Ray Bursts 
(Holland et al. GCN 698) approximately 413 days after the burst.  Combined 
(drizzled) FITS and GIF images are now available at the interim web site
"http://www.astro.uio.no/~ajaunsen/grb-hosts/".  The images will be made 
available at the official survey web site
"http://www.ifa.au.dk/~hst/grb_hosts/data/index.html" next week.

     At the location of the radio afterglow (Taylor et al. astro-ph/0005379) 
there is a very compact galaxy (FWHM ~ 0.14") which we identify as the probable 
host galaxy for GRB 990506.  This galaxy does not appear to be associated or 
interacting with a larger galaxy (2" in extent) located 2 arcsec to the north 
east (the "northeast knot" of Taylor et al.).  A preliminary photometric 
calibration of the STIS data yields R = 25.0 +- 0.3 for the host galaxy. It 
thus appears to be marginally fainter than the value R = 24.4 +- 0.3 measured 
on 11 June 1999 (36 days after the burst) in LRIS/Keck II images. This could 
indicate a contribution from an optical transient (afterglow or supernova) at 
the time of the Keck observations.  A more accurate transformation from 50CCD 
and F28X50LP to Cousins R is however necessary to rule out calibration errors.

     We finally note that the radio source R2, identified by Taylor et al. to
be a QSO at z = 0.273, is resolved in the STIS images.  The morphology is that
of a spiral galaxy (2 arcsec in diameter) with a bright nucleus and several
knots in the spiral arms. Thus, R2 is a radio loud QSO with a spiral host 
galaxy.
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