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GCN Circular 255

GRB 990123: Reduced HST Images
1999-02-09T19:22:51Z (25 years ago)
Andrew S. Fruchter at STScI <>
Andrew Fruchter, Kailash Sahu, Harry Ferugson, Mario Livio 
      and Mark Metzger on behalf of the larger HST GRB 
      collaboration report:

We have reduced the HST STIS CCD clear (50CCD) images of
GRB 990123 announced earlier today by the Director of STScI,
Steven Beckwith, in GCN 254.

We find the optical transient to be superposed on an extended
irregular galaxy.   A quick photometric reduction shows that
the OT has a magnitude of V=25.4 +/- 0.1 and the galaxy has 
V=24.3 +/- 0.15.  The total integrated magnitude of the galaxy 
and OT is therefore V~24, which agrees with Palomar 5-m observations 
taken approximately 12 hours before the HST observations, and
which will be reported in a succeeding GCN.  No correction
to the STIS magnitude has yet been made to take into account
the colors of the objects, which could change the estimated 
magnitudes from the broad STIS clear filter by ~0.1 mag.

The faint magnitude of the OT suggests that it may be declining
more rapidly than the earlier power-law would predict, as 
suggested by the MDM group in GCN 248.

The probable host galaxy is itself composed of several irregular 
pieces, extended over a region more than 1" across.  The major 
fraction of the light in the host is to the north of the OT, thus 
agreeing with the probable extension reported by Djorgovski et
al. in GCN 243.

A gif image as well as the reduced FITS files will be posted
by 16:00 EST today (9 February 1999) on

We welcome the use of the reduced FITS image by others; 
however, we ask that those who do use this image cite 
this GCN, or a formal publication that may succeed it
(the bibliographic reference of which would be available 
on the above web page).
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