GCN Circular 627
Subject
GRB 000301C: Late-Time HST/STIS CCD Imaging of the field
Date
2000-04-10T01:38:58Z (25 years ago)
From
Andrew S. Fruchter at STScI <fruchter@stsci.edu>
A. Fruchter (STScI), A. Smette (GSFC), T. Gull (GSFC), H. Ferguson, L. Petro,
J. Rhoads, and K. Sahu (STScI) for a larger HST GRB Collaboration:
We have re-imaged the field of GRB 000301C with HST using the STIS CCD
in both 50CCD (open) and LP (long-pass) mode. The observations were
centered about 3.9 April 2000 UT with total exposure times of 2280s
in both filters.
We detect a bright source on a fainter extended object at the position
of the optical transient (OT). The position of the peak of emission
from the object agrees with that of the OT on previous HST images taken
on 6 March 2000 (see GCN 602) to better than 0."01, based on astrometry
relative to other objects visible in both HST images. We believe
therefore we are observing continued emission from the OT of GRB 000301c,
as well as from its host galaxy. One cannot give a precise magnitude
for the OT without knowing a priori the surface brightness profile of
the host. However, what we consider the best point source subtraction
implies an OT magnitude of R=26.9; in any case, the point source is
no brighter than R=26.7. The total magnitude of the OT plus
host is 26.5 +/- 0.15 on 3.9 April 2000. Although no upper limit
to the magnitude of the OT can truly be given without knowledge
of the host, we note that R=26.9 is within 0.1 mag of the value
predicted for this date by the fit to earlier R band data given
in Rhoads and Fruchter (astro-ph/0004057). This provides some further
confidence that our best estimate of the OT strength is not far off.
If this value is used for the magnitude of the OT, then the host galaxy
has a magnitude R = 27.8 +/- 0.25.
The STIS filter set only gives limited color information, however,
our observations agree well with the spectral index of -0.9
reported by Halperin (GCN 585). A change to a spectral index
of -3, as has been seen in the late time spectra of some other
GRBs, would most likely have been detected.
The HST images of GRB 000301c are available at:
http://www.stsci.edu/~fruchter/GRB/000301C