GCN Circular 1117

P.A. Price, S.R. Kulkarni, D.W. Fox, E. Berger, J.S. Bloom,
S.G. Djorgovski, D.A. Frail, T.J. Galama, F.A. Harrison,
A. Mahabal, D.E. Reichart, R. Sari and S.A. Yost of the
Caltech-NRAO-CARA GRB collaboration report:

We re-observed the optical transient associated with
GRB 010921 (GCN ##1107,1108) with the Palomar 200-inch
telescope in Sloan g'r'i'z' on 2001 Oct 19.1 UT.  Magnitudes
of the counterpart were measured relative to stars in the
field calibrated with the Palomar 60-inch telescope and
the USNOFS 1.0-metre telescope (GCN #1100
Not found
 
 
).  We find that,
at this epoch, the counterpart has a spectral flux distribution
that peaks between the r' and i' bands, and falls away on
the red and blue sides as ~ nu^3.5 and ~ nu^-2.1 respectively.

This spectral flux distribution finds a natural explanation
in terms of a supernova underlying the GRB afterglow (Bloom
et al. 1999; Reichart 1999; Galama et al. 2000).  If this
interpretation is correct, the source should continue to
fade beyond R ~ 22 mag over a timescale of a few weeks.

We strongly encourage further monitoring of this source,
especially in the blue and near infrared.

This message may be cited.

References:
Bloom, J.S. et al., 1999, Nature, 401, 453.
Reichart, D.E., 1999, ApJ, 521, L111.
Galama, T.J. et al., 2000, ApJ, 536, 185.