GCN Circular 2481

---------- Forwarded message ----------
Date: Fri, 5 Dec 2003 23:45:21 -0500 (EST)
From: Joshua Bloom <jbloom@cfa0.cfa.harvard.edu>
To: gcncirc@lheawww.gsfc.nasa.gov
Cc: scott@milkyway.gsfc.nasa.gov
Subject: GRB 031203: Optical/IR Astrometry

GRB 031203: Optical/IR Astrometry

J. S. Bloom, C. Bailyn, M. Buxton, B. Cobb, P. van Dokkum (Yale) and
D. Gonzalez (CTIO),

part of the larger SMARTS consortium, report:

"The position of the radio source in the XMM error box (Frail, priv.
communication) is 0.43" E and 0.80" N from the bright source noted in Hsia
et al. (GCN #2470). However, as explained in Bloom et al. (GCN #2472) that
source itself is unlikely to be the afterglow since it was present in the
DSS-II and did not vary significantly in the first night.

Additional data obtained between Dec. 5 UT=5:43 and UT=7:19 showed the
source at the same I-band flux as on Dec. 4 to within 0.05 mag.  On both
Dec. 4 and Dec. 5 the source is slightly but clearly elongated in ~1"
seeing.

The source-radio offset of 0.91" is larger than the formal joint
1 sigma uncertainty between the IR and the radio positional tie.
It is still unclear whether this bright source is the low redshift
host of the GRB or a foreground galaxy.

Separately, we note that inspection of the J-band ANDICAM imaging
reported in the Bailyn et al. (GCN #2463) reveals a faint (J ~ 20)
source at:

       RA: 08:02:30.36  DEC: -39:51:00.1 (J2000)
       rms uncertainty relative to ICRF= 0.3 arcsec in RA and DEC"

This is consistent with the XMM (#1) position.  A finding chart may
be found at:
      http://www-cfa.harvard.edu/~jbloom/grb031203

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