GCN Circular 2555

A. Gal-Yam, D. Fox, and E. Berger (Caltech), with P. Wyatt (OCIW)
report on behalf of a larger collaboration:

We have observed the INTEGRAL localization of GRB040323 (Mereghetti et
al., GCN 1551
Not found
 
 
) using the PANIC NIR camera on the Baade 6.5-m telescope
at Las Campanas Observatory.  The PANIC field of view covers the
central ~50% of the INTEGRAL error circle (Mereghetti et al. 2004; GCN
2551
Not found
 
 
). Two epochs of J-band (1.25 micron) and one epoch of K-band
(2.16 micron) imaging have been obtained on the nights of March 24 (J
and K) and March 25 (J only) UT.

PSF-matched image subtraction of the two J-band epochs reveals a
bright point-like source at RA 13:53:53.20, Dec -52:20:31.3 (J2000;
uncertainty ~0.3 arcsec), which decays by ~0.3 mag from the first
epoch (March 24.35 UT; 0.81 days post-burst) to the second epoch
(March 25.37 UT; 1.83 days post-burst), with approximate magnitude
J=18.0 at the second (later) epoch.  Referenced to the time of the
burst, this corresponds to a power-law decay with index alpha~-0.34.  

A faint source is present at the position of this variable J-band
object on the red DSS plates.  We are therefore uncertain whether this
fading source is related to GRB040323 or is an unrelated variable star
or AGN.

Continued monitoring of the field is advocated.