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GCN Circular 1866

Subject
GRB 030131: marginal optical detection
Date
2003-02-13T15:25:33Z (21 years ago)
From
Javier Gorosabel at LAEFF-INTA, Madrid <jgu@laeff.esa.es>
J. Gorosabel (IAA-CSIC/STScI), A.  Levan (U. Leicester/STScI),
A. Fruchter, J. Rhoads, J.M.  Castro Cer�n (STScI), T. Tripp (Princeton)
report for a larger collaboration:

We have imaged  the optical candidate (GCN 1857) of  the INTEGRAL burst GRB
030131 (GCN 1836, GCN 1838, GCN 1847) with the 4-m KPNO telescope (equipped
with  Mosaic,  FOV=36'x36').  The  observations  were  carried  out on  Feb
1.526-1.542 UT 2003 (~29 hours after the GRB) with a total exposure time of
4x500s and a seeing of 0.85".

We find a marginal detection  (~3.5 sigma above the detection threshold) at
RA(J2000)=13:28:22.27  DEC(J2000)=30:40:23.7.  The  astrometry is  based on
the  USNO  catalog and  shows  an internal  uncertainty  of  0.5" for  each
coordinate. We have compared the offset of the object in our image from the
nearest USNO  star with  that found by  D. Fox (personal  communication) in
their   discovery  image.   These  offsets   agree  within   0.2",  further
strengthening the association.

Preliminary aperture photometry centered on the object yields B=25.4+/-0.3.
Our photometric calibration is based on  11 USNO stars in the field.  Under
the  zero   point  obtained   the  star  located   at  RA(J200)=13:28:18.16
DEC(J2000)=30:38:20.79 has B=18.18.

A smoothed image of the field can be seen at:
http://www.stsci.edu/~fruchter/GRB/030131/kpno/grb030131.kpno.gif

We thank D. Fox for providing valuable astrometric information.
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