GCN Circular 1866
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.