TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2720 SUBJECT: XRF040912, BVRcIc field calibration DATE: 04/09/17 17:09:35 GMT FROM: Arne A. Henden at USNO/USRA A. Henden (USRA/USNO) reports on behalf of the USNO GRB team: We have acquired BVRcIc all-sky photometry for a 11x11 arcmin field centered on the HETE coordinates for GRB/XRF040912 (trigger 3557; Butler et al. GCN 2701) with the USNOFS 1.0-m telescope on one photometric night. Stars brighter than V=13.5 are saturated and should be used with care. We have placed the photometric data on our anonymous ftp site: ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/xrf040912.dat The astrometry in this file is based on linear plate solutions with respect to UCAC2. The external errors are less than 100mas. The estimated external photometric error is about 0.03mag and will be improved with additional calibration nights if an afterglow is discovered. As always, you should check the dates on the .dat file prior to final publication to get the latest photometry. There is a README file on the ftp directory to give you information about the procedures used to calibrate these fields.