TITLE: GCN CIRCULAR NUMBER: 7528 SUBJECT: GRB080319B, BVRcIc field calibration DATE: 08/03/28 12:39:47 GMT FROM: Arne A. Henden at AAVSO A. Henden (AAVSO) reports: While the field of GRB080319B has been observed by SDSS, we have also obtained a four-night BVRcIc field calibration using the 35cm robotic telescope at Sonoita Research Observatory. The calibration file has a limiting magnitude around V=16, with good standards brighter than V=11 or so. The file is available at ftp://ftp.aavso.org/public/calib/grb/grb080319b.dat This calibration is based on numerous Landolt standards, and has an external zeropoint error of about 0.02mag. We are continuing calibration of this field, moving to the west to pick up the 9th magnitude star SAO 64192, and will extend the calibration file when that photometry is available. Our system is available for any other bright BVRI calibrations (4