TITLE: GCN CIRCULAR NUMBER: 7631 SUBJECT: GRB080310, BVRcIc field calibration DATE: 08/04/19 14:17:49 GMT FROM: Arne A. Henden at AAVSO A. Henden (AAVSO) reports: While the field of GRB080310 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=17, with good standards brighter than V=11 or so. The file is available at ftp://ftp.aavso.org/public/calib/grb/grb080310.dat This calibration is based on numerous Landolt standards, and has an external zeropoint error of about 0.02mag. Our system is available for any other bright BVRI calibrations (4