GCN Circular 5894
J. Holtzman, T. Harrison, B. Mcnamara of New Mexico State University report: The robotic NMSU 1m telescope at Apache Point Observatory responded to Swift trigger 240766 (Sbarufatti et al. GCN 5854) shortly after the burst announcement. Our first 10s I band image was started 47s after the trigger (31s after the notification). This was followed by images in R, V, B, and U; an optical source at the location of the optical counterpart was clearly detected in all of the images with the following brightness: filter | exptime | midtime after burst | magnitude +/- error I 10s 52s 12.24 +/- 0.004 R 10s 97s 13.86 +/- 0.007 V 20s 149s 14.94 +/- 0.009 B 40s 213s 15.95 +/- 0.011 U 60s 303s 15.85 +/- 0.037 Our magnitudes were calibrated relative to a nearby star for which transformed UBVRI magnitudes were obtained from the SDSS magnitudes (Cool et al, GCN 5863) using transformations given on the SDSS web site, http://www.sdss.org/dr5/algorithms/sdssUBVRITransform.html, which were taken from a paper by Jester et al. (2005). Error bars are statistical only and do not include uncertainties in the SDSS photometry, the adopted SDSS to UBVRI transformations, nor internal transformations; systematic errors are probably on the order of several percent. Ten cycles of UBVRI observations were continued for about an hour after the burst. Analysis of temporal and spectral evolution is underway. Late epoch imaging is also continuing.