TITLE: GCN CIRCULAR NUMBER: 10665 SUBJECT: GRB 100418A: ROVOR optical measurements at 35 hours DATE: 10/04/23 23:41:42 GMT FROM: J. Ward Moody at BYU J. W. Moody, D. Laney, R. Pearson, and C. Pace report for the BYU ROVOR team: Beginning approximately 35 hours after the initial detection of GRB 100418A we obtained BVR optical data using the BYU WMO 0.9m telescope. Preliminary magnitudes were found by referencing against USNO-B1.0 star 1014-0271368 (RA(J2000) = 17:05:26.42, Dec(J2000) = +11:27:32.9). Assuming its values are B=18.66, R=17.32 (from catalog) and V=18.0 (our estimate) we obtain the following values: post burst t_mid(hr) exp.(min) filter mag. error 37.18 25 B 19.9 0.15 35.91 25 V 19.3 0.1 35.25 20 R 18.5 0.1 Poor weather has prevented subsequent observations.