TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2771 SUBJECT: GRB 041006: Optical decay DATE: 04/10/06 15:25:44 GMT FROM: Paul Price at IfA,UH P.A. Price (IfA, UH), G. Da Costa (MSO) and N. Noel (IAC) report: Preliminary analysis of six V-band frames from the SSO 40-inch from Oct 6.54 UT (t_GRB + 35 min) to 6.59 UT (t_GRB + 120 min) reveal that the afterglow has a temporal decay index of alpha ~ 0.7 over these observations, with an estimated magnitude of R ~ 18.5 mag at Oct 6.59 UT. Assuming this decay holds, this predicts the GRB should be roughly R ~ 20 mag at local midnight, US Eastern daylight savings time (UTC-4h). The afterglow is also detected in the B band. This message may be cited. [GCN OPS NOTE (16:00 UT 06oct04): "da Costa" was changed to "Da Costa".]