TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2019 SUBJECT: GRB030329: ROTSE network observes steepening of decay curve DATE: 03/03/30 08:29:16 GMT FROM: Don Smith at U michigan D. A. Smith reports on behalf of the ROTSE collaboration: The ROTSE-IIIb instrument at McDonald Observatory in Texas began observing the optical counterpart to GRB 030329 as soon as it was possible to do so. The first calibrated image began at 30 March 02:27:31 (UTC). Images were calibrated against the R-band magnitudes of the USNO A2.0 catalog, and the source was initially found to be at an unfiltered magnitude of 15.35+-0.06 and fading. Analysis of the first 70 images showed clearly that the rate of decay had increased when compared to the observations recorded by ROTSE-IIIa the night before (Rykoff & Smith, GCN Circ. 1995). Separate power-law fits to each instrument's data set indicated that the flux decay slope had shifted from about 1.0 (consistent with the decay slope reported by Price, et al. GCN Circ. 2017) to about 1.9 (consistent with the decay reported by Garnavich et al. GCN Circ. 2018). A plot of these decay curves along with the power-law fits can be seen at http://www.rotse.net/transients/grb030329/). An extrapolation of these curves predicts a break time of about 12.1 h after the burst. ROTSE-IIIb will continue to observe GRB 030329 as long as it is able to do so.