TITLE: GCN CIRCULAR NUMBER: 7580 SUBJECT: GRB 080330 optical observations DATE: 08/04/09 18:36:58 GMT FROM: AAVSO GRB Network at AAVSO A. Block (Seeing In The Dark Internet Telescope, and Steward Observatory, Tucson, AZ) and M. Templeton (AAVSO) report on behalf of the AAVSO International High Energy Network the following observations and analysis of the optical afterglow of GRB 080330 (Mao et al., GCN Circular #7537; Klotz, Boer, and Atteia, GCN #7536): Adam Block reports unfiltered photometry of the GRB 080330 afterglow spanning 2008 March 30.1675 UT to 2008 March 30.3273, taken with the Seeing In The Dark Internet Telescope 14-inch Celestron SCT, using an SBIG ST1001 camera, located near Mayhill, New Mexico. Forty-seven, 300-second unfiltered exposures were obtained beginning 20 minutes post-burst, and continuing through t0 + 0.1736 days. Data acquisition began after the reported peak (D'Avanzo, et al., GCN #7554), but during the early decay epoch. A break in the light curve is apparent at approximately 25 minutes after the trigger; only one data point was obtained prior to this point, and so a slope cannot be reliably derived. After t0 + 25 minutes, the data are reasonably well fit with a power law index of -1.104 +/- 0.001, with a zero point unfiltered magnitude of 22.65 (m = m(t+1day)). However, the light curve appeared to briefly rebrighten by more than 0.2 magnitudes (1-sigma error = 0.09 mag) approximately 70 minutes post-burst, suggesting a late-time manifestation of the rebrightening seen during early light (Schaefer and Guver, GCN #7538). These observations are consistent with other optical observations taken during this time frame; observations through t0 + 250 minutes do not show evidence for the steeper slope described by Sergeev et al (GCN #7556) for data taken at t > t0 + 0.5 days, suggesting this break occurred between the end of these observations and the start of observations by Sergeev et al. A report detailing these observations is available at the following URL: ftp://ftp.aavso.org/grb/AdamBlock_GRB080330_2454558.33910_.txt The initial image of the GRB field is available at the following URL: ftp://ftp.aavso.org/grb/AdamBlock_GRB080330_2454558.33910_.fits A light curve of the unfiltered photometry is available at the following URL: http://www.caelumobservatory.com/outgoing/grb080330LOG.jpg Photometry and a full description of the observations will appear in the Journal of the AAVSO, and are available from A. Block upon request to ngc1535@caelumobservatory.com. The AAVSO thanks the Curry Foundation for their continued support of the AAVSO International High Energy Network.