TITLE: GCN CIRCULAR NUMBER: 7972 SUBJECT: GRB 080710: TLS observations, steepening afterglow decay DATE: 08/07/11 14:14:53 GMT FROM: Alexander Kann at TLS Tautenburg S. Schulze, D. A. Kann, A. Rossi, E. Gonsalves, C. Hoegner and B. Stecklum (TLS Tautenburg) report: We observed the optical afterglow location (Li et al., GCN 7959) of Swift GRB 080710 (Sbarufatti et al., GCN 7957) with the TLS 1.34m Schmidt telescope under inclement but improving conditions. 600 second B and V observations were affected by passing clouds and yielded no detections and shallow upper limits only. We detect the afterglow clearly in a single Rc image as well as in four Ic images (600 seconds each) before dawn shut us down. We measure afterglow magnitudes against eight USNOB1.0 stars in each case: time (days) filter magnitude exposure 0.7275 Rc 20.05 +/- 0.12 600 0.7468 Ic 19.75 +/- 0.13 4 x 600 In comparison with the magnitude as well as the slope reported from the Faulkes Telescope North (Bersier et al., GCN 7963) (R = 17.8 at 4.4h, alpha = 0.82), our measurement implies a significant steepening of the decay, we find alpha = 1.5 between 4.4 and 17.5 hours after the GRB. This implies that a break must have occurred inbetween, and possibly the slope during the time of our observations is already > 2 and the break is a jet break. Using the redshift of 0.845 (Perley et al., GCN 7962) as well as the values derived in the BAT refined analysis (Tueller et al., GCN 7969) and estimating the peak energy following equation 3 of Liang et al. (2007, ApJ, 670, 565), we derive a bolometric isotropic energy release of 6.8 +2.0 -1.9 x 10^51 erg. If there is a jet break before 17 hours, this would imply a low collimation-corrected energy release. No further observations from TLS are possible due to an instrument change. This message may be cited.