GCN Circular 7972
Subject
GRB 080710: TLS observations, steepening afterglow decay
Date
2008-07-11T14:14:53Z (16 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
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.
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