TITLE: GCN CIRCULAR NUMBER: 7688 SUBJECT: GRB 080506: TLS afterglow detection in VRIZ DATE: 08/05/07 04:02:27 GMT FROM: Alexander Kann at TLS Tautenburg D. A. Kann, C. Hoegner and S. Ertel (TLS Tautenburg) report: We observed the afterglow of Swift GRB 080506 (Baumgartner et al., GCN 7685, Kawabata et al., GCN 7686) with the Tautenburg 1.34m Schmidt telescope 0.32 days after the GRB in good conditions (moderate transparency but excellent seeing). We obtained a total of six 600 sec exposures, in the sequence Rc, V, Ic, Z, Z, Z before twilight forced us to shut down. The afterglow is well (Rc, V, Ic) and faintly (Z) detected in single images, and well detected in the 1800 sec stack of the three Z images. We find an afterglow position R.A. (J2000) = 21:57:41.775 Dec. (J2000) = +38:59:05.86 in comparison with the USNOB1.0 catalog, with a precision of 0".5 in each coordinate. This is fully in agreement with the UVOT (Baumgartner et al., GCN 7685) and enhanced XRT (Osborne et al., GCN 7687) positions. Assuming the star at R.A. (J2000) = 21:57:39.84 Dec. (J2000) = +38:58:28.25 to have Rc = 16.7 (magnitude is basically identical in R1 and R2 magnitudes), we find for the afterglow: time Rc dRc 0.31576 20.77 0.13 Taking the two measurements from Kawabata et al. (GCN 7686), we find a shallow decay slope of alpha = 0.6 between 0.0025 and 0.316 days after the GRB. Our (and Swift's) clear detection in the V band implies z <~ 4. On the other hand, this was an image trigger, with faint emission seen up to ~ 200 seconds. The initial XRT light curve (XRT repository, Evans et al. 2007) is flat until 200 seconds before dropping off very steeply. This may suggest that this GRB lies at moderately high redshift (3 - 4). Spectroscopy is encouraged. This message may be cited.