TITLE: GCN CIRCULAR NUMBER: 9436 SUBJECT: GRB 090529: TLS Afterglow Observations DATE: 09/05/30 00:12:12 GMT FROM: Alexander Kann at TLS Tautenburg D. A. Kann, U. Laux and B. Stecklum (TLS Tautenburg) report: We observed the optical afterglow (Xin et al., GCN 9431) of the Swift GRB 090529 (Sakamoto et al., GCN 9430) with the 1.34m Schmidt telescope of the Thueringer Landessternwarte Tautenburg, Germany. Observations began at twilight, which, together with the setting moon, caused an elevated sky background. Airmass was low and conditions were excellent until clouds came in during the last Rc image. We obtained 6 x 300 sec dithered images in the Ic band and 3 x 600 sec images in the Rc band. The afterglow is very faintly visible on several Ic frames, clearly visible on the first two Rc frames and hardly visible on the last Rc frame. Using the USNOB1.0 catalog as a reference, we derive the following position (J2000) for the afterglow: RA = 14:09:52.53 Dec. = +24:27:32.77 with an error of 0".5. This position lies 0".7 from the UVOT position (Schady et al., GCN 9435), in full agreement with it. We find several sources of roughly similar magnitude within 10" of the afterglow. These may slightly affect the photometry. To calibrate, we use the isolated star with USNO catalog # 1144-0210566 at position RA = 14:09:47.50 Dec. = +24:27:44.5 which has R2 = 18.32 mag and I = 17.54 mag. (Note that it is 0.54 mag brighter in R1.) We derive the following magnitudes 0.3 days after the GRB: time (d) Mag dMag Exposure Filter 0.287871 20.98 0.13 6 x 300 Ic 0.304668 21.39 0.12 1 x 600 Rc 0.312191 21.40 0.12 1 x 600 Rc 0.319703 21.47 0.35 1 x 600 Rc Compared to the magnitude found by Xin et al., GCN 9431, this indicates the afterglow has faded by two magnitudes. The normal Rc - Ic color as well as the confirmation by Swift UVOT of a rising afterglow (Schady et al., GCN 9435) implies that it is not overly reddened, an alternate explanation by Holland et al., GCN 9432. No further observations are planned. This message may be cited.