GCN Circular 11247
D. A. Kann, A. Nicuesa Guelbenzu, F. Ludwig and B. Stecklum (TLS Tautenburg) report: Further to Kann et al. (GCN 11238), we continued monitoring the afterglow of GRB 100906A (Markwardt et al., GCN 11227) with the 1.34m TLS Schmidt telescope under excellent conditions in intermittent intervals all night. Beyond the 15 detections reported in Kann et al. (GCN 11238), we obtained further nine Rc images (300 sec each) spread over the night, as well as one further Ic (300 sec) and one further Z (600 sec) image at the end of the night, during morning twilight. The afterglow is clearly detected in all our images. Due to crowding, we use SExtractor under GAIA to subtract background mesh maps, then perform aperature photometry without needing to measure the surrounding sky background (which is around 0). Errors are estimates based on how clear the detection is, the last Rc frame was taken in strong twilight already. We assume R2 = 15.9 for the USNOB1.0 star at RA = 01:54:55.247, Dec. = +55:38:31.40, and measure: Midtime Rc dRc 0.247478 18.97 0.05 0.251517 19.06 0.05 0.255556 19.04 0.05 0.390570 19.08 0.05 0.430154 19.27 0.05 0.451022 19.18 0.05 0.498974 19.64 0.05 0.521231 19.62 0.05 0.525421 19.67 0.05 0.554113 19.80 0.05 0.570108 19.97 0.15 The afterglow seems to transition from a plateau phase (0.25 - 0.4 days) to a much steeper decay. Further observations are improbable due to upcoming inclement weather. This message may be cited.