TITLE: GCN CIRCULAR NUMBER: 13337 SUBJECT: GRB 120521C: Early Tautenburg limits DATE: 12/05/22 22:17:24 GMT FROM: Alexander Kann at TLS Tautenburg D. A. Kann, B. Stecklum and U. Laux (TLS Tautenburg) report: We observed to position of Swift GRB 120521C (Trigger 522656, Baumgartner et al., GCN 13318) with the TLS 1.34m Schmidt telescope. Conditions were mediocre, with good seeing but bad transparency. Observations were triggered manually and began 28 minutes after the trigger (17 minutes after the alert). We obtained 5 x 60 s images in Rc, 4 x 180 s images also in Rc, and 1 x 600 s each in Z and Ic. The Ic image is affected in depth by passing clouds. At the position of the enhanced X-ray afterglow (Beardmore et al., GCN 13324), we do not detect any source, in agreement with earlier results (Klotz et al., GCN 13319; Bersier et al., GCN 13320; De Cia et al., GCN 13321; Levan et al., GCN 13322; Jelinek et al., GCN 13323; Morgan et al., GCN 13325; Gorbovskoy et al., GCN 13329; Oates et al., GCN 13331). The possible host galaxy (Perley et al., GCN 13332) is not detected. We us the SDSS star at RA, Dec. (J2000) = 14:17:02.836, +42:6:07.62 (214.26181759, 42.10211787, catalog ID 1237661874023500000) as a comparison star. Using the transformations of Lupton (2005), we find Rc = 18.33, Ic = 17.93 and Z = 17.78 for this star. We find the following 2 sigma limiting magnitudes: Time (days) Exposure (s) Filter UL 0.019827 1 x 60 Rc 21.0 0.022275 5 x 60 Rc 21.8 0.027171 1 x 180 Rc 21.5 0.030760 4 x 180 Rc 22.5 0.040247 1 x 600 Z 20.2 0.048757 1 x 600 Ic 19.3 We note that while the non-detections we as well as other telescopes have found point to this being a dark GRB, the X-ray absorption seen by Swift is small. The Keck detection of a possible host galaxy in g' band likely rules out a high-z interpretation, though. No further observations are planned. This message may be cited.