TITLE: GCN CIRCULAR NUMBER: 6259 SUBJECT: GRB 070406: Gemini South Imaging and XRT analysis DATE: 07/04/08 05:05:48 GMT FROM: Josh Bloom at UC Berkeley J. S. Bloom (UC Berkeley), H-W. Chen (Chicago), J. X. Prochaska (UC Santa Cruz), N. R. Bulter (UC Berkeley) report: We observed the field of GRB 070406 (Cummings et al.; GCN 6247) with the GMOS instrument on Gemini South in r and i-band filters. An i- band finder is provided (*) with mean epoch 7.26 April 2007 UT (~29.4 hours after the GRB). The images cover the region of the XRT source (Troja et al.; GCN 6255). Our re-analysis of the XRT data, based on the first 20 ks and allowing for the possiblity of an astrometric XRT frame offset, yields a moderately larger XRT error circle (labeled "Butler") of: RA(J2000) = 13:15:51.16 DEC = +16:30:47.7 (6.4" at 90% confidence) We cannot confirm any variability of the X-ray source. The SDSS galaxy noted by Kann (GCN 6256) and the faint source noted by Malesani et al. (GCN 6257) are well detected. We note that the Malesani source appears to be resolved and it thus unlikely to be the afterglow (it also appears marginally detected in the SDSS i-band image from Cool et al. GCN 6248). We note 5 additional sources in the XRT error circle (J2000): RA DEC s1 13:15:51.41 +16:30:42.6 s2 13:15:51.19 +16:30:41.9 s3 13:15:50.94 +16:30:42.6 s4 13:15:50.75 +16:30:48.0 s5 13:15:51.48 +16:30:52.7 We make no claims about variability at this time. We find no source at the location of the Xin et al. transient (GCN 6253). However, we do detect a faint source ~2.3 arcseconds to the South West of that position at: OT? 13:15:40.91 16:34:13.1 This source is several magnitudes fainter than the galaxy to the northwest noted by Xin et al., whereas Xin et al. indicate that their source was 4 magnitudes brighter at 35.4 hour after the GRB." This message can be cited. (*) http://lyra.berkeley.edu/~jbloom/grb070406_ep1.pdf GRAASP thanks to Henry Lee and the observing team at Gemini South for performing these ToO observations.