GCN Circular 3291
E. Berger (Carnegie Observatories) and D. B. Fox (Caltech) report: "We observed the position of GRB 050412 (GCN 3237) with the Chandra X-ray Observatory + ACIS for 20 ksec beginning on 2005 April 17.392 UT. A comprehensive "wavdetect" analysis reveals no X-ray sources in the XRT 5-arcsec error circle (GCN 3253). The 90%-confidence upper limit is 5 counts, or 2.5e-4 counts/sec. Assuming a photon index of 1.35 as inferred from the XRT data, and a Galactic column density of 2.2e20 cm^-2, we estimate that the upper limit on the unabsorbed 0.5-10 keV flux is 3.6e-15 erg/cm^2/sec. A comparison to the 0.5-10 keV flux measured by the XRT at 0.116 days after the burst indicates an average fading rate steeper than alpha=-1.8, suggestive of a jet break between the two observations." We are grateful to the Chandra Science Data Center for providing rapid data processsing of this observation, and we thank Harvey Tananbaum for his allocation of Director's Discretion Time.