TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3419 SUBJECT: Refined Chandra analysis of GRB 050509b DATE: 05/05/12 22:43:26 GMT FROM: David Burrows at PSU/Swift S. Patel, C. Kouveliotou (MSFC), D. N. Burrows, D. Grupe (PSU), N. Gehrels (GSFC), P. Meszaros (PSU), B. Zhang (UNLV), and R. Wijers (U. Amsterdam) report: Further analysis of our 50 ks Chandra observation of GRB 050509b (Burrows et al. 2005; GCN 3415) has shown that the XRT error circle is embedded in the diffuse X-ray emission from the cluster NSC J123610+285901. We find that the two X-ray sources reported in GCN 3415 are due to fluctuations in the counts from the cluster emission and are spurious. Our refined analysis finds no Chandra point sources within the XRT error circle down to an estimated 99% unabsorbed flux upper limit of about 1.2 x 10e-15 ergs s^-1 cm^-2 (0.5-10.0 keV; assuming galactic column density 1.52e20 cm^-2 and spectral photon index of -2).