TITLE: GCN CIRCULAR NUMBER: 10232 SUBJECT: GRB 091117: Chandra Observations DATE: 09/12/02 19:36:40 GMT FROM: Derek Fox at PSU D. B. Fox (Penn State) and E. Berger (Harvard) report: "We observed the Swift/BAT localization region for GRB 091117 (Cummings et al., GCN 10171; Sakamoto et al., GCN 10180) with the Chandra X-ray Observatory + ACIS, positioned at the ACIS-S3 aimpoint, in a 20.1 ksec integration with mean epoch Nov 21.85 UT, 4.1 days after the burst trigger. Analysis of these data reveals the presence of nine X-ray sources within and near the BAT localization region, including the two X-ray sources identified in previous Swift XRT observations (Berger, GCN 10173; D'Elia et al., GCN 10177). Comparison to deep optical imaging of the region from Magellan (Berger & Mulchaey, GCN 10174; Berger & Momcheva, GCN 10183) reveals point-like (nuclear, stellar, or unresolved galactic) optical counterparts to all but three of these sources: # CXOU J Sigma Cts Unc Comments ========================================================== 1 020353.36-165830.0 54.0 119 11 XRT-1; Nuclear 2 020356.65-165659.1 44.5 101 10 XRT-2; Nuclear 3 020353.68-165428.1 14.7 34.9 6.5 Stellar 4 020338.35-165547.3 8.7 23.0 5.0 Stellar 5 020347.45-165927.6 6.2 13.4 3.7 (not imaged) 6 020342.46-165706.7 4.8 9.7 3.2 Stellar 7 020345.74-165817.1 4.2 8.7 3.0 Near galaxy 8 020345.21-165818.2 3.8 7.7 2.8 Stellar 9 020349.61-165430.5 3.7 7.6 2.8 No counterpart ========================================================== The table above provides source names/coordinates (J2000) as determined from the Chandra astrometric solution, the significance of detection in "wavdetect" analysis over the 0.3-8.0 keV bandpass, and estimated counts and uncertainties (0.3-8.0 keV) for each source. The nature of the optical counterpart, if any, is also provided. We note that the two brightest X-ray sources, also observed by Swift, are coincident to within <1 arcsec with the active nuclei of the two brightest galaxies in the region: Chandra source #1 (XRT-1) with the active nucleus of the face-on spiral galaxy at z=0.096 (Chornock & Berger, GCN 10176), and Chandra source #2 (XRT-2) with the active nucleus of 2MASX J02035665-1656585 at z=0.092. Source #1 appears (2.8-sigma confidence) to have faded since the first epoch of Swift observations, consistent with inferences from Swift XRT data (Fox, GCN 10179); however, the coincidence of sources #1 and #2 with AGN suggests that neither of these objects is associated with GRB 091117. Chandra source #7 is notable for being located 2.4 arcsec from the center of an edge-on galaxy that is resolved in our Magellan imaging."