TITLE: GCN CIRCULAR NUMBER: 12580 SUBJECT: GRB 111117A: Chandra detection of the afterglow DATE: 11/11/21 21:40:47 GMT FROM: Takanori Sakamoto at NASA/GSFC T. Sakamoto (GSFC/UMBC), E. Troja (NASA/GSFC/ORAU), N. Gehrels (GSFC), J. Norris (BSU), S. D. Barthelmy (GSFC), J. L. Racusin (GSFC), N. Kawai (Tokyo Tech), A. Fruchter (STScI) A Chandra ToO observation of GRB 111117A (Mangano et al., GCN Circ. 12559; Sakamoto et al., GCN Circ. 12561) started on November 20 12:39 UT (~3 days after the GRB trigger) for a total of 19.8 ksec. The X-ray afterglow of the burst in the 0.3-8 keV band was detected at a position RA, Dec 12.69286, +23.01108 which is equivalent to: RA (J2000) = 00 50 46.29 Dec(J2000) = 23 00 39.9 The 1-sigma statistical error is 0.09 and 0.15 arcsec on RA and Dec respectively. The systematic error of the Chandra aspect solution is 0.6 arcsec (radius, 90% containment; i.e, http://cxc.harvard.edu/cal/ASPECT/celmon/) which dominates the localization uncertainty. The detection significance is 3.9 sigma (7.8 net source counts and 0.2 estimated background counts) by the ciao wavdetect software. The Chandra location is consistent with the enhanced XRT error circle (Melandri et al., GCN Circ. 12565) and the reported optical afterglow/host galaxy candidate from the NOT observation (Andersen et al., GCN Circ. 12563). However, we note that the optical candidate reported from the Magellan observation (Fong et al., GCN Circ 12566) is offset by 1.3 arcsec from the Chandra location. We would like to thank Harvey Tananbaum and the Chandra operation team for rapidly approving and making this observation.