GCN Circular 1387
D. W. Fox (Caltech) reports on behalf of the Caltech-NRAO-CARA GRB Collaboration: "We have observed the error region of the X-ray flash XRF020427 (GCN 1383, 1384, 1386) with the Chandra X-ray Observatory for 13.8 ksec beginning May 6.2456 UT. Reduction of the data using standard Ciao procedures yields the following source catalog (listed in decreasing order of significance) for the most recent BeppoSAX/MECS localization region (GCN 1386): ID IAU Name Sig Cts HR ======================================================= 1 CXOU J220928.2-651932 26.8 57.6(78) 0.34(11) 2 CXOU J220925.9-651855 11.9 15.8(41) 0.13(9) 3 CXOU J220925.0-651919 7.3 20.0(46) 0.07(7) ======================================================= where "Sig" is the wavdetect-quoted significance of the source in the 0.3 to 7.0 keV band, "Cts" is the counts in this band over the 13.8 ks exposure, "HR" is the hardness ratio of 2.1-7.0 keV counts to 0.3-2.1 keV counts, and uncertainties in the trailing digits are indicated in parentheses. J2000 coordinates of the sources are implicit in their IAU names. Source CXOU J220925.0-651919 (ID 3) is coincident with a weak source (not a USNO star) from the Digitized Sky Survey (DSS/SES). Identification of the brightest source, CXOU J220928.2-651932 (ID 1), with the afterglow of XRF020427 would imply an average power-law decay index of approximately 1.8 from the epoch of the second BeppoSAX MECS observation (Apr 29.4439 UT) when referenced to the time of the burst (Apr 27.1588 UT). We therefore consider this source to be the most likely candidate counterpart."