TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1415 SUBJECT: GRB020531: Observations with the Chandra X-ray Observatory DATE: 02/06/06 21:59:33 GMT FROM: George Ricker at MIT GRB020531: Observations with the Chandra X-ray Observatory N. Butler, A. Dullighan, P. Ford, G. Monnelly, G. Ricker, R. Vanderspek (MIT); K. Hurley (U.C.- Berkeley); and D. Lamb (U.Chicago) on behalf of the Chandra GRB ToO Team and the HETE Science Team write: On 5 June, the Chandra Observatory targeted the field of the short duration gamma-ray burst GRB020531 that was initially localized by the HETE satellite (Ricker et al., GCN1399). The observations, lasting 20 ksec, spanned the interval 04:00-10:04 UT, 5.15 - 5.40 days after the burst. The refined IPN error region from Hurley et al. (GCN1407) was completely contained within the field-of-view of the Chandra ACIS-I array. The ACIS-I data set for the 20 ksec observation was received at 22:23 UT, 18.4 hours after the observation began. Within the refined IPN error region, we detect 10 sources in the 0.5-8 keV band: # Chandra Name RA DEC dR(s) dD(") Cts 28 CXOU J151459.7-192532 15 14 59.74 -19 25 31.91 0.019 1.36 12 36 CXOU J151459.2-192609 15 14 59.18 -19 26 8.50 0.021 1.36 8 41 CXOU J151503.6-192423 15 15 3.59 -19 24 23.49 0.022 1.36 7 47 CXOU J151514.7-192221 15 15 14.69 -19 22 21.42 0.020 1.37 6 48 CXOU J151455.8-192454 15 14 55.76 -19 24 54.02 0.023 1.36 6 51 CXOU J151513.3-192450 15 15 13.30 -19 24 49.94 0.019 1.36 5 52 CXOU J151501.9-192358 15 15 1.86 -19 23 58.48 0.022 1.36 5 55 CXOU J151457.0-192439 15 14 56.96 -19 24 39.26 0.022 1.36 4 56 CXOU J151514.1-192428 15 15 14.14 -19 24 27.58 0.022 1.37 4 58 CXOU J151508.0-192338 15 15 7.96 -19 23 37.69 0.021 1.36 3 The # column refers to the source's relative ranking (in terms of total counts) among all the sources detected in the entire ACIS-I field-of-view. In addition, we detect 3 bright sources just outside of the refined IPN error region: 0 CXOU J151515.3-192511 15 15 15.31 -19 25 10.71 0.019 1.35 67 5 CXOU J151517.8-192102 15 15 17.80 -19 21 2.20 0.020 1.36 44 15 CXOU J151458.3-192322 15 14 58.34 -19 23 22.32 0.020 1.35 19 For these three bright sources, we note that there are conspicuous optical counterparts visible in an observation carried out with the Baade 6.5 meter telescope at the Magellan Observatory on 1 June, 1.19 days after the GRB (see Dulligan et al., GCN1411, for observation details). The three counterparts for #0, #5, and #15 have approximate R magnitudes of 20.4, 23.6, and 20.8, respectively. For both the TAROT A and B source locations (Boer et al., GCN1408), no X-ray counts are detected in excess of the background rate. The astrometry was calibrated using three USNO A2 catalog stars with detectable X-ray emission and lying within the ACIS-I field-of-view. In the above 2 tables, dR, the uncertainty in RA, and dD, the uncertainty in DEC, were established by summing the following in quadrature for each coordinate: the error reported by celldetect, the correlation error between the X-ray and optical positions, and the error estimate from the star reference catalog. We gratefully acknowledge the timely assistance of the personnel at the Chandra Science Center in the acquisition and preliminary processing of these data. This message may be cited.