TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2502 SUBJECT: GRB031220(=H2976): Observation with the Chandra X-ray Observatory DATE: 03/12/28 03:37:12 GMT FROM: Luigi Piro at IAS/CNR Frascati GRB031220(=H2976): Observation with the Chandra X-ray Observatory M. De Pasquale, B. Gendre (also CESR, Toulouse), L. Piro, E. Costa, M. Feroci (IASF-INAF/Rome), M. Garcia (Harvard, CFA), L. A. Antonelli (OaR/INAF-Rome), G. Garmire (PSU), G. Ricker (MIT) on behalf of a lager collaboration report: On 25 Dec. 18:18 UT, the Chandra Observatory targeted the field of GRB031220, which was localized by the HETE satellite (HETE trigger 2976). The 40 ksec observation spanned the interval 5.6 - 6.1 days after the burst. More than 99% of the HETE/SXC error region was contained within the field-of-view of the Chandra ACIS-I chip. >From a preliminary analysis of the data we detected seven sources in this region in the 0.2-10 keV band: # Chandra Name RA DEC dR(s) dD(") Cts 6 CXOU J043946.5+072220 4 39 46.47 7 22 20.19 0.005 0.13 89 27 CXOU J044003.8+072055 4 40 3.76 7 20 55.26 0.016 0.26 79 2 CXOU J043939.8+072319 4 39 39.77 7 23 18.64 0.005 0.07 45 37 CXOU J043857.1+072449 4 38 57.14 7 24 48.84 0.06 0.7 33 17 CXOU J043954.8+072149 4 39 54.83 7 21 49.33 0.018 0.27 25 7 CXOU J043946.1+072256 4 39 46.14 7 22 56.46 0.011 0.16 25 1 CXOU J043944.3+072037 4 39 44.35 7 20 36.74 0.009 0.13 21 Source #37 is near the border of the chip. None of these source is present in the SIMBAD and 2-MASS catalogues. At this stage of the analysis, the astrometry is dominated by the systematic error in the attitude reconstruction. The nominal attitude reconstruction has been checked by using 3 stars with detectable X-ray emission, giving an average systematic error of about 1", that has to be added in quadrature to the statistical error reported above. A second observation with Chandra should be carried out around mid January. We thank the personnel at the Chandra Science Center for the assistance in the acquisition and preliminary processing of these data. [GCN OPS: This Circular was delayed in distribution 7.5 hrs due to an address problem.]