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TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2279 SUBJECT: GRB030528(=H2724): X-ray Afterglow Identified in Second Epoch DATE: 03/06/10 12:30:19 GMT FROM: George Ricker at MIT <grr@space.mit.edu> GRB030528(=H2724): X-ray Afterglow Identified in Second Epoch Observations with the Chandra X-ray Observatory N. Butler, A. Dullighan, P. Ford, G. Ricker, R. Vanderspek (MIT); K. Hurley , G. Jernigan (U.C.- Berkeley); and D. Lamb (U.Chicago) on behalf of the Chandra GRB ToO Team and the HETE Science Team write: From 9 June 8:14 UT to 9 June 14:19 UT, the Chandra Observatory targeted the field of the X-ray rich GRB030528, which was localized by the HETE satellite (Atteia et al. GCN2256; Villasenor et al. GCN2261). The 20 ksec second epoch (E2) observation with ACIS-S3 was a follow up to the 25 ksec first epoch (E1) observation performed with ACIS-S3 on 3 June (Butler et al. GCN 2269). Of the 4 sources reported in GCN2269 lying within the revised SXC error region (Villasenor et al. GCN2261) and the 7 sources lying beyond this error region but inside the ACIS-S3 field-of-view, only one source declined in brightness with a significance greater than 2 sigma: # Chandra Name RA DEC E1 Cnts E2 Cnts 1 CXOU J170400.3-223710 17 4 0.31 -22 37 9.99 39 8 Thus, Chandra Source #1 faded by a factor of about 4 between our two observations (level of significance of approximately 4 sigma; the implied power law decay index is 2.0 +/- 0.8). Hence, we are quite confident that Chandra Source #1 is indeed the X-ray afterglow of GRB030528. Based on the coincidence in position and moderate early fading in Ks reported by Greiner et al. (GCN 2271) and the faint lower limit on Ks reported by Bogosavljevic et al. (GCN 2275), Chandra Source #1 appears to be associated with the NIR candidate first reported in GCN 2271. In view of the imminent possibility of a "supernova bump" becoming visible from GRB030528, we urge continued deep optical and IR monitoring of Chandra Source #1. This message may be cited.
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