TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1272 SUBJECT: GRB011130 (XRF011130) Second Epoch Chandra Observations DATE: 02/03/15 03:33:31 GMT FROM: George Ricker at MIT GRB011130 (=XRF011130): Results of a Second Epoch Observation with the Chandra X-ray Observatory N. Butler, G. Monnelly, G. Ricker, J. Doty, P. Ford, R. Vanderspek, G. Crew, A. Dullighan (MIT); D. Lamb (U.Chicago); and P. Plucinsky (CFA) on behalf of the Chandra GRB ToO Team and the HETE Science Team write: On 20 February, from 10:02 UT - 14:30 UT, the Chandra Observatory targeted the field of the X-ray rich gamma-ray burst XRF011130, localized by the HETE satellite (Ricker et al., GCN1165) This was a 16 ksec observation with ACIS-I, following up the 30 ksec observation performed with ACIS-I on 10 December (Ricker et al., GCN 1185). Of the 20 brightest sources reported in GCN 1190 (Monnelly et al.), none were observed to fade in a manner that is consistent with the power-law behavior that is characteristic of gamma-ray burst afterglows. (A power law index of -1.3 implies a fade by a factor ~15, between our 1st and 2nd epoch observations.) Corrected for exposure, the largest fade for any of the sources in the list was by a factor of 3. We note that our brightest epoch 1 source (CXOU J030527.9+034657), which appears to be associated with a 20th magnitude galaxy (Mirabal & Halpern, GCN 1187), faded by a factor of approximately 2. Beyond the top 20 brightest, we note that our 24th and 27th brightest 1st epoch sources (see partial table below) faded to levels consistent with the background. We estimate a 50% probability for chance fading to the background in one or more of our 24 brightest sources; we estimate a 75% probability for chance fading to the background in one or more of our 27 brightest sources. Chandra Name RA DEC E1C E1B E2C E2B CXOU J030515.1+034457 3 5 15.12 3 44 57.02 8.1 2.9 4.0 -0.7 0.7 CXOU J030527.8+035548 3 5 27.81 3 55 48.09 13.8 4.2 6.5 -1.3 4.3 Here E1C denotes the epoch 1 net counts for the source, E1B the epoch 1 background counts estimate, the expected epoch 2 net number of counts based on epoch 1, E2C the observed net counts in epoch 2, and E2B the epoch 2 background counts estimate. A complete table in this form, containing all of our 1st epoch sources, can be found at: http://space.mit.edu/HETE/Bursts/GRB011130/epoch2_table.html This message may be cited.