TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2797 SUBJECT: Search for SN light in XRF 040912 with MEGACAM DATE: 04/10/12 15:18:08 GMT FROM: Jean-Luc Atteia at Lab d Astrophys.,OMP,Toulouse G. Stratta (OMP), F. Malacrino (OMP), M. Boer (OHP), A. Klotz (OMP), J-L Atteia (OMP), P. Martin (CFHT), C. Veillet (CFHT), J-C Cuillandre (CFHT) and Lisa Wells (CFHT) communicate: We observed the HETE WXM error region of XRF 040912 (Butler et al. GCN 2701) with the wide-field imager MegaCam (36 2048 x 4612 pixel CCDs, 1 square degree FOV), mounted on the 3.6-m CFH Telescope. Two exposures with integration time of 860s each, in the i' band have been performed consecutively starting on October 5.4197 UT (T_grb+22.8 days). We looked for a possible SN emission for the 22 X-ray sources detected with Chandra (Butler et al., GCN Circ=2716). The observation results follow: First exposure (T) Second exposure (T+15min) ------ --------------------------- -------------------------- CXO Distance to i-band Distance to i-band source X-ray position mag X-ray position mag (") (") ------ --------------------------- -------------------------- #1 * 1.5 20.60 - - #2 1.6 22.25 1.5 22.26 #3 1.4 20.17 1.5 20.20 #4 - - - - #5 1.4 21.21 1.5 21.00 #6 1.5 18.96 1.3 18.99 #7 1.0 21.82 1.1 21.61 #8 1.8 23.02 1.3 23.09 #9 - - - - #10 3.2 20.74 2.1 20.66 #11 1.0 21.68 0.9 22.44 #12 - - - - #13 * - - 0.5 22.21 #14 1.2 21.84 1.6 21.39 #15 1.6 22.79 - - #16 - - - - #17 - - - - #18 0.7 21.35 0.6 20.86 #19 - - - - #20 - - - - #21 - - - - #22 - - - - -------------------------------------------------------------------- * Source was at the CCD line separation and was missed in one image -------------------------------------------------------------------- We did not consider sources at distances greater than 2.5" from the X-ray source position. Our conclusions from these observations are: 1- If source #4 is the afterglow of XRF 040912 (as suggested in GCN 2731), we do not observed any SN emission down to i=23.2+/0.2 mag at 22.8 days after the burst event. 2- Source #13, which has been considered as the tentative afterglow of XRF 040912 (GCN 2728) does not appear to vary from the second Magellan observation. We note that source #6 is coincident with an underlying galaxy with i'=19 mag, it has a decaying behavior in X-rays (Butler et al. GCN=2716) and shows the highest V-i' color index (V-i'=2.05, V magnitude reported by Gorosabel et al., GCN 2724), requiring a very red galaxy, or a rebrightning. This resemble the case of XRF 040701 (Barraud et al. GCN 2620) for which the potentially associated Chandra source (Fox et al. GCN 2626) was coincident with a z=0.2146 emission-line galaxy (Kelson et al. GCN 2631) with lower limit R~17.9 mag that possibly prevented the observation of a delayed SN emission, assuming a SN fainter than SN 1998bw and more similar to SN2002ap or SN1994I (Pian et al. GCN 2638). Further observations of source #6 are welcome. A comparison of the two CFHT images that show the nearest objects to the Chandra sources detected in the i' band, can be found at http://www.cfht.hawaii.edu/~grb/XRF040912.html