TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2724 SUBJECT: XRF 040912, identification of CXO sources DATE: 04/09/17 21:55:13 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia J. Gorosabel (IAC-CSIC Granada), J. Cepa (IAC Tenerife), A. de Ugarte Postigo (IAA-CSIC), D. Martínez-Delgado (MPIfA Heidelberg), V. Casanova, S. Guziy, M. Jelínek (IAA-CSIC, Granada), J. M. Castro Cerón (San Fernando), H. Castaneda (IAC Tenerife), D. Zucker, E. F. Bell (AIP Potsdam) and A. J. Castro-Tirado (IAA-CSIC) report: "We have acquired optical images covering the entire error box of the XRF 040912 detected by HETE-2 (Ricker et al. GCN Circ. 2701) starting on 12 Sep 21:27 UT (i.e. 7.25 hr after the event). The observations were performed with the 4.2m WHT (+PFC) at La Palma (16'x 16' FOV). The observing log follows: ----------------------------------- Date 2004 UT Exp.Time (s) Filter ----------------------------------- 12 Sep 21:27:56 1455 B 12 Sep 21:53:45 900 V 13 Sep 04:26:41 900 V 13 Sep 21:07:58 1200 V 16 Sep 01:49:11 300 I 16 Sep 01:58:17 300 I 16 Sep 02:05:06 300 I 16 Sep 02:11:17 300 I 16 Sep 02:18:16 300 I 16 Sep 02:31:05 180 V 16 Sep 02:35:14 1200 V ---------------------------------- Additional images (I-band, 720-s) were also taken at the 1.5m telescope at IAA Sierra Nevada Observatory on 13 Sep (03:00 UT). Internal comparison between the three V-band frames did not reveal any optical variable source in the entire HETE-2 error box. For the 22 X-rays sources detected by the Chandra X-ray Observatory (Butler et al., GCN Circ 2716) we detect the following optical counterparts in the co-added V-band image (3 sigma limiting magnitude = 25.1): ------------------------------------- CXO V-band Distance to source magnitude X-ray position (") ------------------------------------- #1 21.6 2.0 #2 24.0 2.0 #3 21.1 2.0 #4 24.0 2.0 #5 21.9 1.4 #6 21.0 1.7 #7 22.9 1.7 #8 23.9 1.4 #9 23.9 1.8 #10 21.1 1.6 #11 23.0 1.4 #12 24.2 1.9 #13 23.6 0.5 #14* 23.9 0.9 22.7 1.8 #15 23.9 2.1 #16** >25.1 - #17 24.5 2.0 #18 23.3 0.1 #19 >25.1 - #20 >25.1 - #21 >25.1 - #22 >25.1 - -------------------------------------- * Two possible counterparts * V = 22.1 optical source at 3".5 -------------------------------------- Optical magnitudes are based on the calibration provided by A. Henden (GCN Circ. 2720)." This message can be quoted. [GCN OPS NOTE (21sep04): The affiliation for D. Martinez-Delgado from "AIP Potsdam" to "MPIfA Heidelberg".]