TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3499 SUBJECT: GRB050504: Ashra-P2/3 monitor and Ashra-AFT response DATE: 05/05/28 14:38:57 GMT FROM: Koji Noda at ICRR,U of Tokyo M.Sasaki, N.Manago, Y.Aita, T.Aoki, Y.Asaoka, M.Jobashi, K.Noda, A.Okumura (ICRR, Univ.Tokyo), S.Ogawa (Toho Univ.), T.Chonan, Y.Watanabe (Titech) report on behalf of the Ashra collaboration: We have observed the field of GRB050504 (08:00:59 UT) covering the Integral error circle (Mereghetti et al, GCN 3348) by Ashra-P2/3 (Prototype of 2/3 scale) and Ashra-AFT at the Haleakala observatory in Hawaii (latitude = 20d 42' 37" N, longitude = 156d 15' 31" W, altitude = 3020m) in conditions of variable clouds across the field. The Ashra-P2/3 continuously monitored the Integral field with 5sec-repeat of unfiltered 4sec exposures from 1 second before the burst. The Ashra-AFT automatically responded to the Integral trigger and took the first image of 4sec-exposure at 08:01:57 UT (58 seconds after the burst and 37 seconds after the alert socket). We also took following 10 unfiltered images of 4sec-exposure every 9 to 10 seconds (08:01:57 UT - 08:03:29 UT). No new source was found within the Integral position by the two telescopes. We compared the co-added 10 images (10 x 4sec) from Ashra-P2/3 with BT in the Tycho catalog and the earliest 3 images and the co-added images (10 x 4sec) from Ashra-AFT with the USNO-B1.0 respectively. We preliminarily obtained 4-sigma limiting magnitudes as follows: Ashra-P2/3 limiting magnitude ----------------------------------------------------- start end exposure limit mag. after GRB (s) (s) BT ----------------------------------------------------- -1 49 40.0 8.0 ----------------------------------------------------- Ashra-AFT limiting magnitude ----------------------------------------------------- start end exposure limit mag. after GRB (s) (s) B1 R1 ----------------------------------------------------- 58 62 4.0 16.7 15.0 68 72 4.0 16.9 15.1 77 81 4.0 16.8 15.1 ----------------------------------------------------- 58 150 40.0 17.7 16.0 ----------------------------------------------------- URL: http://www.icrr.u-tokyo.ac.jp/~ashra/ This message can be cited.