TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2846 SUBJECT: GRB041211: Ashra Prototype optical observation DATE: 04/12/15 07:31:58 GMT FROM: Koji Noda at ICRR,U of Tokyo M.Sasaki, Y.Aita, T.Aoki, Y.Asaoka, M.Jobashi, N.Manago, K.Noda, A.Okumura (ICRR,Univ.Tokyo), S.Ogawa (Toho Univ.), and H.Usami (Tohoku Univ.), on behalf of the Ashra collaboration, report: We have observed the field covering the WXM error box of GRB041211 with the prototype unit of All-sky Survey High Resolution Air-shower detector (Ashra, http://www.icrr.u-tokyo.ac.jp/~ashra) at the Haleakala Observatory Site on Maui contimuously between 10:25 UT (1h7m before GRB041211) and 13:13 UT (1h41m after GRB041211) on 2004-12-11. The prototype unit utilizes a 11M-pixel CMOS sensor following a 0.4m diameter image intensifier on a modified Baker-Nunn optical system with 0.6m diameter pupil and 1.2m projected diameter spherical reflector for viewing a 50 degree circle region of sky. The achieved resolution is 2arcmin. We obtained about 2000 images covering the WXM error box of GRB041211 every 5s with 4s exposure time respectively. The sensitive region of wavelength is similar with the B-band. We detected no new objects in the WXM error box. As a result of our preliminary analysis of four sets of combined images, the following 3-sigma limiting magnitudes are derived: Time from GRB ExpTime Limit Mag. (s) (s) ---------------------------------------------------------------------- -1468 ~ 0 1175 11.3 0 ~ 100 80 11.0 100 ~ 1000 720 11.5 1000 ~ 4035 2428 11.3 ----------------------------------------------------------------------- Limiting magnitudes were estimated by comparison with stars in Tycho-2 Catalog. Figures of limiting magnitudes vs time and so on may be found at: http://www.icrr.u-tokyo.ac.jp/~ashra/GRB041211 This message may be cited.