GCN Circular 2846

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

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