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 continuously 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.
 | We observed the field covering the WXM error box of GRB041211 in the fiducial field with the prototype unit of All-sky Survey High Resolution Air-shower detector at the Haleakala Observatory Site on Maui continuously 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:
| ||||||||||||||||||
 | |||||||||||||||||||
 | Livetime of Ashra prototype detector Green line ... Hours in good condition, i.e. the sun is more than 18 degree below the horizon, the moon is below the horizon or fraction of the moon illuminated is less than 10%. Red line ... Hours with detecter active. Black line ... Integrated #images taken by the detector. |