[vsnet-grb-info 9823] GRB100906A: Ashra-1 observation of early optical emission

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11291
SUBJECT: GRB100906A: Ashra-1 observation of early optical emission
DATE:    10/09/19 07:17:24 GMT
FROM:    Makoto Sasaki at ICRR/U.Tokyo  <sasakim at icrr.u-tokyo.ac.jp>

Y.Asaoka, S.Hirai, T.Itoh, M.Masuda, Y.Morimoto, K.Ota, M.Sasaki
(ICRR,Univ.Tokyo), D.Kogure, S.Ogawa, H.Tsujikawa (Toho Univ.),
P.Binder (Univ.Hawaii Hilo), J.Learned (Univ.Hawaii Manoa)
report on behalf of the Ashra-1 collaboration:

We have searched for optical emission in the field of GRB100906A
(Markwardt, et al., GCN Circ. 11227) around the BAT-triggered GRB time
(T0) with one of the light collector units in the Ashra-1 detector
(http://www.icrr.u-tokyo.ac.jp/~ashra) on Mauna Loa on Hawaii Island
(latitude = 19.5412 deg. N, longitude =155.5676 deg. W, altitude =3330m).

The Ashra-1 light collector unit has the achieved resolution of a few
arcmin, viewing 42 degree circle region of which center is located at
Alt = 60 deg, Azi = 0 deg. The sensitive region of wavelength is
similar to the B-band.

We quickly analyzed 200 images covering the field of GRB100906A every
6s with 4s exposure time respectively during the observation between
T0-600s and T0+600s. We detected no new optical object within the PSF
resolution around the GRB100906A determined by Swift-UVOT (Markwardt,
et al., GCN Circ. 11227)

As a result of our preliminary analysis, the following 3-sigma limiting
magnitudes are derived:

----------------------------------------------------------------------
Starting&Ending Exp.Time,  3-sigma Limit. Mag.
----------------------------------------------------------------------
-593.2 	 -589.2 		   12.1
-587.3 	 -583.3 		   12.2
    .        .                       .
    .        .                       .
  -1.4      2.6 		   12.0
   4.5      8.5 		   12.1
    .        .                       .
    .        .                       .
 590.5    594.5 		   12.2
 596.4    600.4 		   12.1
----------------------------------------------------------------------
The limiting magnitudes were estimated in comparison with stars in
Tycho-2 Catalog to be distributed between 12.0 and 12.2 as above
partly listed.

Figures of limiting optical magnitudes vs time comparing with other
measurements and can be found at: http://www.icrr.u-tokyo.ac.jp/~ashra/GRB100906A.

This message may be cited.

====================================
SASAKI Makoto
ICRR, University of Tokyo
5-1-5 Kashiwa-no-ha Kashiwa 277-8582
tel/fax +81-4-7136-3143
====================================