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 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 ====================================