TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4496
SUBJECT: GRB 060111B: MITSuME detection of optical afterglow
DATE:    06/01/12 14:55:54 GMT
FROM:    Nobuyuki Kawai at Tokyo Tech  <nkawai@hp.phys.titech.ac.jp>

K. Yanagisawa (OAO/NAOJ), H. Toda, and N. Kawai (Tokyo Tech) report
on behalf of the MITSuME collaboration: 

"We have observed the field of GRB 060111B (Perri et al. GCN 4487,
Tueller et al. GCN 4492) with the three-color MITSuME 50 cm telescope
at Okayama, Japan starting at 20:26:18 UT (T_burst+10.6 min) for an
effective exposure of 45 min (60sec x 45).

Comparison of the two stacked images 
at midtime 20:28:56 UT (T_burst+13.2min, exp=60sec x5)  and 
at midtime 20:56:26 UT (T_burst+40.7min, exp=60sec x5) 
revealed a fading object at the same location in the Rc and Ic band
images.   The coordinates of the fading object are:

RA 19:05:42.47, DEC +70:22:33.1 (error = 0.3 arcsec)

We identify this object as the optical afterglow of GRB 05111B for the
following reasons:
 1) these coordinates are consistent with those of the UVOT afterglow
candidate by Perri et al. (GCN 4487), and 
 2) while we do not confirm the possible host galaxy noted by Khamitov
et al. (GCN 4493) in our images, it is not likely to confuse our
identification as it is 4.2 arcsec away.

The magnitudes of the OT at midtime 20:28:56 UT (T_burst+13.2min) were
following: 

  　g': > 19.1 (3 sigma detection limit)
    Rc:   18.9 +/- 0.4
    Ic:   18.3 +/- 0.4

The Rc and Ic magnitudes were calibrated with the R2 and  I2 magnitudes
of the USNO-B1.0 stars.  The g' magnitudes was derived from the NOMAD
B, V magnitudes using the formula by Smith et al. (2002).

The images obtained at Okayama can be viewed at 
http://bragi.oao.nao.ac.jp/support/telescope/grb50/images/GRB060111B.pdf"