GCN Circular 12410

K. Tokoyoda, M. Hayashi, Y. Yatsu, Y. Aoki, K. Kawakami, S. Song,
R. Usui, and N. Kawai (Tokyo Tech) �report on behalf of the MITSuME
collaboration:

As reported in GCN12378
Not found
 
 
 (Tokoyoda et al.), we detected a very faint object
within the XRT error circle of GRB 110921A (W. H. Baumgartner et al, GCN12373
Not found
 
 
)
with the MITSuME-Akeno 50cm telescope.
Here we report the results of aperture photometry.

We started the follow-up observation at 13:53:08 (UT), ~108 sec after the BAT
trigger(W. H. Baumgartner et al, GCN12373
Not found
 
 
).  The optical counterpart can be seen
both in R and I band only in the earliest data-set from T0+108s to T0 + 348s.

For zero-point calibration we used GSC2.3 catalog.
The g' magnitudes of the reference stars were estimated based on Sesar
et al. (2006).
For I-band data we could not find any usable catalog data, therefore we
performed a field photometry.
The Photometric results are summarized below.

Filter �T0+[s] �MID-UT �T-EXP[sec] � Mag �Mag_err � LimitMag
-----------------------------------------------------------------------------------
g' � � � �+108 � �13:55:31 � � � �240 � � � �--- � � �--- � � � � � >19.4
Rc � � �+108 � �13:55:31 � � � �240 � � � 18.8 � �0.2 � � � � �  ---
Ic � � � �+108 � �13:55:13 � � � �210 � � � 18.8 � �0.3 � � � � � ---
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