{
  "bibcode": "2011GCN.12410....1T",
  "body": "K. Tokoyoda, M. Hayashi, Y. Yatsu, Y. Aoki, K. Kawakami, S. Song,\nR. Usui, and N. Kawai (Tokyo Tech) �report on behalf of the MITSuME\ncollaboration:\n\nAs reported in GCN12378 (Tokoyoda et al.), we detected a very faint object\nwithin the XRT error circle of GRB 110921A (W. H. Baumgartner et al, GCN12373)\nwith the MITSuME-Akeno 50cm telescope.\nHere we report the results of aperture photometry.\n\nWe started the follow-up observation at 13:53:08 (UT), ~108 sec after the BAT\ntrigger(W. H. Baumgartner et al, GCN12373).  The optical counterpart can be seen\nboth in R and I band only in the earliest data-set from T0+108s to T0 + 348s.\n\nFor zero-point calibration we used GSC2.3 catalog.\nThe g' magnitudes of the reference stars were estimated based on Sesar\net al. (2006).\nFor I-band data we could not find any usable catalog data, therefore we\nperformed a field photometry.\nThe Photometric results are summarized below.\n\nFilter �T0+[s] �MID-UT �T-EXP[sec] � Mag �Mag_err � LimitMag\n-----------------------------------------------------------------------------------\ng' � � � �+108 � �13:55:31 � � � �240 � � � �--- � � �--- � � � � � >19.4\nRc � � �+108 � �13:55:31 � � � �240 � � � 18.8 � �0.2 � � � � �  ---\nIc � � � �+108 � �13:55:13 � � � �210 � � � 18.8 � �0.3 � � � � � ---\n-----------------------------------------------------------------------------------",
  "circularId": 12410,
  "createdOn": 1317401194000,
  "email": "yatsu@hp.phys.titech.ac.jp",
  "subject": "GRB 110921A: MITSuME-Akeno Optical photometry",
  "submitter": "Yoichi Yatsu at Tokyo Tech.  <yatsu@hp.phys.titech.ac.jp>",
  "eventId": "GRB 110921A"
}