MAXI J1807+132: MITSuME Akeno Optical Observation

ATel #10223; Y. Tachibana, T. Yoshii (Tokyo Tech), M. Shidatsu (RIKEN), Y. Saito, R. Itoh, K. Morita, H. Ohuchi, Y. Yano, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki, K. Saisho, Y. Ozawa, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration:
on 29 Mar 2017; 11:05 UT
Credential Certification: Yutaro Tachibana (tachibana@hp.phys.titech.ac.jp )

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Following the detection of the X-ray transient MAXI J1807+132 and its optical counterpart (ATEL #10208, #10215, #10216, #10217, #10221, #10222), we performed optical observation on March 27 and 28 with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan.

The source is clearly detected in all bands in both days, and we observed an optical decay of ~0.4 mag/day. The calibrated magnitudes are listed as follows.

MJD   T-EXP[hour]   g'   Rc   Ic  
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57839.7737   1.18   18.5 +/- 0.1   17.9 +/- 0.1   17.6 +/- 0.1
57840.7726   1.08   18.8 +/- 0.1   18.3 +/- 0.1   18.0 +/- 0.2
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T-EXP: Total Exposure time
We used GSC2.3 catalog for flux calibration and the errors are statistical only.

Combining with Swift/UVOT data (ATEL #10216), we found that the spectral energy distribution from optical to UV can be explained by a single power-law with a spectral index ~0.5 (f_nu is proportional to nu^0.5) on March 27 when we apply E(B-V)=0.28 (ATEL #10221) and Rv=3.1.