GCN Circular 32730

M. Sasada, Y. Imai, K. L. Murata, R. Hosokawa, M. Niwano, I.Takahashi,
M. Tateda, N. Ito, S. Sato, N. Higuchi, Y. Yatsu, and N. Kawai (Tokyo
Tech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 221009A (Dichiara et al. #32632, Kennea
et al. #32635, Veres et al. #32636, Bissaldi et al. #32637, Perley et
al. #32638, Broens et al. #32640, Svinkin et al. #32641, Lesage et al.
#32642, Karambelkar et al. #32643, Hu et al. #32644, Belkin et al.
#32645, Wet et al. #32646, Xu et al. #32647, Postigo et al. #32648,
Ursi et al. #32650, Kennea et al. #32651, Brivio et al. #32652, Bright
et al. #32653, Durbak et al. #32654, Farah et al. #32655, Piano et al.
#32657, Pillera et al. #32658, Paek et al. #32659, Gotz et al. #32660,
Xiao et al.#32661, Kumar et al. #32662, Lapshov et al. #32663, Romanov
et al. #32664, The IceCube Collaboration et al. #32665, Odeh et al.
#32666, Chen et al. #32667, Frederiks et al. #32668, Vidal et al.
#32669, Kim et al. #32670, Tohuvavohu et al. #32671, Postigo et al.
#32676, Huang et al. #32677, Groot et al. #32678, Romanov et al.
#32679, Tiengo et al. #32680, Ayala et al. #32683, Belkin et al.
#32684, Ripa et al. #32685, Castro-Tirado et al. #32686, Krimm et al.
#32688, Negro et al. #32690, Savchenko et al. #32691, Watson et
al.#32692, Strausbaugh et al. #32693, Iwakiri et al. #32694, Brethauer
et al. #32695, Rhodes et al. #32700, Butler et al. #32705, Rhodes et
al. #32707, Vinko et al. #32709, Mao et al. #32727, Zaznobin et al.
#32729) with the optical three color (g', Rc, and Ic) CCD cameras
attached to the MITSuME 50 cm telescope Okayama.

The observation with a series of 60 sec exposures started at
2022-10-09 9:51:38 UT (0.857 day after the Swift detection). We
stacked the images with good conditions. Here we report a Ic-band
magnitude by the forced-photometry at the Swift/UVOT position
(Dichiara et al. GCN Circular #32632
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 ), and the 5-sigma limits of the
stacked images in the g' and Rc bands.

T0+[day] |MID-UT | T-EXP[sec] | magnitudes of forced-photometry
------------------------------------------------------------------------------------------------
0.9320 | 2022-10-10 11:39:09| 8340 | g'>18.3, Rc>17.0, Ic=17.1+/-0.2
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time

We used PS1 catalog for flux calibration. The magnitudes are expressed
in the AB system. The images were processed in real-time through the
MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73,
Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).