GRB 221009A: MITSuME Okayama optical observation

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), 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).