GCN Circular 35831

M. Sasada, I. Takahashi, M. Niwano, S. Sato, N. Higuchi, S. Hayatsu, H. Takei, H. Seki, Y. Yatsu and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 240225B (Nakajima et al. GCN 35796
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) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope Akeno. 

The observation with a series of 60 sec exposures started at 2024-02-27 09:49:24 UT (1.565 days after the MAXI trigger). We stacked the images in good conditions. Here we report the g’- and Rc-band magnitudes of the optical candidate and upper limits by the aperture photometry.

T0+[days] | MID-UT | T-EXP[sec] | candidate magnitude and 5-sigma limits
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1.638 | 2024-02-27 11:35:11 | 9480 | g’=19.78+/-0.13, Rc=19.53+/-0.10, Ic>19.7
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T0+ : Elapsed time after the trigger
T-EXP: Total Exposure time

The position of the optical candidate is consistent with Gompertz et al., GCN 35805
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. The obtained magnitudes are broadly consistent with Gompertz et al., GCN 35805
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; Liu et al., GCN 35812
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; Malesani et al., GCN 35819
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; Wise et al., GCN 35820
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; Gompertz et al., GCN 35824
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; Pankov et al., GCN 35826
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; Moskvitin et al., GCN 35828
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; and Geoffrey et al., GCN 35829
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; and Ror et al., GCN 35830
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.

We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g'-, Rc- and Ic-band magnitudes following Tonry et al. (2012), Table 6. 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).