GCN Circular 35824

B. P. Gompertz (U. Birmingham), D. B. Malesani (DAWN/NBI and Radboud Univ.) report:

We observed the position of the optical afterglow (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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) of GRB 240225B (Nakajima et al., GCN 35796
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; Joshi et al., GCN 35798
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; Kawakubo et al., GCN 35811
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) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 21:37:18 on 2024-02-27, 2.06 days after trigger, and consisted of 15x120 s exposures in the SDSS r filter.

We detect the afterglow with an AB magnitude of r = 20.04 +/- 0.05, calibrated against nearby SDSS stars and not corrected for foreground extinction. Between this epoch and the initial detection by GOTO (Gompertz et al., GCN 35805
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), the afterglow is well described by a power-law decay with an index of 0.8, which is consistent with the magnitudes reported by NOT (Malesani et al., GCN 35819
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) and LT (Wise et al., GCN 35820
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), though under-predicts those reported by Nanshan/HMT (Liu et al., GCN 35812
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), potentially suggestive of flaring behaviour at the time of their observation. The steepening in the light curve noted in GCN 35819
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 may be thus due to local variability, rather than a break in the power-law evolution.

We note the presence of a faint underlying source at the afterglow position in Legacy Survey archival imaging, which may be the host galaxy of GRB 240225B.