GCN Circular 35819

D. B. Malesani (DAWN/NBI and Radboud Univ.), B. P. Gompertz (Birmingham), Z.-P. Zhu, D. Xu (NAOC), L. Izzo (INAF/OACN and DARK/NBI), on behalf of a larger collaboration, and R. Forsberg (Lund), S. Bijavara Seshashayana (Malmo univ.), report:

We observed the optical afterglow (Gompertz et al., GCN 35805
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; D'Ai et al., GCN 35810
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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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). We used the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started on 2024 Feb 26.934 UT (1.09 days after the MAXI trigger time).

In a single 300-s exposure in the r band, we measure r = 19.53 +- 0.03 (AB), calibrated against nearby Pan-STARRS stars.

This confirms the decay of the GOTO candidate noted by Liu et al. (GCN 35812
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). Assuming an unbroken power law decay (F propto t^-alpha) between their observation and ours, the inferred decay slope is alpha = 1.8 +- 0.3, suggesting a faster decay then indicated in Liu et al. (GCN 35812
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).