TITLE:   GCN CIRCULAR
NUMBER:  35819
SUBJECT: GRB 240225B: NOT optical observations
DATE:    24/02/27 12:24:03 GMT
FROM:    Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>

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; D'Ai et al., GCN 35810) of GRB 240225B (Nakajima et al., GCN 35796; Joshi et al., GCN 35798; Kawakubo et al., GCN 35811). 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). 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).