TITLE: GCN CIRCULAR NUMBER: 37295 SUBJECT: GRB 240825A: REM detection of the optical/NIR afterglow DATE: 24/08/26 12:03:35 GMT FROM: Riccardo Brivio riccardo.brivio@inaf.it
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of GRB 240825A (Gupta et al., GCN 37274; Fermi GBM team, GCN 37273; Di Lalla et al., GCN 37288) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H and K bands, starting on 2024 Aug 26 at 00:28:43 UT (i.e. about 8.6 hours after the Swift trigger) and lasted for about 1 hour.
The optical afterglow is detected in the r band at a position coincident with that reported by Swift-UVOT (Gupta et al., GCN 37274) and other optical observations (Jian et al., GCN 37275; Dutton et al., GCN 37276; Odeh et al., GCN 37277; Zhang et al., GCN 37278; Li et al., GCN 37280; Izzo & Malesani, GCN 37287). The NIR afterglow is detected in the J band at a position consistent with the optical counterpart. From preliminary photometry, we derive the following magnitudes:
r = 20.5 +/- 0.3 (AB; calibrated against the Pan-STARRS catalogue) at a mid-time of t-t0 ~ 9.1 hours after the trigger,
J = 17.7 +/- 0.3 (Vega; calibrated against the 2MASS catalogue) at a mid-time of t-t0 ~ 9.2 hours after the trigger.
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