TITLE: GCN CIRCULAR NUMBER: 39339 SUBJECT: GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening DATE: 25/02/15 17:52:20 GMT FROM: mariaedvige.ravasio@ru.nl

Daniele B. Malesani (DAWN/NBI and Radboud Univ.), Jonathan Quirola-Vasquez (Radboud Univ.), Antonio Martin-Carrillo (UCD), Andrew J. Levan (Radboud Univ. and Warwick Univ.), Maria E. Ravasio (Radboud and INAF), Peter G. Jonker (Radboud Univ.) report on behalf of a larger collaboration:

We observed the optical counterpart (Liu et al., GCN 39330; Xie et al., GCN 39333) of EP250215a / GRB 250215A (Fermi GBM Team, GCN 39327; Wang et al., GCN 39329; Barria et al., GCN 39331; Tembhurnikar et al., GCN 39334; Zheng et al., GCN 39335) using the GMOS instrument installed on the Gemini-South telescope.

While no spectroscopy could be unfortunately performed due to a technical fault with the instrument, in a single 60-s i-band image, taken starting on 2025 Feb 15 at 08:48:23 UT (6.27 hr after the EP/WXT trigger), the afterglow is well detected with a magnitude i = 20.05 +- 0.07 AB (calibrated against nearby stars from the Pan-STARRS catalog).

We note that our (i-band) magnitude is brighter than the z-band measurement reported at an earlier epoch by Liu et al. (GCN 39330). The VT_R magnitude (Xie et al., GCN 39333), taken at an intermediate epoch, is brighter than both other reports. This is likely to indicate a rebrightening.

View this GCN Circular online at https://gcn.nasa.gov/circulars/39339. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...