TITLE:   GCN CIRCULAR
NUMBER:  40698
SUBJECT: GRB 250610B: MISTRAL/T193 and T120 OHP further observations
DATE:    25/06/12 11:57:50 GMT
FROM:    Christophe Adami at LAM <christophe.adami@lam.fr>

C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), A. de Ugarte Postigo (LAM), Y. Degot-Longui (Pytheas/OHP), J. Balcaen (Pytheas/OHP), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), report on behalf of a larger collaboration:

We re-observed the field of the GRB 250610B (Saccardi et al., GCN 40671; Wang et al., GCN 40672; Gompertz et al., GCN 40674; Schneider et al., GCN 40676; Gompertz et al., GCN 40677; Li et al., GCN 40678; Evans et al., GCN 40679; Liang et al., GCN 40681; Wang et al., GCN 40682; Wang et al., GCN 40683;  Bochenek et al., GCN 40684; Qiu  et al., GCN 40685; Brivio et al., GCN 40687; Schneider et al., GCN 40689; Breeveld et al., GCN 40691; Hamburg et al., GCN 40692; Godet al., GCN 40695) using the T120cm and T193cm (MISTRAL instrument) telescopes at Observatoire de Haute-Provence (France). We obtained 60 minutes with MISTRAL and 75 minutes with the T120 CCD camera simultaneously in the r-band, from 2025-06-11 at 20:41 to 22:17 UTC (from 28.13 to 29.73 hr after the trigger).

In the stacked and combined image from both instruments, the optical counterpart is detected at a preliminary magnitude of:

r = 22.59 +/- 0.21 mag (AB)

The photometric calibration was performed using nearby stars from the PanStarrs catalog and the magnitude is not corrected for Galactic extinction.

We acknowledge the excellent support from Observatoire de Haute-Provence and in particular the students and professors from the summer camp OHP 2025 and the SOPHIE observer T. Llopis