TITLE: GCN CIRCULAR NUMBER: 39078 SUBJECT: GRB 250129A: OHP/T193 optical and spectroscopy observations DATE: 25/01/29 10:51:22 GMT FROM: Benjamin Schneider at MIT <bschn@mit.edu> B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), J. Balcaen (OHP/Pytheas), A. Saccardi (CEA/Irfu), E. Le Floc'h (CEA/Irfu), J. Schmitt (OHP/Pytheas), J. P. Palmerio (CEA/Irfu), S. Basa (LAM/OHP/Pytheas/AMU), D. Turpin (CEA/Irfu) report on behalf of a larger collaboration: We observed the field of the GRB 250129A (Beardmore et al., GCN 39066) with the T193 cm telescope at the Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained one exposure of 60s in the i-band using the red MISTRAL setting at 2025-01-29T05:14:39 (30 min after the trigger). In the reduced image, the optical afterglow (Francile et al., GCN 39065; Schneider et al., GCN 39071; Belkin et al., GCN 39072; Izzo et al., GCN 39073; Izzo et al., GCN 39074; Ghosh et al., GCN 39077) is clearly detected at: i = 16.34 +/- 0.02 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and is not corrected for Galactic extinction. In addition, we obtained 15 min exposures during the twilight with the MISTRAL spectroscopic red setting, covering from 6400 to 9950 AA. In a preliminary reduction of the spectrum, the continuum is detected but the low S/N makes the redshift estimate difficult. Given the redshift provided by Schneider et al. (GCN 39071) and Izzo et al. (GCN 39073), we likely detected FeII (@2600 AA) and a hint of the MgII doublet at a corresponding redshift of 2.15. We acknowledge the excellent support from Observatoire de Haute-Provence, in particular the Sophie observer Alice Radcliffe. View this GCN Circular online at https://gcn.nasa.gov/circulars/39078. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...