GCN Circular 39560
Subject
EP250302a: OHP/T193 optical and spectroscopic observations
Date
2025-03-03T08:13:10Z (6 days ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), S. Basa (LAM/OHP/Pytheas/AMU), M. Dennefeld (IAP/CNRS/Sorbonne U.), E. Le Floc'h (CEA/Irfu), J. P. Palmerio (CEA/Irfu), A. Saccardi (CEA/Irfu), J. Schmitt (OHP/Pytheas/AMU), F. Schüssler (CEA/DPhP), D. Turpin (CEA/Irfu), S. D. Vergani (CNRS, Paris Obs./LUX) report on behalf of the larger collaboration:
We observed the field of the EP250302a (Dai et al. GCN 39556) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 2 exposures (2x600 s) in the r-band. The first epoch started at 23:38:10 UT on 2025-03-02 (8.03h after the trigger) and the second one at 01:02:41 UT on 2025-03-03 (9.43h after the trigger). In both images, we clearly detected the optical counterpart reported by Zhu et al., GCN 39550, Busmann et al., GCN 39551, Leonini et al., GCN 39553 and Xin et al., GCN 39558.
The preliminary magnitudes derived for that source are:
r = 20.75 +/- 0.06 mag (AB)
r = 20.85 +/- 0.07 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction.
In addition, we obtained 2x30 min exposures with the MISTRAL spectroscopic blue setting, covering from 4200 to 8000 AA starting at 00:20:45UT (midtime = T0+8h45).
In a preliminary reduction of the spectrum, we detect a very faint continuum at the GRB position, covering the whole spectral range and suggesting a redshift lower than 2.5.
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Neda Heidari and Stephane Favard for the MISTRAL observations.