GCN Circular 33790

B. Schneider (MIT), C. Adami (LAM/Pytheas/AMU), J. T. Palmerio (GEPI, 
Obs. de Paris), S. Basa (LAM), E. Le Floc'h, D. Götz (CEA Paris-Saclay), 
S. D. Vergani (GEPI, Obs. de Paris), C. Barthelemy, Q. Desvigne, 
J. Latour (AMU), D. Turpin (CEA Paris-Saclay), report on behalf of a 
larger collaboration:

We observed the field of GRB 230510A (Fermi GBM team, GCN 33751
Not found
 
 
; Eyles-Ferris 
et al., GCN 33752
Not found
 
 
) using the T193cm and T120cm telescopes at Observatoire de 
Haute-Provence (France) respectively equipped with the MISTRAL spectro-imager
and the T120 CCD camera. A total of 8 exposures were obtained in the imaging 
mode of MISTRAL in the r-band filter (6x600s + 2x300s) and 50 exposures 
were obtained with the T120 CCD camera in the r-band filter (50x90s). 
Observations were made from 2023 11 May 01:24:26 UT to 2023 11 May 03:00:47 UT 
(mid time ~13.2h after trigger).

In the combined frames, we detect a faint source consistent with the 
X-ray afterglow position reported by Evans et al. (GCN 33756
Not found
 
 
) and 
with the optical afterglow position reported by Jiang et al. (GCN 33761
Not found
 
 
). 
The source is detected by both instruments at the same position.

Combining the MISTRAL and T120 images, we measured a magnitude of 
r = 21.8 +/- 0.2, in agreement with the value determined individually for 
each instrument. The faintest PanStarr DR1 object detected at 3 sigma 
in the combined image is at r = 22. The photometric calibration was 
performed using nearby stars from the PS1 catalog and the magnitude 
is not corrected for Galactic extinction.

We acknowledge the excellent support from Observatoire de Haute-Provence, 
in particular Jean Balcaen for the MISTRAL observations, Yoann Degot-Longhi, 
Stephane Favard, Luc Favre, and Christelle Eyraud for the T120 observations.