GCN Circular 36702

C. Adami (LAM/Pytheas/AMU), E. Le Floc’h (CEA Paris-Saclay), F. Fortin (IRAP, Toulouse), 
B. Schneider (MIT), J. Palmerio, A. Saccardi, S. Vergani (GEPI/Obs. de Paris), M. Dennefeld (IAP), 
J. Schmitt, E. Schmitt, E. Molina (OHP/Pytheas), F. Schussler (DPhP CEA), 
report on behalf of a larger collaboration:

We observed the field of EP240618a (GCN 36690; Sun et al., GCN 36701
Not found
 
 
; Wu et al.) using the T193cm 
telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We 
obtained 5400s (9x600s with dithering) in the Y-band between 21h13 and 22h47 UT on the 2024-06-18 
(~16h after trigger) and 3900s (13x300s with dithering) in the i'-band between 22h53 on the 2024-06-
18 and 00h18 UT on the 2024-06-19 (~18h after trigger).

We do not detect any significant new objects in our MISTRAL images within the X-ray position 
uncertainty area, nor in i band (3-sigma detection limit of 20.9) or Y band (3-sigma detection limit 
of 19.85). We however have a hint of a detection close to the ~2-sigma detection limit in the 
MISTRAL Y-band image at an approximate magnitude of Y~20.3 (with a large error bar) and located at  
18:46:36.3, +23:49:55.2. This putative source is not visible at all in the MISTRAL i-band image.
We encourage further deeper follow-ups of this possible source to assess its existence.

The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the 
magnitudes are not corrected for Galactic extinction.

We acknowledge the excellent support from Observatoire de Haute-Provence and in particular Jean 
Pierre Troncin for the MISTRAL observations.