GCN Circular 38296

C. Adami (LAM/Pytheas/AMU), M. Dennefeld (IAP), S. Basa (LAM/OHP/Pytheas/AMU) report on behalf of a 
larger collaboration:

We observed the field of GRB241120A (Gotz et al., GCN 38280
Not found
 
 
; Fermi GRM team, GCN 38279
Not found
 
 
; Hamburg 
et al., GCN 38285
Not found
 
 
; Pankov et al., GCN 38291
Not found
 
 
; Cherry et al., GCN 38295
Not found
 
 
) using the T193cm telescope 
at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. Four exposures 
were obtained in the r-band (300s + 3x420s) from 2024 21 November 04:39 UT to 2024 21 November 
05:05 UT (~+23h after detection) with two positions on the sky (position "1" for exposures 1 and 
4, and position "2" for exposures 2 and 3) separated by a dithering of ~10arcsec. The moon was at an 
illumination of ~68% and at a distance of 56deg from target.

The combined frame has a detection upper limit of r~22.5+/-0.6 (5sigma limit). The photometric 
calibration was performed using objects from the PanSTARRS catalog. The magnitudes are not 
corrected for Galactic extinction.

There is no clear additional objects in the MISTRAL image as compared with the PanStarrs r-band 
image except a source at 12:57:06.0 +52:08:26.6 (r~22.2+/-0.2). This source (apparently extended) 
is however only present in two of the four exposures we performed (position "2" exposures) and is 
possibly an internal reflection within the instrument due to the intense Moon illumination. More 
observations are requested to check this point.

We also checked the candidate of Pankov et al. We clearly detect this object and measured a 
magnitude of r~20.40+/-0.08 23h after the original detection. This object is also present in the 
PanStarrs r-band catalog at r~20.39+/-0.02. If this was the transient, it was back to its initial 
magnitude 0.96 days after detection. This would be in good agreement with the light curve proposed by 
Pankov et al.

We acknowledge the excellent support from Observatoire de Haute-Provence, in particular Jean Pierre 
Troncin and the SOPHIE observer Aleyna Adamson.