GCN Circular 37948

C. Adami, S. Basa (LAM/Pytheas/AMU), E. Le Floc'h, D. Turpin, F. Schussler (CEA Paris-Saclay), 
J. Palmerio (GEPI, Obs. de Paris), B. Schneider (MIT), A. Saccardi (GEPI/Obs. de Paris & CEA 
Paris-Saclay), report on behalf of the MISTRAL GRB collaboration:

We first performed imaging of the field of GRB 241029A (Fermi GBM team, GCN 37932
Not found
 
 
; Schanne et al., 
GCN 37934
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; Chenwei Wang et al., GCN 37935
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; Evans et al., GCN 37936
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; Jiang et al., GCN 37937
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; 
Weikang Lin et al., GCN 37939
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; Jiang et al., GCN 37940
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; Francile et al., GCN 37941
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; Ackley et al., 
GCN 37943
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; Odeh et al., GCN 37944
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; Myers et al., GCN 37945
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; Bernardini et al., GCN 37946
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) with 
MISTRAL mounted on the 1.93 m telescope at Observatoire du Haut Provence (OHP, France). 

The observations consisted of 300s + 600s exposures in r-band plus 2x600s in g-band. We have 
very clear detections of the transient object both in g and r-band images: using as reference 
field stars from the Pan-STARRS catalogue, we determine preliminar magnitudes of r(AB) = 
21.6 +/- 0.1 mag and g(AB) = 21.4 +/- 0.1 mag at a mean date of 2024-10-29T18:12:00 UT, ~16 
hours after the burst.

We immediately after took a spectrum of the object using the MISTRAL blue grism (end of data 
collection at 2024-10-29T19:45:21UT, ~17h30 after ther burst). Our spectrum cover the wavelength 
range 4200-8000 AA and consist of one exposure of 1500 seconds. We detect a weak but significant 
continuum between ~5700/5900 and ~6500AA and this suggests an upper limit of 3.7/3.9 for the 
redshift.

We acknowledge the excellent support from Observatoire de Haute-Provence and in particular 
Yoann Degot-Longhi for the MISTRAL observations and Thomas Baycroft.