GCN Circular 37310

A. Melandri (INAF-OAR), P. D'Avanzo, M. Ferro (INAF-OAB), V. D'Elia (INAF/OAR & ASI/ASDC),  D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Rossi (INAF-OAS),  A. Harutyunyan , and D. Carosati (INAF-TNG) report on behalf of the CIBO collaboration:


We observed the optical afterglow of long bright GRB 240825A (Gupta et al., GCN 37274
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; Fermi GBM team, GCN 37273
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; Di Lalla et al., GCN 37288
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; Frederiks et al., GCN 37302
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) with the 3.6m Telescopio Nazionale Galileo (TNG) equipped  with the DOLoRes camera in spectroscopic mode. Observations were carried out with the LR-B grism, covering the range 3500-8000 AA. The observations consisted of one spectrum carried out at a mean time of Aug 25.9562 UT (~7.4 hours after the burst). 

In the acquisition image we clearly detect the optical afterglow (Gupta et al., GCN 37274
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; Jiang et al. GCN 37275
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; Dutton et al. GCN 37276
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; Odeh et al. GCN 37277
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; Zhang et al. GCN 37278
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; Li et al. GCN 37280
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; Izzo & Malesani, GCN 37287
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; Lipunov et al. GCN 37289
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; Leonini et al. GCN 37291
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; Wu et al. GCN 37292
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; Brivio et al. GCN 32795
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; Odeh, GCN 37299
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) with a magnitude r~20, calibrated against the Pan-STARRS catalogue.

The spectrum has a low SNR. From a preliminary reduction, we identify a single absorption feature consistent with Mg II at a redshift of z~0.66, in agreement with the results reported by Martin-Carrillo et al. (GCN 37293
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).