TITLE:   GCN CIRCULAR
NUMBER:  43293
SUBJECT: GRB 260101A: NOT spectroscopic observations
DATE:    26/01/01 21:05:21 GMT
FROM:    Andrea Saccardi at CEA/Irfu <andrea.saccardi@cea.fr>

A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), K. Valeckas (NOT & NBI), report on behalf of a larger collaboration:

We observed the optical afterglow (Cenko et al., GCN 43285; Perez-Fournon et al., GCN 43286; de Ugarte Postigo et al., GCN 43287) of GRB 260101A detected by Fermi (Fermi GBM team, GCN 43284), Swift (Cenko et al., GCN 43285) and SVOM/GRM (Yu et al., GCN 43292) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A spectrum using grism #4 was secured starting on 2026 Jan 1 at 01:43:54 UT (47 min after the GRB trigger).

Due to bad weather and seeing, we only got two spectra, one of which had a very short exposure time, resulting in a relatively low S/N for the stacked spectrum. The total exposure time is ~ 1500 s covering the wavelength range 3800-9300 AA.

From the unfiltered acquisition 30 s image we measure an AB magnitude of 17.30 +/- 0.07, at a mid-time of 45 minutes after the trigger. Our photometry was calibrated against nearby stars from the r-band PanSTARRS catalogue and not corrected for Galactic extinction.

In a preliminary reduction of the stacked spectrum, we detect a trace over the whole observed wavelength range. At the redshift of z = 2.623 reported by de Ugarte Postigo et al. (GCN 43287) we identify different absorption features, which we interpret as due to Si IV, C IV, and Al II. We note that we do not see a clear absorption corresponding to the weak Ly-alpha.

Further analysis is ongoing.