TITLE:   GCN CIRCULAR
NUMBER:  31596
SUBJECT: GRB 211023A: evidence of supernova in LBT spectra
DATE:    22/02/16 08:49:19 GMT
FROM:    Andrea Rossi at INAF  <andrea.rossi@inaf.it>

A. Rossi, E. Pian, E. Palazzi (INAF-OAS), A. Melandri (INAF-OAB), on 
behalf of the CIBO collaboration, B. Rothberg (LBTO/GMU), A. Pozanenko, 
S. Belkin (IKI), and D. A. Kann (HETH/IAA-CSIC) report :

We report the results of the photometric and spectroscopic follow-up 
observations of GRB 211023A (Fermi GBM team, GCN 30958; Di Lalla et al., 
GCN 30961; Lesage et al, GCN 30965; Ursi et al, GCN 30969; Poolakkil, 
GCN 30998; Ridnaia et al., GCN 31022) at z = 0.390 (Pozanenko et al., 
GCN 31053) obtained with the Multi-Object Double Spectrographs (MODS) 
instrument mounted on the 2x8.4-m LBT telescope (Mt. Graham, AZ, USA). 
Data were obtained at ~12 UT on 2021-11-05, ~13 days (i.e. 9 rest-frame 
days) after the burst trigger.

Spectroscopy of the source was obtained for a total of 4x900 s, covering 
the wavelength range 3200-10000 AA. The spectrum has been corrected for 
Galactic extinction (A_V = 0.45 mag). The contribution of the host 
galaxy was removed via a galaxy template matching the emission line 
fluxes. The low S/N spectrum shows features similar to those exhibited 
by XRF-associated SN2006aj at a similar phase (Mazzali et al. 2006, 
Nature, 442, 1018). This confirms the bump observed by Belkin et al. 
(GCN 31098), as due to the emerging contribution of the SN.

We acknowledge the excellent support from the LBTO in particular O. Kuhn 
and S. Allanson, and from the LBT-INAF staff, particularly F. Cusano, S. 
Paiano, and E. Marini in obtaining these observations.