TITLE:   GCN CIRCULAR
NUMBER:  31053
SUBJECT: GRB 211023A: BTA spectroscopic redshift
DATE:    21/11/08 15:16:33 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

A. Pozanenko (IKI), A. Moiseev (SAO RAS), A. Moskvitin (SAO RAS), E. 
Malygin (SAO RAS), S. Belkin (IKI, HSE), N. Pankov (IKI, HSE), V. Kim 
(HSE, FAI) on behalf of GRB IKI FuN, A. Rossi (INAF-OAS), D. A. Kann 
(HETH/IAA-CSIC) report:

We observed the afterglow of GRB 211023A (Zhirkov et al, GCN 30977, see 
also  Kann et al, GCN 30982; Hu et al,  GCN 30990; Belkin et al, GCN 
31004; Vinko et al, GCN 31008; Belkin et al, GCN 31018; Belkin et al, 
GCN 31020; Kumar et al, GCN 31023; Gupta et al., GCN 31041; Strobl et 
al., GCN 31042)  with BTA  SAO RAS telescope equipped with SCORPIO-2 
(VPHG940@600 grism). A total of 7200 s (6x1200 s) of spectra were 
obtained starting on 21-11-05 (UT) 20:50:00, i.e. approximately 13.3016 
days after burst. The afterglow is well detected in the acquisition 
imaging with R = 21.61 +/- 0.04 (3 x 90 sec. 21-11-05 (UT) 20:43:59 -- 
20:50:58), and a continuum is visible across the bandwidth of a spectrum 
4000 - 8500 A. The spectrum contain  significant emission lines H_beta, 
[OII] 3727, [OIII] 5007,  at a common redshift of z=0.390. We assume 
that the lines are from a host galaxy and, therefore, this is the 
redshift of GRB 211023A. No evident lines of a possible SN were found.

Calibration of photometry is preliminary and based on nearby stars of 
PS1 catalogue, gri -> R by Lupton transformations.

We are grateful to the directorate of SAO RAS for the TOO allocation.