TITLE:   GCN CIRCULAR
NUMBER:  14669
SUBJECT: GRB 130427A:: BTA spectroscopic observations on May 10/11.
DATE:    13/05/16 21:22:08 GMT
FROM:    Alberto Castro-Tirado at Inst.de Astro. de Andalucia  <ajct@iaa.es>

Vladimir V. Sokolov (SAO-RAS), Alberto J. Castro-Tirado (IAA-CSIC),
Alexander S. Moskvitin, Elena A. Barsukova, Viktoria N. Komarova, Nikolaj
V. Borisov, Azamat F. Valeev, Tatyana N. Sokolova (SAO-RAS) and Vitaly P.
Goranskij (SAI-MSU, SAO-RAS), report:

"We have obtained 3 epochs of spectroscopy for the GRB 130427A optical
afterglow (Maselli et al. GCNC 14448, Elenin et al. GCNC 14450) with the
6-meter BTA equipped with Scorpio. The spectra (with exposure times of
4 x 900 s, 5 x 900 s and 4 x 1200 s) were taken on May 2/3, 5/6 and
10/11 respectively. We used the VPHG 550G grating which covers the
3700-7900 A spectral range and provides a 13 A spectral resolution.

Narrow host galaxy lines such as 3727 A [OII], [OIII] 4959 A, 5007 A and
Balmer lines are noticeable in all spectra. The measured redshift is 0.3393,
in good agreement with the previously reported values (Levan et al. GCNC
14455; Xu et al. GCNC 14478; Flores et al. GCNC 14491; Garnavich GCNC 14605
and Perley & Tang, GCNC 14615). Particularly, we detect marginal excess
emission in the range 6000-7000 A on the later spectrum obtained on May
10/11, which can be interpreted as evidence of the underlying SN (de
Ugarte Postigo et al., GCNC 14646), what is also supported by the
long-term photometric observations (Trotter et al., GCNC 14662; Watson et
al., GCNC 14666).

Our preliminary flux-calibrated spectra can be seen at:

http://www.sao.ru/hq/grb/GRB130427A/GRB130427A_BTA_May2-10.jpg

We thanks S.N. Fabrika, O.P. Zhelenkova, Yu.Yu. Balega, V.V. Vlasyuk and
A.S. Moiseev for their help in obtaining the observations."