TITLE:   GCN CIRCULAR
NUMBER:  19944
SUBJECT: GRB 160925A: Optical spectroscopy of MASTER optical transient
DATE:    16/09/27 08:53:03 GMT
FROM:    Cristiano Guidorzi at Ferrara U,Italy  <guidorzi@fe.infn.it>

I.A.Steele (LJMU), C. Guidorzi (U. Ferrara), C. G. Mundell (Bath), A. Gomboc (U. Nova Gorica), J. Japelj (INAF-OAT) report on behalf of a larger collaboration.

We report optical spectroscopy of the MASTER optical transient (GCN 19938, 19939, 19941) which is a possible optical counterpart to the FERMI GBM trigger 496473540 (GRB160925A).

The optical transient has the ID MASTER OT J222817.90-145657.4.

A low resolution (R~350) optical (400-800nm) spectrum was obtained using the SPRAT spectrograph of the Liverpool Telescope (La Palma) on 26-09-16 at  21:25:49 UT. The 300 second exposure shows a strong, blue continuum with clear H-beta and H-gamma absorption lines at zero redshift. H-alpha is not  present either in emission or absorption (implying a degree of H-alpha emission).  The spectrum is consistent with a dwarf nova during outburst and therefore not likely to be associated with the Fermi trigger.