TITLE:   GCN CIRCULAR
NUMBER:  28649
SUBJECT: GRB 201015A: Redshift from GTC/OSIRIS
DATE:    20/10/16 09:13:32 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte@iaa.es>

A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D.A. Kann, M. Blazek, J.F. Agui Fernandez, C. Thoene (all HETH/IAA-CSIC), G. Gomez Velarde (GTC) report:

We observed the afterglow of GRB 201015A (D’Elia et al. GCN 28632, Lipunov et al. GCN 28633) with the 10.4m GTC telescope, at Roque de los Muchachos Observatory (La Palma, Spain) equipped with OSIRIS. The observation started at 4:07 UT (5.28 hrs after the GRB onset) and consisted of 3x900s with the R1000B grism, covering the range between 3700 and 7800 Å. 

The spectrum shows a featureless continuum throughout the full spectral range. However, we do identify emission features superposed on the trace, which we identify as [OIII], [OII], and H-beta at a common redshift of 0.426.

The automatic BAT analysis shows that this is a peculiar short but soft spectrum burst. We encourage follow-up to search for the associated supernova that could confirm the long nature of the burst, or the lack of such a supernova which  would indicate a possible short origin.