GCN Circular 11125

J. Gorosabel (IAA-CSIC, Granada),  A.J. Castro-Tirado (IAA-CSIC), N. Tanvir (U. Leicester), A. de Ugarte Postigo (INAF-OAB), M. Jelinek (IAA-CSIC), P. Kubanek (IAA-CSIC & U. Valencia), R. Cunniffe (IAA-CSIC), M.D. P�rez-Ram�rez (U. Jaen), J.M. Castro Cer�n (ESAC), S. Guziy (IAA-CSIC), G. G�mez (GTC, La Palma), and J. Cepa (IAC, Tenerife), report on behalf of a larger collaboration:

"We acquired long-slit spectra of the optical afterglow of the possible short-duration GRB 100816A (Oates et al., GCNC 11102) with the 10.4-m Gran Telescopio Canarias (GTC) at the Observatorio del Roque de los Muchachos on the island of La Palma. Three spectra were taken under non optimal weather conditions with the OSIRIS instrument on Aug 16.1736 - 16.2060 UT (3.5-4.3 hr post-burst) with a total exposure time of 3x900s and covering an approximate spectral range of 4200-8700 A. A comparison of the GTC and the Gemini-N spectra (Tanvir et al., GCNC 11123) shows faint absorption features consistent with the MgII doublet at a preliminary redshift of z = 0.8049. At the present stage of the reduction we can not confirm the existence of emission lines."

We acknowledge the support of the GTC staff.