TITLE:   GCN CIRCULAR
NUMBER:  33704
SUBJECT: GRB 230427A: OSIRIS+/GTC observations
DATE:    23/04/28 15:05:51 GMT
FROM:    J. F. Agui Fernandez at IAA-CSIC <feli@iaa.es>

J. F. Agui Fernandez (IAA-CSIC), A. de Ugarte Postigo
(OCA), C. C. Thoene (ASU-CAS), Fabricio Perez, Alvaro
Tejero and A. L. Cabrera Lavers (GTC, IAC) report:

We observed the afterglow of GRB 230427A at ~ 11.3
hours after burst (Page et al. GCN 33687; Takahashi
et al. GCN 33690; Hu et al. GCN  33695; Tohuvavohu
et al. 33703) with OSIRIS+ at the 10.4m GTC telescope,
at the Roque de los Muchachos Observatory (La Palma,
Spain). Observations consisted of 3x1200 s spectroscopy
with grism R1000B, covering the spectral range between
3700 and 7800 AA under good observing conditions.

From the acquisition image we detect a source at the
GRB location and we measure a magnitude of r ~ 24.2
compared to PanSTARRS field stars. We detect a faint
trace at GRB location above ~3950A which set a limit
for the redshift of z < 3.3.