GCN Circular 17758

A. J. Castro-Tirado (IAA-CSIC, ISA-UMA), R. Sanchez-Ramirez (UPV/EHU,
IAA-CSIC), G. Lombardi (IAC, ULL, GRANTECAN) and M. A. Rivero (GRANTECAN),
on behalf of a larger collaboration, report:

Following the detection of the short-duration GRB 150424A by Swift/BAT
(Beardmore et al. 2015, GCNC 17743) and Konus-Wind (Golenetskii et al.
GCNC 17752), we have obtained an optical spectrum (2 x 900s) with the
10.4m GTC telescope (+OSIRIS) in La Palma (Spain), starting on Apr 24,
21:30 UT (i.e. 13.8 hr postburst), covering the 3700-10000 wavelength
range. The slit included the position of the proposed optical afterglow
(Perley and McConnell, GCNC 17745; Marshall and Beardmore, GCNC 17751;
Malesani et al., GCNC 17756; Kann et al. GCNC 17757) as well as the
extended galaxy 5 arcsec to the southwest (Perley and McConnell GCNC
17745).

At the position of the optical afterglow, we see no obvious absorption
features with the continuum extending to 3700 A (implying an upper limit
of z < 3 to the redshift of the GRB). At the position of the nearby
galaxy, we detect [O II] and H-alpha in emission at a redshift z = 0.30.
At this redshift, 5 arcsec corresponds to 22.5 kpc. A more detailed data
reduction is ongoing.

We acknowledge D. Perley for providing the corresponding ID-chart.