GCN Circular 17738

D. A. Kann (TLS Tautenburg), T. Kruehler (ESO Chile), S. Klose (TLS
Tautenburg) and J. Greiner (MPE Garching) report:

We obtained a photometry sequence in BVRIz with VLT FORS2 of the optical 
afterglow (Varela et al., GCN # 17729, # 17732; Perley, GCN # 17733;
Littlejohns et al., GCN # 17736) of the short GRB 150423A (Swift-638808,
Pagani et al., GCN # 17728).

Observations started on April 23, 2015, 08:02:19 UT, 94 minutes after the
GRB. Seeing was 1".0 and airmass was 1.7.

The afterglow is clearly detected in BVR. Analysis of Iz is pending.

We find Rc = 22.8 +/- 0.1 in the first image (calibrated against SDSS
standard stars transformed to Rc) and find it fades by approximately 0.4
magnitudes in the course of an hour (see also Perley, GCN # 17733;
Littlejohns et al., GCN # 17736).

We are indebted to Jonathan Smoker and Fernando Selman for VLT UT1 support.