R. Yates, F. Knust (both MPE Garching), D. A. Kann (TLS Tautenburg), and
J. Greiner (MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 150514A (Fermi trigger 453321308; LAT
detection: Kocevski et al., GCN # 17816; GBM detection: Roberts et al.,
GCN # 17819) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla
Observations started at 23:36 UT on 2015-05-15, 29.0 hrs after the GRB
trigger. They were performed at an average seeing of 1".5 and at an
average airmass of 2.1.
Coincident with the UVOT source reported by Marshall & Cannizzo (GCN #
17820), we detect a bright source.
Based on 7.7 min of total exposure time in g'r'i'z' and 8 min in JHK
centered 29.15 hrs after the GRB, we estimate the following preliminary
magnitudes (all in the AB system):
g' = 20.5 +/- 0.1 mag,
r' = 20.1 +/- 0.1 mag,
i' = 19.9 +/- 0.1 mag,
z' = 19.6 +/- 0.1 mag,
J = 19.2 +/- 0.2 mag, and
H = 18.6 +/- 0.2 mag.
Compared with the UVOT detections reported by Marshall & Cannizzo (GCN #
17820; 18th magnitude), the source has clearly faded, establishing it as
the afterglow of GRB 150514A.
We note that similar to other LAT-detected GRBs, this is a very bright
afterglow. Spectral follow-up is encouraged.
Given magnitudes are calibrated against GROND zero points (g'r'i'z') as
well as 2MASS field stars (JHK) and are not corrected for the expected
Galactic foreground extinction corresponding to a reddening of E_(B-V) =
0.02 mag in the direction of the burst (Schlegel et al. 1998).