[vsnet-grb-info 15583] GRB 140930B: GROND observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16872
SUBJECT: GRB 140930B: GROND observations
DATE:    14/10/01 20:16:18 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose at tls-tautenburg.de>

J. Graham (MPE Garching), A. Nicuesa Guelbenzu (TLS Tautenburg), J. Bolmer 
and J. Greiner (both at MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 140930B (Swift trigger 614094; De Pasquale et 
al., GCN #16857) 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 La Silla 
Observatory (Chile).

Observations started at 02:25 UT on 1 October 2014, around 7 hours after 
the GRB trigger. They were performed at an average seeing of 1.4" and at 
an average airmass of 1.9.

We detect the afterglow candidate reported by Tanvir et al. (GCN #16861) 
and confirmed by Fong et al. (GCN #16863). At a midtime of 03:00 UT we 
measure a preliminary AB magnitude of

r' = 23.2 +/- 0.2 mag.

The analysis of the other GROND photometric bands is still on-going. We 
note that the photometry is slightly affected by a bright star next to the 
afterglow.

The given magnitude is calibrated against SDSS field stars and not 
corrected for the expected Galactic foreground extinction corresponding to 
a reddening of E_(B-V)=0.04 mag in the direction of the burst (Schlegel et 
al. 1998).