[vsnet-grb-info 14033] GRB 131014A: GROND observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15347
SUBJECT: GRB 131014A: GROND observations
DATE:    13/10/17 07:11:16 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann at tls-tautenburg.de>

D. A. Kann (MPE Garching), T. Kruehler (ESO), K. Varela and J. Greiner
(both MPE Garching) report on behalf of the GROND team:

We observed the field of the Fermi GBM/LAT GRB 131014A (Fitzpatrick &
Xiong, GCN #15332) simultaneously in g'r'i'z'JHKs 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 07:07 UT on 16 October 2013, 2.08 days after the
GRB. They were performed at an average seeing of 1".0 and at an average
airmass of 1.1. Observations were slightly affected by passing clouds. We
obtained a total exposure of 4500 sec in g'r'i'z' and 3600 sec in JHK.

We detect several sources in and near the refined XRT error circle by
Evans & Amral-Rogers (GCN #15339). Source 1 is the one reported by Schulze
et al. (GCN #15337), also detected by Troja et al. (GCN #15340) and
claimed to be fading by Troja et al. (GCN #15346).

We estimate preliminary magnitudes and upper limits (all in the AB system)
in an aperture of 1".8:

g' = 24.1 ± 0.2 mag
r' = 22.8 ± 0.1 mag,
i' = 22.5 ± 0.1 mag,
z' = 22.2 ± 0.1 mag,
J > 21.5 mag,
H > 21.0 mag,
K > 19.4 mag

This source lies significantly outside the refined XRT error circle
(Evans & Amral-Rogers, GCN #15339), is extended in our images and we find
no evidence of fading as compared to the earlier (t = 1 day) measurement
of Schulze et al. (GCN #15337), also using image subtraction versus the
NOT image. We thus do not consider it the afterglow of GRB 131014A. The
colors and the apparent extent of the source are consistent with a
low-redshift galaxy.

Source 2 is consistent with being point-like in our images and found at:

RA (J2000) = 06:41:12.41
Dec. (J2000) = -19:05:53.5

We estimate preliminary magnitudes and upper limits (all in AB) for a
point source of:

g' > 25.0 mag
r' = 24.8 ± 0.3 mag,
i' = 23.8 ± 0.2 mag,
z' = 22.8 ± 0.1 mag,
J = 21.7 ± 0.2 mag,
H = 21.6 ± 0.4 mag,
K > 19.8 mag

This source is extremely red and lies on the edge of the refined XRT error
circle.

Source 3 also lies on the edge of the error circle at

RA (J2000) = 06:41:12.56
Dec. (J2000) = -19:05:50.1

We estimate preliminary magnitudes and upper limits (all in AB) for a
point source of:

g' = 25.1 ± 0.4 mag
r' = 24.5 ± 0.2 mag,
i' = 24.1 ± 0.2 mag,
z' = 23.8 ± 0.3 mag,
J > 22.0 mag,
H > 21.5 mag,
K > 19.8 mag,

At present, no statement about variability for either source 2 or 3 can be
made.

Magnitudes are calibrated against SDSS (griz) and 2MASS (JHK) stars, and
are not corrected for the Galactic foreground extinction corresponding to
a reddening of E_(B-V)= 0.26 mag in the direction of the burst (Schlegel
et al. 1998).