GCN Circular 12132
Subject
GRB 110709B: Gemini-South additional analysis and photometry
Date
2011-07-10T02:10:22Z (13 years ago)
From
Edo Berger at Harvard <eberger@cfa.harvard.edu>
E. Berger (Harvard) reports on behalf of a larger collaboration:
"Additional inspection and photometry of our Gemini-South r-band image (GCN
12128) reveals a second, fainter source (S2) at the following coordinates
(J2000):
RA = 10:58:36.955
DEC = -23:27:20.62
with an uncertainty of about 0.8" (due to centroid uncertainty). This
position is consistent with the faint source detected by GROND (GCN 12129).
Photometry of the two sources using the Gemini-South/GMOS standard
photometric zero-point yields the following magnitudes:
S1: r = 21.28+/-0.05 mag ("DSS" source)
S2: r = 22.18+/-0.12 mag
Taken at face value, the brightness of S2 is consistent with the GROND value
(r=22.15+/-0.15 mag; GCN 12129), suggesting that S1 has actually faded by
about 0.3+/-0.15 mag between 1 and 3.2 hours after the initial trigger.
Alternatively, if the offset relative to the GROND photometry of S1
(r=20.9+/-0.1 mag) is due to a zero-point offset, the resulting brightness
of S2 is r = 21.9+/-0.1 mag. This is marginally consistent with the GROND
value (r=22.15+/-0.15 mag) which was obtained about 2.2 hours earlier than
our observations.
To determine which scenario is correct relative to the GROND photometry, we
measure the brightness of the star at:
RA = 10:58:38.053
DEC = -23:26:31.78
to be r = 18.25 mag."