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GCN Circular 17288

Subject
GRB 150101B / Swift J123205.1-105602: 9.8 GHz VLA observations
Date
2015-01-09T16:06:35Z (9 years ago)
From
Wen-fai Fong at U of Arizona <wfong@email.arizona.edu>
W. Fong (U. Arizona) reports on behalf of a larger collaboration:

"We observed the field of the short/soft GRB 150101B (Cummings; GCN
17267) with the Karl G. Jansky Very Large Array (VLA) beginning on
2015 Jan 07.378 UT (5.73 days post-burst) at a mean frequency of 9.8
GHz. These observations are contemporaneous with the WSRT observations
at 4.9 GHz (van der Horst et al.; GCN 17286) and cover the
BAT position (90% containment). In 1 hour of observations, we detect
two sources within the BAT position also identified by WSRT.

The first source coincides with the galaxy 2MASX J12320498-1056010,
the XRT position (Cummings et al.; GCN 17268) and the bright source at
4.9 GHz (van der Horst et al.; GCN 17286). The 9.8 GHz flux density is
3.15 +/- 0.02 milliJy which translates to nuLnu ~ 1.5e40 erg/s (at
z=0.134; Levan et al.; GCN 17281), consistent with the interpretation
that this source is an AGN (Fong et al.; GCN 17285).

The second, fainter source is located at:

RA(J2000) = 12:32:08.19
Dec(J2000) = -10:56:14.2

with an uncertainty of 1" in each coordinate, and coincides with the
WSRT position (van der Horst et al.; GCN 17286). This
source has a 9.8 GHz flux density of 0.45 +/- 0.01 milliJy. Assuming a
single power law between 4.9 and 9.8 GHz, we calculate a spectral
index of -1.13 +/- 0.25 for this source. We note that there is no
optical source at this position in our Magellan r-band observations
(Fong et al.; GCN 17285) or in deeper r-band imaging we
obtained with Gemini-South/GMOS (17x90-sec) at 5.67 days post-burst.

We do not detect any other radio sources within the BAT position to a
3-sigma limit of 27 microJy.

We thank the VLA staff for quickly executing these observations."
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