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ATCA search for a radio counterpart of the GeV transient near TXS 1731+152A

ATel #6415; Leonid Petrov (Astrogeo Center), Kirill Sokolovsky (ASC Lebedev/SAI MSU), Jamie Stevens (CSIRO)
on 25 Aug 2014; 06:39 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

Subjects: Radio, Gamma Ray, >GeV, AGN, Blazar, Quasar, Transient

Referred to by ATel #: 6449

Following the Fermi/LAT detection of a new flaring gamma-ray source on August 13, 2014 (ATel #6393, #6410) we performed a search for its possible radio counterpart with the Australia Telescope Compact Array (ATCA) on August 21 08-12h UT. ATCA in its 6B configuration performed 4.5-6.5 and 8-10 GHz mosaic observations covering a 12' radius field centered at 17:32:51.8 +15:15:27 J2000. Three radio sources are detected in this field:

           Right ascension     Declination       Flux density mJy            Spectral 
                                                  5.5GHz         9.0 GHz      Index     Dist 
J1733+1513 17:33:21.71 -+0.4  +15:13:23.1 -+10.0  191.6 -+0.2  134.4 -+0.4  -0.7 +-0.1  7.5' 
J1732+1517 17:32:20.89 -+0.4  +15:17.48.4 -+10.0    1.7 -+0.1    1.3 -+0.1  -0.5 +-0.2  7.8' 
J1732+1515 17:32:16.71 -+0.4  +15:15:03.0 -+10.0    0.7 -+0.1    0.5 -+0.1  -0.7 +-0.5  8.5' 
(Spectral index is defined as S^{+alpha})

All sources have NVSS counterparts at 1.4 GHz (Condon et al. 1998 AJ, 115, 1693):

173322+151321  227.6 +-6.8 mJy 
173220+151738    2.3 +-0.4 mJy 
173217+151458    3.1 +-0.4 mJy

Comparison of J1733+1513 flux density at 5.5 GHz with historic single dish observations in October 1987 (Gregory & Condon 1991 ApJS, 75, 1011), 141 +-20 mJy at 4.85 GHz, suggests its slight variability.

We detect no other source brighter than 0.5 mJy, including no radio counterpart of the unidentified X-ray source 1RXS J173230.1+151612. Although according to the ATCA observations J1733+1513 (also known as TXS 1731+152A) does not fit a criterion of a flat spectrum source, it remains the most plausible candidate to association. Detection of parsec (VLBI) scale radio emission (typically found in GeV-bright AGN) would help one to confirm the association.