ATCA radio follow-up of Fermi J1717-5156
ATel #4048; P. G. Edwards (CASS/ATNF), M. H. Wieringa (CASS/ATNF), S. Corbel (Univ. Paris Diderot & CEA Saclay)
on 17 Apr 2012; 15:51 UT
Distributed as an Instant Email Notice Transients
Credential Certification: S. CORBEL (corbel@discovery.saclay.cea.fr)
Subjects: Radio, Optical, X-ray, >GeV, AGN, Blazar, Variables
Referred to by ATel #: 4777
Following the Fermi-LAT detection of a flare on April 7, 2012 from Fermi J1717-5156, a new gamma-ray source near the Galactic Plane (ATel #4023),
we have used the Australia Telescope Compact Array (ATCA) to observe PMN J1717-5155, the radio source in the LAT error circle which has been found to be in
a high state in other wavebands (ATels #4029, #4032, #4042, #4045).
ATCA snapshot observations were made at 5.5 GHz, 9.0 GHz, 17.0 GHz and 19.0 GHz on April 16, 2012, between 21:00 and 22:00 UT.
The ATCA was in 1.5B array configuration at the time, with a maximum baseline of 4.3km.
Observations used 2-GHz bandwidths, centred on the frequencies given above.
The ATCA primary flux density calibrator, PKS 1934-638 was used at all frequencies, and the data reduced in the standard manner with the miriad software package.
The wide bandwidths provided by CABB (Wilson et al. 2011 MNRAS 416, 832) enable the spectral index to be determined in each band.
At 5.5 GHz, the flux density was S = 238 mJy, with a spectral index of alpha = 0.35 (S = k nu^+alpha);
at 9.0 GHz, S = 271 mJy, alpha = 0.04; at 17 GHz, S = 246 mJy, alpha = -0.47; at 19 GHz, S = 232 mJy, alpha = -0.67.
The 5.5 GHz flux density can be compared with the PMN catalog value of S = 165 mJy at 4.9 GHz (Wright et al. 1994 ApJS 91, 111).
The increased flux density and inverted spectrum at 5.5 GHz are further confirmation that the source is currently in a flaring state.
The source was spatially unresolved on the longest baselines at all frequencies.
Further ATCA observations are planned.
