ATCA and Metsahovi AGN monitoring programs find a long-term radio outburst of PKS 0805-07 coincident with gamma-ray flaring activity

ATel #15692; Philip G. Edwards (CSIRO Space and Astronomy), Jamie Stevens (CSIRO Space and Astronomy), Matthias Kadler (JMU Wuerzburg), Roopesh Ojha (NASA HQ), Merja Tornikoski (Aalto University Metsahovi Radio Observatory), and Anne Lahteenmaki (Aalto University Metsahovi Radio Observatory)
on 18 Oct 2022; 19:33 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

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The Fermi-LAT gamma-ray telescope has found enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar PKS 0805-07 (z = 1.837, White et al. 1988, ApJ 327, 561) as reported in ATel#15676. This source is well known for its exceptionally high apparent jet motions (41.5+-5.6 c; Lister et al. 2019, ApJ 874,43). Here, we report that the ongoing high-energy flaring of PKS 0805-07 is associated with a long-term outburst in the radio band.

ATCA has monitored PKS0805-07 at multiple frequencies ranging from 2.1GHz to 45GHz since 2006. Most observations took place within the scope of the Observatory-led AGN monitoring program (C007), with the most recent measurements coming from the TANAMI/C1730 program that targets gamma-ray bright blazars in the southern sky. The source has been included in the Metsahovi AGN monitoring program in mid-2002 and since 2009 it has been monitored at 37 GHz at a high cadence.

Beginning in early 2021, the high-frequency emission of PKS 0805-07 has started to rise significantly over its long-term average state. As of Oct 15, 2022, the monotonic increase at the high frequencies has reached values of 2.2 Jy at 5.5 GHz, 3.2 Jy at 9.0 GHz, 4.1 Jy at 16.7 GHz, 4.3 Jy at 21.2 GHz, and 4.3 Jy at 39 GHz. This radio outburst is independently seen in the data of the Metsahovi AGN monitoring program: the 37 GHz flux started to rise between May 2021 and July 2021. The highest values of 4.0 +- 0.2 Jy and 4.1 +- 0.2 Jy were measured most recently on September 25 and October 12, respectively. These values are historically the highest flux densities recorded for this source in the ATCA and Metsahovi monitoring programs.

Primary ATCA flux density calibration was performed against similar scans on PKS 1934-638 at all frequencies and epochs. Uncertainties are dominated by systematic errors, which are conservatively estimated to ~5% at the lower frequencies and ~10% at the higher frequencies.

The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. Metsahovi Radio Observatory is operated by the Aalto University in Finland.