ATCA Detection of a Radio Flare in the Blazar PKS 0438-43 Detected in Elevated Gamma-ray State by Fermi-LAT

ATel #14468; Jamie Stevens (CSIRO Astronomy and Space Science), Roopesh Ojha (NASA HQ), Philip G. Edwards (CSIRO Astronomy and Space Science), and Matthias Kadler (JMU Wuerzburg)
on 17 Mar 2021; 22:07 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

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We report multi-band Australia Telescope Compact Array (ATCA) radio observations of the FSRQ PKS 0438-43 from which the Fermi Gamma-ray Space Telescope's LAT instrument has observed strong gamma-ray emission on 2021 March 6 (ATel#14446). A previous gamma-ray flare on 2016 Dec 11 was also reported by Fermi LAT (ATel#9854).

The most recent observations were made on the same day the gamma-ray flare was detected and were centered at 5.5, 9.0, 17, and 19 GHz, each with a bandwidth of 2GHz. The array was in the 6D configuration which results in the highest angular resolution possible with ATCA. A snapshot of ~3 minutes duration was made at each frequency. Primary flux density calibration was performed against similar scans on PKS 1934-638 at all frequencies.

The resulting flux densities for PKS 0438-03 were 2.2 Jy at 5.5 GHz, 3.1 Jy at 9 GHz, 4.2 Jy at 17GHz and 4.4 Jy at 19 GHz. The (one-sigma) errors in these values are estimated to be 5% for all frequencies and these are dominated by systematic effects. The source is core dominated, but there is some evidence of structure on the longest ATCA baselines.

Past ATCA observations show that the 17/19 GHz flux density started increasing from a level of about 1 Jy between 2015 Feb 8 and 2016 Mar 7. It has brightened steadily to its current level over four times its pre-2016 flux density. Past observations at 5.5/9 GHz show the flux density started increasing from a level of about 1.7/1.8 Jy at the beginning of 2019 to its current level about 40/80% brighter. The spectrum has been inverted since about 2016.

The Australia Telescope Compact Array is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO.