Kavli Affiliate: Erin Kara
| First 5 Authors: Eileen T. Meyer, Sibasish Laha, Onic I. Shuvo, Agniva Roychowdhury, David A. Green
| Summary:
We present multi-frequency (5-345 GHz) and multi-resolution radio
observations of 1ES 1927+654, widely considered one of the most unusual and
extreme changing-look active galactic nuclei (CL-AGN). The source was first
designated a CL-AGN after an optical outburst in late 2017 and has since
displayed considerable changes in X-ray emission, including the destruction and
rebuilding of the X-ray corona in 2019-2020. Radio observations prior to 2023
show a faint and compact radio source not unusual for radio-quiet AGN. Starting
in February 2023, 1ES 1927+654 began exhibiting a radio flare with a steep
exponential rise, reaching a peak 60 times previous flux levels, and has
maintained this higher level of radio emission for nearly a year. The 5-23 GHz
spectrum is broadly similar to gigahertz-peaked radio sources, which are
understood to be young radio jets less than ~1000 years old. Recent
high-resolution VLBA observations at 23.5 GHz now show resolved extensions on
either side of the core, with a separation of 0.14 pc, consistent with a new
and mildly relativistic bipolar outflow. A steady increase in the soft X-ray
band (0.3-2 keV) concurrent with the radio may be consistent with jet-driven
shocked gas, though further observations are needed to test alternate
scenarios. This source joins a growing number of CL-AGN and tidal disruption
events which show late-time radio activity, years after the initial outburst.
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