Radio Flaring of the Blazar S2 0109+22 on Historical Levels

ATel #16093; F. Roesch (University of Wurzburg), M. Kadler (University of Wurzburg), P. Benke (MPIfR Bonn), F. Eppel (University of Wurzburg), A. Gokus (Washington University St. Louis), S. Haemmerich (ECAP/Remeis-Observatory Bamberg), J. Hessdoerfer (University of Wurzburg), D. Kirchner (University of Wurzburg), G. F. Paraschos (MPIfR Bonn), P. Weber (University of Wurzburg) for the TELAMON team; D. Reinhart, K. Rosenlehner, F. Feige, C. Lorey (all Hans-Haffner-Sternwarte - Friedrich-Koenig-Gymnasium), D. Elsaesser (TU Dortmund)
on 21 Jun 2023; 12:53 UT
Credential Certification: Matthias Kadler (matthias.kadler@astro.uni-wuerzburg.de)

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We report radio flaring of the intermediate synchrotron peaked BL Lac object S2 0109+22 at high radio frequencies observed as part of the TELAMON program. We have observed the source during the night of June 15, 2023, in the 14mm (19 – 25 GHz) and 7mm (36 – 44 GHz) bands. We measured averaged flux densities of (4.10 ± 0.75) Jy and (4.05 ± 0.18) Jy at 14mm and 7mm, respectively. This corresponds to an increase in flux density by more than a factor of 2.5 in about six months. The fastest rise has been observed in the past seven weeks (May 1, 2023: (2.30 ± 0.30) Jy and (2.18 ± 0.20) Jy at 14mm and 7mm, respectively). The flare now exceeds historical maximum flux densities reported for this source at similar frequencies. This historical event does not seem to be associated with any outstanding high-energy flaring activity preceding the radio flare, judging from the public Fermi light-curve repository data.

The optical R-band brightness of S2 0109+22 has been measured between June 17 and June 21 with the 0.5m CDK-astrograph by using Bessel-filters at the Hans-Haffner Observatory in D-97265 Hettstadt, Germany (https://schuelerlabor-wuerzburg.de/en/observatory/).

Compared to long-term light curves, the measured values indicate a high but not exceptional optical brightness of the blazar.

We report the following preliminary R-band magnitudes:

JD 2460112.5538: 13.872 ± 0.008

JD 2460113.5589: 13.611 ± 0.009

JD 2460113.5647: 13.647 ± 0.010

JD 2460116.5159: 13.768 ± 0.012

JD 2460116.5396: 13.738 ± 0.014

JD 2460116.5608: 13.743 ± 0.008

 

The TELAMON program uses the Effelsberg 100-m telescope to monitor the radio spectra of very-high-energy emitting active galactic nuclei (AGN), namely TeV blazars and candidate neutrino-associated AGN, with high-cadence high-frequency observations every ~3 weeks and at multiple frequencies up to 44 GHz.

We will continue monitoring the source regularly and encourage more observations especially at other wavelengths to further characterize the dynamic multiwavelength light curve associated with this unusual radio event.