TELAMON Detection of a High-State Compact Radio Source and Gamma-Bright AGN Positionally Coincident with Two IceCube Bronze Neutrino Events (IceCube-191231A and IceCube-211125A)

ATel #15076; Matthias Kadler (JMU Wuerzburg), Florian Eppel (JMU Wuerzburg), Jonas Hessdoerfer (JMU Wuerzburg), Philip Weber (JMU Wuerzburg), Jonas Sinapius (DESY), Raniere de Menezes (JMU Wuerzburg) for the TELAMON team
on 29 Nov 2021; 19:32 UT
Credential Certification: Matthias Kadler (matthias.kadler@astro.uni-wuerzburg.de)

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The TELAMON program (Kadler et al. 2021, Proc. ICRC 2021) is using the Effelsberg 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) to monitor the radio spectra of active galactic nuclei (AGN) under scrutiny in astroparticle physics, namely TeV blazars and candidate neutrino-associated AGN.

We have observed all nine compact radio sources listed in the the rfc_2021c_catalog that are within 3 degree distance of the nominal position of the recently detected high-energy neutrino IceCube-211125A (GCN #31126) on Nov 28/29, 2021, at frequencies between 4.85GHz and 24.75GHz. Seven sources are detected at flux densities near their historical (low-frequency) RFC levels. We point out two sources that are noteworthy:

1. J0245+2405, the brightest compact radio source in the field, is found at significantly enhanced radio flux density at 4.85GHz, 14.25GHz, and 16.75GHz at about 540mJy. At higher frequencies its brightness decreases monotonically to about 440mJy at 40GHz.
2. J0258+2030 is detected at substantially higher flux densities than listed in the RFC catalog (63mJy at X band) and another previous VLBI observation (Lindford et al. 2021; 66.3mJy at C band). At 14.25GHz, we detect it at (91+-1.5)mJy on Nov 29 and at (72+-3)mJy on Nov 28.

J0258+2030 is furthermore particularly noteworthy as it is associated with the Fermi-LAT gamma-ray source 4FGL J0258.1+2030 and also positionally coincident with an earlier IceCube bronze neutrino event (IceCube-191231A, see GCN # 26620). To our knowledge this is the first case of a gamma-ray bright AGN consistent with two IceCube neutrino bronze or gold events and the radio flare coincident with IceCube-211125A makes it a particularly promising possible association.