TELAMON Radio Observations of Compact Radio Sources in the Field of IceCube-220624A

ATel #15489; Matthias Kadler (JMU Wuerzburg), Florian Eppel (JMU Wuerzburg), Jonas Hessdoerfer (JMU Wuerzburg), Florian Roesch (JMU Wuerzburg), Philip Weber (JMU Wuerzburg) for the TELAMON team and Yuri A. Kovalev (ASC Lebedev)
on 1 Jul 2022; 10:52 UT
Credential Certification: Matthias Kadler (matthias.kadler@astro.uni-wuerzburg.de)

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

On June 26, 2022, we have observed four compact radio sources listed in the rfc_2021d_catalog that are within the 90% uncertainty region of the recently detected high-energy neutrino IceCube-220624A (GCN #32260) at 6.30GHz and 6.55GHz: J1449+4221, J1451+4154, J1453+4148, and J1457+4158. All four sources are detected at flux densities near their historical (low-frequency) RFC levels. We point out one additional source slightly (0.13deg) outside the nominal region that is noteworthy:

• We observed J1506+4239 (B3 1505+428) on June 29, 2022, with a strongly inverted radio spectrum, raising from 616+-4mJy at 4.5cm to 838+-32mJy at 2cm, to 883+-47mJy at 1.4cm and 1080+-130mJy at 7mm. For comparison, historical flux densities of this source listed in the RFC catalog between 13cm and 3.6cm range from 450mJy to 650mJy. Higher-frequency values listed in NED range from 0.4Jy to 1.0Jy. Flat or inverted spectra with high-frequency flux densities up to 1Jy of this source have also been observed by RATAN-600 in selected epochs in the past.

We also observed the position of the blazar WISEA J145820.77+412101.9 (aka 3HSP J145820.8+412102) at RA=224.58658 deg, Dec=41.35028 deg which has been reported as the probable counterpart of the newly detected gamma-ray source Fermi J1458.0+4119 (ATel #15478) in positional coincidence with the neutrino event IceCube-220624A. We did not detect the radio source at 45mm, implying that the current flux density does not significantly exceed its historical low-frequency brightness (9mJy/beam in the FIRST survey).