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TELAMON detection of an inverted spectrum and radio flare of PKS 0446+11 coincident with IceCube-240105A

ATel #16399; F. Eppel (University of Wurzburg), M. Kadler (University of Wurzburg), L. Debbrecht (MPIfR Bonn), J. Eich (University of Wurzburg), A. Gokus (Washington University St. Louis), J. Hessdoerfer (University of Wurzburg), S.-H. Kim (KASI & UST), D. Kirchner (University of Wurzburg), W. Schulga (University of Wurzburg)
on 10 Jan 2024; 10:37 UT
Credential Certification: Matthias Kadler (matthias.kadler@astro.uni-wuerzburg.de)

Subjects: Radio, Millimeter, Sub-Millimeter, X-ray, Gamma Ray, Neutrinos, Request for Observations, AGN, Blazar, Quasar

Referred to by ATel #: 16402, 16407, 16409, 16417

We report on strong radio flaring activity of PKS 0446+11, a radio-loud AGN possibly associated with the recently detected high-energy neutrino IceCube-240105A (GCN#35485, GCN#35498) and the gamma-ray source 4FGL J0449.1+1121. We find that the source is currently in a very high radio state and exhibits an inverted radio spectrum up to 44GHz. Increased activity has also been reported in the gamma-ray (ATel#16398), X-ray (ATel#16397) and at submillimeter frequencies (GCN#35499).

We observed PKS 0446+11 on Jan 7, 2024, with the Effelsberg 100-m telescope as part of the TELAMON program in the 45mm (6.3GHz - 8.3GHz), 20mm (14.0GHz - 17.0GHz), 14mm (19.0GHz - 24.75GHz), and 7mm (36.25GHz - 43.75 GHz) bands. The source currently shows an inverted spectrum with flux densities of (1.112 ± 0.019) Jy, (1.715 ± 0.025) Jy, (1.920 ± 0.071) Jy and (2.35 ± 0.11) Jy in the 45mm, 20mm, 14mm, and 7mm bands, respectively. The fitted spectral index (S ∝ ν^α) from 6.3 GHz to 43.75 GHz is 0.523 ± 0.017. Compared to archival MOJAVE data at 15 GHz (available here) the source is currently close to its historical maximum.

We will continue to monitor the source regularly and encourage more observations especially at other wavelengths to further characterize its dynamic multiwavelength light curve during this exceptional flaring event. 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.