TELAMON: Effelsberg monitoring of AGN jets with very-high-energy astroparticle emission

• Published in: Astronomy and astrophysics (Berlin) 2024-04, Vol.684
• Main Authors: Eppel, F, Kadler, M, Heßdörfer, J, Benke, P, Debbrecht, L, Eich, J, Gokus, A, Hämmerich, S, Kirchner, D, Paraschos, G F, Rösch, F, Schulga, W, Sinapius, J, Weber, P, Bach, U, Dorner, D, Edwards, P G, Giroletti, M, Kraus, A, Hervet, O, Koyama, S, Krichbaum, T P, Mannheim, K, Ros, E, Zacharias, M, Zensus, J A
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Blazars; Correlation analysis; Emitters; Flux density; Light curve; Neutrinos; Northern Hemisphere; Radio spectra; Spectrum allocation
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202348262

Aims. We introduce the TELAMON program which is using the Effelsberg 100-m telescope to monitor the radio spectra of active galactic nuclei (AGN) under scrutiny in astroparticle physics, specifically TeV blazars and candidate neutrino-associated AGN. Here, we present and characterize our main sample of TeV-detected blazars. Methods. We analyzed the data sample from the first ∼2.5 yr of observations between August 2020 and February 2023 in the range from 14 GHz to 45 GHz. During this pilot phase, we observed all 59 TeV-detected blazars in the Northern Hemisphere (i.e., Dec > 0°) known at the time of observation. We discuss the basic data reduction and calibration procedures used for all TELAMON data and introduce a sub-band averaging method used to calculate average light curves for the sources in our sample. Results. The TeV-selected sources in our sample exhibit a median flux density of 0.12 Jy at 20 mm, 0.20 Jy at 14 mm, and 0.60 Jy at 7 mm. The spectrum for most of the sources is consistent with a flat radio spectrum and we found a median spectral index (S(ν)∝να) of α = −0.11. Our results on flux density and spectral index are consistent with previous studies of TeV-selected blazars. Compared to the GeV-selected F-GAMMA sample, TELAMON sources are significantly fainter in the radio band. This is consistent with the double-humped spectrum of blazars being shifted towards higher frequencies for TeV-emitters (in particular for high-synchrotron peaked BL Lac type objects), which results in a lower radio flux density. The spectral index distribution of our TeV-selected blazar sample is not significantly different from the GeV-selected F-GAMMA sample. Moreover, we present a strategy to track the light curve evolution of sources in our sample for future variability and correlation analysis.