The loud and the quiet: Searching for radio counterparts of two radio-weak BL Lac candidates with VLBI
Journal article, 2019

BL Lac objects are known to have compact jets inclined to our line of sight at a small angle, showing prominent radio emission. Two radio-weak BL Lac candidates with no counterparts in current radio surveys were recently reported by Massaro et al. Both sources were selected as candidate low-energy counterparts of unassociated Fermi γ -ray sources. We carried out very long baseline interferometry (VLBI) observations with the European VLBI Network (EVN) at 5 GHz to explore their radio properties at the milliarcsecond (mas) scale. One target, J1410+7405, is clearly detected with the EVN. Its measured 5-GHz flux density, 2.4 mJy, is consistent with recent interferometricmeasurementswith theKarlG. JanskyVery LargeArray, suggesting that the radio emission is confined to the inner ≲10-mas region. J1410+7405 is therefore identified as a radio-loud jetted active galactic nucleus, and its brightness temperature exceeds ~109 K. Its properties are similar to those of other γ -ray-detected BL Lac objects. On the other hand, the second target, J0644+6031, remains undetected with the EVN with a 6s brightness upper limit of 0.12 mJy beam-1. This source is thus radio-quiet, confirming its peculiarity, or possibly questioning its BL Lac nature.

Galaxies: individual: J1410+7405

BL Lacertae objects: general

Galaxies: individual: J0644+6031

Galaxies: active

Quasars: general


Hong Min Cao

Shangqiu Normal University

Chinese Academy of Sciences

Sándor Frey

Hungarian Academy of Sciences

Krisztina E. Gabányi

Hungarian Academy of Sciences

Jun Yang

Chalmers, Space, Earth and Environment, Onsala Space Observatory

Lang Cui

Chinese Academy of Sciences

X. Y. Hong

Shanghai Astronomical Observatory

Tao An

Shanghai Astronomical Observatory

Monthly Notices of the Royal Astronomical Society: Letters

17453925 (ISSN) 17453933 (eISSN)

Vol. 482 1 L34-L39

Subject Categories

Astronomy, Astrophysics and Cosmology

Fusion, Plasma and Space Physics



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