Characterising the Extended Morphologies of BL Lacertae Objects at 144 MHz with LOFAR
Artikel i vetenskaplig tidskrift, 2021

We present a morphological and spectral study of a sample of 99 BL Lac objects using the LOFAR Two-Metre Sky Survey Second Data Release (LDR2). Extended emission has been identified at gigahertz frequencies around BL Lac objects, but with LDR2 it is now possible to systematically study their morphologies at 144 MHz, where more diffuse emission is expected. LDR2 reveals the presence of extended radio structures around 66/99 of the BL Lac nuclei, with angular extents ranging up to 115 '', corresponding to spatial extents of 410 kpc. The extended emission is likely to be both unbeamed diffuse emission and beamed emission associated with relativistic bulk motion in jets. The spatial extents and luminosities of the extended emission are consistent with the unification scheme for active galactic nuclei, where BL Lac objects correspond to low-excitation radio galaxies with the jet axis aligned along the line of sight. While extended emission is detected around the majority of BL Lac objects, the median 144-1400 MHz spectral index and core dominance at 144 MHz indicate that the core component contributes similar to 42% on average to the total low-frequency flux density. A stronger correlation was found between the 144 MHz core flux density and the gamma-ray photon flux (r = 0.69) than between the 144 MHz extended flux density and the gamma-ray photon flux (r = 0.42). This suggests that the radio-to-gamma-ray connection weakens at low radio frequencies because the population of particles that give rise to the gamma-ray flux are distinct from the electrons producing the diffuse synchrotron emission associated with spatially extended features.


Sean Mooney

University College Dublin

Francesco Massaro

Universita degli Studi di Torino

John Quinn

University College Dublin

Alessandro Capetti

Istituto nazionale di astrofisica (INAF)

Ranieri D. Baldi

University of Southampton

Istituto nazionale di astrofisica (INAF)

Guelay Guerkan

Thüringer Landessternwarte Tautenburg

Martin J. Hardcastle

University of Hertfordshire

Cathy Horellou

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik

Beatriz Mingo

Open University

Raffaella Morganti

Rijksuniversiteit Groningen

Netherlands Institute for Radio Astronomy (ASTRON)

Shane O'Sullivan

Dublin City University

Urszula Pajdosz-Smierciak

Uniwersytet Jagiellonski w Krakowie

Mamta Pandey-Pommier

Université de Lyon

Observatoire de Paris

Huub Roettgering

Universiteit Leiden

Astrophysical Journal, Supplement Series

0067-0049 (ISSN) 1538-4365 (eISSN)

Vol. 257 2 30


Subatomär fysik

Astronomi, astrofysik och kosmologi

Atom- och molekylfysik och optik



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