The jet collimation profile at high resolution in BL Lacertae
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Date
2021-06-01
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Language
en
Pages
9
Series
Astronomy and Astrophysics, Volume 649
Abstract
Context. Controversial studies on the jet collimation profile of BL Lacertae (BL Lac), the eponymous blazar of the BL Lac objects class, complicate the scenario in this already puzzling class of objects. Understanding the jet geometry in connection with the jet kinematics and the physical conditions in the surrounding medium is fundamental for better constraining the formation, acceleration, and collimation mechanisms in extragalactic jets. Aims. With the aim of investigating the jet geometry in the innermost regions of the BL Lac jet, and resolving the controversy, we explore the radio jet in this source using high-resolution millimeter-wave VLBI data. Methods. We collect 86 GHz GMVA and 43 GHz VLBA data to obtain stacked images that we use to infer the jet collimation profile by means of two comparable methods. We analyze the kinematics at 86 GHz, and we discuss it in the context of the jet expansion. Finally, we consider a possible implication of the Bondi sphere in shaping the jet of BL Lac. Results. The jet in BL Lac expands with an overall conical geometry. A higher expanding rate region is observed between ∼5 and 10 pc (de-projected) from the black hole. Such a region is associated with the decrease in brightness usually observed in high-frequency VLBI images of BL Lac. The jet retrieves the original jet expansion around 17 pc, where the presence of a recollimation shock is supported by both the jet profile and the 15 GHz kinematics (MOJAVE survey). The change in the jet expansion profile occurring at ∼5 pc could be associated with a change in the external pressure at the location of the Bondi radius (∼3.3 × 105RS).Description
Funding Information: Acknowledgements. We thank Eduardo Ros for the valuable suggestions that helped improve this manuscript. This research has been consulting data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2009). C. Casadio acknowledges support from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation programme under the grant agreement No. 771282. The research at Boston University was supported by NASA through Fermi Guest Investigator program grants NNX17K0649 an 80NSSC20K1567. This research has made use of data obtained with the Global Millimeter VLBI Array (GMVA), which consists of telescopes operated by the MPIfR, IRAM, Onsala, Metsahovi, Yebes, the Korean VLBI Network, the Greenland Telescope, the Green Bank Observatory and the Very Long Baseline Array (VLBA). The VLBA is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The data were correlated at the correlator of the MPIfR in Bonn, Germany. We thank W. Alef, A. Bertarini, H. Rottmann and I. Wagner for their support at the MPIfR VLBI correlator. We also thank Pablo Torne for his help at the IRAM 30m telescope. Publisher Copyright: © ESO 2021.
Keywords
BL Lacertae objects: individual: BL Lacertae, Galaxies: active, Galaxies: jets, Instrumentation: high angular resolution, Instrumentation: interferometers
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Citation
Casadio, C, MacDonald, N R, Boccardi, B, Jorstad, S G, Marscher, A P, Krichbaum, T P, Hodgson, J A, Kim, J Y, Traianou, E, Weaver, Z R, Gómez Garrido, M, González García, J, Kallunki, J, Lindqvist, M, Sánchez, S, Yang, J & Zensus, J A 2021, ' The jet collimation profile at high resolution in BL Lacertae ', Astronomy and Astrophysics, vol. 649, 153 . https://doi.org/10.1051/0004-6361/202039616
