A Kpc-scale radio polarization study of PG BL Lacs with the uGMRT
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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17
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Monthly Notices of the Royal Astronomical Society, Volume 527, issue 1, pp. 672-688
Abstract
We present here uGMRT band 4 (∼650 MHz) polarization images of 8 BL Lac objects belonging to the Palomar-Green (PG) ‘blazar’ sample. A large fraction of the sources (∼ 63 per cent) reveal core-halo radio structures with most of the polarization detected in the inner core-jet regions. PG1101 + 385 and PG2254 + 075 exhibit a ‘spine-sheath structure’ in polarization. The core-halo and ‘spine-sheath’ structures are consistent with the Unified Scheme suggestion that BL Lacs are the pole-on beamed counterparts of Fanaroff–Riley (FR) type I radio galaxies. PG1418 + 546 and PG0851 + 203 (OJ287) show the presence of terminal hotspots similar to FR type II radio galaxies. They were also found to be low-spectrally peaked BL Lacs, supportive of the ‘blazar envelope’ scenario for BL Lacs and quasars. Fractional polarization ranges from 1 to 13 per cent in the cores and 2 to 26 per cent in the inner jets/lobes of the sample BL Lacs. Compared to the varied radio morphology of quasars from the PG ‘blazar’ sample, the BL Lacs appear to be less diverse. A comparison of the inferred core magnetic (B-) field structures on arcsec(kpc-) scales w.r.t. the Very Long Baseline Interferometry jet direction does not reveal any preferred orientation, suggesting that if large-scale ordered B-fields exist, they do so on scales smaller than probed by the current observations. However, the presence of polarized emission on arcsec-scales suggests that any mixing of thermal plasma with the synchrotron emitting plasma is insufficient to fully depolarize the emission via the internal depolarization process.Description
Funding Information: We thank the referee for their constructive suggestions that have improved the manuscript. JB, PK, SG, and SS acknowledge the support of the Department of Atomic Energy, Government of India, under the project 12-R&D-TFR-5.02-0700. PK acknowledges the support of the Centre for Astrophysics | Harvard & Smithsonian, as a visiting scientist. TH was supported by the Academy of Finland projects 317383, 320085, 322535, and 345899. EL was supported by the Academy of Finland projects 317636, 320045, and 346071. We thank the staff of the GMRT that made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. We acknowledge the support of the Department of Atomic Energy, Government of India, under the project 12-R&D-TFR-5.02-0700. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI: 10.26093/cds/vizier). The original description of the VizieR service was published in 2000, A&AS 143, 23. Funding Information: We thank the referee for their constructive suggestions that have improved the manuscript. JB, PK, SG, and SS acknowledge the support of the Department of Atomic Energy, Government of India, under the project 12-R&D-TFR-5.02-0700. PK acknowledges the support of the Centre for Astrophysics | Harvard & Smithsonian, as a visiting scientist. TH was supported by the Academy of Finland projects 317383, 320085, 322535, and 345899. EL was supported by the Academy of Finland projects 317636, 320045, and 346071. We thank the staff of the GMRT that made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. We acknowledge the support of the Department of Atomic Energy, Government of India, under the project 12-R&D-TFR-5.02-0700. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI: 10.26093/cds/vizier). The original description of the VizieR service was published in 2000, A&AS 143, 23. Publisher Copyright: © 2023 The Author(s).
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Baghel, J, Kharb, P, Hovatta, T, Gulati, S, Lindfors, E & Silpa, S 2024, 'A Kpc-scale radio polarization study of PG BL Lacs with the uGMRT', Monthly Notices of the Royal Astronomical Society, vol. 527, no. 1, pp. 672-688. https://doi.org/10.1093/mnras/stad3173