4 research outputs found
A Polarization Study of 3 Blazars using the uGMRT at ~600 MHz
We present results from our radio polarimetric study with the upgraded Giant
Metrewave Radio Telescope (uGMRT) at Band 4 (550-850 MHz) of 3 blazars:
radio-loud quasars 3C390.3, 4C71.07 and BL Lac object 1ES 2344+514. The aim of
this study was (i) to carry out a feasibility study for Band 4 polarization
with the uGMRT, and (ii) to compare and contrast the kpc-scale polarization
properties between the blazar sub-classes. We have detected linear polarization
in all the three sources. The degree of linear polarization in the cores of the
two quasars is higher than in the BL Lac object, consistent with similar
differences observed on parsec-scales in blazars. The highest fractional
polarization of 15% is observed in the hotspot region of 3C390.3, which also
shows extended polarized lobe structures. 1ES 2344+514 shows a core-halo
structure whereas 4C71.07 remains unresolved. A rotation of polarization
electric vectors along the northern hotspot of 3C390.3, and the core of 1ES
2344+514, suggest jet bending. Greater depolarization in the southern lobe of
3C390.3 compared to the northern lobe indicates the presence of the
`Laing-Garrington effect'. Multi-frequency uGMRT polarimetric data are underway
to study the kpc-scale rotation measures across these sources in order to look
for differences in the surrounding media.Comment: 13 pages, 6 figures, accepted by Journal of Astrophysics and
Astronom
A Polarimetric Study of 9 PG Quasars with the VLA
We present polarization images of 9 radio-loud (RL) quasars from the VLA
B-array at 6 GHz. These quasars belong to the Palomar-Green (PG) "blazar"
sample comprising 16 RL quasars and 8 BL Lac objects. Extensive polarization is
detected in the cores, jets and lobes of all the quasars, with cores primarily
displaying magnetic (B-) fields transverse to, and jets displaying fields
aligned with the jet direction. Hotspots display either transverse B-fields
signifying B- field compression at terminal shocks or more complex structures.
The fractional polarization in the cores ranges from 1-10% and jets/lobes from
10-40%. Several of the quasars show distorted or hybrid FRI/FRII radio
morphologies with indications of restarted AGN activity. We attribute this to
the optical/UV selection criteria of the PG sample that remains unbiased at
radio frequencies. The in-band spectral indices of the radio cores are
relatively flat while they are steep in the hotspots. This is consistent with
the polarization structures where the hotspots appear to be locations of jet
bends or bow-shocks. We present global properties for the entire PG "blazar"
sample. We find that jet powers correlate with accretion rates for the quasars;
higher accretion rates result in more powerful radio jets. A correlation
between the radio core fractional polarization and the 150 MHz total radio
luminosity for the 9 quasars studied here may imply that more organized
B-fields at the jet bases lead to higher core fractional polarization and to
more powerful radio jets.Comment: 24 pages, 21 figures, MNRAS accepte
A Kpc-scale Radio Polarization Study of PG BL Lacs with the uGMRT
We present here uGMRT band 4 (~650MHz) polarization images of 8 BL~Lac
objects belonging to the Palomar-Green (PG) `blazar' sample. A large fraction
of the sources (~63%) 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 1-13% in the cores and
2-26% 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 (VLBI) 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.Comment: 17 pages; 12 figures; MNRAS accepte
A Kpc-scale radio polarization study of PG BL Lacs with the uGMRT
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).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 Lacsappear 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.Peer reviewe