POLAMI Multiwavelength Polarization Study of Active Galactic Nuclei Jets: A Millimeter–Optical Comparison

Casadio, C ORCID: 0000-0003-1117-2863, Blinov, D ORCID: 0000-0003-0611-5784, Agudo, I ORCID: 0000-0002-3777-6182, Myserlis, I ORCID: 0000-0003-3025-9497, Thum, C ORCID: 0009-0006-5292-6974, Jorstad, S ORCID: 0000-0001-6158-1708, Marscher, A ORCID: 0000-0001-7396-3332, Zhang, H ORCID: 0000-0001-9826-1759, Escudero Pedrosa, J ORCID: 0000-0002-4131-655X, Álvarez-Ortega, D ORCID: 0000-0002-9998-5238, Weaver, ZR ORCID: 0000-0001-6314-0690, Joshi, M ORCID: 0000-0003-1134-7352, McCall, C ORCID: 0000-0002-3375-3397, Jermak, H ORCID: 0000-0002-1197-8501, Steele, IA ORCID: 0000-0001-8397-5759, Borman, GA ORCID: 0000-0002-7262-6710, Grishina, TS ORCID: 0000-0002-3953-6676, Larionova, EG ORCID: 0000-0002-2471-6500, Morozova, DA ORCID: 0000-0002-9407-7804, Savchenko, SS ORCID: 0000-0003-4147-3851 et al (2026) POLAMI Multiwavelength Polarization Study of Active Galactic Nuclei Jets: A Millimeter–Optical Comparison. The Astrophysical Journal Supplement Series, 283 (1). ISSN 1538-4365

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Abstract

Millimeter-band polarimetry offers a powerful probe of active galactic nuclei jets, accessing regions less affected by opacity and Faraday rotation than at longer radio wavelengths. As part of the POLAMI program, we have conducted 14 yr of 1 and 3 mm polarization monitoring of a sample of gamma-ray-bright blazars with the IRAM 30 m telescope, complemented here with long-term optical polarimetric observations from multiple facilities. We aim to test whether current models of parsec-scale jet physics are consistent with observed multiband polarization behavior. Using a Bayesian framework, we derive intrinsic mean flux densities and modulation indices for total flux and fractional polarization, and characterize electric vector position angle (EVPA) variability using circular statistics. We then examine how these quantities reflecting variability properties across millimeter and optical bands relate to synchrotron peak frequency, jet orientation, and radio/gamma-ray luminosities. BL Lacertae (BL Lac) objects exhibit, on average, higher fractional polarization and lower EVPA variability than flat-spectrum radio quasars (FSRQs) at all wavelengths. Fractional polarization increases with frequency, consistent with increasingly ordered magnetic fields at shorter wavelengths. BL Lacs also show more frequent alignment of EVPAs between optical and millimeter bands, whereas FSRQs display weaker coherence. EVPA variability correlates positively with radio and gamma-ray luminosities and negatively with synchrotron peak frequency, most strongly in the optical. We further find a positive correlation between EVPA spread and fractional polarization variability, suggesting a direct link between magnetic-field structure and polarization dynamics.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics; 5101 Astronomical sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	14 January 2026
Date of first compliant Open Access:	8 June 2026
Date Deposited:	08 Jun 2026 13:57
Last Modified:	08 Jun 2026 13:57
DOI or ID number:	10.3847/1538-4365/ae39c7
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28778

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