VAPOLA - A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA II. Spectropolarimetric properties and their evolution from 2017 to 2023
Abstract
We present a systematic analysis of the spectropolarimetric properties of a sample of 39 active galactic nuclei and Sagittarius A* observed with the Atacama Large Millimeter/submillimeter Array during five VLBI campaigns between 2017 and 2023. We characterize the compact cores in total intensity and polarization, focusing on the behavior or the linear polarization fraction (LP), electric vector position angle (EVPA), and Faraday rotation measure (RM) over time and spectral domains. We investigate both individual objects--such as M87, Sgr A*, 3C273, and 3C279--and ensemble properties of different source classes, including flat-spectrum radio quasars, BLLac objects, and other active galaxies. While total intensity and spectral index are generally stable on weekly timescales, polarization properties often exhibit strong variability, with significant day-to-day changes in LP, EVPA, and RM. Several sources display large EVPA rotations accompanied by variations in LP and RM, in some cases coinciding with flaring activity. We observe that the magnitude of RM increases with observing frequency for all sources for which we have reliable multi-band measurements, consistent with Faraday rotation arising in a magnetized sheath surrounding the relativistic jet, although an origin in the accretion flow--particularly in the case of Sgr A*--cannot be ruled out.
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BibTeX
@misc{carlos2026vapola,
title = {{VAPOLA - A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA II. Spectropolarimetric properties and their evolution from 2017 to 2023}},
author = {Douglas Carlos and Ciriaco Goddi and Alejandro Mus and Nicola Marchili and Kazi L. J. Rygl and Ezequiel Albentosa-Ruíz and Iván Martí-Vidal and The Event Horizon Telescope Collaboration},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.14900},
eprint = {2608.14900},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.14900},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - VAPOLA - A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA II. Spectropolarimetric properties and their evolution from 2017 to 2023
AU - Douglas Carlos
AU - Ciriaco Goddi
AU - Alejandro Mus
AU - Nicola Marchili
AU - Kazi L. J. Rygl
AU - Ezequiel Albentosa-Ruíz
AU - Iván Martí-Vidal
AU - The Event Horizon Telescope Collaboration
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2608.14900
UR - https://arxiv.org/abs/2608.14900
AB - We present a systematic analysis of the spectropolarimetric properties of a sample of 39 active galactic nuclei and Sagittarius A* observed with the Atacama Large Millimeter/submillimeter Array during five VLBI campaigns between 2017 and 2023. We characterize the compact cores in total intensity and polarization, focusing on the behavior or the linear polarization fraction (LP), electric vector position angle (EVPA), and Faraday rotation measure (RM) over time and spectral domains. We investigate both individual objects--such as M87, Sgr A*, 3C273, and 3C279--and ensemble properties of different source classes, including flat-spectrum radio quasars, BLLac objects, and other active galaxies. While total intensity and spectral index are generally stable on weekly timescales, polarization properties often exhibit strong variability, with significant day-to-day changes in LP, EVPA, and RM. Several sources display large EVPA rotations accompanied by variations in LP and RM, in some cases coinciding with flaring activity. We observe that the magnitude of RM increases with observing frequency for all sources for which we have reliable multi-band measurements, consistent with Faraday rotation arising in a magnetized sheath surrounding the relativistic jet, although an origin in the accretion flow--particularly in the case of Sgr A*--cannot be ruled out.
ER -