A Two-week IXPE Monitoring Campaign on Mrk 421

Maksym, WP ORCID: 0000-0002-2203-7889, Liodakis, I ORCID: 0000-0001-9200-4006, Saade, ML ORCID: 0000-0001-7163-7015, Kim, DE ORCID: 0000-0001-5717-3736, Middei, R ORCID: 0000-0001-9815-9092, Di Gesu, L ORCID: 0000-0002-5614-5028, Kiehlmann, S ORCID: 0000-0001-6314-9177, Matzeu, G, Agudo, I ORCID: 0000-0002-3777-6182, Marscher, AP ORCID: 0000-0001-7396-3332, Ehlert, SR ORCID: 0000-0003-4420-2838, Jorstad, SG ORCID: 0000-0001-6158-1708, Kaaret, P ORCID: 0000-0002-3638-0637, Marshall, HL ORCID: 0000-0002-6492-1293, Pacciani, L ORCID: 0000-0001-6897-5996, Perri, M ORCID: 0000-0003-3613-4409, Puccetti, S ORCID: 0000-0002-2734-7835, Kouch, PM ORCID: 0000-0002-9328-2750, Lindfors, E, Aceituno, FJ et al (2025) A Two-week IXPE Monitoring Campaign on Mrk 421. The Astrophysical Journal, 986 (2). ISSN 0004-637X

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Abstract

X-ray polarization is a unique new probe of the particle acceleration in astrophysical jets made possible through the Imaging X-ray Polarimetry Explorer. Here we report on the first dense X-ray polarization monitoring campaign on the blazar Mrk 421. Our observations were accompanied by an even denser radio and optical polarization campaign. We find significant short-timescale variability in both X-ray polarization degree and angle, including an ∼90° angle rotation about the jet axis. We attribute this to random variations of the magnetic field, consistent with the presence of turbulence but also unlikely to be explained by turbulence alone. At the same time, the degree of lower-energy polarization is significantly lower and shows no more than mild variability. Our campaign provides further evidence for a scenario in which energy-stratified shock-acceleration of relativistic electrons, combined with a turbulent magnetic field, is responsible for optical to X-ray synchrotron emission in blazar jets.

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; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	12 April 2025
Date of first compliant Open Access:	1 July 2025
Date Deposited:	01 Jul 2025 09:23
Last Modified:	03 Jul 2025 12:45
DOI or ID number:	10.3847/1538-4357/adce6b
URI:	https://researchonline.ljmu.ac.uk/id/eprint/26673

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