Preprint PUBDB-2025-00099

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First characterization of the emission behavior of Mrk 421 from radio to very high-energy gamma rays with simultaneous X-ray polarization measurements

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2024

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Report No.: arXiv:2312.10732

Abstract: Aims. We have performed the first broadband study of Mrk 421 from radio to TeV gamma rays with simultaneous measurements of the X-ray polarization from IXPE.Methods. The data were collected as part of an extensive multiwavelength campaign carried out between May and June 2022 using MAGIC, Fermi-LAT, NuSTAR, XMM-Newton, Swift, and several optical and radio telescopes to complement IXPE data.Results. During the IXPE exposures, the measured 0.2–1 TeV flux was close to the quiescent state and ranged from 25% to 50% of the Crab Nebula without intra-night variability. Throughout the campaign, the very high-energy (VHE) and X-ray emission are positively correlated at a 4σ significance level. The IXPE measurements reveal an X-ray polarization degree that is a factor of 2–5 higher than in the optical/radio bands; that implies an energy-stratified jet in which the VHE photons are emitted co-spatially with the X-rays, in the vicinity of a shock front. The June 2022 observations exhibit a rotation of the X-ray polarization angle. Despite no simultaneous VHE coverage being available during a large fraction of the swing, the Swift-XRT monitoring reveals an X-ray flux increase with a clear spectral hardening. This suggests that flares in high synchrotron peaked blazars can be accompanied by a polarization angle rotation, as observed in some flat spectrum radio quasars. Finally, during the polarization angle rotation, NuSTAR data reveal two contiguous spectral hysteresis loops in opposite directions (clockwise and counterclockwise), implying important changes in the particle acceleration efficiency on approximately hour timescales.Key words: radiation mechanisms: non-thermal / galaxies: active / BL Lacertae objects: individual: mrk421 / gamma rays: general / X-rays: galaxies⋆ All data shown in Figs. 1, 2, 5, 7, and 8 are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/684/A127⋆⋆ Corresponding authors: A. Arbet-Engels, F. Schmuckermaier and D. Paneque, e-mail: contact.magic@mpp.mpg.de

Classification:

Note: Accepted for publication in Astronomy & Astrophysics. 29 pages, 22 figures. Corresponding authors: Axel Arbet Engels, Felix Schmuckermaier, David Paneque

Contributing Institute(s):
  1. CTA IKC (Z_CTAS)
Research Program(s):
  1. 611 - Fundamental Particles and Forces (POF4-611) (POF4-611)
  2. DFG project G:(GEPRIS)390783311 - EXC 2094: ORIGINS: Vom Ursprung des Universums bis zu den ersten Bausteinen des Lebens (390783311) (390783311)
  3. SMILE - Search for Milli-lenses to discriminate between dark matter models (101040021) (101040021)
  4. PASIPHAE - Overcoming the Dominant Foreground of Inflationary B-modes: Tomography of Galactic Magnetic Dust via Measurements of Starlight Polarization (771282) (771282)
Experiment(s):
  1. Cherenkov Telescope Array

Appears in the scientific report 2024
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 Record created 2025-01-10, last modified 2025-01-15


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