Polarization and Multiwavelength Observations of Mrk 501 Reveal Polarization Variability across Different Energies and Fluxes
Abstract
Mrk 501 is a prototypical high-synchrotron-peaked blazar (HBL) and serves as one of the primary targets for the Imaging X-ray Polarimetry Explorer (IXPE). In this study, we report X-ray polarization measurements of Mrk 501 based on six IXPE observations. The $>99\%$ confidence detection of X-ray polarization is obtained in four out of six observations in the entire energy band (2--8 keV) of IXPE, with a maximum polarization degree ($\Pi_{\rm X}$) of $15.8\%\pm2.8\%$ and a polarization angle ($\psi_{\rm X}$) of $98.0^{\circ}\pm5.1^{\circ}$ at a confidence level of $5.2\sigma$. During the other two observations, the source only exhibits the $>99\%$ confidence detection of X-ray polarization within an energy bin of 1 keV. Interestingly, both the second and sixth IXPE observations present energy-dependent variability in X-ray polarization, which is also observed in our optical spectropolarimetry. The chromatic behavior of $\Pi$ and the consistent values of $\psi$ across different frequencies, along with the agreement between $\psi$ and jet position angle, strongly support the interpretation of the energy-stratified model with shock-accelerated particles in the jet of Mrk 501. Additionally, the possibility of the presence of a global helical magnetic field in the jet of Mrk 501 is discussed.
- Publication:
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arXiv e-prints
- Pub Date:
- February 2024
- DOI:
- 10.48550/arXiv.2402.11949
- arXiv:
- arXiv:2402.11949
- Bibcode:
- 2024arXiv240211949H
- Keywords:
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- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 19 pages, 8 figures, 5 tables, submitted