2024/02/19 by Xin-Ke Hu, Hu, Xin-Ke, Yuwei Yu +39 · 1 citation
Earth and Planetary Sciences · Physics and Astronomy · Engineering · #Geophysics and Gravity Measurements #Ionosphere and magnetosphere dynamics #Particle Accelerators and Free-Electron Lasers
paper · pdf · doi:10.48550/arxiv.2402.11949
Mrk 501 is a prototypical high-synchrotron-peaked blazar (HBL) and serves as one of the primary targets for the \it Imaging X-ray Polarimetry Explorer (\it IXPE). In this study, we report X-ray polarization measurements of Mrk 501 based on six \it IXPE observations. The detection of X-ray polarization at a confidence level exceeding 99% is achieved in four out of the six observations conducted across the entire energy range (2--8 keV) of \it IXPE. The maximum polarization degree (Π\rm X) is measured to be 15.8%±2.8%, accompanied by a polarization angle (ψ\rm X) of 98.0°±5.1° at a confidence level of 5.6 σ. During the remaining two observations, only an upper limit of Π\rm X<12% could be derived at the 99% confidence level. No temporal variability in polarization is observed throughout all six \it IXPE observations for Mrk 501. A discernible trend of energy-dependent variation in the polarization degree is detected in optical spectropolarimetry; however, no analogous indication is observed in Π\rm X. The chromatic behavior of Π and the consistent values of ψ across different frequencies from X-rays to radio waves, along with the agreement between ψ 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.