Title: Probing dissipation mechanisms in BL Lac jets through X-ray polarimetry

Journal Article · · Monthly Notices of the Royal Astronomical Society
 [1];  [2];  [3];  [4]
  1. Istituto Nazionale di Astrofisica (INAF), Merate (Italy). Osservatorio Astronomico di Brera; DOE/OSTI
  2. Istituto Nazionale di Astrofisica (INAF), Merate (Italy). Osservatorio Astronomico di Brera
  3. Columbia Univ., New York, NY (United States)
  4. Yale Univ., New Haven, CT (United States)
+ Show Author Affiliations

The dissipation of energy flux in blazar jets plays a key role in the acceleration of relativistic particles. Two possibilities are commonly considered for the dissipation processes, magnetic reconnection – possibly triggered by instabilities in magnetically dominated jets – or shocks – for weakly magnetized flows. In this paper, we consider the polarimetric features expected for the two scenarios analyzing the results of state-of-the-art simulations. For the magnetic reconnection scenario we conclude, using results from global relativistic MHD simulations, that the emission likely occurs in turbulent regions with unstructured magnetic fields, although the simulations do not allow us to draw firm conclusions. On the other hand, with local particle-in-cell simulations we show that, for shocks with a magnetic field geometry suitable for particle acceleration, the self-generated magnetic field at the shock front is predominantly orthogonal to the shock normal and becomes quasi-parallel downstream. Based on this result we develop a simplified model to calculate the frequency-dependent degree of polarization, assuming that high-energy particles are injected at the shock and cool downstream. We apply our results to HBLs, blazars with the maximum of their synchrotron output at UV-soft X-ray energies. While in the optical band the predicted degree of polarization is low, in the X-ray emission it can ideally reach 50 per cent, especially during active/flaring states. The comparison between measurements in the optical and in the X-ray band made during active states (feasible with the planned IXPE satellite) is expected to provide valuable constraints on the dissipation and acceleration processes.

Research Organization:
Columbia Univ., New York, NY (United States)
Sponsoring Organization:
A. Bianco; National Aeronautic and Space Administration (NASA); National Science Foundation (NSF); USDOE Office of Science (SC)
Grant/Contract Number:
SC0016542
OSTI ID:
1612627
Journal Information:
Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 3 Vol. 480; ISSN 0035-8711
Publisher:
Royal Astronomical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Energetic Particles of Cosmic Accelerators II: Active Galactic Nuclei and Gamma-ray Bursts preprint January 2019
Astro2020 Science White Paper: Using X-Ray Polarimetry to Probe the Physics of Black Holes and Neutron Stars preprint January 2019
Probing Magnetic Fields and Acceleration Mechanisms in Blazar Jets with X-ray Polarimetry preprint January 2021
Perspectives of blazar studies with future space missions journal November 2019
Radiative signatures of plasmoid-dominated reconnection in blazar jets journal October 2018
Probing the Emission Mechanism and Magnetic Field of Neutrino Blazars with Multiwavelength Polarization Signatures journal May 2019
Probing the Emission Mechanism and Magnetic Field of Neutrino Blazars with Multi-Wavelength Polarization Signatures text January 2019

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79 ASTRONOMY AND ASTROPHYSICS
Astronomy & astrophysics
X-rays: galaxies
galaxies: jets
magnetic reconnection
radiation mechanisms: non-thermal
shock waves