X-ray Polarization of Inverse Compton Scattering by Thermal and Nonthermal Electrons

Abstract

X-ray emission from accretion-powered astrophysical systems is widely interpreted as inverse Compton (IC) scattering between energetic electrons and soft photons. Besides the emitted intensity, the polarization of this radiation provides important information about the physical properties of the electrons involved. We investigate how different electron populations shape both the spectrum and polarization of IC emission in the X-ray band. We consider three electron populations: purely thermal, purely nonthermal power-law, and a hybrid population combining both components. We take both numerical simulations and semi-analytic calculations. We first attempt the cases for thermal and nonthermal electrons, respectively. We then focus on the hybrid population, which is expected to be realistic in high-energy object environments. For the case of hybrid electrons, the scattered emission separates into three energy regimes. At low energies ($\lesssim 0.1$ keV), it is dominated by thermal electrons; at high energies ($\gtrsim 4$ keV), it is governed by the nonthermal component. Between these limits, a transition band ($\sim 0.1$-$4$ keV) appears in which both components contribute. The degree of polarization varies smoothly across these regimes, and the behavior in the transition band directly traces the relative importance of thermal and nonthermal electrons. We further show that for partially polarized seed photons, the scattered polarization scales linearly with the incident polarization while its frequency dependence remains unchanged. These results show that X-ray polarimetry provides a powerful diagnostic of the electron energy distribution in accretion-powered systems.

arXiv comment14 pages, 12 figures, accepted for publication in MNRAS

References in corpus (25)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Advection-Dominated Accretion: Underfed Black Holes and Neutron Stars
• Hot Accretion Flows Around Black Holes
• Advection-Dominated Accretion and the Spectral States of Black Hole X-Ray Binaries: Application to Nova Muscae 1991
• Modelling the behaviour of accretion flows in X-ray binaries
• Quantitative Interpretation of Quasar Microlensing Light Curves
• X-ray Polarization from Accreting Black Holes: Coronal Emission
• Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1
• On the size and location of the X-ray emitting coronae around black holes
• grmonty: a Monte Carlo Code for Relativistic Radiative Transport
• Properties of AGN coronae in the NuSTAR era II: hybrid plasma
• Polarized Synchrotron Emissivities and Absorptivities for Relativistic Thermal, Power-Law, and Kappa Distribution Functions
• Signatures of a Maxwellian Component in Shock-Accelerated Electrons in GRBs
• The Polarization Properties of Inverse Compton Emission and Implications for Blazar Observations with the GEMS X-Ray Polarimeter
• The X-ray Polarization of the Accretion Disk Coronae of Active Galactic Nuclei
• Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16
• Prospects for differentiating extended coronal geometries in AGNs with the IXPE mission
• X-ray Polarization of the Black Hole X-ray Binary 4U 1630-47 Challenges Standard Thin Accretion Disk Scenario
• IXPE and NICER view of Black hole X-ray binary 4U 1630-47: First significant detection of polarized emission in thermal state
• Detection of X-ray polarized emission and accretion-disk winds with IXPE and NICER in the black-hole X-ray binary 4U 1630-47
• Polarization of photons scattered by electrons in any spectral distribution
• A New Fast Monte Carlo Code for Solving Radiative Transfer Equations based on Neumann Solution
• Monte-Carlo Applications for Partially Polarised Inverse External-Compton Scattering (MAPPIES) -- I. Description of the code and First Results
• Polarization-sensitive Compton scattering by accelerated electrons