IXPE Detection of Polarized X-rays from Magnetars and Photon Mode Conversion at QED Vacuum Resonance

Abstract

The recent observations of the anomalous X-ray pulsars 4U 0142+61 and 1RXS J170849.0-400910 by the Imaging X-ray Polarimetry Explorer (IXPE) opened up a new avenue to study magnetars, neutron stars endowed with superstrong magnetic fields ($B\gtrsim 10^{14}$~G). The detected polarized X-rays from 4U 0142+61 exhibit a 90${}^{\circ }$ linear polarization swing from low photon energies ($E\lesssim 4$~keV) to high energies ($E\gtrsim 5.5$~keV). We show that this swing can be explained by photon polarization mode conversion at the vacuum resonance in the magnetar atmosphere; the resonance arises from the combined effects of plasma-induced birefringence and QED-induced vacuum birefringence in strong magnetic fields. This explanation suggests that the atmosphere of 4U 0142 be composed of partially ionized heavy elements, and the surface magnetic field be comparable or less than $10^{14}$~G, consistent with the dipole field inferred from the measured spindown. It also implies that the spin axis of 4U 0142+61 is aligned with its velocity direction. The polarized X-rays from 1RXS J170849.0-400910 do not show such $90^{\circ }$ swing, consistent with magnetar atmospheric emission with $B\gtrsim 5\times 10^{14}$~G.

arXiv comment8 pages. Updated to include discussions on both magnetars detected by IXPE. To appear in PNAS in 4/2023

References in corpus (36)

• Magnetars
• Time-dependent force-free pulsar magnetospheres: axisymmetric and oblique rotators
• The enhanced X-ray Timing and Polarimetry mission - eXTP
• Gravitational Bending of Light Near Compact Objects
• Pulsar Jets: Implications for Neutron Star Kicks and Initial Spins
• Evidence for alignment of the rotation and velocity vectors in pulsars
• Magnetar Spin-Down
• Atmospheres and Spectra of Strongly Magnetized Neutron Stars
• Atmospheres and Spectra of Strongly Magnetized Neutron Stars II: Effect of Vacuum Polarization
• Discovery of hard non-thermal pulsed X-ray emission from the anomalous X-ray pulsar 1E 1841-045
• Solar Neutrinos Before and After KamLAND
• Physical Mechanisms for the Variable Spin-down of SGR 1900+14
• Birefringence and Dichroism of the QED Vacuum
• Atmosphere Models of Magnetized Neutron Stars: QED Effects, Radiation Spectra, and Polarization Signals
• Pulsar Spin-Velocity Alignment: Kinematic Ages, Birth Periods and Braking Indices
• Neutron Star Kicks in Isolated and Binary Pulsars: Observational Constraints and Implications for Kick Mechanisms
• Transfer of Polarized Radiation in Strongly Magnetized Plasmas and Thermal Emission from Magnetars: Effect of Vacuum Polarization
• Condensed Surfaces of Magnetic Neutron Stars, Thermal Surface Emission, and Particle Acceleration Above Pulsar Polar Caps
• Resonant Conversion of Photon Modes Due to Vacuum Polarization in a Magnetized Plasma: Implications for X-Ray Emission from Magnetars
• THE SOLAR NEUTRINO PROBLEM
• Electromagnetic polarization in partially ionized plasmas with strong magnetic fields and neutron star atmosphere models
• Supernova Fallback as Origin of Neutron Star Spins and Spin-kick Alignment
• Polarized X-Ray Emission from Magnetized Neutron Stars: Signature of Strong-Field Vacuum Polarization
• The Hidden Magnetic Field of The Young Neutron Star in Kesteven 79
• Radiation from condensed surface of magnetic neutron stars
• Unveiling the thermal and magnetic map of neutron star surfaces though their X-ray emission: method and lightcurves analysis
• Polarized x-rays from a magnetar
• Density-Functional-Theory Calculations of Matter in Strong Magnetic Fields: II. Infinite Chains and Condensed Matter
• Equation of state for magnetized Coulomb plasmas
• The High-Energy Polarization-Limiting Radius of Neutron Star Magnetospheres I -- Slowly Rotating Neutron Stars
• X-ray spectra and polarization from magnetar candidates
• Radiative properties of magnetic neutron stars with metallic surfaces and thin atmospheres
• The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
• Polarization Evolution in A Strongly Magnetized Vacuum: QED Effect and Polarized X-ray Emission from Magnetized Neutron Stars
• Probing magnetar emission mechanisms with spectropolarimetry
• Pair Plasma in Super-QED Magnetic Fields and the Hard X-ray/Optical Emission of Magnetars

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• Prospects for Time-Domain and Multi-Messenger Science with eXTP
• X-ray polarisation signatures in bombarded magnetar atmospheres
• Vacuum birefringence and the polarized X-ray emission from a radio magnetar
• Monte Carlo Simulations of Polarized Radiative Transfer in Neutron Star Atmospheres
• Photon polarization tensor at finite temperature and density in a magnetic field
• Pulsed, Polarized X-ray Emission from Neutron Star Surfaces: the Effects of Vacuum Birefringence in the Magnetosphere
• Resonant Inverse Compton Scattering and Hard X-ray Emission in Magnetar Magnetospheres