Pair Plasma in Super-QED Magnetic Fields and the Hard X-ray/Optical Emission of Magnetars

Abstract

The photon spectrum emitted by a transrelativistic pair plasma is calculated in the presence of an ultrastrong magnetic field, and is shown to bear a remarkable resemblance to the rising hard X-ray spectra of quiescent magnetars. This emission is powered by pair annihilation which, in contrast with a weakly magnetized pair plasma, shows an extended low-frequency tail similar to bremsstrahlung. Cross sections for electron-positron annihilation/scattering, two-photon pair creation, and photon-$e^{\pm }$ scattering are adopted from our earlier ab initio QED calculations in the regime $10{\alpha }_{\mathrm{em}}^{-1}{B}_{\mathrm{Q}}\gg B\gg B_{\mathrm{Q}}$. Careful attention is given to the $u$-channel scattering resonance. Magnetospheric arcades anchored in zones of intense crustal shear and extending to about twice the magnetar radius are identified as the sites of the persistent hard X-ray emission. We deduce a novel and stable configuration for the magnetospheric circuit, with a high plasma density sustained by ohmic heating and in situ pair creation. Pairs are sourced non-locally by photon collisions in zones with weak currents, such as the polar cap. Annihilation bremsstrahlung extends to the optical-IR band, where the plasma cutoff is located. The upper magnetar atmosphere experiences strong current-driven growth of ion-acoustic turbulence, which may limit positron diffusion. Coherent optical-IR emission is bounded near the observed flux by induced scattering. This model accommodates the rapid X-ray brightening of an activating magnetar, concentrated thermal hotspots, and the subdominant thermal X-ray emission of some active magnetars. Current injection is ascribed to continuous magnetic braiding, as seen in the global yielding calculations of Thompson, Yang & Ortiz.

arXiv comment28 pages, 18 figures, accepted for publication in the Astrophysical Journal after minor revisions

References in corpus (56)

• Magnetars
• Physics of Strongly Magnetized Neutron Stars
• Electrodynamics of Magnetars: Implications for the Persistent X-ray Emission and Spindown of the Soft Gamma Repeaters and Anomalous X-ray Pulsars
• Transient pulsed radio emission from a magnetar
• The Giant Flare of 1998 August 27 from SGR 1900+14: II. Radiative Mechanism and Physical Constraints on the Source
• Corona of Magnetars
• Untwisting magnetospheres of neutron stars
• 1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds
• Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE
• Changes in the X-ray Emission from the Magnetar Candidate 1E 2259+586 during its 2002 Outburst
• On the mechanism of hard X-ray emission from magnetars
• Discovery of hard non-thermal pulsed X-ray emission from the anomalous X-ray pulsar 1E 1841-045
• Physical Mechanisms for the Variable Spin-down of SGR 1900+14
• X-ray spectra from magnetar candidates. I. Monte Carlo simulations in the non-relativistic regime
• Magnetars as persistent hard X-ray sources: INTEGRAL discovery of a hard tail in SGR 1900+14
• Dynamics of Strongly Twisted Relativistic Magnetospheres
• High Energy Emission from Magnetars
• Evidence for a Sudden Magnetic Field Reconfiguration in SGR 1900+14
• Resonant Cyclotron Scattering in Three Dimensions and the Quiescent Non-thermal X-ray Emission of Magnetars
• The first outburst of the new magnetar candidate SGR 0501+4516
• Resonant Compton Upscattering in Anomalous X-ray Pulsars
• Magnetic field evolution in magnetar crusts through three dimensional simulations
• A XMM-Newton View of the Soft Gamma-ray Repeater SGR 1806--20: Long Term Variability in the pre-Super Giant Flare Epoch
• Diagnosing magnetars with transient cooling
• INTEGRAL discovery of persistent hard X-ray emission from the Soft Gamma Ray Repeater SGR 1806-20
• Outburst of the 2 s Anomalous X-ray Pulsar 1E 1547.0-5408
• Electron-positron flows around magnetars
• A possible faint near-infrared counterpart to the AXP 1E~2259+58.6
• An Unusual Burst from Soft Gamma Repeater SGR 1900+14: Comparisons with Giant Flares and Implications for the Magnetar Model
• Magnetar Broadband X-ray Spectra Correlated with Magnetic Fields: Suzaku Archive of SGRs and AXPs Combined with NuSTAR, Swift, and RXTE
• Fading of the Transient Anomalous X-ray Pulsar XTE J1810-197
• Simultaneous multifrequency radio observations of the Galactic Centre magnetar SGR J1745-2900
• X-ray spectra from magnetar candidates. II Resonant cross sections for electron-photon scattering in the relativistic regime
• Global Crustal Dynamics of Magnetars in Relation to their Bright X-ray Outbursts
• From outburst to quiescence: the decay of the transient Anomalous X-ray Pulsar XTE J1810-197
• X-ray and Near-IR Variability of the Anomalous X-ray Pulsar 1E 1048.1-5937: From Quiescence Back to Activity
• Correlated Infrared and X-ray Flux Changes Following the 2002 June Outburst of the Anomalous X-ray Pulsar 1E 2259+586
• Compton Scattering in Ultra-Strong Magnetic Fields: Numerical and Analytical Behavior in the Relativistic Regime
• Resonant Inverse Compton Scattering Spectra from Highly-magnetized Neutron Stars
• Particle-in-cell simulations of the twisted magnetospheres of magnetars
• The Broad-Band Spectrum and Infrared Variability of the Magnetar AXP 1E1048.1-5937
• Electrodynamics of Magnetars III: Pair Creation Processes in an Ultrastrong Magnetic Field and Particle Heating in a Dynamic Magnetosphere
• Deep NuSTAR and Swift Monitoring Observations of the Magnetar 1E 1841-045
• Plastic damping of Alfvén waves in magnetar flares and delayed afterglow emission
• Repeated, Delayed Torque Variations Following X-ray Flux Enhancements in the Magnetar 1E1048.1$-$5937
• NuSTAR Observations of the Magnetar 1E 2259+586
• Compton scattering S-matrix and cross section in strong magnetic field
• Electrodynamics of Magnetars IV: Self-Consistent Model of the Inner Accelerator, with Implications for Pulsed Radio Emission
• Coherent Emission from Magnetars
• Phase-resolved NuSTAR and Swift-XRT Observations of Magnetar 4U 0142+61
• Two new outbursts and transient hard X-rays from 1E 1048.1$-$5937
• QED Phenomena in an Ultrastrong Magnetic Field. I. Electron-Photon Scattering, Pair Creation, and Annihilation
• Detection of the magnetar XTE J1810-197 at 150 and 260 GHz with the NIKA2 Kinetic Inductance Detector camera
• Detailed X-ray spectroscopy of the magnetar 1E 2259+586
• NuSTAR Observations of Magnetar 1E 1048.1-5937
• QED Phenomena in an Ultrastrong Magnetic Field. II. Electron-Positron Scattering, $e^{\pm }$-Ion Scattering, and Relativistic Bremsstrahlung

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• Polarized x-rays from a magnetar
• IXPE Detection of Polarized X-rays from Magnetars and Photon Mode Conversion at QED Vacuum Resonance
• Probing magnetar emission mechanisms with spectropolarimetry
• Direct Emission of Strong Radio Pulses During Magnetar Flares
• Relativistic Alfvén Waves Entering Charge Starvation in the Magnetospheres of Neutron Stars
• Radio Emission of Pulsars. I. Slow Tearing of a Quantizing Magnetic Field
• Photon-axion mixing in thermal emission of isolated neutron stars
• Radio Emission of Pulsars. II. Coherence Catalyzed by Cerenkov-Unstable Shear Alfvén Waves
• Collisionless tearing instability in a relativistic pair plasma with a power-law distribution function
• Resonant Inverse Compton Scattering and Hard X-ray Emission in Magnetar Magnetospheres