2024/07/11 by Jonathan Zhang, Christopher C. Thompson, Zhang, Jonathan +1
Physics and Astronomy · #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #High-Energy Particle Collisions Research #Pulsars and Gravitational Waves Research
paper · pdf · doi:10.48550/arxiv.2407.08810
openalex publication_date 2024/07/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Magnetars in quiescent states continue to emit hard X-rays with a power far exceeding the loss of rotational energy. It has recently been noted that this hard X-ray continuum may bear a direct signature of quantum electrodynamic (QED) effects in magnetic fields stronger than the Schwinger field (B\rm Q = 4.4× 1013 G). Where the current flowing into the magnetosphere is driven by narrow structures in the solid crust, the e^± pair plasma supporting the current relaxes to a collisional and trans-relativistic state. The decay of a pair into two photons produces a broad, bremsstrahlung-like spectrum of hard X-rays, similar to that observed and extending up to 0.5-1 MeV. The conversion of two gamma rays to a pair is further enhanced by a factor ∼ B/B\rm Q. Monte Carlo calculations of pair creation in a dipole magnetic field are presented. Non-local particle injection is found to be strong enough to suppress the high voltage that otherwise would accompany a weaker, global twist; the hard X-rays are mostly emitted away from the magnetic poles. Some of the pairs annihilate in an optically thin surface layer. The prototypical anomalous X-ray pulsar 1E 2259+586, which shows a hard X-ray continuum but relatively weak torque noise, slow spindown, and no radio emission, is a Rosetta Stone for understanding the magnetar circuit, consistent with the picture advanced here. For a 15-60 keV luminosity as low as 1034 erg s-1, the polar flux of sub-relativistic pairs produces an optical depth 3-30 to electron cyclotron scattering in the 1-10 keV band, reducing the net X-ray polarization.