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| Format: | Preprint |
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2024
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| Online Access: | https://arxiv.org/abs/2407.08810 |
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| _version_ | 1866913661405102080 |
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| author | Zhang, Jonathan Thompson, Christopher |
| author_facet | Zhang, Jonathan Thompson, Christopher |
| contents | 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 ($B_{\rm Q} = 4.4\times 10^{13}$ G). Where the current flowing into the magnetosphere is driven by narrow structures in the solid crust, the $e^\pm$ 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 $\sim B/B_{\rm Q}$. 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 $10^{34}$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2407_08810 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Quantum Plasma Creation near a Magnetar Zhang, Jonathan Thompson, Christopher High Energy Astrophysical Phenomena 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 ($B_{\rm Q} = 4.4\times 10^{13}$ G). Where the current flowing into the magnetosphere is driven by narrow structures in the solid crust, the $e^\pm$ 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 $\sim B/B_{\rm Q}$. 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 $10^{34}$ 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. |
| title | Quantum Plasma Creation near a Magnetar |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2407.08810 |