科研之友
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摘要
Gamma-ray pulsars constitute a class of high and very high energy emitters for which the known population is steadily increasing thanks to the Fermi/Large Area Telescope. More than a hundred such pulsars have been detected, offering a reasonable sample on to which to apply statistical techniques in order to outline relevant trends in the averaged properties of this (maybe not so) special class of pulsars. In this paper, their gamma-ray luminosity and spectral features are explained in the framework of synchrotron radiation from particles located in the stripe of the pulsar wind. Apart from radiative losses, particles are also subject to a constant re-acceleration and reheating for instance by a magnetic-reconnection-induced electric field. The high-energy luminosity scales as L gamma approximate to 2 x 1026?W?(Lsd/1028?W)1/2?(P/1?s)-1/2, where Lsd is the pulsar spin-down luminosity and P its period. From this relation, we derive important parameters of pulsar magnetosphere and wind theories. Indeed, we find the bulk Lorentz factor of the wind scaling as Gamma v approximate to 10 tau rec 1/5(L sd /1028W)1/2, pair multiplicity ? related to the magnetization parameter sigma by kappa sigma tau rec 1/5 approximate to 108 and efficiency ? of spin-down luminosity conversion into particle kinetic energy according to the relation eta sigma approximate to 1. A good guess for the associated reconnection rate is then trec tau 0.5 approximate to(Lsd/1028?W)-5/12. Finally, pulses in gamma-rays are visible only if Lsd/P greater than or similar to 1027?W?s-1. This model differs from other high-energy emission mechanisms because it makes allowance not only for rotational kinetic energy release but also for an additional reservoir of energy anchored to the magnetic field of the stripe and released for instance by some magnetic reconnection processes.
- 出版日期2012-8
