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Twinkling pulsar wind nebulae in the synchrotron cut-off regime and the gamma-ray flares in the Crab Nebula | | A. M. Bykov
; G. G. Pavlov
; A. V. Artemyev
; Yu. A. Uvarov
; | | Date: |
14 Dec 2011 | | Abstract: | Synchrotron radiation of ultra-relativistic particles accelerated in a pulsar
wind nebula may dominate its spectrum up to gamma-ray energies. Because of the
short cooling time of the gamma-ray emitting electrons, the gamma-ray emission
zone is in the immediate vicinity of the acceleration site. The particle
acceleration likely occurs at the termination shock of the relativistic striped
wind, where multiple forced magnetic field reconnections provide strong
magnetic fluctuations facilitating Fermi acceleration processes. The
acceleration mechanisms imply the presence of stochastic magnetic fields in the
particle acceleration region, which cause stochastic variability of the
synchrotron emission. This variability is particularly strong in the steep
gamma-ray tail of the spectrum, where modest fluctuations of the magnetic field
lead to strong flares of spectral flux. In particular, stochastic variations of
magnetic field, which may lead to quasi-cyclic gamma-ray flares, can be
produced by the relativistic cyclotron ion instability at the termination
shock. Our model calculations of the spectral and temporal evolution of
synchrotron emission in the spectral cut-off regime demonstrate that the
intermittent magnetic field concentrations dominate the gamma-ray emission from
highest energy electrons and provide fast, strong variability even for a
quasi-steady distribution of radiating particles. The simulated light curves
and spectra can explain the very strong gamma-ray flares observed in the Crab
nebula and the lack of strong variations at other wavelengths. The model
predicts high polarization in the flare phase, which can be tested with future
polarimetry observations. | | Source: | arXiv, 1112.3114 | | Services: | Forum | Review | PDF | Favorites | |
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