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Magnetar heating | | Andrei M. Beloborodov
; Xinyu Li
; | | Date: |
30 May 2016 | | Abstract: | We examine four candidate mechanisms that could explain the high surface
temperatures of magnetars. (1) Heat flux from the liquid core heated by
ambipolar diffusion. It could sustain the observed surface luminosity
$L_sapprox 10^{35}$ erg s$^{-1}$ if core heating offsets neutrino cooling at a
temperature $T_{
m core}>6 imes 10^8$ K. This scenario is viable if the core
magnetic field exceeds $10^{16}$ G, the magnetar has mass $M<1.4 M_odot$, and
its heat-blanketing envelope has a light element composition. We find however
that the lifetime of such a hot core should be shorter than the typical
observed lifetime of magnetars. (2) Mechanical dissipation in the solid crust.
This heating can be quasi-steady, powered by gradual (or frequent) crustal
yielding to magnetic stresses. We show that it obeys a strong upper limit. As
long as the crustal stresses are fostered by the field evolution in the core or
Hall drift in the crust, mechanical heating is insufficient to sustain
persistent $L_sapprox 10^{35}$ erg s$^{-1}$. The surface luminosity is
increased in an alternative scenario of mechanical deformations triggered by
external magnetospheric flares. (3) Ohmic dissipation in the crust, in volume
or current sheets. This mechanism is inefficient because of the high
conductivity of the crust. Only extreme magnetic configurations with crustal
fields $B>10^{16}$ G varying on a 100 meter scale could provide $L_sapprox
10^{35}$ erg s$^{-1}$. (4) Bombardment of the stellar surface by particles
accelerated in the magnetosphere. This mechanism produces hot spots on
magnetars. Observations of transient magnetars show evidence for external
heating. | | Source: | arXiv, 1605.9077 | | Services: | Forum | Review | PDF | Favorites | |
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