Centrifugal breakout reconnection as the electron acceleration mechanism powering the radio magnetospheres of early-type stars
Date Issued
2022
Author(s)
Abstract
Magnetic B-stars often exhibit circularly polarized radio emission thought to
arise from gyrosynchrotron emission by energetic electrons trapped in the
circumstellar magnetosphere. Recent empirical analyses show that the onset and
strength of the observed radio emission scale with both the magnetic field
strength and the stellar rotation rate. This challenges the existing paradigm
that the energetic electrons are accelerated in the current sheet between
opposite-polarity field lines in the outer regions of magnetised stellar winds,
which includes no role for stellar rotation. Building on recent success in
explaining a similar rotation-field dependence of H$\alpha$ line emission in
terms of a model in which magnetospheric density is regulated by centrifugal
breakout (CBO), we examine here the potential role of the associated CBO-driven
magnetic reconnection in accelerating the electrons that emit the observed
gyrosynchrotron radio. We show in particular that the theoretical scalings for
energy production by CBO reconnection match well the empirical trends for
observed radio luminosity, with a suitably small, nearly constant conversion
efficiency $\epsilon \approx 10^{-8}$. We summarize the distinct advantages of
our CBO scalings over previous associations with an electromotive force, and
discuss the potential implications of CBO processes for X-rays and other
observed characteristics of rotating magnetic B-stars with centrifugal
magnetospheres.
Volume
513
Issue
1
Start page
1449
Issn Identifier
0035-8711
Ads BibCode
2022MNRAS.513.1449O
Rights
open.access
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