Repeating Fast Radio Bursts from Magnetars with Low Magnetospheric Twist. (arXiv:1904.12036v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wadiasingh_Z/0/1/0/all/0/1">Zorawar Wadiasingh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Timokhin_A/0/1/0/all/0/1">Andrey Timokhin</a>
We analyze the statistics of pulse arrival times in FRB 121102 and We analyze the statistics of pulse arrival times in FRB 121102 and http://arxiv.org/icons/sfx.gif
demonstrate that they are remarkably similar to statistics of magnetar
high-energy short bursts. Motivated by this correspondence, we propose that
repeating FRBs are generated during short bursts in the closed field line zone
of magnetar magnetospheres via a pulsar-like emission mechanism. Crustal
slippage events dislocate field line footpoints, initiating intense particle
acceleration and pair production, giving rise to coherent radio emission
similar to that generated near pulsar polar caps. We argue that the energetics
of FRB 121102 can be readily accounted if the efficiency of conversion of
Poynting flux into coherent radio emission is $sim10^{-4}-10^{-2}$, values
consistent with empirical efficiencies of radio emission in pulsars and
radio-loud magnetars. Such a mechanism could operate only in magnetars with
preexisting low twist of the magnetosphere, so that the charge density in the
closed zone is initially insufficient to screen the electric field provoked by
the wiggling of magnetic field lines and is low enough to let 1GHz radio
emission escape the magnetosphere, which can explain the absence of FRBs from
known magnetars. The pair cascades crowd the closed flux tubes with plasma,
screening the accelerating electric field, thus limiting the radio pulse
duration to $sim1$ ms. Within the framework of our model, the current dataset
of polarization angle variation in FRB 121102 suggests a magnetic obliquity
$alphalesssim40^circ$ and viewing angle $zeta$ with respect to the spin
axis $alpha
demonstrate that they are remarkably similar to statistics of magnetar
high-energy short bursts. Motivated by this correspondence, we propose that
repeating FRBs are generated during short bursts in the closed field line zone
of magnetar magnetospheres via a pulsar-like emission mechanism. Crustal
slippage events dislocate field line footpoints, initiating intense particle
acceleration and pair production, giving rise to coherent radio emission
similar to that generated near pulsar polar caps. We argue that the energetics
of FRB 121102 can be readily accounted if the efficiency of conversion of
Poynting flux into coherent radio emission is $sim10^{-4}-10^{-2}$, values
consistent with empirical efficiencies of radio emission in pulsars and
radio-loud magnetars. Such a mechanism could operate only in magnetars with
preexisting low twist of the magnetosphere, so that the charge density in the
closed zone is initially insufficient to screen the electric field provoked by
the wiggling of magnetic field lines and is low enough to let 1GHz radio
emission escape the magnetosphere, which can explain the absence of FRBs from
known magnetars. The pair cascades crowd the closed flux tubes with plasma,
screening the accelerating electric field, thus limiting the radio pulse
duration to $sim1$ ms. Within the framework of our model, the current dataset
of polarization angle variation in FRB 121102 suggests a magnetic obliquity
$alphalesssim40^circ$ and viewing angle $zeta$ with respect to the spin
axis $alpha<zeta<180^circ-alpha$.
