### Abstract

Just as a rotating magnetized neutron star has material pulled away from its surface to populate a magnetosphere, a similar process can occur as a result of neutron-star pulsations rather than rotation. This is of interest in connection with the overall study of neutron star oscillation modes but with a particular focus on the situation for magnetars. Following a previous Newtonian analysis of the production of a force-free magnetosphere in this way Timokhin et al., we present here a corresponding general-relativistic analysis. We give a derivation of the general relativistic Maxwell equations for small-amplitude arbitrary oscillations of a non-rotating neutron star with a generic magnetic field and show that these can be solved analytically under the assumption of low current density in the magnetosphere. We apply our formalism to toroidal oscillations of a neutron star with a dipole magnetic field and find that the low current density approximation is valid for at least half of the oscillation modes, similarly to the Newtonian case. Using an improved formula for the determination of the last closed field line, we calculate the energy losses resulting from toroidal stellar oscillations for all of the modes for which the size of the polar cap is small. We find that general relativistic effects lead to shrinking of the size of the polar cap and an increase in the energy density of the outflowing plasma. These effects act in opposite directions but the net result is that the energy loss from the neutron star is significantly smaller than suggested by the Newtonian treatment.

Original language | English |
---|---|

Pages (from-to) | 443-461 |

Number of pages | 19 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 395 |

Issue number | 1 |

DOIs | |

Publication status | Published - May 2009 |

Externally published | Yes |

### Fingerprint

### Keywords

- Pulsars: general
- Stars: magnetic field
- Stars: neutron
- Stars: oscillations

### ASJC Scopus subject areas

- Space and Planetary Science
- Astronomy and Astrophysics

### Cite this

*Monthly Notices of the Royal Astronomical Society*,

*395*(1), 443-461. https://doi.org/10.1111/j.1365-2966.2009.14540.x

**The magnetosphere of oscillating neutron stars in general relativity.** / Abdikamalov, Ernazar B.; Ahmedov, Bobomurat J.; Miller, John C.

Research output: Contribution to journal › Article

*Monthly Notices of the Royal Astronomical Society*, vol. 395, no. 1, pp. 443-461. https://doi.org/10.1111/j.1365-2966.2009.14540.x

}

TY - JOUR

T1 - The magnetosphere of oscillating neutron stars in general relativity

AU - Abdikamalov, Ernazar B.

AU - Ahmedov, Bobomurat J.

AU - Miller, John C.

PY - 2009/5

Y1 - 2009/5

N2 - Just as a rotating magnetized neutron star has material pulled away from its surface to populate a magnetosphere, a similar process can occur as a result of neutron-star pulsations rather than rotation. This is of interest in connection with the overall study of neutron star oscillation modes but with a particular focus on the situation for magnetars. Following a previous Newtonian analysis of the production of a force-free magnetosphere in this way Timokhin et al., we present here a corresponding general-relativistic analysis. We give a derivation of the general relativistic Maxwell equations for small-amplitude arbitrary oscillations of a non-rotating neutron star with a generic magnetic field and show that these can be solved analytically under the assumption of low current density in the magnetosphere. We apply our formalism to toroidal oscillations of a neutron star with a dipole magnetic field and find that the low current density approximation is valid for at least half of the oscillation modes, similarly to the Newtonian case. Using an improved formula for the determination of the last closed field line, we calculate the energy losses resulting from toroidal stellar oscillations for all of the modes for which the size of the polar cap is small. We find that general relativistic effects lead to shrinking of the size of the polar cap and an increase in the energy density of the outflowing plasma. These effects act in opposite directions but the net result is that the energy loss from the neutron star is significantly smaller than suggested by the Newtonian treatment.

AB - Just as a rotating magnetized neutron star has material pulled away from its surface to populate a magnetosphere, a similar process can occur as a result of neutron-star pulsations rather than rotation. This is of interest in connection with the overall study of neutron star oscillation modes but with a particular focus on the situation for magnetars. Following a previous Newtonian analysis of the production of a force-free magnetosphere in this way Timokhin et al., we present here a corresponding general-relativistic analysis. We give a derivation of the general relativistic Maxwell equations for small-amplitude arbitrary oscillations of a non-rotating neutron star with a generic magnetic field and show that these can be solved analytically under the assumption of low current density in the magnetosphere. We apply our formalism to toroidal oscillations of a neutron star with a dipole magnetic field and find that the low current density approximation is valid for at least half of the oscillation modes, similarly to the Newtonian case. Using an improved formula for the determination of the last closed field line, we calculate the energy losses resulting from toroidal stellar oscillations for all of the modes for which the size of the polar cap is small. We find that general relativistic effects lead to shrinking of the size of the polar cap and an increase in the energy density of the outflowing plasma. These effects act in opposite directions but the net result is that the energy loss from the neutron star is significantly smaller than suggested by the Newtonian treatment.

KW - Pulsars: general

KW - Stars: magnetic field

KW - Stars: neutron

KW - Stars: oscillations

UR - http://www.scopus.com/inward/record.url?scp=64549140723&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=64549140723&partnerID=8YFLogxK

U2 - 10.1111/j.1365-2966.2009.14540.x

DO - 10.1111/j.1365-2966.2009.14540.x

M3 - Article

VL - 395

SP - 443

EP - 461

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 1

ER -