Magnetar Signature - The U Curve

Abstract

This work looks at some definitive signatures of magnetars, in particular of period closures accompanied by a decline of X-ray radiation in two models. We review some of the previous works which are based on the well known dynamo model in which the star is born with a period of a few milliseconds at high temperatures. In such a convection regime the dynamo mechanism can amplify the the magnetic fields to the magnetar value. This is in contrast to a screened core model which posits that a high density phase transition occurs in the inner core of magnetars that dynamically aligns all the neutron magnetic moments producing a large magnetic field in the core. The accompanying change of flux gives rise to shielding or screening currents in the surrounding high conductivity plasma that do not permit the field to exit to the surface. Ambipolar diffusion then transports the field to the crust dissipating energy in neutrinos and X-rays. The up-welling field cleaves the crust resulting in flares and X-ray radiation from ohmic dissipation in the crust till the screening currents are spent and the surface polar field attains its final value. In the dynamo model the polar magnetic field decreases with time whereas in our screened model it increases to its final value. One consequence of this is that in the latter model, as a function of time and period, the ratio of the dipole radiation loss, $\dot{E}$ to the X-ray luminosity, $L_X$, is a 'U' curve, indicating that it is the exponential decline in $L_X$, that brings closure to the periods that are observed for magnetars.

arXiv comment22 pages, 12 figures

References in corpus (25)

• Magnetars
• The McGill Magnetar Catalog
• Physics of Neutron Star Crusts
• Electrodynamics of Magnetars: Implications for the Persistent X-ray Emission and Spindown of the Soft Gamma Repeaters and Anomalous X-ray Pulsars
• An exceptionally bright flare from SGR1806-20 and the origins of short-duration gamma-ray bursts
• Unifying the observational diversity of isolated neutron stars via magneto-thermal evolution models
• Thermal Relaxation in Young Neutron Stars
• Systematic study of magnetar outbursts
• Hall Effect in Neutron Star Crusts: Evolution, Endpoint and Dependence on Initial Conditions
• Three-dimensional simulations of the magnetic stress in a neutron star crust
• Magnetar-like activity from the central compact object in the SNR RCW103
• Magnetars as cooling neutron stars with internal heating
• Electrical conductivity of a warm neutron star crust in magnetic fields
• Evidence for the magnetar nature of 1E 161348-5055 in RCW 103
• The relevance of ambipolar diffusion for neutron star evolution
• Very deep X-ray observations of the Anomalous X-ray Pulsar 4U 0142+614
• Is SGR 1900+14 a Magnetar?
• XMM-Newton observations of CXOU J010043.1-721134: the first deep look at the soft X-ray emission of a magnetar
• SGR 1806-20 about two years after the giant flare: Suzaku, XMM-Newton and INTEGRAL observations
• The imprint of the crustal magnetic field on the thermal spectra and pulse profiles of isolated neutron stars
• A Natural Explanation for Magnetars
• Electronic screening and damping in magnetars
• Magnetars From Magnetized Cores Created by a Strong Interaction Phase Transition
• Friedel crystals and the outer crust of magnetars
• Magnetar Crusts: Matter at $10^{15}$ Gauss