Birth rates of SGRs and AXPs: delayed amplification of magnetic field

TL;DR

This paper proposes that neutron stars are born with normal magnetic fields which are then amplified to magnetar levels after a delay, explaining the high birth rates and magnetic fields of AXPs and SGRs.

Contribution

It introduces a delayed magnetic field amplification mechanism involving quark deconfinement to explain magnetar formation.

Findings

High birth rate of AXPs/SGRs (~1/500 yr)

Magnetic fields amplified after a few hundred years

Proposes a quark-deconfinement related amplification process

Abstract

We present new determination of the birth rate of AXPs and SGRS and their associated SNRs. We find a high birth rate of 1/(500 yr) for AXPs/SGRs and 1/(1700 yr) for associated SNRs. These high rates suggest that all massive stars (greater than ~ 25 M_sun) give rise to remnants with magnetar-like fields. Recent observations indicate that fossil fields cannot explain such high fields in the progenitor stars. Dynamo mechanisms during the birth of the neutron stars require spin rates much faster than either observations or theory indicate. Here, we propose the neutron stars form with normal (~ 10^{12} G) magnetic fields, which are then amplified to 10^{14}-10^{15} G after a delay of a few hundred years. The amplification is speculated to be a consequence of color ferromagnetism and occurs after the neutron star core reaches quark-deconfinement density. This delayed amplification alleviates many difficulties in interpreting simultaneously the high birth rate and high magnetic fields of AXPs/SGRs and their link to massive stars.