CCO Pulsars as Anti-Magnetars: Evidence of Neutron Stars Weakly Magnetized at Birth

TL;DR

This study provides evidence that certain neutron stars, specifically CCO pulsars, are born with weak magnetic fields, influencing their observational properties and possibly explaining their radio-quiet nature.

Contribution

It introduces the idea that CCO pulsars are weakly magnetized at birth due to slow rotation and accretion, challenging previous assumptions about neutron star magnetic field strengths.

Findings

Upper limits on period derivatives imply B_s < 3E11 G.

X-ray luminosities exceed spin-down luminosities, indicating residual cooling or accretion.

Weak magnetic fields allow accretion disks to interact with the magnetosphere without violating torque limits.

Abstract

Our new study of the two central compact object pulsars, PSR J1210-5226 (P = 424 ms) and PSR J1852+0040 (P = 105 ms), leads us to conclude that a weak natal magnetic field shaped their unique observational properties. In the dipole spin-down formalism, the 2-sigma upper limits on their period derivatives, < 2E-16 for both pulsars, implies surface magnetic field strengths of B_s < 3E11 G and spin periods at birth equal to their present periods to three significant digits. Their X-ray luminosities exceed their respective spin-down luminosities, implying that their thermal spectra are derived from residual cooling and perhaps partly from accretion of supernova debris. For sufficiently weak magnetic fields an accretion disk can penetrate the light cylinder and interact with the magnetosphere while resulting torques on the neutron star remain within the observed limits. We propose the following as the origin of radio-quiet CCOs: the magnetic field, derived from a turbulent dynamo, is weaker if the NS is formed spinning slowly, which enables it to accrete SN debris. Accretion excludes neutron stars born with both B_s < 1E11 G and P > 0.1 s from radio pulsar surveys, where such weak fields are not encountered except among very old (> 40 Myr) or recycled pulsars. We predict that these birth properties are common, and may be attributes of the youngest detected neutron star, the CCO in Cassiopeia A, as well as an undetected infant neutron star in the SN 1987A remnant. In view of the far-infrared light echo discovered around Cas A and attributed to an SGR-like outburst, it is especially important to determine via timing whether Cas A hosts a magnetar or not. If not a magnetar, the Cas A NS may instead have undergone a one-time phase transition (corequake) that powered the light echo.