Magnetic and Spin History of Very Young Pulsars
Abstract
After Michel introduced a phenomenological picture of "rapid magnetization" of newly born neutron stars (NSs), Muslimov & Page suggested that the physical conditions accompanying the formation of a NS (convection in the NS envelope, high-rate accretion in a supernova) may result in the large-scale surface magnetic field of the NS having a low value (∼108-109 G), while the bulk of the magnetic flux is submerged under the stellar surface. The subsequent growth of the large-scale surface magnetic field then occurs owing to ohmic diffusion of a strong internal field (∼1012-1013 G) and proceeds over a timescale of 102-103 yr, depending on the early thermal history of the NS, initial distribution of magnetic flux, and electrical resistivity in the crust. Referring to this suggestion, we perform numerical computations to demonstrate its possible relevance to young radio pulsars. In our calculations, we use different NS structures based on a model of dense matter presenting a phase transition to kaon condensation which softens the equation of state. This model implies both slow and fast neutrino cooling, depending on the stellar mass (which is assumed to be in the range of 1.35-1.50 Msun). We present sequences of secular evolution of the surface magnetic field, spin-down luminosity, spin period, "braking index," and spin-down age best matching the corresponding measured and derived quantities for PSR 0531+21 (Crab), PSR 0540-69, and PSR 1509-58. We conclude that the effect under consideration reproduces remarkably well both the observed rotational characteristics and derived values of the surface magnetic field strength for these radio pulsars, the only ones having reliable measurements of the braking indices. In addition, our analysis suggests that NSs in the Crab and PSR 0540-69 have experienced fast neutrino cooling and that their masses are above the critical mass for the phase transition, while the NS in PSR 1509-58 has a mass below this critical mass and has therefore undergone slow neutrino cooling.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1996
- DOI:
- 10.1086/176817
- arXiv:
- arXiv:astro-ph/9505116
- Bibcode:
- 1996ApJ...458..347M
- Keywords:
-
- STARS: PULSARS: INDIVIDUAL ALPHANUMERIC: PSR 0531+21;
- STARS: PULSARS: INDIVIDUAL ALPHANUMERIC: PSR 0540-69;
- STARS: PULSARS: INDIVIDUAL ALPHANUMERIC: PSR 1509-58;
- STARS: NEUTRON;
- STARS: MAGNETIC FIELDS;
- Astrophysics
- E-Print:
- 19 pages in AAS Latex + 5 Figures (uufiled) MUCH EXTENDED VERSION, to be published in Ap. J. (Feb. 10, 1996)