Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2009-07-18
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
42 pages, 22 figures. Accepted for publication in the Astrophysical Journal
Scientific paper
We show that the period clustering of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), their X-ray luminosities, ages and statistics can be explained with fallback disks with large initial specific angular momentum. The disk evolution models are developed by comparison to self-similar analytical models. The initial disk mass and angular momentum set the viscous timescale. An efficient torque, with (1 - w^2) dependence on the fastness parameter w leads to period clustering in the observed AXP-SGR period range under a wide range of initial conditions. The timescale t_0 for the early evolution of the fallback disk, and the final stages of fallback disk evolution, when the disk becomes passive, are the crucial determinants of the evolution. The disk becomes passive at temperatures around 100 K, which provides a natural cutoff for the X-ray luminosity and defines the end of evolution in the observable AXP and SGR phase. This low value for the minimum temperature for active disk turbulence indicates that the fallback disks are active up to a large radius greater than ~10^{12} cm. We find that transient AXPs and SGRs are likely to be older than their persistent cousins. A fallback disk with mass transfer rates corresponding to the low quiescent X-ray luminosities of the transient sources in early evolutionary phases would have a relatively lower initial mass, such that the mass-flow rate in the disk is not sufficient for the inner disk to penetrate into the light cylinder of the young neutron star, making mass accretion onto the neutron star impossible. The transient AXP phase therefore must start later. The model results imply that the transient AXP/SGRs, although older, are likely to be similar in number to persistent sources (abridged).
Ali Alpar M.
Ekşi Yavuz K.
Erkut Hakan M.
Ertan Ü.
No associations
LandOfFree
On the evolution of anomalous X-ray pulsars and soft gamma ray repeaters with fallback disks does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with On the evolution of anomalous X-ray pulsars and soft gamma ray repeaters with fallback disks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and On the evolution of anomalous X-ray pulsars and soft gamma ray repeaters with fallback disks will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-683341