EDP Sciences
Free access
Issue
A&A
Volume 423, Number 3, September I 2004
Page(s) 1023 - 1027
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20041132


A&A 423, 1023-1027 (2004)
DOI: 10.1051/0004-6361:20041132

Subsonic propellers in a strong wind as anomalous X-ray pulsars

N. R. Ikhsanov1, 2, 3 and C.-S. Choi1

1  Korea Astronomy Observatory, 61-1 Hwaam, Yusong, Taejon 305-348, Korea
    e-mail: ikhsanov@kao.re.kr
2  Central Astronomical Observatory of the Russian Academy of Sciences, Pulkovo 65-1, 196140 Saint-Petersburg, Russia
3  Isaac Newton Institute of Chile, St. Petersburg Branch, Russia

(Received 21 April 2004 / Accepted 11 May 2004 )

Abstract
The appearance of subsonic propellers situated in a strong wind is discussed. We show that it is similar to the appearance of anomalous X-ray pulsars (AXPs) provided the mass and the magnetic moment of neutron stars are $M\simeq 1.4~M_{\odot}$, and $\mu\simeq 2\times 10^{30}\,{\rm G\,cm^3}$, respectively, and the strength of the wind is $\dot{M}_{\rm c} \simeq 3\times 10^{17}\,{\rm g\,s^{-1}}$. Under these conditions, the spin periods of subsonic propellers are limited within the range of 5-15 s, and the expected spin-down rates are close to $\dot{P}\simeq 7\times 10^{-11}\,{\rm s\,s^{-1}}$. The mass accretion rate onto the stellar surface is limited to the rate of plasma penetration into its magnetosphere at the boundary. As this process is governed by the reconnection of the field lines, the accretion rate onto the stellar surface constitutes 1-2% of $\dot{M}_{\rm
c}$ . In this case the X-ray luminosity of the objects under consideration can be evaluated as $L_{\rm X} \sim 4\times 10^{35}\,{\rm erg\,s^{-1}}$. The model predicts the existence of at least two spatially separated sources of the X-ray emission: hot spots at the stellar surface, and the hot atmosphere surrounding the magnetosphere of the star. The ages of the subsonic propellers under the conditions of interest are limited to  $\la$ 105 yr.


Key words: accretion, accretion disks -- stars: neutron -- stars: winds, outflows -- X-rays: stars




© ESO 2004