14 research outputs found
On the accretion luminosity of isolated neutron stars
The accretion process onto a magnetized isolated neutron star, which captures
material from the interstellar medium, is discussed. The evolutionary track of
such a star can be presented as a sequence of four states: ejector, supersonic
propeller, subsonic propeller, and steady accretor. I show that subsonic
propeller - accretor transition does not occur as long as the magnetic field of
the star is strong enough to control the accretion flow in the stellar
vicinity. During the subsonic propeller state the accretion rate onto the
stellar surface is limited to the rate of plasma diffusion into its
magnetosphere. The diffusion rate is at least three orders of magnitude smaller
than the maximum possible mass capture rate by the star. Therefore, the
expected accretion luminosity of magnetized isolated neutron stars is at least
three orders of magnitude smaller than that previously evaluated.Comment: 4 pages, accepted for publication in A&
Can the rapid braking of the white dwarf in AE Aquarii be explained in terms of the gravitational wave emitter mechanism?
The spin-down power of the white dwarf in the close binary AE Aquarii
significantly exceeds the bolometric luminosity of the system. The
interpretation of this phenomenon in terms of the gravitational-wave emitter
mechanism has been recently suggested by Choi & Yi. The basic assumption of
their interpretation is that the spatially limited blobs or mounds of the mass
\delta m ~ 10^{-3} M_sun, are present at the magnetic poles of the white dwarf.
We show that the mounds of this mass can be confined by the magnetic field of
the white dwarf only if the dipole magnetic moment of the star exceeds
4x10^{37} G cm^3. Under these conditions, however, the magnetodipole losses of
the white dwarf would exceed the evaluated spin-down power 6 orders of
magnitude. On this basis we discard a possibility that the observed rapid
braking of the white dwarf in AE Aquarii can be explained in terms of the
mechanism proposed by Choi & Yi.Comment: 6 pages, published in ApJ, 576, L5
On a Site of X-ray Emission in AE Aquarii
An analysis of recently reported results of XMM-Newton observations of AE Aqr
within a hypothesis that the detected X-ray source is located inside the Roche
lobe of the white dwarf is presented. I show this hypothesis to be inconsistent
with the currently adopted model of mass-transfer in the system. Possible
solutions of this problem are briefly discussed.Comment: 4 pages, accepted for publication in ApJ Letter
Spin-Down of the Long-Period Accreting Pulsar 4U 2206+54
4U 2206+54 is a high mass X-ray binary which has been suspected to contain a
neutron star accreting from the wind of its companion BD +53 2790. Reig et al.
have recently detected 5560 s period pulsations in both RXTE and INTEGRAL
observations which they conclude are due to the spin of the neutron star. We
present observations made with Suzaku which are contemporaneous with their RXTE
observation of this source. We find strong pulsations at a period of 5554 +/- 9
s in agreement with their results. We also present a reanalysis of BeppoSAX
observations of 4U 2206+54 made in 1998, in which we find strong pulsations at
a period of 5420 +/- 28 seconds, revealing a spin-down trend in this
long-period accreting pulsar. Analysis of these data suggests that the neutron
star in this system is an accretion-powered magnetar.Comment: Submitted to The Astrophysical Journa