8,347 research outputs found
Continuous Gravitational Waves from Isolated Galactic Neutron Stars in the Advanced Detector Era
We consider a simulated population of isolated Galactic neutron stars. The
rotational frequency of each neutron star evolves through a combination of
electromagnetic and gravitational wave emission. The magnetic field strength
dictates the dipolar emission, and the ellipticity (a measure of a neutron
star's deformation) dictates the gravitational wave emission. Through both
analytic and numerical means, we assess the detectability of the Galactic
neutron star population and bound the magnetic field strength and ellipticity
parameter space of Galactic neutron stars with or without a direct
gravitational wave detection. While our simulated population is primitive, this
work establishes a framework by which future efforts can be conducted.Comment: Accepted for publication by Physical Review D, 8 pages, 5 figure
Spectral and Rotational Changes in the Isolated Neutron Star RX J0720.4-3125
RX J0720.4-3125 is an isolated neutron star that, uniquely in its class, has
shown changes in its thermal X-ray spectrum. We use new spectra taken with
Chandra's Low Energy Transmission Grating Spectrometer, as well as archival
observations, to try to understand the timescale and nature of these changes.
We construct lightcurves, which show both small, slow variations on a timescale
of years, and a larger event that occurred more quickly, within half a year.
From timing, we find evidence for a `glitch' coincident with this larger
event, with a fractional increase in spin frequency of 5x10^{-8}. We compare
the `before' and `after' spectra with those from RX J1308.6+2127, an isolated
neutron star with similar temperature and magnetic field strength, but with a
much stronger absorption feature in its spectrum. We find that the `after'
spectrum can be represented remarkably well by the superposition of the
`before' spectrum, scaled by two thirds, and the spectrum of RX J1308.6+2127,
thus suggesting that the event affected approximately one third of the surface.
We speculate the event reflects a change in surface composition caused by,
e.g., an accretion episode.Comment: 4 pages, 2 figures, 2 tables, emulateapj format. ApJL, accepte
Nearby, Thermally Emitting Neutron Stars
We describe a sample of thermally emitting neutron stars discovered in the
ROSAT All-Sky Survey. We discuss the basic observational properties of these
objects and conclude that they are nearby, middle-aged pulsars with moderate
magnetic fields that we see through their cooling radiation. While these
objects are potentially very useful as probes of matter at very high densities
and magnetic fields, our lack of understanding of their surface emission limits
their current utility. We discuss this and other outstanding problems: the
spectral evolution of one sources and the relation of this population to the
overall pulsar population.Comment: 9 pages, one table, 3 figures. To appear in the proceedings of "40
Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17,
2007, McGill University, Montreal, Canad
- …