221 research outputs found
The geometry of the double-pulsar system J0737-3039 from systematic intensity variations
The recent discovery of J0737-3039A & B-two pulsars in a highly relativistic
orbit around one another - offers an unprecedented opportunity to study the
elusive physics of pulsar radio emission. The system contains a rapidly
rotating pulsar with a spin period of 22.7 ms and a slow companion with a spin
period of 2.77 s, hereafter referred to as 'A' and 'B', respectively. A unique
property of the system is that the pulsed radio flux from B increases
systematically by almost two orders-of-magnitude during two short portions of
each orbit. Here, we describe a geometrical model of the system that
simultaneously explains the intensity variations of B and makes definitive and
testable predictions for the future evolution of the emission properties of
both stars. Our model assumes that B's pulsed radio flux increases when
illuminated by emission from A. This model provides constraints on the spin
axis orientation and emission geometry of A and predicts that its pulse profile
will evolve considerably over the next several years due to geodetic precession
until it disappears entirely in 15-20 years
Radio pulsar populations
The goal of this article is to summarize the current state of play in the
field of radio pulsar statistics. Simply put, from the observed sample of
objects from a variety of surveys with different telescopes, we wish to infer
the properties of the underlying sample and to connect these with other
astrophysical populations (for example supernova remnants or X-ray binaries).
The main problem we need to tackle is the fact that, like many areas of
science, the observed populations are often heavily biased by a variety of
selection effects. After a review of the main effects relevant to radio
pulsars, I discuss techniques to correct for them and summarize some of the
most recent results. Perhaps the main point I would like to make in this
article is that current models to describe the population are far from complete
and often suffer from strong covariances between input parameters. That said,
there are a number of very interesting conclusions that can be made concerning
the evolution of neutron stars based on current data. While the focus of this
review will be on the population of isolated Galactic pulsars, I will also
briefly comment on millisecond and binary pulsars as well as the pulsar content
of globular clusters and the Magellanic Clouds.Comment: 16 pages, 6 figures, to appear in Proceedings of ICREA Workshop on
The High-Energy Emission from Pulsars and their Systems, Sant Cugat, Spain,
2010 April 12-16 (Springer
A Search for Pulsars in Quiescent Soft X-Ray Transients. I
We have carried out a deep search at 1.4 GHz for radio pulsed emission from
six soft X-ray transient sources observed during their X-ray quiescent phase.
The commonly accepted model for the formation of the millisecond radio pulsars
predicts the presence of a rapidly rotating, weakly magnetized neutron star in
the core of these systems. The sudden drop in accretion rate associated with
the end of an X-ray outburst causes the Alfv\`en surface to move outside the
light cylinder, allowing the pulsar emission process to operate. No pulsed
signal was detected from the sources in our sample. We discuss several
mechanisms that could hamper the detection and suggest that free-free
absorption from material ejected from the system by the pulsar radiation
pressure could explain our null result.Comment: accepted by Ap
A large age for the pulsar B1757-24 from an upper limit on its proper motion
The "characteristic age" of a pulsar usually is considered to approximate its true age, but this assumption has led to some puzzling results, including the fact that many pulsars with small characteristic ages have no associated supernova remnants. The pulsar B1757-24 is located just beyond the edge of a supernova remnant; the properties of the system indicate that the pulsar was born at the centre of the remnant, but that it has subsequently overtaken the expanding blast-wave. With a characteristic age of 16,000 yr, this implies an expected proper motion by the pulsar of 63-80 milliarcsec per year. Here we report observations of the nebula surrounding the pulsar which limit its proper motion to less than 25 mas/yr, implying a minimum age of 39,000 yr. A more detailed analysis argues for a true age as great as 170,000 yr, significantly larger than the characteristic age. From this result and other discrepancies associated with pulsars, we conclude that characteristic ages seriously underestimate the true ages of pulsars
On the inverse Compton scattering model of radio pulsars
Some characteristics of the inverse Compton scattering (ICS) model are
reviewed. At least the following properties of radio pulsars can be reproduced
in the model: core or central emission beam, one or two hollow emission cones,
different emission heights of these components, diverse pulse profiles at
various frequencies, linear and circular polarization features of core and
cones.Comment: 5 pages, no figures, LaTeX, a proceeding paper for Pacific Rim
Conference on Stellar Astrophysics, Aug. 1999, HongKong, Chin
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