116 research outputs found
On Pulsar-Driven Mass Ejection in Low-Mass X-ray Binaries
There is accumulating evidence for mass ejection in low-mass X-ray binaries
(LMXBs) driven by radio pulsar activity during X-ray quiescence. In this paper
we consider the condition for mass ejection by comparing the radiation pressure
from a millisecond pulsar, and the gas pressure at the inner Lagrange point or
at the surrounding accretion disk. We calculate the critical spin period of the
pulsar below which mass ejection is allowed. Combining with the evolution of
the mass transfer rate, we present constraints on the orbital periods of the
systems. We show that mass ejection could happen in both wide and compact
LMXBs. It may be caused by transient accretion due to thermal instability in
the accretion disks in the former, and irradiation-driven mass-transfer cycles
in the latter.Comment: 11 pages, 3 figures,accepted for publication in RA
On the Mass and Inclination of the PSR J2019+2425 Binary System
We report on nine years of timing observations of PSR J2019+2425, a
millisecond pulsar in a wide 76.5 day orbit with a white dwarf. We measure a
significant change over time of the projected semi-major axis of the orbit,
x-dot/x=(1.3+-0.2)x10^-15 s^-1, where x=(a sin i)/c. We attribute this to the
proper motion of the binary. This constrains the inclination angle to i<72
degrees, with a median likelihood value of 63 degrees. A similar limit on
inclination angle arises from the lack of a detectable Shapiro delay signal.
These limits on inclination angle, combined with a model of the evolution of
the system, imply that the neutron star mass is at most 1.51 solar masses; the
median likelihood value is 1.33 solar masses. In addition to these timing
results, we present a polarization profile of this source. Fits of the linear
polarization position angle to the rotating vector model indicate the magnetic
axis is close to alignment with the rotation axis, alpha<30 degrees.Comment: Accepted by Ap
Multi-telescope timing of PSR J1518+4904
PSR J1518+4904 is one of only 9 known double neutron star systems. These
systems are highly valuable for measuring the masses of neutron stars,
measuring the effects of gravity, and testing gravitational theories. We
determine an improved timing solution for a mildly relativistic double neutron
star system, combining data from multiple telescopes. We set better constraints
on relativistic parameters and the separate masses of the system, and discuss
the evolution of PSR J1518+4904 in the context of other double neutron star
systems. PSR J1518+4904 has been regularly observed for more than 10 years by
the European Pulsar Timing Array (EPTA) network using the Westerbork, Jodrell
Bank, Effelsberg and Nancay radio telescopes. The data were analysed using the
updated timing software Tempo2. We have improved the timing solution for this
double neutron star system. The periastron advance has been refined and a
significant detection of proper motion is presented. It is not likely that more
post-Keplerian parameters, with which the individual neutron star masses and
the inclination angle of the system can be determined separately, can be
measured in the near future. Using a combination of the high-quality data sets
present in the EPTA collaboration, extended with the original GBT data, we have
constrained the masses in the system to m_p1.55 msun (95.4%
confidence), and the inclination angle of the orbit to be less than 47 degrees
(99%). From this we derive that the pulsar in this system possibly has one of
the lowest neutron star masses measured to date. From evolutionary
considerations it seems likely that the companion star, despite its high mass,
was formed in an electron-capture supernova.Comment: 11 pages, 8 figures, accepted by A&
Assessing the Role of Spin Noise in the Precision Timing of Millisecond Pulsars
We investigate rotational spin noise (referred to as timing noise) in
non-accreting pulsars: millisecond pulsars, canonical pulsars, and magnetars.
Particular attention is placed on quantifying the strength and non-stationarity
of timing noise in millisecond pulsars because the long-term stability of these
objects is required to detect nanohertz gravitational radiation. We show that a
single scaling law is sufficient to characterize timing noise in millisecond
and canonical pulsars while the same scaling law underestimates the levels of
timing noise in magnetars. The scaling law, along with a detailed study of the
millisecond pulsar B1937+21, leads us to conclude that timing noise is latent
in most millisecond pulsars and will be measurable in many objects when better
arrival time estimates are obtained over long data spans. The sensitivity of a
pulsar timing array to gravitational radiation is strongly affected by any
timing noise. We conclude that detection of proposed gravitational wave
backgrounds will require the analysis of more objects than previously suggested
over data spans that depend on the spectra of both the gravitational wave
background and of the timing noise. It is imperative to find additional
millisecond pulsars in current and future surveys in order to reduce the
effects of timing noise.Comment: 16 pages and 6 figures. ApJ, accepte
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