327 research outputs found
The Evolution of PSR J0737-3039B and a Model for Relativistic Spin Precession
We present the evolution of the radio emission from the 2.8-s pulsar of the
double pulsar system PSR J0737-3039A/B. We provide an update on the Burgay et
al. (2005) analysis by describing the changes in the pulse profile and flux
density over five years of observations, culminating in the B pulsar's radio
disappearance in 2008 March. Over this time, the flux density decreases by
0.177 mJy/yr at the brightest orbital phases and the pulse profile evolves from
a single to a double peak, with a separation rate of 2.6 deg/yr. The pulse
profile changes are most likely caused by relativistic spin precession, but can
not be easily explained with a circular hollow-cone beam as in the model of
Clifton & Weisberg (2008). Relativistic spin precession, coupled with an
elliptical beam, can model the pulse profile evolution well. This particular
beam shape predicts geometrical parameters for the two bright orbital phases
which are consistent and similar to those derived by Breton et al. (2008).
However, the observed decrease in flux over time and B's eventual disappearance
cannot be easily explained by the model and may be due to the changing
influence of A on B.Comment: 20 pages, 18 figures, Accepted by ApJ on 2 August 201
SimFlex: Statistical Sampling of Computer System Simulation
Timing-accurate full-system multiprocessor simulations can take years because of architecture and application complexity. Statistical sampling makes simulation-based studies feasible by providing ten-thousand-fold reductions in simulation runtime and enabling thousand-way simulation parallelis
Limits on the Stochastic Gravitational Wave Background from the North American Nanohertz Observatory for Gravitational Waves
We present an analysis of high-precision pulsar timing data taken as part of
the North American Nanohertz Observatory for Gravitational waves (NANOGrav)
project. We have observed 17 pulsars for a span of roughly five years using the
Green Bank and Arecibo radio telescopes. We analyze these data using standard
pulsar timing models, with the addition of time-variable dispersion measure and
frequency-variable pulse shape terms. Sub-microsecond timing residuals are
obtained in nearly all cases, and the best root-mean-square timing residuals in
this set are ~30-50 ns. We present methods for analyzing post-fit timing
residuals for the presence of a gravitational wave signal with a specified
spectral shape. These optimally take into account the timing fluctuation power
removed by the model fit, and can be applied to either data from a single
pulsar, or to a set of pulsars to detect a correlated signal. We apply these
methods to our dataset to set an upper limit on the strength of the
nHz-frequency stochastic supermassive black hole gravitational wave background
of h_c (1 yr^-1) < 7x10^-15 (95%). This result is dominated by the timing of
the two best pulsars in the set, PSRs J1713+0747 and J1909-3744.Comment: To be submitted to Ap
A precise mass measurement of the intermediate-mass binary pulsar PSR J1802-2124
PSR J1802-2124 is a 12.6-ms pulsar in a 16.8-hour binary orbit with a
relatively massive white dwarf (WD) companion. These properties make it a
member of the intermediate-mass class of binary pulsar (IMBP) systems. We have
been timing this pulsar since its discovery in 2002. Concentrated observations
at the Green Bank Telescope, augmented with data from the Parkes and Nancay
observatories, have allowed us to determine the general relativistic Shapiro
delay. This has yielded pulsar and white dwarf mass measurements of 1.24(11)
and 0.78(4) solar masses (68% confidence), respectively. The low mass of the
pulsar, the high mass of the WD companion, the short orbital period, and the
pulsar spin period may be explained by the system having gone through a
common-envelope phase in its evolution. We argue that selection effects may
contribute to the relatively small number of known IMBPs.Comment: 9 pages, 4 figures, 3 tables, accepted for publication in the
Astrophysical Journa
Placing limits on the stochastic gravitational-wave background using European Pulsar Timing Array data
Direct detection of low-frequency gravitational waves (
Hz) is the main goal of pulsar timing array (PTA) projects. One of the main
targets for the PTAs is to measure the stochastic background of gravitational
waves (GWB) whose characteristic strain is expected to approximately follow a
power-law of the form , where is the
gravitational-wave frequency. In this paper we use the current data from the
European PTA to determine an upper limit on the GWB amplitude as a function
of the unknown spectral slope with a Bayesian algorithm, by modelling
the GWB as a random Gaussian process. For the case , which is
expected if the GWB is produced by supermassive black-hole binaries, we obtain
a 95% confidence upper limit on of , which is 1.8 times
lower than the 95% confidence GWB limit obtained by the Parkes PTA in 2006. Our
approach to the data analysis incorporates the multi-telescope nature of the
European PTA and thus can serve as a useful template for future
intercontinental PTA collaborations.Comment: 14 pages, 8 figures, 3 tables, mnras accepte
Tests of general relativity from timing the double pulsar
The double pulsar system, PSR J0737-3039A/B, is unique in that both neutron
stars are detectable as radio pulsars. This, combined with significantly higher
mean orbital velocities and accelerations when compared to other binary
pulsars, suggested that the system would become the best available testbed for
general relativity and alternative theories of gravity in the strong-field
regime. Here we report on precision timing observations taken over the 2.5
years since its discovery and present four independent strong-field tests of
general relativity. Use of the theory-independent mass ratio of the two stars
makes these tests uniquely different from earlier studies. By measuring
relativistic corrections to the Keplerian description of the orbital motion, we
find that the ``post-Keplerian'' parameter s agrees with the value predicted by
Einstein's theory of general relativity within an uncertainty of 0.05%, the
most precise test yet obtained. We also show that the transverse velocity of
the system's center of mass is extremely small. Combined with the system's
location near the Sun, this result suggests that future tests of gravitational
theories with the double pulsar will supersede the best current Solar-system
tests. It also implies that the second-born pulsar may have formed differently
to the usually assumed core-collapse of a helium star.Comment: Appeared in Science Express, Sept. 14, 2006. Includes supporting
materia
The High Time Resolution Universe Survey VI: An Artificial Neural Network and Timing of 75 Pulsars
We present 75 pulsars discovered in the mid-latitude portion of the High Time
Resolution Universe survey, 54 of which have full timing solutions. All the
pulsars have spin periods greater than 100 ms, and none of those with timing
solutions are in binaries. Two display particularly interesting behaviour; PSR
J1054-5944 is found to be an intermittent pulsar, and PSR J1809-0119 has
glitched twice since its discovery.
In the second half of the paper we discuss the development and application of
an artificial neural network in the data-processing pipeline for the survey. We
discuss the tests that were used to generate scores and find that our neural
network was able to reject over 99% of the candidates produced in the data
processing, and able to blindly detect 85% of pulsars. We suggest that
improvements to the accuracy should be possible if further care is taken when
training an artificial neural network; for example ensuring that a
representative sample of the pulsar population is used during the training
process, or the use of different artificial neural networks for the detection
of different types of pulsars.Comment: 15 pages, 8 figure
Observations and Modelling of Relativistic Spin Precession in PSR J1141-6545
Observations of the binary pulsar PSR J1141-6545 using the Parkes radio
telescope over 9.3 years show clear time-variations in pulse width, shape and
polarization. We interpret these variations in terms of relativistic precession
of the pulsar spin axis about the total angular momentum vector of the system.
Over the nine years, the pulse width at the 50% level has changed by more than
a factor of three. Large variations have also been observed in the 1400-MHz
mean flux density. The pulse polarization has been monitored since 2004 April
using digital filterbank systems and also shows large and systematic variations
in both linear and circular polarization. Position angle variations, both
across the pulse profile and over the data span, are complex, with major
differences between the central and outer parts of the pulse profile. Modelling
of the observed position angle variations by relativistic precession of the
pulsar spin axis shows that the spin-orbit misalignment angle is about 110 deg
and that the precessional phase has passed through 180 deg during the course of
our observations. At the start of our observations, the line-of-sight impact
parameter was about 4 deg in magnitude and it reached a minimum very close to 0
deg around early 2007, consistent with the observed pulse width variations. We
have therefore mapped approximately one half of the emission beam, showing that
it is very asymmetric with respect to the magnetic axis. The derived
precessional parameters imply that the pre-supernova star had a mass of about 2
Msun and that the supernova recoil kick velocity was relatively small. With the
reversal in the rate of change of the impact parameter, we predict that over
the next decade we will see a reversed "replay" of the variations observed in
the past decade.Comment: 45 pages, 19 figures, 6 tables, accepted by Astrophysical Journa
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