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The main goal of pulsar timing array experiments is to detect
correlated signals, such as those expected from nanohertz-frequency gravitational
waves. Pulsar timing data collected in dense monitoring campaigns can
also be used to study the stars themselves, their binary companions,
and the intervening ionised interstellar medium. Timing observations
are extraordinarily sensitive to changes in path length between the
pulsar and the Earth, enabling precise measurements of the pulsar
positions, distances and velocities, and the shapes of their orbits.
Reardon et al. have recently presented a timing analysis of 25 pulsars
observed as part of the Parkes Pulsar Timing Array (PPTA) project over
time spans of up to 24 yr. The data are from the second data release
(DR2) of the PPTA, which has been extended by including legacy data.
The figure above shows the distribution in right ascension
(horizontal) and declination of the PPTA pulsars. Pulsars in blue are
in an extended DR2, while pulsars in red have no legacy data and are
only present in the main DR2. The cross marks PSR J0437−4715, which is
in PPTA-DR2e. The arrows indicate the direction and relative magnitude
(proportional to the arrow length) of our measurement of the pulsar
proper motion. The marker size is inversely proportional to the
weighted rms residual after subtracting dispersion measure
variations. The dark and light grey bands show the regions within 5
and 10 degrees of the Galactic plane respectively, and the yellow star
marks the Galactic centre.
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