14th of September 2021 |
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Parkes Pulsar Timing Array Data Release 2 |
by Reardon et al. |
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.
In a binary system, if the pulsar’s orbit is observed nearly edge-on, or is modelled
with sufficiently high precision, it is possible to measure the Shapiro
delay incurred by pulses travelling through the gravitational field of the companion.
This gravitational time delay effect is one of the classic tests of general relativity.
Radio signals passing near a massive object take slightly longer to travel from the source
than they would if the mass of the object were not present.
The figure above shows the timing residuals as a function of binary orbital phase for PSR
J1125−6014, showing the Shapiro delay signal.
The dashed vertical line indicates the orbital phase of
superior conjunction, and the colours indicate the different observing
bands with centre frequencies of 700MHz (red), 1400MHz (teal), and
3100MHz (blue).
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