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14th of September 2021
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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