Pulsar Emission Physics

The signature of timing noise
The signature of timing noise as random wandering of the residuals around a simple spin-down model.
Over long datasets this behaviour often appears quasi-periodic. Credit: Lyne et al (2010)

Pulsar Emission Physics is one of the research topics of the Pulsar and Time Domain Astrophysics group. Pulsars are one of the most stable rotators in the universe and the stability of the rotation of some pulsars is comparable to that of an atomic clock (e.g. Petit & Tavella 1996). Pulsars spin down gradually due to the loss of rotational kinetic energy into high-energy plasma and electromagnetic radiation. A simple spin-down model based on the rotational frequency and its first time derivative is sufficient to explain their slow-down in general. However, most pulsars show irregularities in their spin properties, mainly due to glitch events (i.e. a sudden increase in rotational frequency; e.g. Espinoza et al. 2011; Yu et al. 2013) and low-frequency timing noise. These spin irregularities are generally seen in pulsar timing residuals, i.e. the difference between the measured time of arrival (TOA) of the pulse from the pulsar at the observatory and the spin- down model predicted TOA.

In a number of pulsars, this behaviour has been correlated with mode-changing - sudden changes to the pulse profile shape. This is an exciting result as this means it is possible to know, depending on observing cadence and signal-to-noise, when these switches occur in the data by looking at the profile shape thereby allowing us to model and remove timing noise from our data effectively improving the precision of a large number of pulsars which display this behaviour. Our long-term data sets of pulsars provide a great opportunity to study such irregularities in general, and then understand the emission physics of pulsars.

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