vela pulsar
February 10, 2016

Vela Pulsar’s ‘glitching’ found to affect pulse width

The Vela Pulsar, a highly magnetized, spinning, radiation-emitting neutron star that experiences several “micro-glitches” each year, changes its pulse width over time – especially following one of those frequency shifts, researchers from the University of Tasmania have discovered.

According to Phys.org, Ph. D. student Jim Palfreyman and his colleagues collected more than 6,000 hours of single-pulse data from the pulsar using a 26-meter radio telescope at the Mount Pleasant Radio Observatory near Hobart, Australia as part of an 18-month long-term study.

While previous studies had found that the Vela Pulsar speeds up in rotation frequency once every three years or so, the new analysis of approximately 237 million single pulses found that its pulse width changes as well, with “marked” increases following one of its “micro-glitches.”

Also, they found that the abundance of bright pulses changes after some of, but not all of, these events. In addition to helping to explain some of the Vela Pulsar’s unusual behavior, the research could help shed new light on the pulsar emission and glitching process as a whole.

Findings suggest an unusual location for the emissions zone

In a paper now vailable online at arXiv.org and accepted for publication by The Astrophysical Journal, Palfreyman and his colleagues explained that whatever was affecting the pulse width of the pulsar was affecting its entire pulse shape, causing occasional decreases in pulse width.

For instance, after one micro-glitch, they observed a sudden increase in the frequency of brighter pulses and no change in pulse width. Following a second one, however, the opposite happened: a micro-glitch was followed by a sudden decrease in pulse with and no change in bright pulse rate.

As Phys.org explained, the study authors believe that this unusual phenomenon could indicate that the emission zones of the pulsar could be mathematically chaotic by nature, and point out that the width fluctuations could be due to changes in the width of its emission cone. However, this hypothesis would rely on the emission zone being located in the cone, while most younger pulsars like Vela should give off emissions from its core, the website noted.

Palfreyman’s team has determined that the secular changes occurring in Vela’s pulse width may have one of three different possible cyclical periods which match with the X-ray periodicities of a helical jet and which could be interpreted as free precession. As previous studies have already established, the helical X-ray jet streaming from the pulsar’s rotational axis has definite periods of 122, 73 and 91 days – a finding corroborated by the new data.

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Feature Image: The supernova that formed the Vela pulsar exploded over 10,000 years ago. This optical image from the Anglo-Australian Observatory's UK Schmidt telescope shows the enormous apparent size of the supernova remnant formed by the explosion. The full size of the remnant is about eight degrees across, or about 16 times the angular size of the moon. The square near the center shows the Chandra image with a larger field-of-view than used for the movie, with the Vela pulsar in the middle. (Credits: X-ray: NASA/CXC/Univ of Toronto/M.Durant et al; Optical: DSS/Davide De Martin)