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Vela pulsar glitch detection 2010/07/31


The Vela pulsar (PSR J0835-4510) is the brightest radio pulsar in the sky. Pulsars are the collapsed remnants of stars that exploded as supernovae and are only are about 20km in diameter. The Vela pulsar is young and exhibits sudden jumps, or "glitches", in its rotation rate. These typically occur at intervals of a few years. Close monitoring of the way in which it recovers from each event provides clues to the interior structure of the object.

HartRAO astronomer and PhD student Sarah Buchner has been monitoring the Vela pulsar as part of her research. This was disrupted by the failure of the bearing in the 26m telescope at Hartebeesthoek in 2008 October. However, she was given access to the 15m eXperimental Development Model (XDM) prototype for the Karoo Array Telescope built by the South African SKA Project in between tests by the KAT development team. XDM is fitted with a 1.4-1.6GHz receiver and multi-channel "IBOB" FPGA-based backend, designed for rapid sampling. In collaboration with the KAT team, Sarah adapted the XDM software for pulsar timing, which requires continuous recording of rapidly sampled data. Maintaining continuous observing took a lot of effort from Sarah and the KAT team, with various teething problems having to be ironed out.

spectrum
Left click on image for large version.
Typical dynamic spectrum of the Vela pulsar obtained with XDM, showing how the pulse arrival time is frequency-dependent owing to ionised interstellar medium. The graph at top shows the pulse profile after dedispersion.

By the time of the 26m repair in mid-2010, the interval of nearly four years since the last glitch on 2006 August 12 was one of the longer such intervals, so Sarah was very keen to get the 26m telescope back after the repair in order to get data from both telescopes for comparison.

preglitch
Left click on image for large version.
Vela pulse arrival time residuals from XDM (green) and the 26m telescope (purple in squares) before the glitch.

As part of recommissioning testing, Sarah restarted pulsar observing with the 26m telescope on 2010 July 23.

observing
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The 15m XDM (left) and recommissioned 26m telescope (right) observing the Vela pulsar on July 23.

Eight days later the Vela pulsar glitched.

preglitch
Left click on image for large version.
Change in pulse arrival times after the glitch compared to pre-glitch. Data in green from XDM, from 26m in purple.

The glitch occurred shortly after the pulsar had set at HartRAO. Processing the data from XDM shortly after it rose the next morning, the telltale signature of the glitch was apparent (above). XDM has an alt-azimuth mount, so it sees the pulsar when it rises above the hills. The 26m can only see it about two hours later, owing to its polar mounting and the southern declination of the pulsar.

Shortly after the pulsar became observable with the 26m telescope, Sarah was able to confirm the glitch with the second telescope. Thereafter the pulsar was monitored continuously with both telescopes in order to characterize its recovery behaviour.

Sarah reported in Astronomers Telegram #2768 on August 1 that
"An increase in the rotation frequency of PSR J0835-4510 of magnitude [Delta(nu)]/nu = +1.94 E-6 has been observed, using the KAT prototype, with the "glitch" occurring on Jul. 31.802 UT. Fourteen hours of observations, commencing 7.4 hours after the event, indicate an accompanying fractional increase in the spin-down rate of +0.075 +/- 0.001."