July 24, 2012
Astronomers Locate Gamma-ray Pulsar With The Hiccups
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Lee Rannals for redOrbit.com - Your Universe Online
A special gamma-ray pulsar with the hiccups has been discovered by researchers from the Max Planck Institutes for Gravitational Physics and Radio Astronomy (MPIfR) using data constructed from the Fermi Gamma-ray Space Telescope.
The pulsar J1838-0537 is very young, and has experienced the strongest rotation glitch ever observed for a gamma-ray-only pulsar.
Pure gamma-ray pulsars are difficult to identify because their characteristics are unknown, and astronomers are only able to determine their approximate location in the sky from original Fermi observations.
Astronomers have to check a combination of characteristics in a blind search, which is the only way of finding a hidden periodicity in the arrival times of the gamma-ray photons.
High-performance computers reach their limit during the process of finding these pulsars, so researchers have to use algorithms originally developed for the analysis of gravitational-wave data to conduct a more efficient hunt through the Fermi data.
“By employing new optimal algorithms on our ATLAS computer cluster, we were able to identify many previously-missed signals,” Bruce Allen, Director of the Albert Einstein Institute (AEI), said in a recent statement.
Allen's team announced in November last year the discovery of nine new Fermi gamma-ray pulsars. Now, the scientists have made a new find by using the same methods.
“The pulsar is, at 5,000 years of age, very young. It rotates about its own axis roughly seven times per second and its position in the sky is towards the Scutum constellation,” Holger Pletsch, a scientist in Allen´s group and lead author of the study which has now been published in The Astrophysical Journal Letters, said.
“After the discovery we were very surprised that the pulsar was initially only visible until September 2009. Then it seemed to suddenly disappear," Pletsch continued.
After a follow-up analysis, researchers found that pulsar J1838-0537 did not disappear, but experienced a glitch after which it rotated 38 millionths of a Hertz faster than before.
“This difference may appear negligibly small, but it´s the largest glitch ever measured for a pure gamma-ray pulsar,” Allen said.
Pletsch said that if the sudden frequency change was neglected, then after eight hours a complete rotation of the pulsar is lost and the team can no longer determine at which rotational phase the gamma-ray photons reach Fermi.
If the team takes the glitch into account, and correct the change in rotation, the pulsar shows up again in the observational data.
Astronomers consider "star quakes" of the neutron star crust or interactions between the superfluid stellar interior and the crust to be possible explanations for the cause of the glitches seen in young pulsars.
“Detecting a large number of strong pulsar glitches makes it possible to learn more about the inner structure of these compact celestial bodies,” Lucas Guillemot from the Max Planck Institute for Radio Astronomy in Bonn, the second author of the study, said.