Contact information

Dr. Holger J. Pletsch
Dr. Holger J. Pletsch
Research Group Leader
Phone:+49 511 762-17171Fax:+49 511 762-2784

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Prof. Dr. Bruce Allen
Prof. Dr. Bruce Allen
Director
Phone:+49 511 762-17148Fax:+49 511 762-17182

Homepage of Bruce Allen

Press contact

Dr.  Benjamin  Knispel
Dr. Benjamin Knispel
Pressereferent AEI Hannover
Phone:+49 511 762-19104Fax:+49 511 762-17182

Animations

Visual 10

This animation illustrates how analysis of Fermi data reveals new pulsars. Fermi's LAT records the precise time and position of the gamma rays it detects, but to identify a pulsar requires additional information -- its position in the sky, its pulse period, and the way the pulse changes over time. Additionally, even Fermi's sensitive LAT detects few gamma rays from these objects -- as few as one photon per 100,000 rotations. The Hannover team used new methods to execute a so-called blind search, using computers to check many different combinations of position and period against the 8,000 photons Fermi's LAT has collected during its three years in orbit. When photons from the pulses align in time, a new gamma-ray pulsar has been discovered.
© AEI/NASA Goddard Space Flight Center

A pulsar with a tremendous hiccup

Max Planck scientists discover young and energetic neutron star with unusually irregular rotation

July 23, 2012

Pulsars are superlative cosmic beacons. These compact neutron stars rotate about their axes many times per second, emitting radio waves and gamma radiation into space.  Using ingenious data analysis methods, researchers from the Max Planck Institutes for Gravitational Physics and for Radio Astronomy, in an international collaboration, dug a very special gamma-ray pulsar out of data from the Fermi Gamma-ray Space Telescope. The pulsar J1838-0537 is radio-quiet, very young, and, during the observation period, experienced the strongest rotation glitch ever observed for a gamma-ray-only pulsar.

A gamma-ray pulsar is a compact neutron star that accelerates charged particles to relativistic speeds in its extremely strong magnetic field. This process produces gamma radiation (violet) far above the surface of the compact remains of the star, for example, while radio waves (green) are emitted over the magnetic poles in the form of a cone. The rotation moves the emission regions across the terrestrial line of sight, making the pulsar light up periodically in the sky. Zoom Image

A gamma-ray pulsar is a compact neutron star that accelerates charged particles to relativistic speeds in its extremely strong magnetic field. This process produces gamma radiation (violet) far above the surface of the compact remains of the star, for example, while radio waves (green) are emitted over the magnetic poles in the form of a cone. The rotation moves the emission regions across the terrestrial line of sight, making the pulsar light up periodically in the sky.

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Pure gamma-ray pulsars are difficult to identify because their characteristics, such as its sky position, the period of rotation and its change in time, are unknown. And astronomers can only determine their approximate position in the sky from the original Fermi observations. They must therefore check many combinations of these characteristics in a blind search, which requires a great deal of computing time. This is the only way of finding a hidden periodicity in the arrival times of the gamma-ray photons.

Even high-performance computers quickly reach their limit in this process. Therefore, the researchers used algorithms originally developed for the analysis of gravitational-wave data to conduct a particularly 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,” says Bruce Allen, Director of the AEI. Back in November 2011, Allen’s team announced the discovery of nine new Fermi gamma-ray pulsars, which had escaped all previous searches. Now the scientists have made a new extraordinary find with the same methods.

The gamma-ray pulsar J1838-0537 found at the Albert Einstein Institute in Hanover is located towards the Scutum constellation, which is to the south in the sky above the horizon on summer nights. This detailed map shows the position of the pulsar (yellow), which is invisible to terrestrial telescopes, in a simulated celestial sky. Zoom Image

The gamma-ray pulsar J1838-0537 found at the Albert Einstein Institute in Hanover is located towards the Scutum constellation, which is to the south in the sky above the horizon on summer nights. This detailed map shows the position of the pulsar (yellow), which is invisible to terrestrial telescopes, in a simulated celestial sky.

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The name of the newly discovered pulsar – J1838-0537 – comes from its celestial coordinates. “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,” says Holger Pletsch, a scientist in Allen’s group and lead author of the study which has now been published. “After the discovery we were very surprised that the pulsar was initially only visible until September 2009. Then it seemed to suddenly disappear.”

Only a complex follow-up analysis enabled an international team led by Pletsch to solve the mystery of pulsar J1838-0537: it did not disappear, but experienced a sudden 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,” explains Allen. And this behaviour has consequences

“If the sudden frequency change is neglected, then after only eight hours, a complete rotation of the pulsar is lost in our counting, and we can no longer determine at which rotational phase the gamma-ray photons reach the detector aboard Fermi,” adds Pletsch. The “flashing” of the neutron star then disappears. If the researchers take the glitch into account and correct the change in rotation, the pulsar shows up again in the observational data.

 
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