A Pulsar with Only Gamma Ray

With the help of some ingenious data analysis methods, researchers 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.

This discovery was made by the researchers from the Max Planck Institutes for Gravitational Physics and for Radio Astronomy, in an international collaboration. They define pulsars as superlative cosmic beacons. These compact neutron stars rotate about their axes many times per second, emitting radio waves and gamma radiation into space. 

The researchers used algorithms originally 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.

J1838-0537 is the name given to the newly discovered pulsar that is of a rare type as it emits light only in the high-energy gamma-ray range of the electromagnetic spectrum. 

 "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 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."

"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," Pletsch explained.

"Detecting a large number of strong pulsar glitches makes it possible to learn more about the inner structure of these compact celestial bodies," said Lucas Guillemot from the Max Planck Institute for Radio Astronomy in Bonn, the second author of the study.

After the discovery in data from the Fermi satellite, the researchers pointed the radio telescope in Green Bank, West Virginia/USA at the celestial position of the gamma-ray pulsar. In an observation of almost two hours and by analyzing a further, older, one-hour observation of the source they found no indications of pulsations in the radio range, indicating that J1838-0537 is a rare gamma-ray-only pulsar.