Gamma-ray pulsar searches

This group's main research aspects are computing-intense searches for and studies of pulsars - rapidly spinning neutron stars - through gamma-rays in previously unaccessible parameter spaces using efficient data analysis and powerful computing resources.

Departure into unexplored lands

A particularly exciting focus is on extending searches to parameter spaces that in fact have been inaccessible before on computational grounds. Achieving this requires the development of efficient data analysis methodologies and the exploitation of powerful computing resources, such as the Einstein@Home volunteer supercomputer.

Pulsars are some of the most extreme objects in our Universe and important key probes for a wide range of fundamental physics. Yet many aspects are still poorly understood after decades of observations, primarily at radio wavelengths. Now gamma-ray observations with NASA’s Fermi Large Area Telescope provide complementary windows of unprecedented opportunities to discover and study new pulsars.

Gamma-ray pulsars

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.

With the Large Area Telescope (LAT) on board NASA's Fermi satellite, for the first time neutron stars were detected via their periodic gamma-ray pulsations alone. Many of these stars are invisible in the radio band. Continuously surveying the gamma-ray sky, the LAT cataloged several hundred unidentified sources, among which many are thought to be pulsars. However, extracting new pulsars and important science from LAT data is computationally limited and almost impossible with conventional methods.

Searches for gamma-ray pulsars are a computational challenge. Long integration times are needed to detect regular pulsations in the photon arrival times. In searches for gamma-ray pulsars, where the relevant pulsar parameters are unknown a-priori, they must be explicitly searched. For observations spanning multiple years, this requires a dense grid covering a multi-dimensional parameter space, with a tremendous number of points to be individually tested.

The same computational problem issue affects searches for continuous waves in data from laser-interferometric gravitational-wave detectors. The signals have the same phase model and the same search parameter space, and in both cases the data span several years. This has motivated the transfer and adaption of gravitational-wave methods to the analysis of LAT data for new gamma-ray pulsars.

A multitude of discoveries

With these novel search methods developed at the AEI in Hannover, 39 previously unknown gamma-ray pulsars were discovered and the following exciting findings were made:

Distributed volunteer computing project finds neutron star rotating 377 times a second in an exotic binary system using data from NASA’s Fermi Space Telescope more

Volunteer distributed computing project Einstein@Home discovers neutron star in unusual binary system more

Improved search methods for the future

Today, hundreds of LAT-cataloged sources remain unidentified, with a still growing number: some of these could be new types of gamma-ray pulsars. Their detection might require further extension and advancement of the search methods following approaches used in GW astronomy. In addition to the improved search techniques, the computational resources for these searches are significantly enhanced by using the volunteer computing system Einstein@Home.

Overall, the unprecedented search sensitivity from the combination of these advances warrants optimism for further gamma-ray pulsar discoveries.

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