Distributed computing projectEinstein@Home discovers 13 new gamma-ray pulsars11 January 2017

A gamma-ray pulsar is a compact neutron star thataccelerates charged particles to relativistic speeds in itsextremely strong magnetic field. This process producesgamma radiation (violet) far above the surface of thecompact remains of the star, for example, while radiowaves (green) are emitted over the magnetic poles inthe form of a cone. The rotation moves the emissionregions across the terrestrial line of sight, making thepulsar light up periodically in the sky. Credit: ©NASA/Fermi/Cruz de Wilde

An analysis that would have taken more than athousand years on a single computer has foundwithin one year more than a dozen new rapidlyrotating neutron stars in data from the Fermigamma-ray space telescope. With computingpower donated by volunteers from all over theworld an international team led by researchers atthe Max Planck Institute for Gravitational Physicsin Hannover, Germany, searched for tell-taleperiodicities in 118 Fermi sources of unknownnature. In 13 they discovered a rotating neutronstar at the heart of the source. While these all are –astronomically speaking – young with ages

between tens and hundreds of thousands of years,two are spinning surprisingly slow – slower thanany other known gamma-ray pulsar. Anotherdiscovery experienced a "glitch", a sudden changeof unknown origin in its otherwise regular rotation.

"We discovered so many new pulsars for threemain reasons: the huge computing power providedby Einstein@Home; our invention of novel andmore efficient search methods; and the use ofnewly-improved Fermi-LAT data. These togetherprovided unprecedented sensitivity for our largesurvey of more than 100 Fermi catalog sources,"says Dr. Colin Clark, lead author of the paper nowpublished in The Astrophysical Journal.

Neutron stars are compact remnants fromsupernova explosions and consists of exotic,extremely dense matter. They measure about 20kilometers across and weigh as much as half amillion Earths. Because of their strong magneticfields and fast rotation they emit beamed radiowaves and energetic gamma rays similar to acosmic lighthouse. If these beams point towardsEarth once or twice per rotation, the neutron starbecomes visible as a pulsating radio or gamma-raysource – a so-called pulsar.

"Blindly" detecting gamma-ray pulsars

Finding these periodic pulsations from gamma-raypulsars is very difficult. On average only 10 photonsper day are detected from a typical pulsar by theLarge Area Telescope (LAT) onboard the Fermispacecraft. To detect periodicities, years of datamust be analyzed, during which the pulsar mightrotate billions of times. For each photon one mustdetermine exactly when during a single split-secondrotation it was emitted. This requires searching overyears long data sets with very fine resolution inorder not to miss a signal. The computing power

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required for these "blind searches" – when little tono information about the pulsar is knownbeforehand – is enormous.

Previous similar blind searches have detected 37gamma-ray pulsars in Fermi-LAT data. All blindsearch discoveries in the past 4 years have beenmade by Einstein@Home which has found a totalof 21 gamma-ray pulsars in blind searches, morethan a third of all such objects discovered throughblind searches.

The entire sky as seen by the Fermi Gamma-ray SpaceTelescope and the 13 pulsars discovered byEinstein@Home that were now published. The fieldbelow each inset shows the pulsar name and its rotationfrequency. The flags in the insets show the nationalitiesof the volunteers whose computers found the pulsars.Credit: Knispel/Clark/Max Planck Institute forGravitational Physics/NASA/DOE/Fermi LATCollaboration

Computing resource Einstein@Home

Enlisting the help of tens of thousands of volunteersfrom all around world donating idle compute cycleson their tens of thousands of computers at home,the team was able to conduct a large-scale surveywith the distributed computing projectEinstein@Home. In total this search required about10,000 years of CPU core time. It would have takenmore than one thousand years on a singlehousehold computer. On Einstein@Home itfinished within one year – even though it only used

part of the project's resources.

The scientists selected their targets from 1000unidentified sources in the Fermi-LAT Third SourceCatalog by their gamma-ray energy distribution asthe most "pulsar-like" objects. For each of the 118selected sources, they used novel, highly efficientmethods to analyze the detected gamma-rayphotons for hidden periodicities.

One dozen and one new neutron star

"So far we've identified 17 new pulsars among the118 gamma-ray sources we searched withEinstein@Home. The latest publication in The Astrophysical Journal presents 13 of thesediscoveries," says Clark. "We knew that there hadto be several unidentified pulsars in the Fermi data,but it's always very exciting to actually detect one ofthem and at the same time it's very satisfying tounderstand what its properties are." About half ofthe discoveries would have been missed inprevious Einstein@Home surveys, but the novelimproved methods made the difference.

Most of the discoveries were what the scientistsexpected: gamma-ray pulsars that are relativelyyoung and were born in supernovae some tens tohundreds of thousands of years ago. Two of themhowever spin slower than any other gamma-raypulsar known. Slow-spinning young pulsars onaverage emit less gamma-rays than faster-spinningones. Finding these fainter objects is thereforeuseful to explore the entire gamma-ray pulsarpopulation. Another newly discovered pulsarexperienced a strong "glitch", a sudden speedup ofunknown origin in its otherwise regular rotation.Glitches are observed in other young pulsars andmight be related to re-arrangements of the neutronstar interior but are not well understood.

Searching for gamma-ray pulsars in binarysystems

"Einstein@Home searched through 118unidentified pulsar-like sources from the Fermi-LATCatalog," says Prof. Dr. Bruce Allen, director ofEinstein@Home and director at the Max PlanckInstitute for Gravitational Physics in Hanover. "Colinhas shown that 17 of these are indeed pulsars, and

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I would bet that many of the remaining 101 are alsopulsars, but in binary systems, where we lacksensitivity. In the future, using improved methods,Einstein@Home is going to chase after those aswell, and I am optimistic that we will find at leastsome of them."

More information: C. J. Clark et al. THEEINSTEIN@HOME GAMMA-RAY PULSARSURVEY. I. SEARCH METHODS, SENSITIVITY,AND DISCOVERY OF NEW YOUNG GAMMA-RAY PULSARS, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/834/2/106

APA citation: Distributed computing project Einstein@Home discovers 13 new gamma-ray pulsars(2017, January 11) retrieved 21 March 2022 from https://phys.org/news/2017-01-einsteinhome-gamma-ray-pulsars.html

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