A new census of the sky at extreme energies has led to the discovery of 12 new gamma ray sources that have energies exceeding one trillion times that of visible light, and it’s all due to recent improvement made to NASA’s Fermi Gamma-ray Space Telescope.
Using the telescope, members of the Fermi team were able to discover hundreds of high-energy sources, including four dozen that could not be detected at any other wavelength, the US space agency announced Thursday at the 227th Meeting of the American Astronomical Society.
“What made this advance possible was a complete reanalysis, which we call Pass 8, of all data acquired by Fermi’s Large Area Telescope (LAT),” said Marco Ajello, a researcher at Clemson University. “The end result is effectively a complete instrument upgrade without our ever having to leave the ground.”
Ajello and his colleagues, who will detail their findings in a future issue of the Astrophysical Journal Supplement Series, re-examined every particle and gamma-ray detected by the telescope since it launched about eight years ago and found several that had previously been missed.
Blazars, pulsar wind nebulae among newly-discovered objects
Their efforts enhanced the LAT’s ability to determine the directions of incoming gamma rays while also widening its useful energy range, according to NASA. They constructed a new sky map at energies ranging from 50 billion (GeV) to 2 trillion electron volts (TeV) using 61,000 Pass 8 gamma rays collected over an 80 month span.
“Of the 360 sources we cataloged, about 75 percent are blazars, which are distant galaxies sporting jets powered by supermassive black holes,” Fermi team member Alberto Domínguez from the Complutense University in Madrid, explained. “The highest-energy sources, all located in our galaxy, are mostly remnants of supernova explosions and pulsar wind nebulae, places where rapidly rotating neutron stars accelerate particles to near the speed of light.”
These extremely high-energy gamma rays, including those produced by the Crab Nebula (which topped 1 TeV in energy output) are believed to be produced following collisions between lower-energy light and accelerated particles, the US space agency said. The net result is a slight energy loss for the particle and a large gain for the light, which transforms it into a gamma ray.
Thanks to the tweaks to Fermi, it can now collect data previously only detectable by telescopes on the ground. The new study discovered more than 280 candidates for future research by ground based observatories, as well as 25 identified objects that include three new pulsar wind nebulae and a pair of never-before-seen supernova remnants.
“An exciting aspect of this catalog is that we find many new sources that emit gamma rays over a comparatively large patch of the sky,” said Jamie Cohen, a graduate student at the University of Maryland working with the Fermi team at NASA’s Goddard Space Flight Center. “Finding more of these objects enables us to probe their structures as well as better understand mechanisms that accelerate the subatomic particles that ultimately produce gamma-ray emission.”
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Image credit: NASA Goddard
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