There are cosmic rays bombarding our planet constantly with a wide range of energies. Occasionally, there are some with incredible energy, released by catastrophic explosions or interactions in the universe, such as supernovae. New research suggests that even the material left over by a supernova can release these cosmic rays, long after the explosion.
Published in Physical Review Letters, the work focused on supernova remnant G106.3+2.7. A dramatic stellar explosion left behind a pulsar and a cloud of debris that is slamming into interstellar gas. This interaction produces gamma-rays, which suggest that particles are being accelerated to high energy – 1,000 times higher than what the particle accelerator at CERN can achieve.
“Theorists think the highest-energy cosmic ray protons in the Milky Way reach a million billion electron volts, or PeV energies,” lead author Ke Fang, an assistant professor of physics at the University of Wisconsin, Madison, said in a statement. “The precise nature of their sources, which we call PeVatrons, has been difficult to pin down.”
This peculiar cosmic object, located 2,600 light-years away from Earth, had several hallmarks that made it a plausible PeVatron, as previous research considered. Thanks to over a decade's worth of data from NASA’s Fermi Gamma-ray Space Telescope, the team could distinguish between the contribution in gamma-rays from the pulsar and that from the shockwaves in the supernova remnant.
“This object has been a source of considerable interest for a while now, but to crown it as a PeVatron, we have to prove it’s accelerating protons,” explained co-author Henrike Fleischhack at the Catholic University of America in Washington and NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
“The catch is that electrons accelerated to a few hundred TeV can produce the same emission. Now, with the help of 12 years of Fermi data, we think we’ve made the case that G106.3+2.7 is indeed a PeVatron.”
The team found that while the pulsar dominates the lower energies of gamma-rays, the emission at higher energy comes from both the pulsar and shockwave. Evidence that the gamma-rays are being produced by some extremely high-energy phenomenon such as these protons.
“So far, G106.3+2.7 is unique, but it may turn out to be the brightest member of a new population of supernova remnants that emit gamma rays reaching TeV energies,” Fang notes. “More of them may be revealed through future observations by Fermi and very-high-energy gamma-ray observatories.”