Crab pulsar beams most energetic gamma rays ever detected from a pulsar

Astrophysicists have detected pulsed gamma-ray emission from the Crab pulsar at energies far beyond what current theoretical models of pulsars can explain.

With energies exceeding 100 billion electron-volts (100 GeV), the surprising gamma-ray pulses were detected by the VERITAS (very energetic radiation imaging telescope array system) telescope array at the Whipple Observatory in Arizona and reported by an international team of scientists in a paper in the October 7 issue of Science.

Andrew McCann, a PhD candidate from McGill University in Montreal, along with corresponding authors Nepomuk Otte, of the University of California, Santa Cruz, and Martin Schroedter of the Smithsonian Astrophysical Observatory performed most of the analytic work for the study, which involved nearly 100 scientists in the VERITAS collaboration. It is a discovery that McCann has been pursuing for close to seven years.

The Crab pulsar is a rapidly spinning neutron star, the collapsed core of a massive star that exploded in a spectacular supernova in the year 1054, leaving behind the brilliant Crab Nebula, with the pulsar at its heart. It is one of the most intensively studied objects in the sky. Rotating about 30 times a second, the pulsar has an intense, co-rotating magnetic field from which it emits beams of radiation.

The beams sweep around like a lighthouse beacon because they are not aligned with the star's rotation axis. So although the beams are steady, they are detected on Earth as rapid pulses of radiation.

Scientists have long agreed on a general picture of what causes pulsar emission. Electromagnetic forces created by the star's rapidly rotating magnetic field accelerate charged particles to near the speed of light, producing radiation over a broad spectrum. But the details remain a mystery.