More energy than expected from Crab supernova

The Crab Pulsar, a fast-spinning supernova remnant discovered in 1968, appears to emit pulsed gamma-rays at greater energy levels than can be explained by current scientific models, a new study said Thursday. Astrophysicists using the VERITAS telescope array at the Whipple Observatory in the US state of Arizona have detected that the intriguing young neutron star has energies exceeding 100 billion electron-volts (100 GeV). The surprisingly strong gamma-ray pulses were written about by an international team of scientists in a paper in the October 7 issue of Science. "These results put new constraints on the mechanism for how the gamma-ray emission is generated," said Nepomuk Otte, one of the researchers who worked on the study at the University of California at Santa Cruz. Scientists have long believed that pulsar emissions are caused by electromagnetic forces created when a star's rapidly rotating magnetic field accelerate charged particles to near the speed of light, producing radiation over a broad spectrum. The details of how this happens remain a mystery however, and the researchers in this latest study said the findings show just how elusive a complete understanding of this mysterious process remains. "After many years of observations and results from the Crab, we thought we had an understanding of how it worked, and the models predicted an exponential decay of the emission spectrum above around 10 GeV," said David Williams, adjunct professor of physics at UC Santa Cruz and a member of the VERITAS collaboration. "It came as a real surprise when we found pulsed gamma-ray emission at energies above 100 GeV," Williams said. The Crab pulsar was formed from 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. The relatively young neutron star, one of the most intensively studied objects in the sky, rotates about 30 times a second and has a powerful co-rotating magnetic field from which it emits beams of radiation which, seen from Earth, look like rapid pulses of radiation. University of California at Los Angeles scientist Rene Ong, who was also part of the project, said more research will be needed to gain greater insight into the surprising findings. "We need to take more measurements and get the exact shape of the spectrum at these very high energies," he said. There are roughly 100 scientists from 26 institutions who worked on the VERITAS collaboration project. The Very Energetic Radiation Imaging Telescope Array System is a ground-based observatory for gamma-ray astronomy located at the Fred Lawrence Whipple Observatory.