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Gamma-Ray Flares from the Crab Nebula

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Science  11 Feb 2011:
Vol. 331, Issue 6018, pp. 739-742
DOI: 10.1126/science.1199705

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Abstract

A young and energetic pulsar powers the well-known Crab Nebula. Here, we describe two separate gamma-ray (photon energy greater than 100 mega–electron volts) flares from this source detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The first flare occurred in February 2009 and lasted approximately 16 days. The second flare was detected in September 2010 and lasted approximately 4 days. During these outbursts, the gamma-ray flux from the nebula increased by factors of four and six, respectively. The brevity of the flares implies that the gamma rays were emitted via synchrotron radiation from peta–electron-volt (1015 electron volts) electrons in a region smaller than 1.4 × 10−2 parsecs. These are the highest-energy particles that can be associated with a discrete astronomical source, and they pose challenges to particle acceleration theory.

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