Magazine article Science News

Shocking Signals from Crab Nebula: Gamma-Ray Flares from Supernova Remnant Baffle Astronomers

Magazine article Science News

Shocking Signals from Crab Nebula: Gamma-Ray Flares from Supernova Remnant Baffle Astronomers

Article excerpt

Radiation from the Crab nebula supernova remnant is believed to be so constant that astronomers use it as a standard candle with which to measure the energetic radiation of other astronomical sources.

That's why researchers are astounded that two spacecraft recently recorded giant gamma-ray hiccups from the Crab, the remnants of a stellar explosion 6,500 light-years from Earth.

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For three days beginning September 19, the intensity of the Crab's gamma-ray radiation suddenly became two to three times stronger, scientists with the Italian Space Agency's AGILE telescope reported. The Fermi Gamma-raySpace Telescope detected an even larger increase over roughly the same time period.

Both teams also announced they had found evidence of previous similar flares. AGILE recorded an outburst in fall 2007, and Fermi spotted one in February 2009.

The suspected source of the energetic flares, along with steadier radiation emanating from the nebula, is blizzards of electrons spit out by the Crab's pulsar--the rapidly rotating, exploded cinder of a star that lies at the nebula's center. Figuring out exactly how the electrons got revved up to energies of at least [10.sup.15] electron volts--the most energetic charged particles ever associated with a distinct astrophysical object--for so short a time has astronomers scratching their heads.

Finding the flares "was a shock," said AGILE team member Marco Tavani of the INAF-IASF in Rome and the University of Rome Tor Vergata, who spoke about the findings on December 6 and 7. …

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