Crab Nebula Produces Gamma-ray Flares

For many years, astronomers have considered the Crab Nebula to be one of the steadiest light sources on the sky, so much so that it was used to calibrate various instruments for in-depth studies of the Universe. Now, studies reveal three flare-ups in the nebula, challenging established knowledge.

The space object apparently generated three surprising gamma-ray flares recently, say astrophysicists, who are currently struggling to come to terms with why that happened. The events covered the span of a few days, observations have shown.

Flares were observed on the nebula in October 2007 and September 2010 (with the AGILE satellite operated by the Italian Space Agency) and in February 2009 by the Fermi Gamma-ray Space Telescope, which is operated by NASA.

Data collected by AGILE were processed by astronomers at the INAF-IASF (Istituto Nazionale di Astrofisica-Istituto di Astrofisica Spaziale e Fisica Cosmica), in Rome, who were led by Marco Tavani.

The expert is also the lead author of two new papers detailing the discoveries, which were published in the January 7 issue of the esteemed journal Science. The Fermi study was led by SLAC National Accelerator Laboratory expert Stefan Funk and Rolf Buehle.

SLAC is housed at the Stanford University. “Our belief of a stable Crab got smashed completely – now we have to think again,” astronomer Marco Tavani explains.

“We had always thought we understand essentially what is going on in the Crab Nebula, but obviously these flares we didn't expect,” Funk goes on to say, quoted by Space.

One of the reasons why the Crab Nebula was not expected to flare up the way it did is its very structure. At its core lies a pulsar, which is basically a fast-spinning neutron star that emits a constant flow of radiation through its poles.

“It's still a real mystery what is the ultimate cause,” Tavani says of the reasons why the flare-ups occur. They are dimmer in intensity and brightness than gamma-ray bursts (GRB). The mystery is deepened by the fact that no other nebula has ever been observed to emit such gamma-ray flares.

“It's essentially telling us something new about how particles are accelerated in astrophysical objects, in particular in these nebulae,” Funk explains.

“The ultimate goal of the studies is to really understand the process of particle acceleration. This would be really great for models and theories that can address how particles are accelerated to these very large energies,” Tavani concludes.