Gamma Ray Telescope Finds First "Invisible" Pulsar

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"We now think they're these gamma ray-only pulsars," she said. "We have many other sources that EGRET didn't detect because the sensitivity wasn't as good."

The newly discovered pulsar is positioned within the remains of a young supernova called CTA 1, which exploded around 10,000 years ago.

The Large Area Telescope aboard Fermi, which scans the entire sky every three hours in its search for gamma ray sources, saw roughly a gamma ray a minute coming from CTA 1.

(Related: "New Probe's First Gamma Ray Sky Map Unveiled" [August 26, 2008].)

Based on this rate of gamma ray pulses, scientists were able to piece together the neutron star's pulsing behavior and rotation period.

Pulsars slow down and stop emitting radiation beams within a hundred million years or less after their creation, Harding added. In the case of the CTA 1 pulsar, the spin is slowing by about a second every 87,000 years.

Harding and colleagues describe the new pulsar in a paper appearing online in the October 16 edition of Science Express.

Unlocking the Vault

Patrick Slane, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics who is not a study co-author, called the new work an "exciting paper."

He and others had detected the CTA 1 supernova remnant and a whisper of the neutron star using x-rays but hadn't been able to find the telltale pulsations.

"A measurement of the pulse period unlocks the vault containing all of the information about the energetics of the system," Slane wrote in an email. "So this is hugely important."

Study co-author Harding pointed out that scientists don't yet understand the basic physics of pulsars, including the way they send out beams in the first place.

Using Fermi, she said, "we will really revolutionize that."

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