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Pure Gamma-Ray Pulsar Found

October 17, 2008

The Fermi Gamma-Ray Space Telescope—formerly known as GLAST (Gamma-ray Large Area Space Telescope)—has found the first pulsar that is detected only through its gamma-rays.  This pulsar was found in an observation of the supernova remnant CTA 1, which is in the constellation Cepheus.  The paper describing the detection is published in Science Express.

Photograph of the supernova remnant CTA 1.

An image of the supernova remnant CTA 1.  The gamma-ray pulsar, which is invisible in this image, is offset from the center of the spherical shell by half a radius in the direction of the top of the image.  Courtesy NASA/S. Pineault, DRAO.

Pulsars are strongly-magnitized, rapidly-spinning neutron stars that convert their spin energy into radiation.  They are created in supernovae explosions, and many are found at the centers of supernova remnants.  Most spin-powered pulsars are strong radio emitters, and most are found through their radio emission.  Often these radio pulsars are also sources of pulsed optical light, x-rays, and gamma-rays.  A handful of pulsars, however, are found by their x-ray and gamma-ray emission, and their radio emission is weak or undetectable.

The new pulsar found by Fermi has a very young characteristic age of 104 years, with a rate of spin of 316.86 milliseconds. The age is consistent with the age of the supernova remnant.  The pulsar's luminosity is about 1,000 times the Sun's.  The pulsar is located at a synchrotron nebula within the supernova remnant.  A synchrotron nebula is a region of radio emission by hot electrons in a magnetic field; such nebulae, most strikingly the Crab nebula, are powered by pulsars.  The principal scientist for Fermi touted the new pulsar as a new class of objects discovered by a new instrument, although the description of the pulsar resembles an extreme example of the high-energy spin-powered pulsars already seen.

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