First pulsar discovered to “pulse” only in gamma-rays

William Atkins
Friday, 17 October 2008 19:16

Science - Space

The Science Express abstract states, “The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1.”

And, “The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 ms, a period derivative of 3.614 x 10-13 s s-1. Its characteristic age of 104 years is comparable to that estimated for the SNR. It is conjectured that most unidentified Galactic gamma ray sources associated with star-forming regions and SNRs are such young pulsars.”

Stanford University astronomer Peter Michelson, the principal investigator for Fermi’s Large Area Telescope, states, “This is the first example of a new class of pulsars that will give us fundamental insights into how these collapsed stars work.” [NASA]

This pulsar, a collapsed star that has formed into a neutron star and spins very rapidly, formed about 10,000 years ago. It emits about one thousands times more energy than our Sun.

NASA scientist Alice Harding, from the Goddard Space Flight Center (Greenbelt, Maryland), states, “We think the region that emits the pulsed gamma rays is broader than that responsible for pulses of lower-energy radiation. The radio beam probably never swings toward Earth, so we never see it. But the wider gamma-ray beam does sweep our way."

Fermi project scientist Steve Ritz, from Goddard, states, "The Large Area Telescope provides us with a unique probe of the galaxy's pulsar population, revealing objects we would not otherwise even know exist.” [NASA]

The NASA article goes on to say, “The pulsar in CTA 1 is not located at the center of the remnant's expanding gaseous shell. Supernova explosions can be asymmetrical, often imparting a "kick" that sends the neutron star careening through space. Based on the remnant's age and the pulsar's distance from its center, astronomers believe the neutron star is moving at about a million miles per hour -- a typical speed.”

And, “Fermi's Large Area Telescope scans the entire sky every three hours and detects photons with energies ranging from 20 million to more than 300 billion times the energy of visible light. The instrument sees about one gamma ray every minute from CTA 1, enough for scientists to piece together the neutron star's pulsing behavior, its rotation period, and the rate at which it is slowing down.”

For images and animations associated CTA-1, please go to the NASA website http://www.nasa.gov/fermi.