Fermi discovered a pulsar that emits only in the gamma ray range

The pulsar is located inside a supernova remnant known as CTA1, located about 4,600 light-years from Earth in the direction of the Cepheus constellation.

The corpse of a ten-thousand-year-old star, which rotates about 3 times per second, sends a barrage of gamma rays towards the Earth. This radiation was discovered by NASA's new space telescope, Fermi, which takes pictures in the gamma ray range. This is the first pulsar known to flicker in the gamma ray field.

"This is the first example of a new type of pulsars and it allows us fundamental insight into how these collapsing stars work," says Peter Michelson of Stanford University, principal investigator at the Fermi Wide Field Telescope in Palo Alto, California.

The gamma-ray pulsar is found within the supernova remnant known as CTA1, located about 4,600 light-years from Earth in the direction of the Cepheus constellation. The lighthouse beam-like beam crosses the Earth every 316.86 milliseconds. The pulsar, which was created about ten thousand years ago, emits energy with a power one thousand times that of the sun.

A pulsar is a rapidly spinning neutron star whose collapsing core is what remains after a massive explosion that ended that star's solar phase. Astronomers have so far cataloged close to 1,800 pulsars. Although most were discovered when their pulses were picked up in the radio range, some of these objects also emitted energy in other spectral ranges, including visible light and X-rays. However, the source of CTA 1 pulsates exclusively in the gamma ray range.

"We believe that the region responsible for the emission of gamma rays is much wider than the one responsible for pulses in the lower energy radiation frequencies," explains team member Alice Harding from NASA's Goddard Center in Maryland. "The radio pulses are almost certainly not transmitted towards Earth, so we would never see it, but the wider infrared pulses come our way."

The scientists believe that CTA 1 is only the first of a large population of similar objects. "The Wide Field Telescope provides us with a unique means of locating the pulsar population in the galaxy, and revealing objects that we would not have known existed in any other way," said Fermi scientist team member Steve Ritz, also from Goddard.

“The pulsar in CTA 1 is not located at the center of the receding gas envelope. Supernova explosions can also be asymmetric, sometimes they get a boost that sends the neutron star into space. Based on the age of the remains and the distance of the pulsar from the center, the astronomers believe that the neutron star is moving at a speed of one and a half million kilometers per hour, a typical speed.

The Fermi Wide Field Telescope scans the entire sky every three hours and detects photons with energy 20 million to 300 million times more powerful than visible light. The instrument picks up a burst of gamma rays every minute from CTA 1, enough to gather data about the neutron star's pulsing behavior, the duration of its self-rotation, and its rate of deceleration.

The pulsar beams are due to the fact that the neutron star is surrounded by a strong magnetic field and it is also spinning rapidly. A stream of charged particles comes out of the magnetic poles at a speed close to the speed of light and these create the gamma rays that Fermi sees. Because the pulsations are caused by the neutron star's rotation, they gradually slow the pulsar's rotation rate. In the case of CTA 1 the duration of the rotation increases by about a second, every 87 thousand years.

"These observations show the power of the Wide Field Telescope," Michelson said. "It is so sensitive that we could only discover the new type of object by observing gamma ray bursts." An article about the new poster appeared in the October 16 issue of Science Express - the fast reporting site of Science magazine.

For information on the NASA website

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