Neutron star reveals split personality

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By Roger Snodgrass

Distant explosions behaving strangely have created a buzz in the astronomical community and may resolve a cosmic case of mistaken identity.


Two kinds of flaring stars, Anomolous X-Ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) may actually be the same thing.


“It’s like learning the giant beasts who leap out of the ocean and splash down on the surface are the same as the ones you have heard singing in the depths,” said David Palmer, a Los Alamos astrophysicist who develops software for detecting gamma-ray bursts in the universe.


NASA announced Tuesday that a gamma-ray burst some 30,000 light years away has been seen flaring up for several days now in a remarkable fashion.


An object in the same vicinity of the constellation Norma in the southern hemisphere had been identified over the last couple of years as a source of pulsing X-rays and radio signals.


Then in Oct. 2008, the Burst Alert Telescope (BAT) aboard NASA’s Swift satellite reported about 20 bursts of gamma rays.


Palmer, is the principal investigator and for the software that operates BAT, which also uses an imaging technology developed at Los Alamos National Laboratory called coded-aperture imaging.


Nancy Ambrosiano in the LANL Communications Office forwarded an email from Palmer Tuesday that outlined his steps in realizing that the two objects were almost certainly one and the same.


Anomalous X-Ray Pulsars, he described as emitting X-rays brightening and dimming in a regular cycle every few seconds; and Soft Gamma Repeaters  produce brief, bright, irregular flashes of higher energy gamma rays.


“The more we learned about these two categories, the more similarities we found: A few AXPs were seen to produce a few weak flashes, and by looking intently at the flashing SGRs, we could see periodic brightening and dimming in X-rays,” he said.  “It appeared that both types of objects were 'magnetars', a star that has crushed itself into a ball a dozen miles across, with a ludicrously-strong magnetic field.”


NASA’s announcement said magnetars have the strongest magnetic fields of any known object in the universe and they get their powerful flares by tapping into a tremendous well of energy in those fields.


When the BAT signaled twenty bursts of gamma rays, Palmer thought the astronomical community had discovered a new SGR, until they realized there was already a known AXP at that location.


“And then on Jan. 22 the object really opened up with hundreds of bursts, some of them a thousand times brighter in gamma-rays than any steady source in the sky,” Palmer said.


“There is now no doubt that this Anomalous X-ray Pulsar is also a Soft Gamma Repeater.”


Now that it has revealed its alter ego, NASA has catalogued it as SGR-J1550-5418, only the sixth Soft Gamma Repeater that has been discovered. It was clocked at 2.07 rotations per second, which makes it first in that category.