Unique gamma burster discovered in our galaxy

17 Jun 2002

NASA astronomers have discovered a new type of object towards the center of our Milky Way galaxy exhibiting a combination of behaviors never before seen in the 35-year history of gamma-ray astronomy. On the first day it was observed, the source produced over 140 powerful bursts of gamma-rays. Since then the object has settled down to a daily rate of about twenty bursts. It is currently the brightest source of hard x-ray/gamma-rays in the sky, according to NASA officials.

The unusual object in the southern sky was discovered in early December 1995 by researchers using an instrument known as the Burst and Transient Source Experiment, aboard NASA's Compton Gamma Ray Observatory spacecraft. Since December 2, the new burster has produced more than 1,000 hard x-ray bursts. The discovery will be announced this week in the scientific journal "Nature" by scientists from NASA's Marshall Space Flight Center, Huntsville, AL; the University of Alabama in Huntsville; the Massachusetts Institute of Technology in Cambridge, MA; and the University of Amsterdam in the Netherlands.

"The properties of this x-ray source are unlike those of any we know," explained project researcher Dr. Chryssa Kouveliotou. "The burst repetition rate makes this phenomenon very different from gamma ray bursts that we have observed several thousand times from throughout the universe. Also, the longer duration and persistent bursting makes the object very different from so-called Soft Gamma Ray Repeaters, which have been observed to burst in short, isolated episodes separated by several years."

This bursting pulsar was later found by Dr. Mark Finger of the Universities Space Research Association at NASA Marshall to be a member of a binary system, performing one full revolution around its low-mass companion every 12 days. "The most likely explanation at this time is that the bursts of x-ray energy may result when the lighter of the pair of stars loses its material by gravitational or magnetic forces to the neutron star," said Kouveliotou.

In related news, NASA has announced it will name the X-Ray Timing Explorer, placed into orbit in December 1995, in honor of a pioneer in the field of x-ray astronomy, Bruno B. Rossi. Among the objects to be studied by RXTE are stellar black holes, neutron stars and quasars.