Donald L. Savage Headquarters, Washington, D.C. August 24, 1994 (Phone: 202/358-1547) Mike Finneran Goddard Space Flight Center, Greenbelt, Md. (Phone: 301/286-5565) Jim Sahli Marshall Space Flight Center, Huntsville, Ala. (Phone: 205/544-6528) RELEASE: 94-140 COMPTON GAMMA-RAY OBSERVATORY FINDS BRIGHT NEW X-RAY SOURCE An unusually bright X-ray source -- one of the three brightest in the sky -- has been discovered in the southern constellation Scorpius by an instrument aboard NASA's Compton Gamma-Ray Observatory. The new source, which was discovered on July 27 by the Burst and Transient Source Experiment (BATSE), has been named X-ray Nova Scorpii, or GRO J1655-40. X-ray novae such as the one just discovered are thought to be caused by matter spilling from a normal star onto a black hole, which are collapsed stars so dense that not even light can escape them. About 10 such novae have been discovered in the past 30 years. "We are anxious to determine whether the new source is a black hole, a pulsar (a spinning star that emits signals in short, regular bursts), or perhaps even a new type of object," said Dr. B. Alan Harmon of NASA's Marshall Space Flight Center, Huntsville, Ala. Harmon leads the research team analyzing data from a Marshall-managed BATSE instrument. "The X-ray emission from the new source rivals that of two other dominant X-ray sources in the sky, the Crab Nebula and Cygnus X-1. The new object poses several puzzling questions for astrophysicists. For example, Nova Scorpii had an unusually rapid rise to maximum brightness, which may put significant constraints on theories of how X-rays are produced in such objects," Harmon said. "During an X-ray nova outburst, it is thought matter from a normal star spills onto a disk of matter surrounding a companion black hole, causing the disk to heat up dramatically. How this happens, however, is not well understood, and the rapid rise to maximum brightness of Nova Scorpii adds to the mystery," Harmon said. In addition, a property conspicuously absent in Nova Scorpii is a rapid flickering in the intensity of the source. Such flickering is typical of other X-ray novae. Scientists speculate that the lack of flickering may be because the central source that would produce it is obscured, preventing a view deep into the X-ray producing region. Discovery of the new X-ray object has been announced to astronomers around the world so more detailed observations may be made. Another instrument on the Compton Observatory, the Oriented Scintillation Spectrometer Experiment, already has made preliminary spectral observations and obtained an improved location for the object. Meanwhile, plans are being made for other orbiting spacecraft to observe the X-ray source and a search is underway by astronomers in the Southern Hemisphere to find an optical counterpart to Nova Scorpii. "We are especially pleased that BATSE detected the X-ray source. Now, the entire capabilities of the observatory can be used to study this new and exciting object," said Compton Observatory Project Scientist Dr. Neil Gehrels of the Goddard Space Flight Center, Greenbelt, Md. Goddard manages the Compton Observatory for NASA's Office of Space Science, Washington, D.C. The observatory was placed into orbit around the Earth by the Space Shuttle Atlantis in April 1991. - end -