Don Savage Headquarters, Washington, DC April 4, 1996 (Phone: 202/358-1547) Steve Roy Marshall Space Flight Center, Huntsville, AL (Phone: 205/544-0034) Donna Drelick Goddard Space Flight Center, Greenbelt, MD (Phone: 301/286-7995) Brooks McKinney TRW Space & Electronics Group, Redondo Beach, CA (Phone: 310/814-8177) RELEASE: 96-65 THE COMPTON GAMMA RAY OBSERVATORY MARKS FIVE YEARS IN SPACE NASA's Compton Gamma Ray Observatory marks its five year anniversary April 5. Launched in 1991 from the Space Shuttle Atlantis, the Compton Observatory is the second in a series of Great Observatories and is the heaviest spacecraft ever deployed by a Shuttle. The spacecraft, named for American Nobel Prize- winning physicist Arthur Holly Compton, is the first satellite dedicated to making gamma ray observations across a broad spectrum of energies. Scientists believe that gamma rays, which are an invisible highly energetic form of radiation, are emitted during violent cosmic events such as supernovae, quasars, pulsars and black holes. NASA scientists are using the Compton Observatory to create a comprehensive map of celestial gamma ray sources. "The spacecraft and instruments have been remarkably reliable, and all four instruments are performing near their design specification," said Dr. Neil Gehrels, Project Manager of the Compton Observatory at the Goddard Space Flight Center (GSFC), Greenbelt, MD. "Thus far Compton has made extraordinary discoveries, and the science team is looking forward to more discoveries as the observatory begins its sixth year in space." -more- -2- While tape recorders on the observatory failed early in the mission, their failure turned out to be an unexpected scientific bonus. Instead of storing data on the spacecraft and retrieving it every four hours, scientists can now receive a 24-hour-a-day stream of data in real time. This allows scientists to quickly begin monitoring outbursts of energy, such as on Jan. 31, 1993, when the satellite detected the highest energy gamma rays ever seen in a burst, an event dubbed the "Super Bowl Burst." In December 1995, the Compton Observatory detected the sudden appearance of a never-before-seen type of object which bursts and pulses at the same time. This bursting pulsar is currently the brightest source of gamma rays and X-rays in the sky. Among the Compton Observatory's most significant discoveries: ¥ Gamma ray bursts are evenly distributed across the sky, which suggests that gamma rays are coming from the farthest reaches of space and not just from our own Milky Way galaxy, as astronomers once believed; ¥ Gamma ray quasars, a new class of high-energy gamma ray sources, in active galactic nuclei, the bright and active central cores of some galaxies; ¥ A source of gamma rays and X-rays that exhibits the behavior of both a pulsar and a burster; ¥ Gamma ray bursts and solar flares are accompanied not only by a release of low-energy gamma rays over a relatively short period of time (tenths of seconds to seconds) but also by a release of high energy gamma rays over a longer period of time; ¥ Gamma-ray emitting active galactic nuclei, known as Seyfert galaxies, emit most of their gamma-rays at lower energies than previously thought. This is important evidence that such objects may be the source of diffuse gamma rays; ¥ A threefold increase, from two to six, in the number of pulsars known to emit gamma rays (pulsars are rotating neutron stars that spin very rapidly and produce beams of radio energy that appear to flash on and off), among more than 500 known radio pulsars. This gives astronomers a greater opportunity to understand why some pulsars emit gamma rays and others do not; ¥ The first detection of the presence and nuclear decay of cobalt 57, an isotope of cobalt thought to have been created during the explosion of a star known as Supernova 1987A. This detection helps confirm the nucleosynthesis theory of how elements heavier than hydrogen and helium are formed and distributed in our galaxy via the evolution of stars; -more- -3- ¥ That the energy created by the mutual destruction of electrons and positrons in our galaxy is concentrated in a bulge around the center of the galaxy, with a second component extending out along the plane of our galaxy; ¥ The first mapping of the distribution of a radioactive isotope called Aluminum 26 within the Milky Way Galaxy. The instruments on CGRO detect the isotope by measuring gamma ray energy associated with its radioactive decay. Scientists believe that this energy distribution, which has proven to be "patchy" rather than smooth, holds clues to understanding nucleosynthesis in our galaxy; ¥ The detection of the gamma ray energy given off by interactions between cosmic rays and carbon 12 and oxygen 16 nuclei. The energy "signature" associated with the excitation of these molecules and subsequent emission of gamma rays help scientists identify the types of matter and nuclear processes occurring within the region of the Milky Way galaxy known as the Orion Arm. The Compton Observatory is currently in a circular, 240-mile-high orbit inclined 28.5 degrees to the equator. NASA is considering reboosting the 17-ton, low-Earth- orbiting satellite to a higher orbit that would allow the spacecraft to continue to track the gamma ray universe well into the next century. "The Compton Observatory has vastly increased our understanding of some of the most violent events in the universe," said Compton Program Manager Dr. Alan Bunner. "We have every reason to believe we will continue to be amazed by its discoveries in the future." The Compton Observatory is managed for NASA's Office of Space Science, Washington, DC. Information on the spacecraft is available on the Internet at: http://enemy.gsfc.nasa.gov/cossc/cgro.html - end - NASA press releases and other information are available automatically by sending an Internet electronic mail message to domo@hq.nasa.gov. In the body of the message (not the subject line) users should type the words "subscribe press- release" (no quotes). The system will reply with a confirmation via E-mail of each subscription. A second automatic message will include additional information on the service. NASA releases also are available via CompuServe using the command GO NASA.