28 Aug 2008
NASA's newest observatory, the Gamma-Ray Large Area Space Telescope (GLAST), has begun its mission of exploring the universe in high-energy gamma rays. The spacecraft and its revolutionary instruments passed their orbital checkout with flying colors.
NASA announced today that GLAST has been renamed the Fermi Gamma-ray Space Telescope. The new name honors Prof. Enrico Fermi (1901 - 1954), a pioneer in high-energy physics. "Fermi was the first to suggest how cosmic particles could be accelerated to high speeds, and this work provides the foundation for understanding the powerful phenomena his namesake will observe," says Paul Hertz, Chief Scientist for the Science Missions Directorate at NASA Headquarters in Washington.
Scientists expect Fermi will discover many new pulsars in our own galaxy, reveal powerful processes near supermassive black holes at the cores of thousands of active galaxies, and enable a search for signs of new physical laws.
According to the ASI Commissioner Enrico Saggese, "NASA's choice proves the excellence of Italian science". "It is the proof - ads the ASI vice Commissioner Piero Benvenuti - of the contribution from Italian industries and scientists in the very important field of High Energy Astrophysics. The ASI satellites Beppo SAX and AGILE are in fact fundamental precursor for the GLAST mission, now Fermi".
For two months following the spacecraft's June 11 launch, scientists tested and calibrated its two instruments, the Large Area Telescope (LAT) and the GLAST Burst Monitor (GBM). "What impressed me the most is that everything went by the book," says Peter Michelson, LAT principal investigator at Stanford University, Calif. "We're elated." The LAT has already verified sources found by other gamma-ray detectors -- and discovered more.
The LAT team today unveiled an all-sky image showing the glowing gas of the Milky Way, blinking pulsars, and a flaring galaxy billions of light-years away. The map combines 95 hours of the instrument's "first light" observations. A similar image, produced by NASA's now-defunct Compton Gamma-ray Observatory, took years of observations to produce.
Gas and dust in the plane of the Milky Way glows in gamma rays thanks to collisions with accelerated nuclei called cosmic rays. The famous Crab Nebula and Vela pulsars also shine brightly at these wavelengths. These fast-spinning neutron stars, which form when massive stars die, were originally discovered by their radio emissions. The image's third pulsar, named Geminga and located in Gemini, is not a radio source and was discovered by an earlier gamma-ray satellite. Fermi is expected to discover many more radio-quiet pulsars, providing key information about how these exotic objects work.
A fourth bright spot in the LAT image lies some 7.1 billion light-years away, far beyond our galaxy. This is 3C 454.3 in Pegasus, a type of active galaxy called a blazar. It's now undergoing a flaring episode that makes it especially bright.
The LAT scans the entire sky every 3 hours when operating in survey mode, which will occupy most of the telescope's observing time during the first year of operations. These fast snapshots will let scientists monitor rapidly changing sources.
The instrument detects photons with energies ranging from 20 million electron volts to over 300 billion electron volts. The high end of this range, which corresponds to energies more than 5 million times greater than dental X-rays, is little explored.
The spacecraft's secondary instrument, the GBM, spotted 31 gamma-ray bursts in its first month of operations. These high-energy blasts occur when massive stars die or when orbiting neutron stars spiral together and merge.
"Our job is to see the whole sky and identify burst locations well enough to tell the LAT where to look," says Charles Meegan, GBM's principal investigator at NASA's Marshall Space Flight Center in Huntsville, Ala. "We're operational now, and as time goes on we'll get even better by reducing errors in the location measurement."
The GBM is sensitive to less energetic gamma rays (8,000 to 30 million electron volts) than LAT. Bursts seen by both instruments will provide an unprecedented look across a broad gamma-ray spectrum, enabling scientists to peer into the processes powering these events.
NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the U.S.
Captions and credits:
Annotated all-sky image (a link to the non-annotated version should be included): This all-sky view from the Fermi Gamma-ray Space Telescope reveals bright emission in the plane of the Milky Way (center), bright pulsars, and supermassive black holes. NASA/DOE/International LAT Team
Orthographic map/animation: Astronomers wrapped the Fermi Gamma-ray Space Telescope's first all-sky map over a sphere to produce this view of the gamma-ray universe. NASA/DOE/International LAT Team
Vela pulsar/animation: This animated close-up shows the Vela pulsar, which beams radiation every 89 milliseconds as it spins. The pulses are shown slowed by 20 times. NASA/DOE/International LAT Team
Gamma-ray burst light curve: The GLAST Burst Monitor detected this gamma-ray burst on July 23, 2008. A typical burst associated with a star's destruction, the event shows multiple brightness peaks. NASA/MSFC/GBM Team