FERMI SPACE TELESCOPE LOOKS AT UNEXPLORED ELECTROMAGNETIC RANGE

The following excerpt is from the NASA website:

“WASHINGTON -- After more than three years in space, NASA's Fermi
Gamma-ray Space Telescope is extending its view of the high-energy
sky into a largely unexplored electromagnetic range. Today, the Fermi
team announced its first census of energy sources in this new realm.

Fermi's Large Area Telescope (LAT) scans the entire sky every three
hours, continually deepening its portrait of the sky in gamma rays,
the most energetic form of light. While the energy of visible light
falls between about 2 and 3 electron volts, the LAT detects gamma
rays with energies ranging from 20 million to more than 300 billion
electron volts (GeV).

At higher energies, gamma rays are rare. Above 10 GeV, even Fermi's
LAT detects only one gamma ray every four months.

"Before Fermi, we knew of only four discrete sources above 10 GeV, all
of them pulsars," said David Thompson, an astrophysicist at NASA's
Goddard Space Flight Center in Greenbelt, Md. "With the LAT, we've
found hundreds, and we're showing for the first time just how diverse
the sky is at these high energies."

Any object producing gamma rays at these energies is undergoing
extraordinary astrophysical processes. More than half of the 496
sources in the new census are active galaxies, where matter falling
into a supermassive black hole powers jets that spray out particles
at nearly the speed of light.

Only about 10 percent of the known sources lie within our own galaxy.
They include rapidly rotating neutron stars called pulsars, the
expanding debris from supernova explosions, and in a few cases,
binary systems containing massive stars.

More than a third of the sources are completely unknown, having no
identified counterpart detected in other parts of the spectrum. With
the new catalog, astronomers will be able to compare the behavior of
different sources across a wider span of gamma-ray energies for the
first time.

Just as bright infrared sources may fade to invisibility in the
ultraviolet, some of the gamma-ray sources above 1 GeV vanish
completely when viewed at higher, or "harder," energies.

One example is the well-known radio galaxy NGC 1275, which is a
bright, isolated source below 10 GeV. At higher energies it fades
appreciably and another nearby source begins to appear. Above 100
GeV, NGC 1275 becomes undetectable by Fermi, while the new source,
the radio galaxy IC 310, shines brightly.

The Fermi hard-source list is the product of an international team led
by Pascal Fortin at the Ecole Polytechnique's Laboratoire
Leprince-Ringuet in Palaiseau, France, and David Paneque at the Max
Planck Institute for Physics in Munich.

The catalog serves as an important roadmap for ground-based facilities
called Atmospheric Cherenkov Telescopes, which have amassed about 130
gamma-ray sources with energies above 100 GeV. They include the Major
Atmospheric Gamma Imaging Cherenkov telescope (MAGIC) on La Palma in
the Canary Islands, the Very Energetic Radiation Imaging Telescope
Array System (VERITAS) in Arizona, and the High Energy Stereoscopic
System (H.E.S.S.) in Namibia.

"Our catalog will have a significant impact on ground-based
facilities' work by pointing them to the most likely places to find
gamma-ray sources emitting above 100 GeV," Paneque said.

Compared to Fermi's LAT, these ground-based observatories have much
smaller fields of view. They also make fewer observations because
they cannot operate during daytime, bad weather or a full moon.

"As Fermi's exposure constantly improves our view of hard sources,
ground-based telescopes are becoming more sensitive to lower-energy
gamma rays, allowing us to bridge these two energy regimes," Fortin
added.

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle
physics partnership. Fermi is managed by Goddard. It was developed in
collaboration with the U.S. Department of Energy, with important
contributions from academic institutions and partners in France,
Germany, Italy, Japan, Sweden and the United States.”