NASA'S Fermi Detects The Highest-Energy Light From A Solar Flare

June 11, 2012

J. D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

RELEASE: 12-193

NASA'S FERMI DETECTS THE HIGHEST-ENERGY LIGHT FROM A SOLAR FLARE

WASHINGTON -- During a powerful solar blast on March 7, NASA's Fermi
Gamma-ray Space Telescope detected the highest-energy light ever
associated with an eruption on the sun. The discovery heralds Fermi's
new role as a solar observatory, a powerful new tool for
understanding solar outbursts during the sun's maximum period of
activity.

A solar flare is an explosive blast of light and charged particles.
The powerful March 7 flare, which earned a classification of X5.4
based on the peak intensity of its X-rays, is the strongest eruption
so far observed by Fermi's Large Area Telescope (LAT). The flare
produced such an outpouring of gamma rays -- a form of light with
even greater energy than X-rays -- that the sun briefly became the
brightest object in the gamma-ray sky.

"For most of Fermi's four years in orbit, its LAT saw the sun as a
faint, steady gamma-ray source thanks to the impacts of high-speed
particles called cosmic rays," said Nicola Omodei, an astrophysicist
at Stanford University in California. "Now we're beginning to see
what the sun itself can do."

Omodei described Fermi's solar studies to journalists today at the
220th meeting of the American Astronomical Society in Anchorage,
Alaska.

At the flare's peak, the LAT detected gamma rays with two billion
times the energy of visible light, or about four billion electron
volts (GeV), easily setting a record for the highest-energy light
ever detected during or immediately after a solar flare. The flux of
high-energy gamma rays, defined as those with energies beyond 100
million electron volts (MeV), was 1,000 times greater than the sun's
steady output.

The March flare also is notable for the persistence of its gamma-ray
emission. Fermi's LAT detected high-energy gamma rays for about 20
hours, two and a half times longer than any event on record.

Additionally, the event marks the first time a greater-than-100-MeV
gamma-ray source has been localized to the sun's disk, thanks to the
LAT's keen angular resolution.

Flares and other eruptive solar events produce gamma rays by
accelerating charged particles, which then collide with matter in the
sun's atmosphere and visible surface. For instance, interactions
among protons result in short-lived subatomic particles called pions,
which produce high-energy gamma rays when they decay. Nuclei excited
by collisions with lower-energy ions give off characteristic gamma
rays as they settle down. Accelerated electrons emit gamma rays as
they collide with protons and atomic nuclei.

Fermi's LAT scans the entire sky every 3 hours, looking for gamma rays
with energies ranging from 20 MeV to more than 300 GeV. Its high
sensitivity and wide field of view make the LAT an excellent tool for
solar monitoring.

Another Fermi instrument, the Gamma-ray Burst Monitor (GBM), observes
the entire sky not blocked by the Earth at any given moment. Designed
to detect light at energies from 8,000 eV to 40 MeV, the GBM's
complementary capabilities give scientists access to a lower, but
overlapping energy range where solar phenomena produce interesting
features.

Both instruments observed a strong, but less powerful solar flare on
June 12, 2010.

"Seeing the rise and fall of this brief flare in both instruments
allowed us to determine that some of these particles were accelerated
to two-thirds of the speed of light in as little as 3 seconds," said
Michael Briggs, a member of GBM team at the University of Alabama in
Huntsville.

Solar eruptions are on the rise as the sun progresses toward the peak
of its roughly 11-year-long activity cycle, now expected in mid-2013.


"Merged with available theoretical models, Fermi observations will
give us the ability to reconstruct the energies and types of
particles that interact with the sun during flares, an understanding
that will open up whole new avenues in solar research," said Gerald
Share, an astrophysicist at the University of Maryland in College
Park.

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

For images related to this finding, visit:

http://www.nasa.gov/fermi


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