NASA | Fermi Detects Gamma Rays from a Solar Flare

Uploaded by NASAexplorer on 12.06.2012

Narrator: In early March, 2012, a powerful X 5.4
flare erupted on the sun. The blast was observed by the fleet of spacecraft
dedicated to monitoring our one unlikely addition:
NASA's Fermi Gamma-ray Space Telescope.
For Fermi, which detects high-energy gamma rays, the sun is almost never
the brightest steady source in the sky. That distinction is reserved for the
Vela pulsar. But on March 7, the sun outshone
everything else Fermi could see. Thanks to the big flare, the sun had become
the brightest object in the gamma-ray sky. Due to the keen angular
resolution of Fermi's Large Area Telescope, for the first time scientists were
able to narrow down the position of the high-energy gamma-ray emission to a part of the
sun's disk. This gives scientists greater confidence that the gamma rays
come from the same region as the solar flare seen in other wavelengths.
During this event, the LAT detected the highest-energy light ever recorded
from a solar flare. The gamma-rays peaked at 4 billion electron
volts, or 2 billion times the energy of visible light. With
Fermi recording high-energy gamma-ray emission for 20 hours after the event,
the March 7th flare also set a duration record.
Several mechanisms are behind this gamma-ray activity. Flares are thought
to arise when strong magnetic fields undergo a process called "reconnection" and
release pent-up energy. A sudden blast accelerates charged particles,
some of which leave the sun, while others are driven toward it's visible surface.
Many of these accelerated particles are
protons. When they collide with gas in the sun's
atmosphere or surface, the interaction creates a particle called a pion,
which quickly decays into two gamma rays.
These observations herald Fermi's arrival as a solar observatory,
a powerful new tool for understanding the sun as it approaches its maximum
period of activity.