NASA's Fermi Gamma Ray Telescope has detected gamma rays emanating from flares on the back side of our sun
An international science team says NASA's Fermi Gamma-ray Space Telescope has observed high-energy light from solar eruptions located on the far side of the sun, which should block direct light from these events.
This apparent paradox is providing solar scientists with a unique tool for exploring how charged particles are accelerated to nearly the speed of light and move across the sun during solar flares.
"Fermi is seeing gamma rays from the side of the sun we're facing, but the emission is produced by streams of particles blasted out of solar flares on the far side of the sun," said Nicola Omodei, a member of the Fermi research team at Stanford University's Hansen Experimental Physics Lab in California. "These particles must travel some 300,000 miles within about five minutes of the eruption to produce this light."
Omodei presented the findings on January. 30, 2017 at the American Physical Society meeting in Washington, and a paper entitled Fermi-LAT Observations of High-energy Behind-thd-limb Solar Flares, describing the results were published online in The Astrophysical Journal on Jan. 31.
"Observations by Fermi's LAT continue to have a significant impact on the solar physics community in their own right, but the addition of STEREO observations provides extremely valuable information of how they mesh with the big picture of solar activity," said Melissa Pesce-Rollins, a researcher at the National Institute of Nuclear Physics in Pisa, Italy, and a co-author of the paper.
The hidden flares occurred Oct. 11, 2013, and Jan. 6 and Sept. 1, 2014. All three events were associated with fast coronal mass ejections (CMEs), where billion-ton clouds of solar plasma were launched into space. The CME from the most recent event was moving at nearly 5 million miles an hour as it left the sun. Researchers suspect particles accelerated at the leading edge of the CMEs were responsible for the gamma-ray emission.
Large magnetic field structures can connect the acceleration site with distant part of the solar surface. Because charged particles must remain attached to magnetic field lines, the research team thinks particles accelerated at the CME traveled to the sun's visible side along magnetic field lines connecting both locations. As the particles impacted the surface, they generated gamma-ray emission through a variety of processes. One prominent mechanism is thought to be proton collisions that result in a particle called a pion, which quickly decays into gamma rays.
In its first eight years, Fermi has detected high-energy emission from more than 40 solar flares. More than half of these are ranked as moderate, or M class, events. In 2012, Fermi caught the highest-energy emission ever detected from the sun during a powerful X-class flare, from which the LAT detected highenergy gamma rays for more than 20 record-setting hours.
NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.
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For More Information:
NASA Goddard Media Studios: Fermi Sees Gamma Rays from Farside Solar Flares (January 30, 2017)
National Geographic Online Story: Our Sun Produces Bizarre Radiation Bursts—Now NASA Knows Why (February 14, 2017)
Published Paper: Fermi-LAT Observations of High-energy Behind-the-limb Solar Flares by Ackermann et. al. January 31, 2017, The Astrophysical Journal, Volume 835, Number 2
Read the original article at NASA Goddard Space Flight Center
