Fermi and SDO Have Synergy With Sun Energy
During a recent solar flare, the Sun appeared 1000 times brighter in gamma rays than usual, as observed by the Fermi Gamma-ray Space Telescope. The flare was also observed by the Solar Dynamics Observatory, another space mission in which the Stanford community is heavily involved.
The dramatic increase in solar gamma-ray output is seen in these all-sky maps from the Fermi-LAT from two consecutive days in March 2012. For around 20 hours, the Sun was the brightest object in the gamma-ray sky.
In its relatively short life so far, the Fermi Gamma-ray Space Telescope, and its Large Area Telescope (LAT) gamma-ray detector have revolutionized high energy astrophysics. The LAT has seen hundreds of distant active galaxies, some up to a billion light years away, where the interaction of a supermassive black hole and infalling matter create giant jets of particles and radiation, more than a hundred pulsars and binary objects which light up our Galaxy in gamma rays like cosmic lighthouses, and the collective diffuse particle smashing in a number of nearby galaxies as well as our own. To the LAT's catalog of celestial wonders we can also add one closer to home - the Sun.
On March 7, the Fermi-LAT saw the gamma-ray output of the Sun increase by a factor of a thousand from its normally quite modest level. On that day the Sun briefly became by far the brightest object in the gamma-ray sky, outshining - from Fermi's perspective in Earth orbit - even monstrous distant blazars which output a trillion trillion times the Sun's energy. The data - analyzed by the LAT team in an effort led by KIPAC scientist Nicola Omodei - showed that the Sun's gamma-ray tantrum lasted 20 hours, almost three times longer than any previous observed solar gamma-ray event, including the one seen by Fermi in March of 2011. This year's sharp increase coincided with a solar flare observed in ultraviolet light on the surface of the Sun by NASA's Solar Dynamics Observatory (SDO), in which the Stanford Solar Physics group is heavily involved, with Stanford Professor Phil Scherrer as the Principle Investigator of SDO's Heliospheric Magnetic Imager instrument.
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, producing both pions, which emit gamma rays when they decay, and gamma rays directly when high energy electrons interact with other charged particles. This emission via high energy collisions mimics particle physics processes seen in collider experiments on Earth, although on a much larger scale. The X-ray and ultraviolet light output from solar flares, which is much more commonly observed, results from different processes, such as the glowing of the hot material in the case of ultraviolet. That this recent dramatic flare was seen both in gamma-rays with Fermi and also in ultraviolet light by SDO will make it extremely useful in the ongoing quest to understand solar flares and their connection to the solar activity cycle and space weather. In this regard it is handy that expertise for both the Fermi-LAT and SDO are available within the Stanford community.
The Fermi-LAT was designed and built by an international collaboration with members from France, Italy, Japan, Sweden and the United States. SLAC managed the construction and integration of the instrument and KIPAC is the lead for ongoing operation of the instrument. Research at KIPAC is supported by the Department of Energy, the Kavli Foundation, the National Aeronautics and Space Administration, the National Science Foundation and Stanford University, as well as private donors. We are grateful to each of these sponsors for their continued interest and support.
Tidbit Author: Jack Singal