Gamma Rays!

Fermi_LAT_GRB_673Just after 07:47 UTC last Saturday, the Gamma-ray Burst Monitor (GBM) aboard the Fermi satellite triggered on an eruption of high-energy light in the constellation Leo. Click on the image to see an animation showing a more detailed Fermi Large Area Telescope view. GRB 130427A produced the highest-energy light ever detected from gamma ray burst. The sequence shows high-energy (100 MeV to 100 GeV) gamma rays from a 20-degree-wide region of the sky starting three minutes before the burst to 14 hours after. After a one-second spike, the burst’s output remained relatively quiet for the next 15 seconds while Fermi‘s GBM showed bright, variable lower-energy emission. Then the burst re-brightened in the LAT over the next few minutes and remained bright for almost half a day. The record-setting blast of gamma rays came from a dying star in a distant galaxy roughly 3.6 billion light-years away.

Fermi’s Large Area Telescope (LAT) recorded one gamma ray with an energy of at least 94 billion electron volts (GeV), or some 35 billion times the energy of visible light, and about three times greater than any previous GRB. The GeV emission from the burst lasted for several hours, and it remained detectable by the LAT for the most of the day, making it the longest gamma-ray emission from a GRB detected to date.

The burst occurred as NASA’s Swift satellite was slewing between targets, which delayed its Burst Alert Telescope’s (BAT) detection by less than a minute. (The BAT is a wide-angle detector that can quickly determine the bearing to a gamma ray source. I designed the low-noise power regulators that feed the detector array in the BAT.) The burst was detected in optical, infrared and radio wavelengths by ground-based observatories using the rapid, accurate position from Swift.

Swift_XRTSwift‘s X-Ray Telescope took this image of GRB 130427A at 07:50 UTC on 27 April, moments after Swift and Fermi triggered on the GRB.

Gamma-ray bursts are the universe’s most luminous explosions. We believe that most occur when massive stars run out of nuclear fuel and collapse under their own weight. As the core collapses into a black hole, jets of material explode outward at almost the speed of light.

Image Credits: NASA

Fermi Epicycles

The Fermi Gamma-ray Space Telescope (formerly the Gamma-ray Large Area Space Telescope, or GLAST) orbits planet Earth every 95 minutes. It rocks north and south on alternate orbits in order to survey the sky with its Large Area Telescope (LAT). The spacecraft rolls so that solar panels stay pointed at the Sun for power, and the axis of its orbit precesses like a spinning top, making a complete rotation once every 54 days. As a result of these multiple cycles, the paths of gamma-ray sources trace out complex patterns from the spacecraft’s perspective. The plot above shows the path of the brightest persistent gamma ray source in the sky, the Vela Pulsar. The plot is centered on the LAT instrument’s field of view and spans 180 degrees. It follows the pulsar over the two years from August, 2008, through August, 2010. The Vela Pulsar is a neutron star spinning 11 times a second. It is the remnant of the explosion of a massive star within our Milky Way galaxy.

Image Credits: NASA