Both instruments on the Fermi Gamma-ray Space Telescope have seen a gamma-ray burst also detected by other observatories, giving scientists a unique opportunity to learn more about these enigmatic blasts.
Photograph of the Fermi GBM before launch. The detectors consist of scintillator materials in which incoming gamma rays make a track of glowing light.
Gamma-ray bursts, or "GRBs," are the most energetic explosions in the Universe. As the name implies, their defining characteristic is a large temporary blast of gamma rays, the highest energy kind of light. GRBs result from the catastrophic collapse of an enormous star, or the merger of two neutron stars or a neutron star and black hole. The details of going from the collapse or merger to the burst of gamma-rays and other light involves physics at some of the highest energies ever seen in the Universe.
One of the challenges to amassing data from GRBs is that they happen unpredictably and last only a short time, with the flash of gamma rays coming from a tiny point on the sky lasting for as little as a second. Seeing GRBs was originally an exercise in serendipity, but in the past decade two special space telescope instruments have been deployed to watch the sky and quickly pinpoint the location of a flash of gamma rays, signaling other instruments to view the afterglow radiation of x-ray, ultraviolet, and optical light.
One of these vigilant GRB snoops is the Gamma Ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope. Recently, on July 31, the GBM observed a GRB that was fortuitously also seen in gamma rays by Fermi's other instrument, the Large Area Telescope (LAT) and the burst detector aboard NASA's Swift satellite, as well as in X-rays by Swift's X-ray telescope. It was then seen in optical light by ground-based telescopes which were alerted to the presence of the GRB, including the Faulkes robotic telescopes in Australia and awaii, the Nordic Optical Telescope in the Canary Islands, the MITSuME telescope in Japan, and the MOA telescope in New Zealand. An optical spectrum taken by the Gemini North telescope in Hawaii revealed the GRB to be at a redshift of 2.83, meaning the time between the beginning of the Universe and this GRB exploding was much shorter than the time between the explosion and now.
Since the Fermi-GBM and the Swift burst detector are sensitive to gamma-ray photons of a lower energy than the Fermi-LAT, this GRB has been observed with unprecedented spectral coverage. KIPAC is one of the primary institutions in the Fermi collaboration. KIPAC postdoc Daniel Kocevski and scientist Nicola Omodei are leading the LAT analysis for this important burst. With such a large energy coverage in the gamma-ray band as well as other bands, the July 31 burst will provide new insight into the nature of GRBs.