Gamma-Ray Bursts

Gamma-ray bursts (GRBs) were first discovered in 1973 and at the time no one could reasonably explain them. To this day they are one of the greatest enduring mysteries of modern astronomy. The bursts occur approximately once a day and can be seen from all different directions of the sky as brief, but intense flashes of gamma radiation. During its lifetime, BATSE detected over 2700 individual bursts. GRBs are the brightest gamma-ray phenomenon known, outshining all other sources of gamma-rays combined, and last from a few milliseconds to a few hundred seconds.

2704 Gamma-Ray Bursts detected by BATSE

BATSE map of its 2704 detected GRBs

In 1997, there was a breakthrough when scientists using a satellite named BeppoSAX, discovered that at least some gamma-ray bursts display an afterglow. This is best described as a fading "glow", lasting for a few hours or a few days, which can be seen at x-ray and optical wavelengths. This new bit of information allowed scientists to determine that the bursts occur at distances outside of our own Galaxy. Previously, scientists were divided on the question of whether the bursts occurred in our own galaxy or at cosmological distances outside the Milkyway. This new information now at least told scientists that the bursts were distant and they could better understand the amount of energy being released in the burst.

The power that a gamma-ray burst produces is enormous, roughly equal to the energy released by 100 billion Suns in a year's time. So far scientists have few theories on how this amount of energy could be generated. Could the bursts be collisions between highly dense neutron stars or black holes? Could they be signatures of the birth of a black hole?

GLAST will aid the study of GRBs by measuring energy spectra of bursts from a few keV to hundreds of GeV in the short time after onset when the majority of the high-energy is released, something previous missions have not had the ability to accomplish. These spectra will allow scientists to place strong constraints on the production mechanisms and the physical conditions of the source regions of bursts. Between the LAT and the GBM, GLAST should observe more than a 200 bursts per year.