Gamma-ray bursts challenge theoretical models

17 Jun 2002

An international team of astronomers has observed extremely rapid bursts of high-energy gamma rays from a distant galaxy, an observation that is challenging how astronomers explain such phenomena. The research team working at the Smithsonian Institution's Fred Lawrence Whipple Observatory in Arizona has observed high- energy gamma-ray bursts coming from the active galactic nucleus known as Markarian 421, a galaxy some 400 million light-years from Earth.

The researchers counted 15 gamma rays per minute during the first flare from Markarian 421, 10 times as high as the rate observed from the Crab Nebula, which is a steady source of high-energy gamma rays in our own galaxy. Using mathematical equations that relate the duration of the flare to the size of the region emitting the bursts, the rapidity of the second flare suggests to the team that the region emitting the gamma rays is extremely small on an astrophysical scale, perhaps even smaller than our solar system. Another unusual feature of Markarian 421 is that it is bright at both the low and high ends of the energy spectrum, but emits only a weak signal in certain regions of gamma rays, reported James Gaidos, professor of physics at Purdue University and a member of the research team, in the latest edition of Nature.