Observations of a Gamma Ray Flare
A combined optical and radio image of the double-lobed radio galaxy 3C66B, with the BL Lac galaxy 3C66A seen as the red spot with the white dot in the top right. Blue shows the distribution of stars and red shows the radio radiation from relativistic streams of high energy particles.
BL Lacertae objects (BL Lacs) are a particularly enigmatic group of galaxies. In one regard they are like many other galaxies: they have nuclei with very energetic processes ongoing that are thought to be due to the presence of supermassive black holes. In a BL Lac galaxy, however, the environment of the black hole emits powerful jets of radiation that, by chance, are pointed towards us. BL Lacs possess several bizarre properties as a result, including a tendency to vary rapidly in brightness, and the ability to emit ultra high energy gamma radiation, light that is even more energetic than X-rays. Gamma ray flares are the most energetic events known, and astronomers are trying to understand the physical processes that trigger and power them. BL Lac objects offer an opportunity to study these extreme events.
A large team of astronomers, including nine from CfA under the leadership of Trevor Weekes, reports measuring a very high energy gamma ray flare from the BL Lac galaxy known as 3C66A. The scientists used the VERITAS facility, an array of four twelve-meter-diameter telescopes situated at the CfA's Fred L. Whipple Observatory in Arizona. They detected a strong and time-variable flare in the source, but exactly how much energy it contained is still uncertain because the distance to 3C66A is very uncertain; possibly it is as far away as six billion light-years. Extreme gamma-ray bursts are very difficult to measure, and VERITAS is one of only a few facilities in the world capable of detecting them. Although further analysis of the flare is underway, the new results are a step towards understanding what powers the tremendous release of energy in these galactic nuclei.