Cards with pictures and statistics of good players can fetch a high price at collector's conventions, while other cards are more suitable as noise-makers in the spokes of a young person's bicycle. Like baseball players, some gamma-ray bursts are more noteworthy than others for a variety of reasons. Before we attempt to learn more about the nature of gamma-ray bursts, a look at a few of their general properties, their baseball cards if you will, is in order. The gamma-ray bursts are among the most enigmatic phenomena observed in the sky today. Approximately once per day, at an apparently random time and in an unpredictable location of the sky, a gamma-ray burst occurs.
Scientists have many methods of characterizing the gamma-ray bursts that are observed.
The most commonly examined feature of a burst is its time-profile. The time-profile is a graph of the burst's brightness as a function of time. We are all familiar with the seismograph, the instrument that draws wildly fluctuating lines on a piece of paper during an earthquake. The output of the seismograph, the piece of paper with the jerky lines on it, is also a time-profile. It is a measure of the earthquake's intensity as a function of time.