It is a measure of the earthquake's intensity as a function of time. A gamma-ray burst time profile is essentially no different. However the intensity that is plotted for a burst is not a measure of how much the ground is shaking, but is instead a measure of how many gamma-rays are being detected from the source. The time-profiles of bursts are as unique as fingerprints. This has severely curtailed scientists' attempts to classify the bursts into groups or families based on the appearance of their time-profiles.
Some burst profiles are extremely smooth.
The brightness of these bursts does not change very rapidly. Other burst profiles look more like the seismograph output we are familiar with, displaying large fluctuations in brightness over a short period of time. Interestingly, this burst has the property that it appears to have turned on for awhile, then turn off for a period of time, and then turn back on again. This hiatus in emission is not uncommon in bursts and can last for just a few seconds, or for several hundred seconds. After the occurrence of a gamma-ray burst, its position on the sky can often be determined with reasonable accuracy.