Original Caption Released with Image:
These four pictures, taken 2.3 seconds apart, show the early meteor, or "bolide", stage of the impact of the last major fragment of Comet Shoemaker-Levy 9 into Jupiter's night side. In the first image (8:06:12 UTC), no impact is visible. In the second picture, a bright point of light appears superimposed on the dark side of Jupiter's southern hemisphere. In the third image, the impact has grown so bright that it saturates the CCD picture element at the center of the image of the impact flash. By remarkable coincidence, the Hubble Space Telescope took a picture of the W impact, also in green light, within one second of this image, providing a complementary view of very faint associated phenomena at very high altitudes in Jupiter's atmosphere, just above the planet's edge as seen from Earth. In the final Galileo image (8:06:19 UTC), the impact flash has faded appreciably.

These images are pictures 5 through 8 of a series of 56 placed on a single frame in time-lapse fashion.

We interpret the rapid rise and fall of this initial peak over just 7 seconds to be the bolide phase of the W fragment's impact, analogous to the flash of light of meteors entering Earth's atmosphere. Images immediately following this show that the luminosity continues to fade over the next 15 seconds.

The Planetary Photojournal also has this image in multiple formats on their page