How Do Fireflies All Come to Flash and Synchrony?

There are some species of firefly especially in Southeast Asia where the male fireflies will gather in mangrove trees along river banks every night. It's unbelievably spectacular and it looks like Christmas trees. The biologist thought that what's happening is when a firefly flashes, if another firefly sees it, it adjusts its own rhythm. They're also seeing flashes and they adjust the timer of their flash organ to be faster or a little bit slower depending on where in their cycle it was when they received the flash.