The burst sound you hear when turning the engine's kill switch off and on during a highway ride on a Bajaj Pulsar NS200 is likely due to the operation of the bike's exhaust system and the release of excess unburned fuel from the exhaust.
When you turn off the kill switch, the ignition system shuts down, and the fuel supply to the engine is cut off. However, there may still be some fuel remaining in the combustion chamber and exhaust system. When you turn the kill switch back on, the fuel pump starts again, and a small amount of unburned fuel can be pushed into the hot exhaust system.
Once this unburned fuel enters the hot exhaust system, it can ignite and cause a burst or popping sound. This phenomenon is known as an "afterfire" or "exhaust pop."
It's important to note that this burst sound is typically harmless and is a normal occurrence in certain motorcycles, especially those with performance-oriented exhaust systems. However, if you notice any other unusual symptoms or issues with your bike's performance, it's always a good idea to have it checked by a qualified mechanic to ensure everything is functioning correctly.