It is a unique, cleaner, shinier alien blaster used by the alien captain. Unlike the alien blaster, the Captain's sidearm uses the far more common alien power modules instead of alien power cells. It has a silver finish to it, unlike the rusted alien blaster you find in the Capital Wasteland, and actually shoots out a spread of energy like a shotgun. Shooting the sidearm into the air will show the spread of the energy. Each time you fire it, it uses 3 rounds and sends 6 energy projectiles. Like the Metal Blaster, it will do significantly more damage outside of V.A.T.S. due to multiple critical hits. Although it looks like a pristine alien blaster, it can be repaired by alien atomizers, alien epoxy, or vendors.
The captain's sidearm can fire off 2142 modules worth of bolts before breaking. That's a total of 714 bolts, or 4284 separate energy pellets.
Alien blaster, the "common" but still unique, blaster of alien origin.
Firelance, the untie alien blaster that does fire damage in addition to incredible damage.