This is a Police Gunship.
Canon reference: SW Databank: http://www.starwars.com/databank/police-gunship
Databank specs are somewhat scant:
And the Databank writeup is:
During the Clone Wars, security on Coruscant was bolstered with the addition of Republic police gunships. Smaller, sleeker, and less heavily-armed than the military-grade Republic attack gunship, the police gunship was better suited to navigate the skyline and was less likely to cause costly collateral damage with its pair of ball-mounted laser turrets that flanked the cockpit, or the a fixed laser cannon that extended from the rear. Four arm-mounted solar gather panels helped power the repulsorlift vehicle. The control cabin had two stacked seats, with the pilot elevated and slightly behind the gunner. The troop bay had side doors that folded upward for entry, and rear ramp for rapid deployment of police forces. After the Clone Wars, the Empire made equally good use of police gunships, using them to combat rebel threats from world to world.
It originated in Clone Wars, but according to Wikia appears in at least 2 Rebels episodes:
Star Wars Rebels – "Call to Action"
Star Wars Rebels – "Relics of the Old Republic"