If there’s anything good about bands like Helium and Sleater-Kinney breaking up (as long ago and as sad as it was), it’s bands like Wild Flag forming. When Carrie Brownstein’s not out frolicking in Portlandia with Fred Armisen, she’s fronting this four-piece supergroup, playing charged indie punk rock with catchy hooks and tons of energy. Pairing the group with old-school Boston post-punkers Mission of Burma for Celebrate Brooklyn is almost too good to be true, but that’s exactly what’s happening this Friday at Prospect Park. Not only are the two groups playing for free (yes, free!) but they’re also releasing a split 7″ only available at the show. This is one worth camping out all night for!