Understanding the engines and progenitors of gamma-ray bursts Chris L. Fryer, Nicole Lloyd-Ronning, Ryan Wollaeger, Brandon Wiggins, Jonah Miller, Josh Dolence, Ben Ryan and Carl E. Fields Eur. Phys. J. A, 55 8 (2019) 132 Published online: 22 August 2019 DOI: 10.1140/epja/i2019-12818-y