His research focused on transient objects in the universe such as gamma-ray bursts (GRBs), supernova and active galaxy flares. He worked to develop gamma-ray astrophysics from a field of experiments detecting a few objects to a full astronomical discipline with thousands of sources in many classes.

He was elected chair of the Astronomy Section of the National Academy of Sciences in 2013. He published over 600 academic articles, which have been cited 40,000 times for an h-index of 97. His most cited works include papers on the discovery of the origin of short gamma-ray bursts, the Swift satellite, Poisson statistics, observations of gamma-ray bursts at the edge of the visible universe, discovery of a relativistic tidal disruption event, and finding of two classes of active galactic nuclei (AGN) in the gamma-ray band.