 With Dale Frail at NRAO and Toshio Murakami and his colleagues at ISAS (predecessor of JAXA that was led by Yasuo Tanaka at that time) Kulkarni showed that soft gamma-ray repeaters are neutron stars associated with supernova remnants.This discovery eventually led to the understanding that neutron stars with extremely high magnetic field called magnetars are the soft gamma-ray repeaters.Caltech-NRAO team which he led showed in 1997 that gamma-ray bursts came from extra-galactic sources, and identified optical counterparts.