Gravitational waves, the disturbance in spacetime metric to be generated by accelerated motions of massive objects, which had long been predicted by Albert Einstein’s General Relativity, were finally detected in 2015 by the Advanced LIGO detectors, and the year 2017 became a truly remarkable year in Astronomy as we, human beings, observed the first cosmic event in both gravitational waves and electromagnetic waves, hence openning the new era of multi-messenger astronomy. More specifically, a gravitational wave (GW) event, GW170817, which was produced by coalescence of two neutron stars, was detected nearly simultaneously with a gamma-ray burst (GRB), named the GRB 170817A, as seen by NASA’s Fermi Gamma-ray Space Telescope. Now, as GRBs being the unique and invaluable counterpart to the gravitational wave events, the need for understanding the exact physical mechanism of GRBs is even more compelling than ever before. The difficulties in nailing down their physical mechanism come from the facts that (1) the radiative processes involved remained so elusive as revealed by the observed shape of gamma-ray spectra, (2) there has been no clear observational clue on the composition of relativistic jets launched from the explosion, and (3) there has been no clear evidence on how far from the central engine the prompt gamma-rays of GRBs are emitted while the competing physical mechanisms under debate predict different characteristic distances from the engine. In this talk, recent important breakthroughs that answer these questions will be presented.