Author: Kunihito Ioka
Abstract: Gamma-Ray Bursts (GRBs) are the brightest explosions in the universe. It remains a big challenge to reveal the central engine and the emission mechanism that is very efficient with highly nonthermal spectra. The GRB jet propagation and breakout from progenitors are crucial processes that link the GRB appearances (such as duration, opening angle, Lorentz factor and off-center photosphere) to the central engine properties. This is applying to diverse candidates including Population III GRBs, ultra-long GRBs, etc. We will also discuss implications for Amati and Yonetoku spectral relations, photosphere or Poynting emission mechanisms, electromagnetic counterparts to short GRBs, and so on.