Relativistic and Newtonian Shock Breakouts

Observations of the first light from a stellar explosion can open a window to a wealth of information on the progenitor system and the explosion itself. Here I briefly discuss the theoretical expectation of that emission, comparing Newtonian and relativistic breakouts. The former takes place in regular core-collapse supernovae (SNe) while the latter is expected in SNe that are associated with gamma-ray bursts (GRBs), extremely energetic SNe (e.g., SN2007bi) and white dwarf explosions (e.g., type Ia and .Ia SNe, accretion induced collapse). I present the characteristic observable signatures of both types of breakouts, when spherical. Finally, I discuss Newtonian shock breakouts through wind, which produce a very luminous signal, with an X-ray component that is weak around the breakout, and becomes brighter afterwards.