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The collapsar model was proposed to explain the long-duration gamma-raybursts (GRBs), while the short GRBs are associated with the mergers of compactobjects. In the first case, mainly the energetics of the events is consistentwith the proposed progenitor models, while the duration, time variability, aswell as the afterglow emission may shed some light on the detailed propertiesof the collapsing massive stars. In the latter case, the recent discovery ofthe binary neutron star (NS-NS) merger in the gravitational wave observationmade by LIGO (GW170817), and the detection of associated electromagneticcounterparts, for the first time gave a direct proof of the NS-NS merger beinga progenitor of a short GRB.  In general, all GRBs are believed to be powered by accretion through arotationally supported torus, or by fast rotation of a compact object. For longones, the rotation of the progenitor star is a key property in order to supportaccretion over relatively long activity periods, and also to sustain therotation of the black hole itself. The latter is responsible for ejection ofthe relativistic jets, which are powered due to the extraction of the BHrotational energy, mitigated by the accretion torus and magnetic fields. Thejets must break through the stellar envelope though, which poses a question onthe efficiency of this process. Similar mechanisms of powering the jet ejectionmay act in short GRBs, which in this case may freely propagate through theinterstellar medium. The power of the jets launched from the rotating blackhole is at first associated mostly with the magnetic Poynting flux, and then atlarge distances it is transferred to the kinetic and finally radiative energyof the expanding shells.

Gamma Ray Bursts. Progenitors, accretion in the central engine, jet acceleration mechanisms