Black holes are formed as the end product of stellar evolution.
At birth, some of the black holes must be very rapidly spinning, to be able to power the GRBS, which are ultrara-fast jets of plasma, which give a gamma ray burst signal.
Under some conditions, the black holes may be born without formation of a disk/jet engine, and then the star will collapse without an electromagnetic transient.
On the other hand, the gamma ray bursts may originate from the coalescence of binary compact objects, where also the disk/jet engine is formed.
The electromagnetic radiation in gamma rays is accompanied by a gravitational wave signal from the binary merger, while the accretion disk uncollimated outflows may contribute to
the subrelativistic neutron-rich material, which is responsible for blue and red kilonova.
I will discuss the properties of these different types of signals observed in gamma ray bursts, and focus on the role of accretion disk in their origin.
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