On the origin of the dark gamma-ray bursts

The origin of dark bursts—i.e. that have no observed afterglows in X-ray, optical/NIR and radio ranges—is unclear yet. Different possibilities—instrumental biases, very high redshifts, extinction in the host galaxies—are discussed and shown to be important. On the other hand, the dark bursts should not form a new subgroup of long gamma-ray bursts themselves.