A kilonova associated with short-duration gamma-ray burst 130603

Short-duration gamma-ray bursts (SGRBs) are intense flashes of cosmic gamma-rays, lasting less than ⇠ 2 s, whose origin is one of the great unsolved questions of astrophysics today1, 2. While the favoured hypothesis for their production is in relativistic jets created by the merger of two compact stellar objects (specifically, two neutron stars, NS-NS, or a neutron star and a black hole, NS-BH), supported by evidence such as the range of host galaxy properties3, unambiguous confirmation of the model is still lacking. Mergers of this kind are expected also to create significant quantities of neutron-rich radioactive species, whose decay should result in a faint transient in the days following the burst, a so-called “kilonova”4. Indeed, it is speculated that this mechanism may be the predominant source of stable r-process elements in the Universe4, 5. Recent calculations suggest much of the kilonova energy should appear in