A nearby long gamma-ray burst from a merger of compact objects
Troja, E.; Wollaeger, R. T.; Butler, N. R.; Fryer, C. L.; Kutyrev, A.; Pandey, S. B.; Kawai, N.; Norris, J. P.; Castro-Tirado, A. J.; O'Connor, B.; Dichiara, S.; Chase, E. A.; Ryan, G.; Murata, K. L.; Gupta, R.; Kumar, A.; Hu, Y. -D.; Misra, K.; Caballero-Garcia, M. D.; Ito, N.; Aryan, A.; Hosokawa, R.; Niwano, M.; van Eerten, H. J.
Italy, United States, Canada, India, United Kingdom, Japan, Spain
Abstract
Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts of long (greater than two seconds) duration are produced by the core-collapse of massive stars1, and those of short (less than two seconds) duration by the merger of compact objects, such as two neutron stars2. A third class of events with hybrid high-energy properties was identified3, but never conclusively linked to a stellar progenitor. The lack of bright supernovae rules out typical core-collapse explosions4-6, but their distance scales prevent sensitive searches for direct signatures of a progenitor system. Only tentative evidence for a kilonova has been presented7,8. Here we report observations of the exceptionally bright GRB 211211A, which classify it as a hybrid event and constrain its distance scale to only 346 megaparsecs. Our measurements indicate that its lower-energy (from ultraviolet to near-infrared) counterpart is powered by a luminous (approximately 1042 erg per second) kilonova possibly formed in the ejecta of a compact object merger.