Birth of a relativistic outflow in the unusual γ-ray transient Swift J164449.3+573451
Berger, E.; Frail, D. A.; Kulkarni, S. R.; Carpenter, J. M.; Chornock, R.; Rupen, M. P.; Readhead, A. C. S.; Pooley, G. G.; Fox, D. B.; Soderberg, A. M.; Brunthaler, A.; Max-Moerbeck, W.; Richards, J.; Patel, N. A.; Mooley, K.; Margutti, R.; Zauderer, B. A.; Bietenholz, M. F.; Petitpas, G. R.; Volgenau, N. H.; Nakar, E.; Loeb, A.; Narayan, R.; Culverhouse, T. L.; Shepherd, M.; Storm, S.; Hull, C. L. H.
United States, Germany, United Kingdom, Italy, Israel, South Africa
Abstract
Active galactic nuclei, which are powered by long-term accretion onto central supermassive black holes, produce relativistic jets with lifetimes of at least one million years, and the observation of the birth of such a jet is therefore unlikely. Transient accretion onto a supermassive black hole, for example through the tidal disruption of a stray star, thus offers a rare opportunity to study the birth of a relativistic jet. On 25 March 2011, an unusual transient source (Swift J164449.3+573451) was found, potentially representing such an accretion event. Here we report observations spanning centimetre to millimetre wavelengths and covering the first month of evolution of a luminous radio transient associated with Swift J164449.3+573451. The radio transient coincides with the nucleus of an inactive galaxy. We conclude that we are seeing a newly formed relativistic outflow, launched by transient accretion onto a million-solar-mass black hole. A relativistic outflow is not predicted in this situation, but we show that the tidal disruption of a star naturally explains the observed high-energy properties and radio luminosity and the inferred rate of such events. The weaker beaming in the radio-frequency spectrum relative to γ-rays or X-rays suggests that radio searches may uncover similar events out to redshifts of z~6.