High-energy Gamma-Ray Activity from V404 Cygni Detected by AGILE during the 2015 June Outburst

The AGILE satellite detected transient high-energy gamma-ray emission from the X-ray binary V404 Cygni, during the 2015 June outburst observed in radio, optical, X-ray, and soft gamma-ray frequencies. The activity was observed by AGILE in the 50--400 MeV energy band, between 2015 June 24 UT 06 00 00 and 2015 June 26 UT 06 00 00 (MJD 57197.25--57199.25), with a detection significance of ~4.3sigma. The gamma-ray detection, consistent with a contemporaneous observation by Fermi-LAT, is correlated with a bright flare observed at radio and hard X-ray frequencies, and with a strong enhancement of the 511 keV line emission, possibly indicating plasmoid ejections in a lepton-dominated transient jet. The AGILE observations of this binary system are compatible with a microquasar scenario in which transient jets are responsible for the high-energy gamma-ray emission.