Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni

Understand

Microquasars are stellar-mass black holes accreting matter from a companion star and ejecting plasma jets at almost the speed of light.

• They are analogues of quasars that contain supermassive black holes of $10^6$ to $10^{10}$ solar masses.
• Accretion in microquasars varies on much shorter timescales than in quasars and occasionally produces exceptionally bright X-ray flares.
• How the flares are produced is unclear, as is the mechanism for launching the relativistic jets and their composition.