Fermi Gamma-ray Space Telescope

Pair plasma in recent V404 Cyg flares?

J. Greiner
T. Siegert, R. Diehl, M. Krause, A. Beloborodov, M. Cadolle Bel, F. Guglielmetti, J. Rodriguez, A. Strong, X.-L. Zhang

Abstract:

The nature of microquasar jets still is a mystery, although many theoretical models for the release of accretion energy from the black hole include materialisation of energy from the central source in the form of pair creation. It is unclear if this inner region remains optically thick for the annihilation gamma-rays that are expected to be produced there. Also, at some point leptons may escape the dense inner regions, and annihilation of positrons in nearby components such as the corona and accretion disk could be expected. Transient line features have been reported from two sources before, and tentatively associated with positron annihilation. V404 Cyg flaring in June-July 2015 provided a unique opportunity to test this model again, now with SPI on INTEGRAL, which has demonstrated excellent measurement capability for positron annihilation in the Galaxy. We report our analysis of potential positron annihilation signatures, and discuss their implications.