Detection of the Microquasar V404 Cygni at γ-Rays Revisited: Short Flaring Events in Quiescence

Abstract

Abstract The microquasar V404 Cygni (also known as GS 2023+338) was previously reported to have weak GeV γ-ray emission in subday time periods during its 2015 outburst. In order to provide more detailed information at the high energy range for this black hole binary system, we conduct analysis on the data obtained with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi). Both the LAT database and source catalog used are the latest versions. In addition to the previously reported detection at the peak of the 2015 outburst, we find a possible detection (∼4σ) of the source during the 3 day time period of 2015 August 17–19 (at the end of the 2015 outburst) and one convincing detection (≃7σ) in 2016 August 23–25. The latter high-significance detection shows that the γ-ray emission of the source is soft with photon index Γ ∼ 2.9. As γ-ray emission from microquasars is considered to be associated with their jet activity, we discuss the results by comparing with those well-studied cases, namely, Cyg X-3 and Cyg X-1. The detection helps identify V404 Cygni as a microquasar with detectable γ-ray emission in its quiescent state, and adds interesting features to the microquasar group, or in a more general context to X-ray binaries with jets.