The microquasar V404 Cygni ( also known as GS 2023+338 ) was previously reported to have possible GeV \gamma -ray emission in two days during its 2015 outburst .
In order to provide more detailed information at the high energy range for this black hole binary system , we conduct detailed analysis to the data obtained with the Large Area Telescope ( LAT ) onboard the Fermi Gamma Ray Space Telescope ( Fermi ) .
Both LAT database and source catalog used are the latest .
From the analysis , we can not confirm the previous detection .
Instead , we find one possible detection ( \sim 4 \sigma ) of the source at the end of the outburst in the time period of 2015 Aug. 17–19 , and one convincing detection ( \simeq 7 \sigma ) in 2016 Aug. 23–25 .
The latter shows that the \gamma -ray emission of the source is soft with photon index \Gamma \sim 2.9 , mostly detected below \sim 1.3 GeV with Fermi LAT .
As \gamma -ray emission from microquasars is likely 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 establishes V404 Cygni as one of four microquasars with detectable \gamma -ray emission , and adds interesting features to the small group , or in a more general context to X-ray binaries with jets .