Gamma-ray Observations of the Microquasars Cygnus X-1, Cygnus X-3, GRS 1915+105, and GX 339-4 with Fermi-LAT

Detecting gamma-rays from microquasars is a challenging but important endeavor for understanding particle acceleration, the jet mechanism, and for testing leptonic/hadronic emission models. In this talk, we present results from a 1-d and 10-d likelihood analysis of ~4 years worth of gamma-ray observations (0.1--10 GeV) by Fermi-LAT of Cyg X-1, Cyg X-3, GRS 1915+105, and GX 339-4. This allowed us to sample a variety of states and transitions in these X-ray bright microquasars. Our analysis reproduced all but one of the previous gamma-ray outbursts of Cyg X-3 as reported with Fermi or AGILE. In addition, there are 5 days on which Cyg X-3 is detected at a significance of ~5σ that are not reported in the literature. We also find evidence for persistent gamma-ray emission from Cyg X-3 which appears to be unrelated to the jets. There are several days on which Cyg X-1 displays low-significance 3--4σ) excesses, two of which are contemporaneous with reported gamma-ray flares detected (also at low significance) by AGILE. For GRS 1915+105 and GX 339-4, we derive 3σ upper limits of 3.9e-6 ph/cm2/s and 4.0e-6 ph/cm2/s, respectively, on the flux in the 0.1--10 GeV range. These results enable us to propose a list of general conditions which appear to be necessary for the detection of gamma-rays from microquasars.