Gamma rays from microquasars Cygnus X-1 and Cygnus X-3

摘要

Gamma-ray observations of microquasars at high and very-high energies canprovide valuable information of the acceleration processes inside the jets, thejet-environment interaction and the disk-jet coupling. Two high-massmicroquasars have been deeply studied to shed light on these aspects: CygnusX-1 and Cygnus X-3. Both systems display the canonical hard and soft X-rayspectral states of black hole transients, where the radiation is dominated bynon-thermal emission from the corona and jets and by thermal emission from thedisk, respectively. Here, we report on the detection of Cygnus X-1 above 60 MeVusing 7.5 yr of Pass8 Fermi-LAT data, correlated with the hard X-ray state. Ahint of orbital flux modulation was also found, as the source is only detectedin phases around the compact object superior conjunction. We conclude that thehigh-energy gamma-ray emission from Cygnus X-1 is most likely associated withjets and its detection allow us to constrain the production site. Moreover, weinclude in the discussion the final results of a MAGIC long-term campaign onCygnus X-1 that reaches almost 100 hr of observations at different X-raystates. On the other hand, during summer 2016, Cygnus X-3 underwent a flaringactivity period in radio and high-energy gamma rays, similar to the one thatled to its detection in the high-energy regime in 2009. MAGIC performedcomprehensive follow-up observations for a total of about 70 hr. We discuss ourresults in a multi-wavelength context.