Very high energy astrophysics with the SHALON Cherenkov telescopes

Cyg X‐3: A gamma‐ray binary

“…Currently, both leptonic and hadronic origins of the primary particles responsible for the very high energy -ray emission in these objects are considered. The Cyg X-3 binary system has the high luminosity of the companion star of Cyg X-3 (Zdziarski et al 2012) and a close orbit (Abdo et al 2009;Sinitsyna & Sinitsyna 2018). In addition, the modulation of TeV gamma-ray emission in the orbit of the Cyg X-3 binary is detected.…”

“…We compared the SHALON light curve at 800 GeV to 100 TeV (red area in Figure 2) folded on the orbital period to the folded light curves of Cyg X-3 at 100 MeV to 100 GeV from the Fermi LAT observations (red line) (Abdo et al 2009), 20-100 keV from BATSE experiment (blue points), and 2-12 keV X-rays from RXTE-ASM experiment (violet points). All listed light curves have a similar shape, but ones of high and very high energies have an additional local maximum in the region of the global minimum corresponding to phases of ∼0.3 for Fermi LAT (Abdo et al 2009) data and ∼0.2 for SHALON data (Sinitsyna & Sinitsyna 2018).…”

“…The gamma-ray spectrum, especially if it is varied with the orbital phase, is an important tool to probe the mechanisms of emission generation in the source. In further studies, differential spectra for three intervals of orbital phase-inferior conjunction, the additional maximum, and superior conjunction-were extracted (see Figure 1, right and (Sinitsyna & Sinitsyna 2018)) and then fitted as following:…”

“…In long-term observations of Cyg X-3 at energies >800 GeV with SHALON, the periods of high intensity and flares were found, which occur at a certain relationship between the radio and X-ray activity. Namely, the very high energy gamma-ray flux increase is observed during high activity in soft X-rays and low activity in hard X-rays within 6-8 days before the radio flares (Sinitsyna & Sinitsyna 2018). To test the existence of these correlations or anticorrelations, we calculated correlation coefficients (r s ) and probability functions (p) of the Spearman rank order.…”

“…Thus, during the high activity in radio before the minor and major flares, at energies of >800 GeV, the emission from the source is characterized by a hard power law spectrum with an index Γ diff ∼ −2.1; it is detected from a ∼10 ′′ − 20 ′′ region around Cyg X-3 with the presence of jets. In a quiescence state, the TeV gamma rays originate from a ∼40 ′′ region, and their spectrum is described by a softer power law The behavior of Cyg X-3 in the radio (Ryle, GBI, RATAN-600) and X-ray (RXTE) bands were analyzed, and six states, depending on the ratio of the intensities in these ranges and the spectral characteristics in the X-ray energy band, were revealed with an index Γ diff ∼ − 2.5 (for details, see Sinitsyna & Sinitsyna 2018). The illustration of the Cyg X-3 behavior in TeV energies traced from the flare to the intensity decrease is presented in Figure 3.…”