High-energy gamma-rays from Cyg X-1

Abstract

We have obtained a firm detection of Cyg X-1 during its hard and intermediate spectral states in the energy range of 40 MeV-60 GeV based on observations by the Fermi Large Area Telescope, confirming the independent results at ≥60MeV of a previous work. The detection significance is 8σ in the 0.1-10 GeV range. In the soft state, we have found only upper limits on the emission at energies 0.1 MeV. However, we have found emission with a very soft spectrum in the 40-80 MeV range, not detected previously. This is likely to represent the high-energy cutoff of the high-energy power-law tail observed in the soft state. Similarly, we have detected a γ-ray soft excess in the hard state, which appears to be of similar origin. We have also confirmed the presence of an orbital modulation of the detected emission in the hard state, expected if the γ-rays are from Compton upscattering of stellar blackbody photons. However, the observed modulation is significantly weaker than that predicted if the blackbody upscattering were the dominant source of γ-rays. This argues for a significant contribution from γ-rays produced by the synchrotron-self-Compton process. We have found that such strong contribution is possible if the jet is strongly clumped. We reproduce the observed hardstate average broad-band spectrum using a self-consistent jet model, taking into account all the relevant emission processes, e ± pair absorption, and clumping. This model also reproduces the amplitude of the observed orbital modulation.

Discovery of the Galactic High-mass Gamma-Ray Binary 4FGL J1405.1−6119

“…Corbel et al 2012;Zdziarski et al 2018) and Cygnus X-1 (e.g. Bodaghee et al 2013;Zanin et al 2016;Zdziarski et al 2017).…”

A model for high-mass microquasar jets under the influence of a strong stellar wind

“…The high proximity to the star also makes IC emission and GGA more susceptible to change along the orbit, which results in a much stronger orbital modulation than in MB18, especially for high-energy gamma rays with ε 100 MeV. Evidence of such a modulation has been found for Cygnus X-3 (Zdziarski et al 2018), and hints of such an effect have also been observed in Cygnus X-1 (Zanin et al 2016;Zdziarski et al 2017).…”

Similarity and diversity of black holes - view from the Very High Energies

“…Cyg X-1 and Cyg X-3 are both detected in the lower gamma-ray energies by the Fermi satellite and the origin of this emission seems to be the jet (Abdo et al 2009, Zanin et al 2016, Zdziarski et al 2016. Therefore, it is to be expected that during flares the emission would extend also to energies > 100 GeV, unless the gamma-rays are always emitted very close to jet base, where strong photon field absorbing VHE γ-rays is present.…”