Observations of Cygnus X-1 in the MeV band by the INTEGRAL imager
1 Astronomy Department, University of Geneva, Chemin d’Ecogia 16, 1290 Versoix, Switzerland
2 Institute of High Energy Physics, Chinese Academy of Sciences,19B Yuquan Lu, Shijingshan District, 100049 Beijing, PR China
Received: 20 July 2016
Accepted: 22 April 2017
Context. The spectrum of the MeV tail detected in the black-hole candidate Cygnus X-1 remains controversial as it appeared much harder when observed with the INTEGRAL Imager IBIS than with the INTEGRAL spectrometer SPI or CGRO.
Aims. We present an independent analysis of the spectra of Cygnus X-1 observed by IBIS in the hard and soft states.
Methods. We developed a new analysis software for the PICsIT detector layer and for the Compton mode data of the IBIS instrument and calibrated the idiosyncrasies of the PICsIT front-end electronics.
Results. The spectra of Cygnus X-1 obtained for the hard and soft states with the INTEGRAL imager IBIS are compatible with those obtained with the INTEGRAL spectrometer SPI, with CGRO, and with the models that attribute the MeV hard tail either to hybrid thermal/non-thermal Comptonisation or to synchrotron emission.
Key words: gamma rays: stars / X-rays: binaries / stars: black holes / methods: data analysis / acceleration of particles / accretion, accretion disks
© ESO, 2017