IBIS preliminary results on Cygnus X-1 spectral and temporal characteristics

Abstract

We report preliminary results of a broadband spectral and temporal study of the black-hole binary Cyg X-1 performed with the IBIS telescope. Cyg X-1 was the first pointed celestial target of IBIS during the INTEGRAL Performance and Verification Phase, 2002 Nov.-Dec., for a total observing time of 2 Ms in both staring and dithering mode. Here, we report on only the staring, on-axis, observation performed in a stable instrument configuration. During the observing period the source was in its characteristic low/hard state, in which a few flares and dips have been detected. The IBIS/ISGRI results demonstrate that the INTEGRAL observatory offers a unique capability for studying correlations between hardness and/or flux in different bands over a wide photon energy range. One of our new results is finding that the hardness-flux correlation changes the sign twice over the 20-220 keV; first from positive to negative at 50 keV, and then back to positive at 120 keV. The former change appears to be due to the spectral curvature introduced by variable Compton reflection. The latter may be due spectral pivoting.

arXiv comment7 pages, 8 figures (4 in color), accepted for publication in A&A, INTEGRAL special issue

References in corpus (9)

• ISGRI: the INTEGRAL Soft Gamma-Ray Imager
• The INTEGRAL Science Data Centre (ISDC)
• Correlation between Compton reflection and X-ray slope in Seyferts and X-ray binaries
• Simultaneous X-ray and gamma-ray observations of Cyg X-1 in the hard state by Ginga and OSSE
• The INTEGRAL/IBIS Scientific Data Analysis
• Broad-band X-ray/gamma-ray spectra and binary parameters of GX 339-4 and their astrophysical implications
• Understanding the long-term spectral variability of Cygnus X-1 with BATSE and ASM observations
• Broad band spectrum of Cygnus X-1 in two spectral states with BeppoSAX
• Five Years in the Life of Cygnus X-1: BATSE Long-Term Monitoring

Cited by in corpus (13)

• ISGRI: the INTEGRAL Soft Gamma-Ray Imager
• GX 339-4: the distance, state transitions, hysteresis and spectral correlations
• The broad-band spectrum of Cygnus X-1 measured by INTEGRAL
• Bimodal spectral variability of Cygnus X-1 in an intermediate state
• The magnetic field in the X-ray corona of Cygnus X-1
• An intense state of hard X-ray emission of Cyg X-1 observed by INTEGRAL coincident with TeV measurements
• The INTEGRAL view on Black Hole X-ray Binaries
• State transition and flaring activity of IGR J17464-3213/H1743-322 with SPI/INTEGRAL telescope
• First results of IBIS/ISGRI Cygnus X-3 monitoring during INTEGRAL PV phase
• INTEGRAL-ISGRI observations of the CygOB2 region: earching for hard X-ray point sources in a region containing several non-thermal emitting massive stars
• IBIS performances during the Galactic Plane Scan - I. The Cygnus region
• First observations of the X-ray transient EXO 2030+375 with IBIS/ISGRI
• High-energy observations of black hole binaries with the INTEGRAL satellite