High hard X-ray polarization in Cygnus X-1 confined to the intermediate hard state: evidence for a variable jet component

Abstract

Cygnus X-1, the well-known accreting black hole system, exhibits several observational features hinting at an intricate interplay between the accretion disk, its atmosphere known as the corona and the putative relativistic jet. It has been extensively studied using all available observational methods, including using the newly available technique of sensitive X-ray polarimetry. X-ray polarization characteristics are distinct for coronal and jet emissions. The low X-ray polarization measured below $\sim$100 keV is understood as arising from the corona. In contrast, the high polarization measurements reported above $\sim$400 keV required a separate jet-dominated spectral component, which spectroscopy does not demonstrate conclusively. Here we report precise polarization measurements in the 100-380 keV region made during three different sub-classes of spectral states of the source using the CZTI instrument onboard {\em AstroSat}. A high polarization (23$\pm$4 \%) is found mainly in the Intermediate Hard State of the source, and the energy-resolved measurements smoothly connect the coronal and the jet regimes. When high polarization is observed, the simultaneous spectral data hints at a separate power law component above 100 keV. We examine the possible sources of this energy-dependent high polarization in Cygnus X-1.

Accepted for publication in ApJ Letters (ApJL)

References in corpus (13)

• Cygnus X-1 contains a 21-solar mass black hole -- implications for massive star winds
• Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1
• The synchrotron boiler and the spectral states of black hole binaries
• On the origin of spectral states in accreting black holes
• A transient relativistic radio jet from Cygnus X-1
• Jet contributions to the broad-band spectrum of Cyg X-1 in the hard state
• Accretion geometry of the black-hole binary Cygnus X-1 from X-ray polarimetry
• A new lepto-hadronic model applied to the first simultaneous multiwavelength data set for Cygnus X--1
• Hard X-ray polarization catalog for a 5-year sample of Gamma-Ray Bursts using AstroSat CZT-Imager
• Correlated radio--X-ray variability of Galactic Black Holes: A radio--X-ray flare in Cygnus X-1
• Improved background model for the Large Area X-ray Proportional Counter (LAXPC) instrument on-board AstroSat
• Distinct accretion modes of Cygnus X-1 revealed from hard X-rays
• Extending the energy range of AstroSat-CZTI up to 380 keV with Compton Spectroscopy

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• Astroparticles from X-ray Binary Coronae
• INTEGRAL/IBIS polarization detection in the hard and soft intermediate states of Swift J1727.8-1613
• A Hidden Pulse: Uncovering a New Timing Signal in Cygnus X-1 with AstroSat
• A kinetic model of jet-corona coupling in accreting black holes