High Hard X-Ray Polarization in Cygnus X-1 Confined to the Intermediate Hard State: Evidence for a Variable Jet Component

Chattopadhyay, Tanmoy; Kumar, Abhay; Rao, A. R.; Bhargava, Yash; Vadawale, Santosh V.; Ratheesh, Ajay; Dewangan, Gulab; Bhattacharya, Dipankar; Mithun, N. P. S.; Bhalerao, Varun

doi:10.3847/2041-8213/ad118d

ApJL

2023

DOI: 10.3847/2041-8213/ad118d

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High Hard X-Ray Polarization in Cygnus X-1 Confined to the Intermediate Hard State: Evidence for a Variable Jet Component

Tanmoy Chattopadhyay,

Abhay Kumar,

A. R. Rao

et al.

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 ∼100 keV is … Show more

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2024

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Cited by 3 publications

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INTEGRAL/IBIS polarization detection in the hard and soft intermediate states of Swift J1727.8−1613

Bouchet,

Rodriguez,

Cangemi

et al. 2024

A&A

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Soft gamma -ray emission (100 keV -- 10 MeV) has previously been detected in the hard state of several microquasars. In some sources, this emission was found to be highly polarized and was suggested to be emitted at the base of the jet. Until now, no gamma -ray polarization had been found in any other state. Using we studied the soft gamma -ray spectral and polarization properties of throughout its outburst. We detect a highly polarized spectral component in both the hard intermediate state and the early stages of the soft intermediate state above 210\,keV. In the hard intermediate state, the polarization angle significantly deviates from the compact jet angle projected onto the sky, whereas in the soft intermediate they are closely aligned. This constitutes the first detection of jet-aligned polarization in the soft gamma -ray for a microquasar. We attribute this polarized spectral component to synchrotron emission from the jet, which indicates that some of the jet might persist into the softer states.

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INTEGRAL/IBIS polarization detection in the hard and soft intermediate states of Swift J1727.8−1613

Bouchet,

Rodriguez,

Cangemi

et al. 2024

A&A

View full text Add to dashboard Cite

show abstract

Accretion Geometry of GX 339–4 in the Hard State: AstroSat View

Chand,

Dewangan,

Zdziarski

et al. 2024

ApJ

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We perform broadband (0.7–100 keV) spectral analysis of five hard state observations of the low-mass black hole X-ray binary GX 339–4 taken by AstroSat during the rising phase of three outbursts from 2019 to 2022. We find that the outburst in 2021 was the only successful/full outburst, while the source was unable to make the transition to the soft state during the other two outbursts in 2019 and 2022. Our spectral analysis employs two different model combinations, requiring two separate Comptonizing regions and their associated reflection components and soft X-ray excess emission. The harder Comptonizing component dominates the overall bolometric luminosity, while the softer one remains relatively weak. Our spectral fits indicate that the disk evolves with the source luminosity, where the inner disk radius decreases with increasing luminosity. However, the disk remains substantially truncated throughout all the observations at the source luminosity of ∼2%–8%× of the Eddington luminosity. We note that our assumption of the soft X-ray excess emission as disk blackbody may not be realistic, and this kind of soft excess may arise due the nonhomogeneity in the disk/corona geometry. Our temporal analysis deriving the power density spectra suggests that the break frequency increases with the source luminosity. Furthermore, our analysis demonstrates a consistency between the inner disk radii estimated from the break frequency of the power density spectra and those obtained from the reflection modeling, supporting the truncated disk geometry in the hard state.

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An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

Steiner,

Nathan,

et al. 2024

ApJL

Self Cite

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We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer’s (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = −25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1’s au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1’s spin is likely high (a * ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE’s bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.

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High Hard X-Ray Polarization in Cygnus X-1 Confined to the Intermediate Hard State: Evidence for a Variable Jet Component

Cited by 3 publications

References 53 publications

INTEGRAL/IBIS polarization detection in the hard and soft intermediate states of Swift J1727.8−1613

INTEGRAL/IBIS polarization detection in the hard and soft intermediate states of Swift J1727.8−1613

Accretion Geometry of GX 339–4 in the Hard State: AstroSat View

An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

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