Spectropolarimetric study of 4U 1630−47 in steep power-law state with <i>IXPE</i> and <i>NICER</i>

Rawat, Divya; Garg, Akash; Méndez, Mariano

doi:10.1093/mnras/stad2327

Cited by 8 publications

(1 citation statement)

References 36 publications

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“…IXPE previously observed 4U 1630-47 in the HSS where the detected emission was primarily from the thermal accretion disk (Ratheesh et al 2023, henceforth Paper I;and Kushwaha et al 2023;Rawat et al 2023). That observation revealed that the PD increased with energy from ∼6% at 2 keV to ∼10% at 8 keV.…”

Section: Introductionmentioning

confidence: 87%

The First X-Ray Polarization Observation of the Black Hole X-Ray Binary 4U 1630–47 in the Steep Power-law State

Rodriguez Cavero,

Marra,

Krawczynski

et al. 2023

ApJL

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The Imaging X-ray Polarimetry Explorer (IXPE) observed the black hole X-ray binary 4U 1630–47 in the steep power-law (or very high) state. The observations reveal a linear polarization degree of the 2–8 keV X-rays of 6.8% ± 0.2% at a position angle of 21.°3 ± 0.°9 east of north (all errors at 1σ confidence level). Whereas the polarization degree increases with energy, the polarization angle stays constant within the accuracy of our measurements. We compare the polarization of the source in the steep power-law state with the previous IXPE measurement of the source in the high soft state. We find that, even though the source flux and spectral shape are significantly different between the high soft state and the steep power-law state, their polarization signatures are similar. Assuming that the polarization of both the thermal and power-law emission components are constant over time, we estimate the power-law component polarization to be 6.8%–7.0% and note that the polarization angle of the thermal and power-law components must be approximately aligned. We discuss the implications for the origin of the power-law component and the properties of the emitting plasma.

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Section: Introductionmentioning

confidence: 87%

The First X-Ray Polarization Observation of the Black Hole X-Ray Binary 4U 1630–47 in the Steep Power-law State

Rodriguez Cavero,

Marra,

Krawczynski

et al. 2023

ApJL

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X-ray polarization properties of thermal-radiative disc winds in binary systems

Tomaru,

Done,

Odaka

2023

Monthly Notices of the Royal Astronomical Society

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New X-ray polarization results are challenging our understanding of the accretion flow geometry in black hole binary systems. Even spectra dominated by a standard disc can give unexpected results, such as the high-inclination black hole binary 4U 1630−472, where the observed X-ray polarization is much higher than predicted. This system also shows a strong, highly ionized wind, consistent with thermal-radiative driving from the outer disc, leading to speculation that scattering in the wind is responsible for the unexpectedly high polarization degree from a standard optically thick disc. Here, we show that this is not the case. The optically thin(ish) wind polarizes the scattered light in a direction orthogonal to that predicted from a standard optically thick disc, reducing about 2 per cent rather than enhancing the predicted polarization of the total emission. This value is consistent with the polarization difference between the disc-dominated soft state, where absorption lines by the wind are clearly seen, and the steep power-law state, where no absorption lines are seen. If this difference is genuinely due to the presence or absence of wind, the total polarization direction must be orthogonal to the disc plane rather than parallel as expected from optically thick material.

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X-ray polarization changes with the state transition in Cygnus X–1

Jana,

Chang

2023

Monthly Notices of the Royal Astronomical Society

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We studied the polarization properties of Cygnus X–1 in both hard and soft spectral states with Imaging X-ray Polarimetry Explorer (IXPE) observations. The polarization degree is $\sim 4\%$, and $\sim 2.6-2.8\%$ in the hard and soft states, respectively. The polarization angle is observed along the jet axis and remains the same in both states. Energy-dependent analysis revealed an increasing polarization with the energy. The observed polarization rules out the lamp-post corona and prefers a conical corona if the coronal geometry remains the same in the hard and soft states. The disk is not detected in the hard state but is found in the soft state in the IXPE spectra. The spectral analysis revealed that the disk emission contributes $\sim 20\%$ of the total emission in the soft state. The scattering of the seed photons inside the corona is likely to reduce the polarization. This could explain the different polarization in different spectral states. Additionally, if the disk polarization is perpendicular to that of the corona, it could also reduce the polarization in the soft state.

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Spectropolarimetric study of 4U 1630−47 in steep power-law state with IXPE and NICER

Cited by 8 publications

References 36 publications

The First X-Ray Polarization Observation of the Black Hole X-Ray Binary 4U 1630–47 in the Steep Power-law State

The First X-Ray Polarization Observation of the Black Hole X-Ray Binary 4U 1630–47 in the Steep Power-law State

X-ray polarization properties of thermal-radiative disc winds in binary systems

X-ray polarization changes with the state transition in Cygnus X–1

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