Spectro-polarimetric view of bright atoll source GX 9+9 using <i>IXPE</i> and <i>AstroSat</i>

Rwitika, Chatterjee,; Agrawal, Vivek; Jayasurya, Kiran M; Katoch, Tilak

doi:10.1093/mnrasl/slad026

Cited by 16 publications

(7 citation statements)

References 28 publications

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“…IXPE results on the X-ray polarization obtained using the model-independent IXPEOBSSIM-PCUBE analysis show a different behavior of this source with respect to the other atoll and Z-sources observed up to now (Capitanio et al 2023;Chatterjee et al 2023;Cocchi et al 2023;Farinelli et al 2023;Jayasurya et al 2023;Ursini et al 2023). In particular, this is the first source showing a strong increase of the polarization with energyup to 10%in the 7-8 keV energy band.…”

Section: Discussionmentioning

confidence: 77%

“…The IXPE result for 4U 1820−303 shows a different polarization behavior with respect to other atoll sources, GX 9+9 (Chatterjee et al 2023;Ursini et al 2023) and GS 1826−238 (Capitanio et al 2023), but also with respect to the Z-sources Cyg X-2 (Farinelli et al 2023) and XTE J1701 −462 (Cocchi et al 2023;Jayasurya et al 2023). In particular, the need to have a polarized disk emission is more evident.…”

Section: Discussionmentioning

confidence: 89%

“…The resulting PD and PA contour plots for the three wider bins are shown in Figure 5(c), while the numerical results are reported in Table 1. The most significant polarization is measured at CL > 99.99% in the 7-8 keV energy bin, where the PD reaches a value of ∼10%, never observed in other weakly magnetized sources (Capitanio et al 2023;Chatterjee et al 2023;Cocchi et al 2023;Farinelli et al 2023;Jayasurya et al 2023;Ursini et al 2023). We also observe a position-angle change by nearly 90°between 2 and 4 keV, and the higher energy bins (significant at 96% CL).…”

Section: Polarimetric Analysismentioning

confidence: 85%

“…In order to investigate the geometry of the accretion flow in LMXBs, IXPE has so far targeted several sources: the Z-source Cyg X-2 (Farinelli et al 2023), the Z-atoll transient source XTE J1701−462 (Cocchi et al 2023;Jayasurya et al 2023), and two atoll sources, GS 1826−238 (Capitanio et al 2023) and GX 9+9 (Chatterjee et al 2023;Ursini et al 2023). These observations found a higher polarization in the Z-sources than in the atoll ones; moreover, the polarization angle (PA) of Cyg X-2, for the hardest part of the energy spectrum, appears to be aligned with the radio jet.…”

Section: Introductionmentioning

confidence: 99%

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First Detection of X-Ray Polarization from the Accreting Neutron Star 4U 1820−303

Marco

Monaca

Poutanen

et al. 2023

ApJL

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This paper reports the first detection of polarization in the X-rays for atoll-source 4U 1820−303, obtained with the Imaging X-ray Polarimetry Explorer (IXPE) at 99.999% confidence level (CL). Simultaneous polarimetric measurements were also performed in the radio with the Australia Telescope Compact Array. The IXPE observations of 4U 1820−303 were coordinated with Swift X-ray Telescope, Neutron Star Interior Composition Explorer, and Nuclear Spectroscopic Telescope Array aiming to obtain an accurate X-ray spectral model covering a broad energy interval. The source shows a significant polarization above 4 keV, with a polarization degree of 2.0% ± 0.5% and a polarization angle of −55° ± 7° in the 4–7 keV energy range, and a polarization degree of 10% ± 2% and a polarization angle of −67° ± 7° in the 7–8 keV energy bin. This polarization also shows a clear energy trend with polarization degree increasing with energy and a hint for a position-angle change of ≃90° at 96% CL around 4 keV. The spectro-polarimetric fit indicates that the accretion disk is polarized orthogonally to the hard spectral component, which is presumably produced in the boundary/spreading layer. We do not detect linear polarization from the radio counterpart, with a 3σ upper limit of 50% at 7.25 GHz.

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Section: Discussionmentioning

confidence: 77%

Section: Discussionmentioning

confidence: 89%

Section: Polarimetric Analysismentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

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First Detection of X-Ray Polarization from the Accreting Neutron Star 4U 1820−303

Marco

Monaca

Poutanen

et al. 2023

ApJL

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“…Almost 40 yr after the first tentative attempts to measure X-ray polarization, the recent launch of the Imaging X-ray Polarimetry Explorer (IXPE; Soffitta et al 2021;Weisskopf et al 2022) adds X-ray polarization to spectral and timing information to investigate the geometry of the accretion flow in LMXBs. Aiming to obtain this, IXPE observed several weakly magnetized LMXBs: the two Z-sources Cyg X-2 (Farinelli et al 2023) and GX 5−1 (Fabiani et al 2023), the Z-atoll transient XTE J1701−462 (Cocchi et al 2023;Jayasurya et al 2023), the peculiar source Cir X-1 , and three atoll sources: GS 1826−238 (Capitanio et al 2023), GX 9+9 (Chatterjee et al 2023;Ursini et al 2023), and the ultracompact 4U 1820−303 (Di Marco et al 2023a). The average 2-8 keV polarization is higher in the Z-sources than in the atoll ones, and it seems to vary with the position of the sources on the Z-track in the CCD (Cocchi et al 2023;Fabiani et al 2023;.…”

Section: Deceasedmentioning

confidence: 99%

Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1

La Monaca,

Di Marco,

Poutanen

et al. 2024

ApJL

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The Imaging X-ray Polarimetry Explorer measured with high significance the X-ray polarization of the brightest Z-source, Sco X-1, resulting in the nominal 2–8 keV energy band in a polarization degree of 1.0% ± 0.2% and a polarization angle of 8° ± 6° at a 90% confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broadband spectrum from soft to hard X-rays. The source has been observed mainly in its soft state, with short periods of flaring. We also observed low-frequency quasiperiodic oscillations. From a spectropolarimetric analysis, we associate a polarization to the accretion disk at <3.2% at 90% confidence level, compatible with expectations for an electron scattering dominated optically thick atmosphere at the Sco X-1 inclination of ∼44°; for the higher-energy Comptonized component, we obtain a polarization of 1.3% ± 0.4%, in agreement with expectations for a slab of Thomson optical depth of ∼7 and an electron temperature of ∼3 keV. A polarization rotation with respect to previous observations by OSO-8 and PolarLight, and also with respect to the radio-jet position angle, is observed. This result may indicate a variation of the polarization with the source state that can be related to relativistic precession or a change in the corona geometry with the accretion flow.

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Plane polarisation in Comptonization process: A Monte Carlo study

Kumar

2024

Publ. Astron. Soc. Aust.

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High energies emissions observed in X-ray binaries (XRBs), active galactic nuclei (AGNs) are linearly polarized. The prominent mechanism for X-ray is the Comptonization process. We revisit the theory for polarization in Compton scattering with unpolarized electrons, and note that the (k×k′)-coordinate (in which, (k×k′) acts as a z-axis, here k and k′ are incident and scattered photon momentum respectively) is more convenient to describe it. Interestingly, for a fixed scattering plane the degree of polarization PD after single scattering for random oriented low-energy unpolarized incident photons is ~0.3. At the scattering angle θ = 0 orθ≡ [0,25◦], the modulation curve of k′ exhibits the same PD and PA (angle of polarization) of k, and even the distribution of projection of electric vector of k′ (k′e) on perpendicular plane to the k indicates same (so, an essential criteria for detector designing). We compute the polarization state in Comptonization process using Monte Carlo methods with considering a simple spherical corona. We obtain the PD of emergent photons as a function of =-angle (or alternatively, the disk inclination angle i) on a meridian plane (i.e., the laws of darkening, formulated by Chandrasekhar, 1946) after single scattering with unpolarized incident photons. To explore the energy dependency we consider a general spectral parameter set corresponding to hard and soft states of XRBs, we find that for average scattering no. 〈Nsc〉 ~1.1 the PD is independent of energy and PA ~ 90◦ (k′e is parallel to the disk plane), and for hNsci ~5 the PD value is maximum for i = 45◦. We also compare the results qualitatively with observation of IXPE for five sources.

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Spectro-polarimetric view of bright atoll source GX 9+9 using IXPE and AstroSat

Cited by 16 publications

References 28 publications

First Detection of X-Ray Polarization from the Accreting Neutron Star 4U 1820−303

First Detection of X-Ray Polarization from the Accreting Neutron Star 4U 1820−303

Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1

Plane polarisation in Comptonization process: A Monte Carlo study

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