Polarization properties of weakly magnetized neutron stars in low-mass X-ray binaries

Gnarini, Andrea; Ursini, F.; Matt, Giorgio; Bianchi, S.; Capitanio, F.; Cocchi, M.; Farinelli, R.; Zhang, Wenda

doi:10.1093/mnras/stac1523

Cited by 15 publications

(16 citation statements)

References 31 publications

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“…As reported in Gnarini et al (2022), a blackbody spectrum is assumed to model the unpolarized NS surface emission, while the seed photons from the disk are generated according to the disk emissivity. The hot electron corona is illuminated by both the NS and the accretion disk, and, when a photon reaches the corona, it is Compton scattered, assuming the Klein-Nishina cross section.…”

Section: Discussionmentioning

confidence: 99%

“…1. Pseudotoroidal geometry (as defined in Gnarini et al 2022): a rectangular section torus with similar vertical and horizontal length scales (2H ∼ ΔR) corotating with the disk. As reported in Gnarini et al (2022), the slab corona is assumed to cover only part of the disk, starting from the inner disk radius until 15 gravitational radii, while the vertical thickness is set in order to cover most of the NS surface.…”

Section: Discussionmentioning

confidence: 99%

“…Shell geometry: a stationary spherical shell surrounding the NS (roughly mimicking the SL of Inogamov & Sunyaev 1999). We chose the same radius used in Gnarini et al (2022). 55 However, when varying the radius of the shell, the symmetry does not change; consequently, the PD remains substantially unvaried.…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, we can derive a relatively stringent upper limit on the viewing angle: i  47°(see the right panel of Figure 6). The PA for the pseudotoroidal geometry is misaligned and not perpendicular with respect to the disk as a result of the sum of the disk and NS contributions together with general relativity (GR)effects (see Gnarini et al 2022, for more details on this geometry).…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, either the GS 1826-238 system could have a spherical symmetry, or its inclination is lower than previously measured. In fact, most of the simulations show (see, e.g., Schnittman & Krolik 2009;Gnarini et al 2022) that small viewing angles correspond to a lower fraction of polarized light emitted by a source.…”

Section: Discussionmentioning

confidence: 99%

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Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826–238 in the High Soft State

Capitanio

Fabiani

Gnarini

et al. 2023

ApJ

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The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December 9 has opened a new window in X-ray astronomy. We report here the results of the first IXPE observation of a weakly magnetized neutron star, GS 1826−238, performed on 2022 March 29–31 when the source was in a high soft state. An upper limit (99.73% confidence level) of 1.3% for the linear polarization degree is obtained over the IXPE 2–8 keV energy range. Coordinated INTEGRAL and NICER observations were carried out simultaneously with IXPE. The spectral parameters obtained from the fits to the broadband spectrum were used as inputs for Monte Carlo simulations considering different possible geometries of the X-ray emitting region. Comparing the IXPE upper limit with these simulations, we can put constraints on the geometry and inclination angle of GS 1826–238.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 3 more Smart Citations

Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826–238 in the High Soft State

Capitanio

Fabiani

Gnarini

et al. 2023

ApJ

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X-ray polarimetry and spectroscopy of the neutron star low-mass X-ray binary GX 9+9: An in-depth study with IXPE and NuSTAR

Ursini¹,

Farinelli²,

Gnarini³

et al. 2023

A&A

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We report on a comprehensive analysis of simultaneous X-ray polarimetric and spectral data of the bright atoll source GX 9+9 with the Imaging X-ray Polarimetry Explorer (IXPE) and NuSTAR. The source is significantly polarized in the 4–8 keV band, with a degree of 2.2% ± 0.5% (uncertainty at the 68% confidence level). The NuSTAR broad-band spectrum clearly shows an iron line, and is well described by a model including thermal disc emission, a Comptonized component, and reflection. From a spectro-polarimetric fit, we obtain an upper limit to the polarization degree of the disc of 4% (at the 99% confidence level), while the contribution of Comptonized and reflected radiation cannot be conclusively separated. However, the polarization is consistent with resulting from a combination of Comptonization in a boundary or spreading layer, plus reflection off the disc, which significantly contributes in any realistic scenario.

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Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1

Bobrikova,

Forsblom,

Di Marco

et al. 2024

A&A

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Weakly magnetized neutron stars in X-ray binaries show a complex phenomenology with several spectral components that can be associated with the accretion disk, the boundary, and/or a spreading layer, a corona, and a wind. Spectroscopic information alone, however, is not enough to distinguish these components. The analysis of the timing data revealed that most of the variability, and in particular, kilohertz quasi-period oscillations, are associated with the high-energy component that corresponds to the boundary and/or spreading layer. Additional information about the nature of the spectral components, and in particular, about the geometry of the emission region, can be provided by X-ray polarimetry. One of the objects of the class, a bright, persistent, and rather peculiar galactic Type I X-ray burster GX 13+1, was observed with the Imaging X-ray Polarimetry Explorer (IXPE) and the XMM–Newton. Using the XMM–Newton data, we obtained the best-fit values for the continuum spectral parameters and detected strong absorption lines associated with the accretion disk wind. IXPE data showed the source to be significantly polarized in the 2–8 keV energy band, with an overall polarization degree (PD) of 1.4%±0.3% at a polarization angle (PA) of −2° ±6° (errors at the 68% confidence level). During the two-day long observation, we detected rotation of the PA by about 70° with the corresponding changes in the PD from 2% to nondetectable and then up to 5%. These variations in polarization properties are not accompanied by visible spectral state changes of the source. The energy-resolved polarimetric analysis showed a significant change in polarization, from being strongly dependent on energy at the beginning of the observation to being almost constant with energy in the later parts of the observation. As a possible interpretation, we suggest a constant polarization component, strong wind scattering, or a different polarization of the two main spectral components with an individually peculiar behavior. The rotation of the PA suggests a misalignment of the neutron star spin from the orbital axis.

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Polarization properties of weakly magnetized neutron stars in low-mass X-ray binaries

Cited by 15 publications

References 31 publications

Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826–238 in the High Soft State

Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826–238 in the High Soft State

X-ray polarimetry and spectroscopy of the neutron star low-mass X-ray binary GX 9+9: An in-depth study with IXPE and NuSTAR

Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1

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