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

Abstract

The Imaging X-ray Polarimetry Explorer (IXPE) measured with high significance the X-ray polarization of the brightest Z-source Scorpius 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 90% of confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broad-band 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 quasi-periodic oscillations. From a spectro-polarimetric analysis, we associate a polarization to the accretion disk at <3.2% at 90% of 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 to a change in the corona geometry with the accretion flow.

References in corpus (26)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Analyzing the Data from X-ray Polarimeters with Stokes Parameters
• ixpeobssim: a Simulation and Analysis Framework for the Imaging X-ray Polarimetry Explorer
• Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1
• Relativistic iron emission lines in neutron star low-mass X-ray binaries as probes of neutron star radii
• Handling Background in IXPE polarimetric data
• A rapidly-changing jet orientation in the stellar-mass black hole V404 Cygni
• A weighted analysis to improve the X-ray polarization sensitivity of IXPE
• Relativistic X-ray Reflection Models for Accreting Neutron Stars
• Polarized X-rays from windy accretion in Cygnus X-1
• Distances to Galactic X-ray Binaries with Gaia DR2
• Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements
• Discovery of strongly variable X-ray polarization in the neutron star low-mass X-ray binary transient XTE J1701$-$462
• Radius Constraints from Reflection Modeling of Cygnus X-2 with NuSTAR and NICER
• X-ray polarimetry and spectroscopy of the neutron star low-mass X-ray binary GX 9+9: an in-depth study with IXPE and NuSTAR
• In-flight calibration system of Imaging X-ray Polarimetry Explorer
• Polarization properties of weakly magnetized Neutron Stars in Low Mass X-ray Binaries
• Polarization properties of the weakly magnetized neutron star X-ray binary GS 1826-238 in the high soft state
• First detection of X-ray polarization from the accreting neutron star 4U 1820-303
• X-ray spectral and timing behavior of Scorpius X-1. Spectral hardening during the flaring branch
• A connection between accretion states and the formation of ultra-relativistic outflows in a neutron star X-ray binary
• On the illumination of neutron star accretion discs
• Spectro-polarimetric view of bright atoll source GX 9+9 using IXPE and AstroSat
• Detection of significant X-ray polarization from transient NS-LMXB XTE J1701-462 with IXPE and its implication on the coronal geometry
• Fe K$\alpha$ and Fe K$\beta$ line detection in the NuSTAR spectrum of the ultra-bright Z-source Scorpius X-1
• Evidence of hard power-law spectral cutoff and disc reflection features from the X-ray transient XTE J1739-285

Cited by in corpus (12)

• X-ray polarization from accretion disk winds
• Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1
• New polarimetric study of the galactic X-ray burster GX 13+1
• Polarized radiation from the spreading layer of the weakly magnetized neutron stars
• X-ray spectro-polarimetric characterization of GX 340+0 in the horizontal branch: a highly inclined source?
• Constraining the geometry of the dipping atoll 4U 1624-49 with X-ray spectroscopy and polarimetry
• X-ray Dips and Polarization Angle Swings in GX 13+1
• X-ray polarization of Z-type neutron star low-mass X-ray binaries -- I. Model-independent, time-resolved X-ray polarimetry
• X-ray spectropolarimetric characterization of the Z-source GX 340+0 in the normal branch
• IXPE view of the Sco-like source GX 349+2 in the normal branch
• Resolving SLX 1744-299 and SLX 1744-300 in the hard X-ray band: implications for their ultracompact nature
• X-ray polarization of Z-type neutron star low-mass X-ray binaries -- II. Spectropolarimetric analysis