The X-ray polarimetry view of the accreting pulsar Cen X-3

Abstract

Cen X-3 is the first X-ray pulsar discovered 50 years ago. Radiation from such objects is expected to be highly polarized due to birefringence of plasma and vacuum associated with propagation of photons in presence of the strong magnetic field. Here we present results of the observations of Cen X-3 performed with the Imaging X-ray Polarimetry Explorer. The source exhibited significant flux variability and was observed in two states different by a factor of ~20 in flux. In the low-luminosity state no significant polarization was found either in pulse phase-averaged (with the 3$\sigma$ upper limit of 12%) or phase-resolved data (the 3$\sigma$ upper limits are 20-30%). In the bright state the polarization degree of 5.8$\pm$0.3% and polarization angle of $49.6°\pm 1.5°$ with significance of about 20$\sigma$ was measured from the spectro-polarimetric analysis of the phase-averaged data. The phase-resolved analysis showed a significant anti-correlation between the flux and the polarization degree as well as strong variations of the polarization angle. The fit with the rotating vector model indicates a position angle of the pulsar spin axis of about 49$°$ and a magnetic obliquity of 17$°$. The detected relatively low polarization can be explained if the upper layers of the neutron star surface are overheated by the accreted matter and the conversion of the polarization modes occurs within the transition region between the upper hot layer and a cooler underlying atmosphere. A fraction of polarization signal can also be produced by reflection of radiation from the neutron star surface and the accretion curtain.

Submitted to ApJL. 18 pages, 12 figures

References in corpus (24)

• Physics of Strongly Magnetized Neutron Stars
• The critical accretion luminosity for magnetized neutron stars
• Analyzing the Data from X-ray Polarimeters with Stokes Parameters
• ixpeobssim: a Simulation and Analysis Framework for the Imaging X-ray Polarimetry Explorer
• Design, Construction, and Test of the Gas Pixel Detectors for the IXPE Mission
• A weighted analysis to improve the X-ray polarization sensitivity of IXPE
• Optically thick envelopes around ULXs powered by accreating neutron stars
• Pulse phase resolved analysis of the HMXB Cen X-3 over two binary orbits
• On the dependence of the X-ray continuum variations with luminosity in accreting X-ray pulsars
• Determination of X-ray pulsar geometry with IXPE polarimetry
• Distances to Galactic X-ray Binaries with Gaia DR2
• A grid of polarization models for Rayleigh scattering planetary atmospheres
• Relativistic rotating vector model for X-ray millisecond pulsars
• Spectrum formation in X-ray pulsars at very low mass accretion rate: Monte-Carlo approach
• X-ray emission from magnetized neutron star atmospheres at low mass accretion rates. I. Phase-averaged spectrum
• Observations of a GX 301-2 Apastron Flare with the X-Calibur Hard X-Ray Polarimeter Supported by NICER, the Swift XRT and BAT, and Fermi GBM
• A New Two-Fluid Radiation-Hydrodynamical Model for X-ray Pulsar Accretion Columns
• Long-term evolutions of the cyclotron line energies in Her X-1, Vela X-1 and Cen X-3 as observed with Swift/BAT
• Cyclotron line formation by reflection on the surface of a magnetic neutron star
• X-ray variability of the HMXB Cen X-3: evidence for inhomogeneous accretion flows
• Fitting strategies of accretion column models and application to the broadband spectrum of Cen X-3
• New measurements of the cyclotron line energy in Cen X-3
• Statistical features of multiple Compton scattering in a strong magnetic field
• Analysis of Polarimetry Data with Angular Uncertainties

Cited by in corpus (29)

• X-ray polarimetry of X-ray pulsar X Persei: another orthogonal rotator?
• X-ray pulsar GRO J1008$-$57 as an orthogonal rotator
• Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431
• IXPE observations of the quintessential wind-accreting X-ray pulsar Vela X-1
• X-ray polarimetry of the accreting pulsar GX 301-2
• A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375
• Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1
• X-ray Polarimetry of X-ray Pulsars
• Studying geometry of the ultraluminous X-ray pulsar Swift J0243.6+6124 using X-ray and optical polarimetry
• Probing the polarized emission from SMC X-1: the brightest X-ray pulsar observed by IXPE
• Discovery of Polarized X-Ray Emission from the Accreting Millisecond Pulsar SRGA J144459.2-604207
• Detection of the orbital modulation of Fe K$\alpha$ fluorescence emission in Centaurus X-3 using the high-resolution spectrometer Resolve onboard XRISM
• Orbital- and spin-phase variability in the X-ray emission from the accreting pulsar Cen X-3
• Beam pattern evolution of accreting X-ray pulsar 1A 0535+262 during its 2020 giant outburst
• Vacuum polarization alters the spectra of accreting X-ray pulsars
• X-ray Polarimetry of the accreting pulsar 1A~0535+262 in the supercritical state with PolarLight
• X-Ray Views of Galactic Accreting Pulsars in High-Mass X-Ray Binaries
• Revealing two orthogonally polarized spectral components in Vela X-1 with IXPE
• Neutrino beaming in ultraluminous X-ray pulsars as a result of gravitational lensing by neutron stars
• Energy-resolved pulse profile changes in V 0332+53: Indications of wings in the cyclotron absorption line profile
• Exploring polarization and geometry in the X-ray pulsar 4U 1538-52
• Studying the variations of the cyclotron line in Cen X-3 using Insight-HXMT
• Temporal and spectral variations of the X-ray pulsar Cen X-3 observed by NuSTAR
• Orbital variability of polarized X-ray radiation reflected from a companion star in X-ray binaries
• Optimal Summary Statistics for X-ray Polarization
• First Detection of X-ray Polarization and Its Short-term Increase Pre- and Post-Eclipse in HMXB 4U 1700-377
• XMM-Newton view of pulsating iron fluorescent emission from Centaurus X3
• Probing the polarized emission from the accretion-powered pulsar 4U 1907+09 with IXPE
• The X-ray binaries in M83: will any of them form gravitational wave sources for LIGO/VIRGO/KAGRA?