X-ray polarimetry of the accreting pulsar GX 301-2

Abstract

The phase- and energy-resolved polarization measurements of accreting X-ray pulsars (XRPs) allow us to test different theoretical models of their emission, and they also provide an avenue to determine the emission region geometry. We present the results of the observations of the XRP GX 301-2 performed with the Imaging X-ray Polarimetry Explorer (IXPE). A persistent XRP, GX 301-2 has one of the longest spin periods known: $\sim$680s. A massive hyper-giant companion star Wray 977 supplies mass to the neutron star via powerful stellar winds. We did not detect significant polarization in the phase-averaged data when using spectro-polarimetric analysis, with the upper limit on the polarization degree (PD) of 2.3% (99% confidence level). Using the phase-resolved spectro-polarimetric analysis, we obtained a significant detection of polarization (above 99% confidence level) in two out of nine phase bins and a marginal detection in three bins, with a PD ranging between $\sim$3% and $\sim$10% and a polarization angle varying in a very wide range from $\sim$0 degree to $\sim$160 degree. Using the rotating vector model, we obtained constraints on the pulsar geometry using both phase-binned and unbinned analyses, finding excellent agreement. Finally, we discuss possible reasons for a low observed polarization in GX 301-2.

10 pages, 10 figures, accepted for publication in A&A

References in corpus (24)

• Physics of Strongly Magnetized Neutron Stars
• The SRG X-ray orbital observatory, its telescopes and first scientific results
• The critical accretion luminosity for magnetized neutron stars
• ixpeobssim: a Simulation and Analysis Framework for the Imaging X-ray Polarimetry Explorer
• Analyzing the Data from X-ray Polarimeters with Stokes Parameters
• The ART-XC telescope on board the SRG observatory
• Design, Construction, and Test of the Gas Pixel Detectors for the IXPE Mission
• Handling Background in IXPE polarimetric data
• VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2
• Determination of X-ray pulsar geometry with IXPE polarimetry
• Relativistic rotating vector model for X-ray millisecond pulsars
• Stellar Wind Accretion in GX301-2: Evidence for a High-density Stream
• The X-ray polarimetry view of the accreting pulsar Cen X-3
• 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
• X-ray pulsar GRO J1008$-$57 as an orthogonal rotator
• X-ray polarimetry of X-ray pulsar X Persei: another orthogonal rotator?
• Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431
• IXPE observations of the quintessential wind-accreting X-ray pulsar Vela X-1
• A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375
• Unbinned Likelihood Analysis for X-ray Polarization
• Observations of 4U 1626-67 with the Imaging X-ray Polarimetry Explorer
• X-ray reprocessing in accreting pulsar GX 301-2 observed with Insight-HXMT
• Discovery of a retrogradely rotating neutron star in the X-ray pulsar GX 301$-$2
• Expected polarization properties of nonmagnetized CCOs

Cited by in corpus (12)

• 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
• Characterization of High-polarization Stars and Blazars with DIPOL-1 at Sierra Nevada Observatory
• Polarized radiation from an accretion shock in accreting millisecond pulsars using exact Compton scattering formalism
• The giant outburst of EXO 2030+375 I: Spectral and pulse profile evolution
• Variability of X-ray polarization of Cyg X-1
• An in-depth analysis of the variable cyclotron lines in GX 301$-$2
• Revealing two orthogonally polarized spectral components in Vela X-1 with IXPE
• Exploring polarization and geometry in the X-ray pulsar 4U 1538-52
• Orbital variability of polarized X-ray radiation reflected from a companion star in X-ray binaries