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

Abstract

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 $2.2\%\pm 0.5\%$ (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 disk emission, a Comptonized component, and reflection. From a spectro-polarimetric fit, we obtain an upper limit to the polarization degree of the disk of 4% (at 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 gives a significant contribution in any realistic scenario.

10 pages, accepted for publication in A&A

References in corpus (27)

• The role of the reflection fraction in constraining black hole spin
• ixpeobssim: a Simulation and Analysis Framework for the Imaging X-ray Polarimetry Explorer
• Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients
• Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1
• Black hole-like hysteresis and accretion states in neutron star low mass X-ray binaries
• Handling Background in IXPE polarimetric data
• Average hard X-ray emission from NS LMXBs: Observational evidence of different spectral states in NS LMXBs
• A relativistically smeared spectrum in the neutron star X-ray Binary 4U 1705-44: Looking at the inner accretion disc with X-ray spectroscopy
• Analysing the atolls: X-ray spectral transitions of accreting neutron stars
• A new Comptonization model for low-magnetized accreting neutron stars in low mass X-ray binaries
• Constraining the size of the corona with fully relativistic calculations of spectra of extended corona. I - the Monte Carlo radiative transfer code
• A Hard Look at the Neutron Stars and Accretion Disks in 4U 1636-53, GX 17+2, and 4U 1705-44 with $\text{NuSTAR}$
• Polarized x-rays from a magnetar
• Relativistic X-ray Reflection Models for Accreting Neutron Stars
• NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371
• Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements
• Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16
• Radius Constraints from Reflection Modeling of Cygnus X-2 with NuSTAR and NICER
• 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
• NuSTAR view of the Z-type neutron star low-mass X-ray binary Cygnus~X--2
• On the illumination of neutron star accretion discs
• Spectro-polarimetric view of bright atoll source GX 9+9 using IXPE and AstroSat
• Simultaneous X-ray/optical observations of GX 9+9 (4U 1728-16)
• Reflection component in the Bright Atoll Source GX 9+9
• Exploring the spreading layer of GX 9+9 using RXTE and INTEGRAL
• Decades' long-term variations in NS-LMXBs observed with MAXI/GSC, RXTE/ASM and Ginga/ASM

Cited by in corpus (17)

• Dramatic Drop in the X-Ray Polarization of Swift J1727.8$-$1613 in the Soft Spectral State
• Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1
• First detection of X-ray polarization from the accreting neutron star 4U 1820-303
• X-ray polarisation properties of thermal-radiative disc winds in binary systems
• X-Ray Polarized View on the Accretion Geometry in the X-Ray Binary Circinus X-1
• 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
• Detection of significant X-ray polarization from transient NS-LMXB XTE J1701-462 with IXPE and its implication on the coronal geometry
• 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
• Correlated spectro-polarimetric study along the Z track in XTE J1701-462 puts constraints on its coronal geometry
• The detection of high X-ray polarization from an accretion disc corona source and its modelling via Monte Carlo radiation transfer simulation
• X-ray polarization of Z-type neutron star low-mass X-ray binaries -- II. Spectropolarimetric analysis
• Shape and ionization of equatorial matter near compact objects from X-ray polarization reflection signatures