Spectro-polarimetric view of bright atoll source GX 9+9 using IXPE and AstroSat

Abstract

We have carried out the first spectro-polarimetric study of the bright NS-LMXB GX 9+9 using IXPE and AstroSat observations. We report a significant detection of polarization of $1.7\pm 0.4\%$ over the $2-8$ keV energy band, with a polarization angle of $63^{\circ }\pm 7^{\circ }$. The polarization is found to be energy-dependent, with a $3\sigma$ polarization degree consistent with null polarization in $2-4$ keV, and $3.2\%$ in $4-8$ keV. Typical of the spectra seen in NS-LMXBs, we find that a combination of soft thermal emission from the accretion disc and Comptonized component from the optically thick corona produces a good fit to the spectra. We also attempt to infer the individual polarization of these components, and obtain a $3\sigma$ upper limit of $\sim 11\%$ on the polarization degree of the thermal component, and constrain that of the Comptonized component to $\sim 3\%$. We comment on the possible corona geometry of the system based on our results.

5 pages, 6 figures, Accepted for publication in MNRAS Letters

References in corpus (11)

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• Simultaneous X-ray/optical observations of GX 9+9 (4U 1728-16)
• Study of the X-ray properties of the neutron-star binary 4U 1728$-$34 from the soft to hard state
• INTEGRAL and BeppoSAX observations of the transient atoll source 4U 1608-522: from quiescent to hard spectral state
• Exploring the spreading layer of GX 9+9 using RXTE and INTEGRAL
• AstroSat view of `Clocked` burster GS 1826-238:broad-band spectral nature of persistent and burst emission during soft state

Cited by in corpus (8)

• Discovery of strongly variable X-ray polarization in the neutron star low-mass X-ray binary transient XTE J1701$-$462
• 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
• 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
• IXPE and NICER view of Black hole X-ray binary 4U 1630-47: First significant detection of polarized emission in thermal state
• Detection of significant X-ray polarization from transient NS-LMXB XTE J1701-462 with IXPE and its implication on the coronal geometry
• Constraining the geometry of the dipping atoll 4U 1624-49 with X-ray spectroscopy and polarimetry
• Correlated spectro-polarimetric study along the Z track in XTE J1701-462 puts constraints on its coronal geometry