Kavli Affiliate: Herman L. Marshall
| First 5 Authors: Valery F. Suleimanov, Sofia V. Forsblom, Sergey S. Tsygankov, Juri Poutanen, Victor Doroshenko
| Summary:
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.
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