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Title: Multitude of iron lines including a Compton-scattered component in OAO 1657 – 415 detected with Chandra
Authors: Pradhan, Pragati
Raman, Gayathri
Paul, Biswajit
Keywords: stars: pulsars: general
X-rays: binaries
X-rays: individual: OAO 1657 – 415
Issue Date: Mar-2019
Publisher: Oxford University Press on behalf of the Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, 2019, Vol.483, p 5687–5693
Abstract: We present a high-resolution X-ray spectrum of the accreting X-ray pulsar OAO 1657 – 415 obtained with HETG + ACIS-S onboard Chandra, revealing the presence of a broad line component around ∼6.3 keV associated with the neutral iron Kα line at 6.4 keV. This is interpreted as a Compton shoulder arising from the Compton-scattering of the 6.4-keV fluorescence photons, making OAO 1657–415 the second accreting neutron star in which such a feature has been detected. A Compton shoulder reveals the presence of dense matter surrounding the X-ray source. We did not detect any periodicity in the light-curve and we obtained an upper limit of ∼2 per cent for the pulse fraction during this observation. This could be a result of the smearing of the pulses when X-ray photons are scattered from a large region around the neutron star. In addition to the Fe Kα, Fe Kβ and Ni Kα lines already reported for this source, we report for the first time the presence of He-like and H-like iron emission lines at 6.7 and 6.97 keV in the first-order HETG spectrum. The detection of such ionized lines, indicative of a highly ionized surrounding medium, is rare in X-ray binaries.
Description: Open Access.
ISSN: 0035-8711
1365-2966 - (online)
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Copyright: 2019 The Author(s)
Appears in Collections:Research Papers (A&A)

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