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arXiv · 1812.06108

Multitude of iron lines including a Compton scattered component in OAO 1657--415 detected with Chandra

Pragati Pradhan·Gayathri Raman·Biswajit Paul
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Abstract

We present a high resolution X-ray spectrum of the accreting X-ray pulsar, OAO 1657--415 with HETG+ACIS-S onboard \emph{Chandra},revealing the presence of a broad line component around $\sim$ 6.3 keV associated with the neutral iron K$_α$ line at 6.4 \rm{keV}. This is interpreted as Compton shoulder arising from the Compton scattering of the 6.4 \rm{keV} fluorescence photons making OAO 1657--415 the second accreting neutron star where such a feature is detected. A Compton shoulder reveals the presence of dense matter surrounding the X-ray source. We did not detect any periodicity in the lightcurve and obtained an upper limit of $\sim$ 2\% for the pulse fraction during this observation. This could be due to the smearing of the pulses when X-ray photons are scattered from a large region around the neutron star. In addition to the Fe K$_α$, Fe $K_β$ and Ni $K_α$ lines already reported for this source, we also report for the first time, the presence of He-like and H-like iron emission lines at 6.7 and 6.97 \rm{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.

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Pragati Pradhan, Gayathri Raman, Biswajit Paul. 2018-12-14. Multitude of iron lines including a Compton scattered component in OAO 1657--415 detected with Chandra. https://doi.org/10.1093/mnras%2Fsty3441

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