Multitude of iron lines including a Compton scattered component in OAO 1657–415 detected with Chandra. (arXiv:1812.06108v1 [astro-ph.HE])

Multitude of iron lines including a Compton scattered component in OAO 1657–415 detected with Chandra. (arXiv:1812.06108v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Pradhan_P/0/1/0/all/0/1">Pragati Pradhan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Raman_G/0/1/0/all/0/1">Gayathri Raman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Paul_B/0/1/0/all/0/1">Biswajit Paul</a>

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$_alpha$ 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$_alpha$, Fe $K_beta$ and Ni $K_alpha$ 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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