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

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${}_{\alpha }$ 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.

16 pages, 5 figures, accepted for publication in MNRAS

References in corpus (6)

• The ephemeris, orbital decay, and masses of 10 eclipsing HMXBs
• X-ray Spectral Study of the Photoionized Stellar Wind in Vela~X-1
• INTEGRAL observations of the variability of OAO 1657-415
• Sensitivity of the Fe K-alpha Compton shoulder to the geometry and variability of the X-ray illumination of cosmic objects
• Orbital phase resolved spectroscopy of GX 301-2 with MAXI
• Variations in the pulsation and spectral characteristics of OAO 1657-415

Cited by in corpus (6)

• Timing and Spectral Analysis of HMXB OAO 1657-415 with NuSTAR
• Comprehensive broadband study of accreting neutron stars with Suzaku: Is there a bi-modality in the X-ray spectrum?
• A NuSTAR observation of the eclipsing binary system OAO 1657-415: The revival of the cyclotron line
• Variable structures in the stellar wind of the HMXB Vela X-1
• AstroSat observations of eclipsing high mass X-ray binary pulsar OAO 1657-415
• Clumpy wind studies and the non-detection of cyclotron line in OAO 1657-415