Abstract
We present the results obtained from analysis of two AstroSat observations of the high mass X-ray binary pulsar OAO 1657-415. The observations covered 0.681–0.818 and 0.808–0.968 phases of the \(\sim \)10.4 day orbital period of the system, in March and July 2019, respectively. Despite being outside the eclipsing regime, the power density spectrum from the first observation lacks any signature of pulsation or quasi-periodic oscillations. However, during July observation, X-ray pulsations at a period of 37.0375 s were clearly detected in the light curves. The pulse profiles from the second observation consist of a broad single peak with a dip-like structure in the middle across the observed energy range. We explored evolution of the pulse profile in narrow time and energy segments. We detected pulsations in the light curves obtained from 0.808–0.92 orbital phase range, which is absent in the remaining part of the observation. The spectrum of OAO 1657-415 can be described by an absorbed power-law model along with an iron fluorescent emission line and a blackbody component for out-of-eclipse phase of the observation. Our findings are discussed in the frame of stellar wind accretion and accretion wake at late orbital phases of the binary.
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Acknowledgements
We thank the anonymous referee for suggestions on our paper. This publication uses the data from AstroSat mission of the ISRO, archived at the Indian Space Science Data Centre. We thank members of SXT, LAXPC, and CZTI instrument teams for their contribution to the development of the instruments and analysis software. LAXPC data were processed by the Payload Operation Centre at TIFR, Mumbai. This work was performed utilizing the calibration data-bases and auxiliary analysis tools developed, maintained and distributed by the AstroSat-SXT team with members from various institutions in India and abroad, and the SXT Payload Operation Center (POC) at the TIFR, Mumbai (https://www.tifr.res.in/~astrosat_sxt/index.html). SXT data were processed and verified by the SXT POC. SN, BC and AJ acknowledges the support from Physical Research Laboratory which is funded by the Department of Space, India.
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This article is part of the Special Issue on: “AstroSat: Five Years in Orbit”.
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Jaisawal, G.K., Naik, S., Epili, P.R. et al. AstroSat observations of eclipsing high mass X-ray binary pulsar OAO 1657-415. J Astrophys Astron 42, 72 (2021). https://doi.org/10.1007/s12036-021-09701-x
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DOI: https://doi.org/10.1007/s12036-021-09701-x