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Variations in the pulsation and spectral characteristics of OAO 1657-415

Pradhan, Pragati and Maitra, Chandreyee and Paul, Biswajit and Islam, Nazma and Paul, BC (2014) Variations in the pulsation and spectral characteristics of OAO 1657-415. In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 442 (3). pp. 2691-2700.

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Official URL: http://dx.doi.org/ 10.1093/mnras/stu1034

Abstract

We present broad-band pulsation and spectral characteristics of the accreting X-ray pulsar OAO 1657-415 with a 2.2 d long Suzaku observation carried out covering its orbital phase range similar to 0.12-0.34, with respect to the mid-eclipse. During the last third of the observation, the X-ray count rate in both the X-ray Imaging Spectrometer (XIS) and the HXD-PIN instruments increased by a factor of more than 10. During this observation, the hardness ratio also changed by a factor of more than 5, uncorrelated with the intensity variations. In two segments of the observation, lasting for similar to 30-50 ks, the hardness ratio is very high. In these segments, the spectrum shows a large absorption column density and correspondingly large equivalent widths of the iron fluorescence lines. We found no conclusive evidence for the presence of a cyclotron line in the broad-band X-ray spectrum with Suzaku. The pulse profile, especially in the XIS energy band, shows evolution with time but not so with energy. We discuss the nature of the intensity variations, and variations of the absorption column density and emission lines during the duration of the observation as would be expected due to a clumpy stellar wind of the supergiant companion star. These results indicate that OAO 1657-415 has characteristics intermediate to the normal supergiant systems and the systems that show fast X-ray transient phenomena.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the OXFORD UNIV PRESS, GREAT CLARENDON ST, OXFORD OX2 6DP, ENGLAND
Keywords: pulsars: general; X-rays: binaries; X-rays: individual: OAO 1657-415
Department/Centre: Division of Physical & Mathematical Sciences > Joint Astronomy Programme
Depositing User: Id for Latest eprints
Date Deposited: 03 Sep 2014 07:49
Last Modified: 03 Sep 2014 07:49
URI: http://eprints.iisc.ac.in/id/eprint/49717

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