Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1

Abstract

Most ultraluminous X-ray sources (ULXs) are believed to be stellar mass black holes or neutron stars accreting beyond the Eddington limit. Determining the nature of the compact object and the accretion mode from broad-band spectroscopy is currently a challenge, but the observed timing properties provide insight into the compact object and details of the geometry and accretion processes. Here, we report a timing analysis for an 800 ks XMM–Newton campaign on the supersoft ultraluminous X-ray source, NGC 247 ULX-1. Deep and frequent dips occur in the X-ray light curve, with the amplitude increasing with increasing energy band. Power spectra and coherence analysis reveals the dipping preferentially occurs on ∼5 and ∼10 ks time-scales. The dips can be caused by either the occultation of the central X-ray source by an optically thick structure, such as warping of the accretion disc, or from obscuration by a wind launched from the accretion disc, or both. This behaviour supports the idea that supersoft ULXs are viewed close to edge-on to the accretion disc.

Additional Information

© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2021 May 18. Received 2021 May 18; in original form 2021 April 20. Published: 25 May 2021. WNA is supported by an ESA research fellowship. AD, MDS, and FP acknowledge financial contribution from the agreement ASI-INAF n.2017-14-H.0 and INAF main-stream. HPE acknowledges support under NASA contract NNG08FD60C. TPR gratefully acknowledges support from the Science and Technology Facilities Council (STFC) as part of the consolidated grant award ST/000244/1. This paper is based on observations obtained with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Data Availability: All of the data underlying this article are publicly available from ESA's XMM–Newton Science Archive (XSA; https://www.cosmos.esa.int/web/xmm-newton/xsa) and NASA's HEASARC archive (https://heasarc.gsfc.nasa.gov/). Light curves are available from the author upon request.

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Accepted Version - 2104.11163.pdf

Published - stab1473.pdf

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