Soft and hard X-ray dips in the light curves of γ Cassiopeiae

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dc.contributor.authorSmith, M. A.
dc.contributor.authorOliveira, R. Lopes de
dc.date.accessioned2019-10-09T15:10:13Z
dc.date.available2019-10-09T15:10:13Z
dc.date.issued2019-07-26
dc.description.abstractThe available six archival XMM–Newton observations of the anomalous X-ray emitter γ Cas (B0.5 IVe) have been surveyed for the presence of soft X-ray ‘dips’ in X-ray light curves. In addition to discovering such events in the soft band (≤2 keV), we show that sometimes they are accompanied by minor, nearly simultaneous dips in the hard X-ray band. Herein, we investigate how these occurrences can be understood in the ‘magnetic star–disc interaction’ hypothesis proposed in the literature to explain the hard, variable X-ray emission of this Be star. In this scenario, the soft X-ray dips are interpreted as transits by comparatively dense, soft X-ray-absorbing blobs that move across the lines of sight to the surface of the Be star. We find that these blobs have similar properties as the ‘cloudlets’ responsible for migrating subfeatures in UV and optical spectral lines and therefore may be part of a common distribution of co-rotating occulters. The frequencies, amplitudes, and longevities of these dips vary widely. Additionally, the most recent spectra from 2014 July suggest that the ‘warm’ (kT ≈ 0.6–4 keV) plasma sources responsible for some of the soft flux are much more widely spread over the Be star’s surface than the hot plasma sites that dominate the flux at all X-ray energies. We finally call attention to a sudden drop in all X-ray energies of the 2014 light curve of γ Cas and a similar sudden drop in a light curve of the ‘analog’ HD 110432. We speculate that these could be related to appearances of particularly strong soft X-ray dips several hours earlier.en_US
dc.format.extent9 pagesen_US
dc.genreJournal Articlesen_US
dc.identifierdoi:10.13016/m2s2p8-zdna
dc.identifier.citationM A Smith, R Lopes de Oliveira, Soft and hard X-ray dips in the light curves of γ Cassiopeiae, Monthly Notices of the Royal Astronomical Society, Volume 488, Issue 4, October 2019, Pages 5048–5056, https://doi.org/10.1093/mnras/stz2049en_US
dc.identifier.urihttps://doi.org/10.1093/mnras/stz2049
dc.identifier.urihttp://hdl.handle.net/11603/15000
dc.language.isoen_USen_US
dc.publisherOxford University Pressen_US
dc.relation.isAvailableAtThe University of Maryland, Baltimore County (UMBC)
dc.relation.ispartofUMBC Center for Space Sciences and Technology
dc.relation.ispartofUMBC Faculty Collection
dc.rightsThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.
dc.rightsThis article has been accepted for publication in Soft and hard X-ray dips in the light curves of γ Cassiopeiae ©:2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
dc.subjectstarsen_US
dc.subjectemission lineen_US
dc.subjectmassiveen_US
dc.subjectX-raysen_US
dc.subjectBe – starsen_US
dc.titleSoft and hard X-ray dips in the light curves of γ Cassiopeiaeen_US
dc.typeTexten_US

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