The origin of optical emission lines in the soft state of X-ray binary outbursts: The case of MAXI J1820+070

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dc.contributorAalto-yliopistofi
dc.contributorAalto Universityen
dc.contributor.authorKoljonen, K. I.I.en_US
dc.contributor.authorLong, K. S.en_US
dc.contributor.authorMatthews, J. H.en_US
dc.contributor.authorKnigge, C.en_US
dc.contributor.departmentMetsähovi Radio Observatoryen
dc.contributor.organizationSpace Telescope Science Instituteen_US
dc.contributor.organizationUniversity of Oxforden_US
dc.contributor.organizationUniversity of Southamptonen_US
dc.date.accessioned2023-06-14T08:53:13Z
dc.date.available2023-06-14T08:53:13Z
dc.date.issued2023-05-01en_US
dc.descriptionPublisher Copyright: © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
dc.description.abstractThe optical emission line spectra of X-ray binaries (XRBs) are thought to be produced in an irradiated atmosphere, possibly the base of a wind, located above the outer accretion disc. However, the physical nature of - and physical conditions in - the line-forming region remain poorly understood. Here, we test the idea that the optical spectrum is formed in the transition region between the cool geometrically thin part of the disc near the mid-plane and a hot vertically extended atmosphere or outflow produced by X-ray irradiation. We first present a VLT X-Shooter spectrum of XRB MAXI J1820+070 in the soft state associated with its 2018 outburst, which displays a rich set of double-peaked hydrogen and helium recombination lines. Aided by ancillary X-ray spectra and reddening estimates, we then model this spectrum with the Monte Carlo radiative transfer code python, using a simple biconical disc wind model inspired by radiation-hydrodynamic simulations of irradiation-driven outflows from XRB discs. Such a model can qualitatively reproduce the observed features; nearly all of the optical emission arising from the transonic 'transition region' near the base of the wind. In this region, characteristic electron densities are on the order of 1012-13 cm-3, in line with the observed flat Balmer decrement (H α/H β ≈ 1.3). We conclude that strong irradiation can naturally give rise to both the optical line-forming layer in XRB discs and an overlying outflow/atmosphere that produces X-ray absorption lines.en
dc.description.versionPeer revieweden
dc.format.extent17
dc.format.extent4190-4206
dc.format.mimetypeapplication/pdfen_US
dc.identifier.citationKoljonen, K I I, Long, K S, Matthews, J H & Knigge, C 2023, ' The origin of optical emission lines in the soft state of X-ray binary outbursts: The case of MAXI J1820+070 ', Monthly Notices of the Royal Astronomical Society, vol. 521, no. 3, pp. 4190-4206 . https://doi.org/10.1093/mnras/stad809en
dc.identifier.doi10.1093/mnras/stad809en_US
dc.identifier.issn0035-8711
dc.identifier.issn1365-2966
dc.identifier.otherPURE UUID: f2693edf-adce-4617-8fd0-4ec42adb0761en_US
dc.identifier.otherPURE ITEMURL: https://research.aalto.fi/en/publications/f2693edf-adce-4617-8fd0-4ec42adb0761en_US
dc.identifier.otherPURE LINK: http://www.scopus.com/inward/record.url?scp=85160283404&partnerID=8YFLogxKen_US
dc.identifier.otherPURE FILEURL: https://research.aalto.fi/files/113381887/stad809.pdfen_US
dc.identifier.urihttps://aaltodoc.aalto.fi/handle/123456789/121480
dc.identifier.urnURN:NBN:fi:aalto-202306143857
dc.language.isoenen
dc.publisherOxford University Press
dc.relation.ispartofseriesMonthly Notices of the Royal Astronomical Societyen
dc.relation.ispartofseriesVolume 521, issue 3en
dc.rightsopenAccessen
dc.subject.keywordAccretion, accretion discsen_US
dc.subject.keywordbinaries: closeen_US
dc.subject.keywordstars: individual: MAXI J1820+070en_US
dc.subject.keywordstars: winds, outflowsen_US
dc.subject.keywordX-rays: binariesen_US
dc.titleThe origin of optical emission lines in the soft state of X-ray binary outbursts: The case of MAXI J1820+070en
dc.typeA1 Alkuperäisartikkeli tieteellisessä aikakauslehdessäfi
dc.type.versionpublishedVersion
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