A persistent ultraviolet outflow from an accreting neutron star binary transient

N Castro Segura; C Knigge; K S Long; D Altamirano; M Armas Padilla; C Bailyn; D A H Buckley; D J K Buisson; J Casares; P Charles; J A Combi; V A Cúneo; N D Degenaar; S Del Palacio; M Díaz Trigo; R Fender; P Gandhi; M Georganti; C Gutiérrez; J V Hernandez Santisteban; F Jiménez-Ibarra; J Matthews; M Méndez; M Middleton; T Muñoz-Darias; M Özbey Arabacı; M Pahari; L Rhodes; T D Russell; S Scaringi; J van den Eijnden; G Vasilopoulos; F M Vincentelli; P Wiseman

doi:10.1038/s41586-021-04324-2

A persistent ultraviolet outflow from an accreting neutron star binary transient

Nature. 2022 Mar;603(7899):52-57. doi: 10.1038/s41586-021-04324-2. Epub 2022 Mar 2.

Authors

N Castro Segura¹, C Knigge², K S Long^{3

4}, D Altamirano², M Armas Padilla^{5

6}, C Bailyn⁷, D A H Buckley⁸, D J K Buisson², J Casares^{5

6}, P Charles², J A Combi⁹, V A Cúneo^{5

6}, N D Degenaar¹⁰, S Del Palacio⁹, M Díaz Trigo¹¹, R Fender¹², P Gandhi², M Georganti², C Gutiérrez^{2

13

14}, J V Hernandez Santisteban¹⁵, F Jiménez-Ibarra^{16

17}, J Matthews¹⁸, M Méndez¹⁹, M Middleton², T Muñoz-Darias^{5

6}, M Özbey Arabacı², M Pahari^{2

20}, L Rhodes¹², T D Russell^{10

21}, S Scaringi²², J van den Eijnden^{10

12}, G Vasilopoulos^{7

23}, F M Vincentelli², P Wiseman²

Affiliations

¹ Department of Physics & Astronomy, University of Southampton, Southampton, UK. N.Castro-Segura@soton.ac.uk.
² Department of Physics & Astronomy, University of Southampton, Southampton, UK.
³ Space Telescope Science Institute, Baltimore, MD, USA.
⁴ Eureka Scientific, Inc., Oakland, CA, USA.
⁵ Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain.
⁶ Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Tenerife, Spain.
⁷ Department of Astronomy, Yale University, New Haven, CT, USA.
⁸ South African Astronomical Observatory, Cape Town, South Africa.
⁹ Instituto Argentino de Radioastronoma (CONICET; CICPBA; UNLP), Villa Elisa, Argentina.
¹⁰ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands.
¹¹ ESO, Garching bei München, Germany.
¹² Astrophysics, Department of Physics, University of Oxford, Oxford, UK.
¹³ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Turku, Finland.
¹⁴ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Turku, Finland.
¹⁵ SUPA School of Physics & Astronomy, University of St Andrews, St Andrews, UK.
¹⁶ Department of Physics and Astronomy, Macquarie University, Sydney, New South Wales, Australia.
¹⁷ Research Centre in Astronomy, Astrophysics and Astrophotonics, Macquarie University, Sydney, New South Wales, Australia.
¹⁸ Institute of Astronomy, University of Cambridge, Cambridge, UK.
¹⁹ Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands.
²⁰ Department of Physics, IIT Hyderabad, Hyderabad, India.
²¹ INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Palermo, Italy.
²² Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham, UK.
²³ Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550, Strasbourg, France.

PMID: 35236977
DOI: 10.1038/s41586-021-04324-2

Abstract

All disc-accreting astrophysical objects produce powerful disc winds. In compact binaries containing neutron stars or black holes, accretion often takes place during violent outbursts. The main disc wind signatures during these eruptions are blue-shifted X-ray absorption lines, which are preferentially seen in disc-dominated 'soft states'^1,2. By contrast, optical wind-formed lines have recently been detected in 'hard states', when a hot corona dominates the luminosity³. The relationship between these signatures is unknown, and no erupting system has as yet revealed wind-formed lines between the X-ray and optical bands, despite the many strong resonance transitions in this ultraviolet (UV) region⁴. Here we report that the transient neutron star binary Swift J1858.6-0814 exhibits wind-formed, blue-shifted absorption lines associated with C IV, N V and He II in time-resolved UV spectroscopy during a luminous hard state, which we interpret as a warm, moderately ionized outflow component in this state. Simultaneously observed optical lines also display transient blue-shifted absorption. Decomposing the UV data into constant and variable components, the blue-shifted absorption is associated with the former. This implies that the outflow is not associated with the luminous flares in the data. The joint presence of UV and optical wind features reveals a multi-phase and/or spatially stratified evaporative outflow from the outer disc⁵. This type of persistent mass loss across all accretion states has been predicted by radiation-hydrodynamic simulations⁶ and helps to explain the shorter-than-expected duration of outbursts⁷.