Time-resolved UV spectroscopy of the accretion disk and wind in a super-Eddington black-hole X-ray transient

Noel Castro Segura, Christian Knigge, Knox S. Long, Diego Altamirano, Montserrat Armas Padilla, Jorges Casares, Philip A. Charles, Nathalie Degenaar, Rob Fender, Poshak Gandhi, Juan Venancio Hernandez Santisteban, Nick Higginbottom, Felipe Jimenez-Ibarra, James Matthews, Mariano Mendez, Matthew Middleton, Teo Munoz Darias, Mehtap Ozbey Arabaci, Mayukh Pahari, John PaiceMiguel Perez-Torres, Lauren Rhodes, Tom Russell, Simone Scaringi, Georgios Vasilopoulos, Federico Vicentelli, David Richard Alexander Williams, Jakob van den Eijnden

OnderzoeksoutputProfessional

Samenvatting

In October 2018, Swift announced the discovery of a new Galactic X-ray transient, Swift J1858. Just before Sun-angle constraints rendered the system unobservable, follow-up observations revealed extreme flaring activity, of a kind that has so far only been seen in the famous black hole X-ray binary (BHXRB) V404 Cyg during its 2015 eruption and in V4641 Sgr. The peculiar behaviour of these sources is thought to be a consequence of super-Eddington accretion regime. After several months of unusual strong and rapid flaring in its high-luminosity state, Swift J1858 is currently exhibiting impressive optical P-Cygni profiles, suggesting the pres- ence of a dense and cool wind from the outer accretion disk. The dominant spectroscopic signatures of such winds are actually expected to lie in the far-ultraviolet region, but they are usually inaccessible in black-hole X-ray binaries, due to interstellar reddening. Given its low extinction, Swift J1858 provides us with a rare chance to study the accretion disk wind in the crucial ultraviolet band - an opportunity that was missed in the other two systems. Building on an ongoing multi-wavelength campaign (X-rays: NICER; optical: GTC; radio: VLA & AMI), we therefore request far- and near-UV time-resolved spectroscopic observations of this system with HST/STIS+COS in order to (a) study its extreme accretion disk wind; (b) test proposed wind driving mechanisms; (c) characterize its UV variability properties and determine the origin of these variations; (d) construct the broad-band SED of the outer accretion disk that dominates the UV flux; and (e) determine the extinction towards the system in order to constrain the mass accretion rate.
Originele taal-2English
Pagina's (van-tot)15984
TijdschriftHST Proposal. Cycle 26
StatusPublished - 1-jul.-2019

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