Ubiquitous equatorial accretion disc winds in black hole soft states

Abstract

High resolution spectra of Galactic Black Holes (GBH) reveal the presence of highly ionised absorbers. In one GBH, accreting close to the Eddington limit for more than a decade, a powerful accretion disc wind is observed to be present in softer X-ray states and it has been suggested that it can carry away enough mass and energy to quench the radio jet. Here we report that these winds, which may have mass outflow rates of the order of the inner accretion rate or higher, are an ubiquitous component of the jet-free soft states of all GBH. We furthermore demonstrate that these winds have an equatorial geometry with opening angles of few tens of degrees, and so are only observed in sources in which the disc is inclined at a large angle to the line of sight. The decrease in Fe XXV / Fe XXVI line ratio with Compton temperature, observed in the soft state, suggests a link between higher wind ionisation and harder spectral shapes. Although the physical interaction between the wind, accretion flow and jet is still not fully understood, the mass flux and power of these winds, and their presence ubiquitously during the soft X-ray states suggests they are fundamental components of the accretion phenomenon.Comment: Accepted for publication in MNRAS Letter

Disc reflection and a possible disc wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9–342058

“…These winds are preferentially detected during soft X-ray spectral states (e.g., Miller et al 2006aMiller et al , 2008Neilsen & Lee 2009;Ponti et al 2012). Typical outflow velocities are ≃400-3000 km s −1 (≃0.001-0.01c) and the properties are very similar in black hole and neutron star LMXBs (e.g., Díaz Trigo & Boirin 2016).…”

“…Other narrow absorption features were seen in the Chandra/HEG data and two of the Swift/XRT soft-state observations at energies of ≃7-8 keV, but at lower significance (≃2-4σ after accounting for trials). Blue-shifted, narrow absorption lines have been seen in several black hole and neutron star LMXBs during their soft states, and are interpreted as outflowing disk winds (e.g., Brandt Neilsen et al 2011;King et al 2012King et al , 2015Ponti et al 2012;Degenaar et al 2014a;Bozzo et al 2016).…”

“…Firstly, observational evidence suggests that disk winds are concentrated in the accretion disk plane (e.g., Miller et al 2006aMiller et al ,b, 2015King et al 2012;Ponti et al 2012;Degenaar et al 2014b). Indeed, simulations of (thermally-driven) disk winds suggest that at near-polar angles, the low density and high ionization of the gas may prevent its detection (e.g., Sim et al 2008;Higginbottom & Proga 2015).…”

“…The most abundant elements seen in absorption in the X-ray spectra of LMXBs are Fe XXV (rest wavelength 6.70 keV) and Fe XXVI (rest wavelength 6.97 keV), which can be red/blue shifted in case of an in/outflow (e.g., Ponti et al 2012;Díaz Trigo & Boirin 2016). We found that any model fitting the ≃7.64 keV line as blue-shifted Fe XXV predicts a strong Fe XXVI line at commensurate blue-shift (≃7.98 keV), which is not seen.…”

“…Typical outflow velocities are ≃400-3000 km s −1 (≃0.001-0.01c) and the properties are very similar in black hole and neutron star LMXBs (e.g., Díaz Trigo & Boirin 2016). Powerful disk winds may carry away a significant amount of mass, similar to or even exceeding the amount of mass that is accreted (e.g., Lee et al 2002;Neilsen et al 2011;King et al 2012King et al , 2015Ponti et al 2012;Degenaar et al 2014a). Winds are therefore important in considering the energy budget of the accretion process, and may also lead to instabilities in the accretion flow (e.g., Begelman & McKee 1983;Shields et al 1986).…”