Ubiquitous equatorial accretion disc winds in black hole soft states (1201.4172v1)

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.

• The paper reveals that equatorial disc winds are ubiquitous in black hole soft states, carrying mass outflow rates comparable to accretion rates.
• The study employs high-resolution X-ray spectroscopy to show that wind visibility depends on system inclination and ionization conditions.
• Findings indicate that these winds, observed during jet-less soft states, play a critical role in balancing mass and energy in Galactic Black Holes.

Analysis of Equatorial Accretion Disc Winds in Black Hole Soft States

The paper by Ponti et al. addresses the occurrence and characteristics of ionized winds from accretion discs around Galactic Black Holes (GBH) in their soft X-ray states. Their findings contribute significantly to the understanding of the dynamics within GBH systems, indicating these wind mechanisms are an intrinsic element of the accretion process.

The authors examine high-resolution X-ray spectra of GBH to detect the presence of these equatorial winds, particularly during states where the radio jet is absent. They conclude that these winds, observed from high inclination angles due to the geometry of the accretion disc, are ubiquitous in jet-free soft states across all GBH. This equatorial geometry implies that the winds are not detectable unless the accretion disc is adequately inclined relative to the observer's line of sight.

Key Findings

1. Ubiquity of Disc Winds: Observations show that equatorial disc winds are a common phenomenon in the soft states of GBH. The winds are significant because they carry mass outflow rates comparable to or exceeding the inner accretion rates. This is seen in the data from GBH like GRS1915+105, demonstrating a strong correlation between the quenching of the jet and the presence of these winds in the soft state.
2. Equatorial Geometry: The winds have opening angles of a few tens of degrees, inferring their equatorial nature. This implies that while the winds are present in all systems, they are only observable in systems with a high enough inclination, causing the disc to obscure the central black hole less and letting the wind be visible against the X-ray source.
3. State Dependency and Ionization: The presence of these winds is strongly state-dependent, appearing predominantly in soft states and diminishing in hard states. This dependency might be linked to the ionization conditions within the wind. The line ratio of ions decreases with increasing Compton temperature, suggesting higher ionization with harder spectrum shapes.
4. Mass and Energy Considerations: The paper also measures wind outflow velocities and uses these along with ionization parameters to estimate mass outflow rates. In many cases, the mass outflow via the wind rivals or exceeds the mass accretion rate onto the black hole, indicating that these winds are fundamental in the balance of mass and energy in accreting black holes.

Implications and Future Work

The confirmation of winds in GBH during soft states, with significant mass loads and energy potential, implies they have a profound impact on the accretion processes and feedback mechanisms in such systems. The paper suggests that these winds could potentially inhibit the formation of jets or other outflow mechanisms during specific accretion states.

Future research should further explore the detailed physics behind the interaction of these winds with the accretion and emission mechanisms, possibly using more extensive observational campaigns or advanced simulations. Investigating the specific conditions under which these winds are ionized could elucidate more about the transitional nature between different accretion states and the nature of AGN feedback driven by analogous processes on larger scales. Understanding these dynamics is crucial for a comprehensive model of black hole evolution and their interaction with the surrounding medium.