CONSTRAINTS ON COMPTON-THICK WINDS FROM BLACK HOLE ACCRETION DISKS: CAN WE SEE THE INNER DISK?

Journal Article · Thu Nov 01 04:00:00 EDT 2012 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/759/1/L15· OSTI ID:22078464

Strong evidence is emerging that winds can be driven from the central regions of accretion disks in both active galactic nuclei and Galactic black hole binaries. Direct evidence for highly ionized, Compton-thin inner-disk winds comes from observations of blueshifted (v {approx} 0.05-0.1c) iron-K X-ray absorption lines. However, it has been suggested that the inner regions of black hole accretion disks can also drive Compton-thick winds-such winds would enshroud the inner disk, preventing us from seeing direct signatures of the accretion disk (i.e., the photospheric thermal emission, or the Doppler/gravitationally broadened iron K{alpha} line). Here, we show that, provided the source is sub-Eddington, the well-established wind-driving mechanisms fail to launch a Compton-thick wind from the inner disk. For the accelerated region of the wind to be Compton-thick, the momentum carried in the wind must exceed the available photon momentum by a factor of at least 2/{lambda}, where {lambda} is the Eddington ratio of the source, ruling out radiative acceleration unless the source is very close to the Eddington limit. Compton-thick winds also carry large mass fluxes, and a consideration of the connections between the wind and the disk shows this to be incompatible with magneto-centrifugal driving. Finally, thermal driving of the wind is ruled out on the basis of the large Compton radii that typify black hole systems. In the absence of some new acceleration mechanisms, we conclude that the inner regions of sub-Eddington accretion disks around black holes are indeed naked.

• OSTI ID: 22078464
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 759; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
ACCELERATION
ACCRETION DISKS
BLACK HOLES
COMPTON EFFECT
EMISSION
GALAXY NUCLEI
IRON
MASS
PHOTONS
PHOTOSPHERE
STELLAR WINDS
X RADIATION