Culture and Religion

A world view where the guide for society is based on human nature,
 not on ancient scriptures.  Home  or Topic Groups

 

AGN Accretion Disk

The post's pdf title:

The panchromatic polarization signatures of Active Galactic Nuclei

my comment:

Despite his observations, the paper's author is convinced there is an accretion disk.

The explanations are awkward. I find them not believable.

There is an accretion disk whose large particles generate high energy photons based on the disk's black body temperature (a solid in thermal equilibrium). These large particles are so hot and yet they do not disintegrate or melt but they radiate in UV.
excerpt:
'
it is believed that a plasma of hot electrons is situated on top of the disk, in an atmosphere-like region or in a compact or patchy corona situated at an unknown distance above the disk. The corona may be generated by buoyancy instabilities in the disk and heated by magnetic reconnection, i.e. shocks at reconnection sites where strong impulsive heating occurs when magnetic field lines are brought together. The temperature of the plasma is such that ultraviolet photons, thermally emitted by the disk, are boosted up to the X-ray energies by multiple inverse-Compton scattering.
'

my comment: the temperature of hot electrons, or plasma, in a 'patchy corona' results in boosting the UV from the disk to X-rays. How?

There is heat from 'magnetic reconnection.' How?

'
Part of the X-ray photons that are emitted by the corona are bent back to the disk by general relativistic effects.
'
What is bending how?

excerpt:
'
Soft X-rays are mainly absorbed by photoelectric absorption followed by fluorescent line emission, or photoelectric absorption followed by Auger de-excitation. Hard Xray photons mainly scatter on the disk due to Compton scattering by free or bound electrons. The most prominent signature of these physical effects is the presence of a strong iron fluorescence line at approximately 6.4 keV. The emission line profile is often broad, skewed towards the soft X-rays by Doppler shifts and relativistic boosting due to the motion of the disk and the gravitational redshifting of the black hole. Iron line fitting then allows to determine the radius of the ISCO, hence the dimensionless spin parameter and the inclination of the accretion disk.
'
my comment:

'skewed toward X-rays' sounds like a blue shift so the iron atoms are moving away from the AGN, toward us.
'Iron line fitting and gravitational redshifting' and 'elativistic boosting' are required. Are those adjustments justified?

also:

'
For ultraviolet luminosities between 1043 and 1044 erg/sec, the inner torus radius is typically comprised between 0.01 and 0.1 pc. The maximal extension of this opaque dusty region was first though to expand as large as 100 pc, which is challenged by dynamical stability arguments, but the compact core of the torus is now observationally constrained to be only a dozen parsecs wide. A clumpy distribution of graphite grains embedded in a non-spherical geometry can easily reproduce the 2 – 4 Ám excess for temperatures close to the dust sublimation limit . With increasing distances from the torus inner edges, the outer shells present colder dusty grains, only heated by reprocessed infrared radiation with characteristic temperatures lower than 100 K. The resulting infrared emission peaks at near- to mid-infrared wavelengths.
'
my comment:
Apparently the author concluded this accretion disk is a torus of clumpy opaque dust. The outer shells are colder but 'heated by reprocessed infrared radiation.'


A technical paper like this is subject to interpretation.

I wonder if a physicist started with a plasmoid not a black hole whether the observations could be explained rather directly without so much boosting, fitting, and shifting.


Hit back to go to previous page in history.

Here is the list of topics in this Cosmology Topic Group .

Ctrl + for zoom in;  Ctrl - for zoom out ;  Ctrl 0 for no zoom;
triple-tap for zoom to fit;  pinch for zoom change;  pinched for no zoom