Coronal Properties of AGN Galaxies

Committee
Ioannis Georgantopoulos
Apostolos Mastichiadis
Despina Hatzidimitriou
Giorgos Dimopoulos
Coronal properties of Active Galactic
Nuclei using a sample of Seyfert I
galaxies

The Sample
● A brief introduction
○ AGN
○ Seyferts
○ Different Components
Outline
Giorgos Dimopoulos | master thesis | g.dimopoulos@noa.gr
● The physical framework
○ Compton Scattering
○ Inverse Compton
Scattering
○ Comptonization
● Our analysis
○ Sample
○ Spectral modeling
○ Results & Conclusions

The Sample
Why should we study AGN?
Motivation
What kind of physical processes drive
the phenomena near SMBH?
What can we learn from the
Corona of an AGN?

The SampleAGN Unification model

The SampleThe major AGN components
Supermassive Black
Hole (SMBH)
● 106 - 109 Mo
● Rg = 2GM/c2
Accretion Disk
● Polychromatic
thermal medium
● Eddington Limit
Corona
● Hot plasma cloud
● Optically thick
Dusty Torus
● Atoms and
molecules
● Strong IR source

The SampleSpectral footprint...
Padovanietal2017

The Sample
The physical
framework

The SampleRadiation Reprocess

The SampleCompton scattering
● Photon - Electron collision
● When photons lose energy, it is
“Recoil Effect”
● For low energy interactions, the
scattering follows Thompson
cross-section σT

The SampleCompton scattering
Wavelength change
Thompson
cross-section
Normalized energy;
Electron radius

The SampleCompton Scattering, Total cross-section
Klein-Nishina formula
● For low energy interactions (x<<1)
● For high energy interactions (γ>>1)

[Longair2011]

The SampleInverse Compton Scattering (ICS)
● Photon - Electron collision
● Photons gain energy
● Cooling mechanism for hot
electron cloud
Net energy gain

The SampleSpectrum of ICS
Ertley2014

The SampleComptonization
If Inverse Compton Scattering is the dominant
process in a medium, then the process is called
Comptonization

In the low energy
regime:
For thermal electrons
Photon Energy
Gain/Electron
energy loss

In the low energy
regime:
For symmetrical Thompson
scattering
Photon Energy
Loss/Electron
energy gain

Hence...
● 4kT >> hν: Energy transfer from electrons to
photons
● 4kT = hν: Equilibrium
● 4kT << hν: Energy transfer from photons to
electrons (recoil effect)

Finally... Optical depth
Comptonization
Parameter
Number scattering
Mean free path
[Rybicki & Lightman 1986]

The SampleGeneralized Comptonization [Titarchuk 1994]
● Low energy photons upscattered in hot plasma cloud
● The plasma cloud is thermal
● The hard X-ray tail (spectral shape) is formed by photons that
have undergone
● The shape of the hard radiation spectrum does not depend on
the low frequency photon source distribution

Photons described by
occupation number function
Diffusion in Energy and
Configuration Space
Energy space
function can be
derived by solving
the Comptonization
Stationary Equation
(CSE)
Spatial function
describes the
escape rate
Independent diffusion

Outcome…
● An asymptotic power law in soft
energies
● A hard X-ray tail:
○ Wien tail in the non-relativistic
case
○ Modified Wien tail in the
relativistic case

The computational interpretation of this model in XSPEC is:
compTT (5 parameters)
Other componization models are:
● compPS (19 parameters) [Poutanen & Svensson 1996]
● Nthcomp (5 parameters) [ Zdziarski, Johnson & Magdziarz 1996]

The Sample
Analysis

The SampleOutline
● Study Seyfert I galaxies
● Swift/BAT 70-month all sky survey
● Spectral fitting using a Comptonization model
● Seek potential correlation between the corona and
○ SMBH Mass
○ Soft X-ray luminosity 2-10 keV
○ Eddington ratio λEDD
● Look for a physical mechanism that can explain the results

The SampleOur sample (1)
67 sources
● Seyfert I type
● NuSTAR observations
● Known redshifts
● Available black hole mass

Why NuSTAR?
● Excellent spectra quality
● An order of magnitude
greater than BAT
● Unprecedented hard X-ray
quality
Specifications
● 10 meter focusing
telescope (1st > 10 keV)
● Two identical censors
(FPMA, FPMB)
● Operation energy band 3-
79 keV
● Energy resolution
○ 0.4 at 6 keV
○ 0.9 at 60 keV

Why not Swift/BAT data?
Low quality; An order
of magnitude
difference
Not contemporary
observations; Variability
effects; Cross-calibration
problems

The SampleBlack hole mass
Velocity Dispersion
(Kormendy and Ho,
2013)
FWHM of Ha and Hβ
emission lines
(Trakhtenbrot and
Netzer, 2012;
Greene and Ho, 2005)
BAT AGN Spectroscopic Survey (BASS)
(see Koss et al 2017; Ricci et al 2017)
AGN Mass catalog
By Bentz and Katz, 2015
http://www.astro.gsu.edu
/AGNmass/
03
01 02
Sources flagged as
“Excellent” and “Accepted”
have been used

The SampleRedshift and Mass Histogram

The SampleSpectral modeling
(Arnaud,1996)
Wabs compTT Pexrav Gaussian
Par 1 NH (1022 # cm-2) Redshift z (fixed) Γ photon index E line (keV)
Par 2 Input photons (keV) Ec = 3 kt (keV) E width (keV)
Par 3 Plasma Temp. (keV) Rel refl (fixed -1)
Par 4 Optical depth Abund >He
Par 5 Geometry (fixed 2) Abund Fe
Par 6 Redshift z (fixed)
In XSPEC notation: WA*COMPTT+PEX+GA
Normalization
[Morrison & McCammon (1983); Titarchuk (1994); Magdziarz & Zdiarski (1995)]

The SamplePlasma Temperature and Optical Depth Histogram

The Sample
Having parsed kt and τ...
Extra properties...
Eddington
Luminosity
Eddington
ratio
[Vasudevan & Fabian 2009]

The Sample
Median values of our results...
Results

The Sample
In order to check whether
the pairs of kT and τ have
physical meaning, we draw
the photon index line in the
τ-kT plane
The photon index Γ...
[Petrucci et al 2001]

The SampleThe Optical Depth, Plasma Temperature plane

The SampleAny correlation..?
Plasma
Temperature
Optical Depth
SMBH Mass
Soft X-ray luminosity
2-10 keV
Eddington
Ratio λEDD

The SamplePlasma Temp. and Optical Depth vs Black Hole Mass
Tortosaetal2018

Tortosa et al 2018
Ricci et al 2018

The SamplePlasma Temp. and Optical Depth vs L 2-10 keV

The SamplePlasma Temp. and Optical Depth vs λEDD
Tortosaetal2018

Ricci et al 2018

The SampleIs there any physical “Thermostat” ?
The Θ-l plane
Dimensionless
Temperature Θ
Compactness l
[Ricci et al 2018]
[e.g. Fabian et al. (2009); Chartas et al. (2009)]

The Θ-l plane
Dimensionless
Temperature Θ
Compactness l
[Ricci et al
2018]
[e.g. Fabian et al. (2009);
Chartas et al. (2009)]
Pair production in the Θ-l plane
Svensson (1984) describes a thermal plasma
cloud in pair balance, where the pair
production region in the Θ-l plane is given by

Kamrajetal2018

Ricci et al 2018

The SampleTake home message...
● Comptonization model works well on coronae
● No correlation between the corona and the AGN has been
found
● Pair production mechanism is likely to regulate the coronal
conditions; “Thermostat”
● Non-thermal states may allow sort “visits” in the pair
production region [Fabian+15;Fabian+17}
● Future deeper observations will (probably) fill the cool and
low luminosity region

The SampleTake home message...
● Comptonization model works well on coronae
● No correlation between the corona and the AGN has been
found
● Pair production mechanism is likely to regulate the coronal
conditions; “Thermostat”
● Non-thermal states may allow sort “visits” in the pair
production region
● Future deeper observations will (probably) fill the cool and
low luminosity region

The Sample
Appendix

Photons are being diffused in
both the energy and
configuration space

Solution...
u corresponds to the number
of scatterings

For escape
rate...

The SampleAbout black hole mass...

Coronal Properties of AGN Galaxies

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