1. X-ray spectra modeling for accretion plasma of magnetic white dwarfs
ESAC Summer Alumni Trainee Meeting 2010
X-ray spectra modeling for accretion plasma of magnetic white dwarfs
Speaker: Alexander Kolodzig
Origin: Humboldt-Universität, Berlin, Germany
Institute: AIP (Astrophysical Institute Potsdam),
Potsdam, Germany
Tutor: Axel Schwope
Date:
7 month on the work
excitement of work
- brief glance of my work
Background Picture Credits : Mark A. Garlick

2. Magnetic Cataclysmic Variable
Terminology:
accreting magnetic white dwarfs = MCV
alternative names:
Polar
“AM Herculis” - type
Picture Credits : Mark A. Garlick
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

3. Picture Credits : Mark A. Garlick
MCV
Roche-lobe overflow
Compact Binary:
mass ratio: MSec./MWD
period: 80 min hours
separation: R
accretion rate: M /yr
late-type
main sequence star
(Secondary)
accretion stream
no accretion disc
White Dwarf
(Primary)
Picture Credits : Mark A. Garlick
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

4. Picture Credits : Mark A. Garlick
MCV
White Dwarf (WD):
strong magnetic field (B ≥ 10MG)
synchronized rotation: PSpin = POrbit
accretion onto magnetic pole(s)
stagnation region
late-type
main sequence star
(Secondary)
accretion stream
partially ionized
magnetic field lines
White Dwarf
(Primary)
Shock
Picture Credits : Mark A. Garlick
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

5. Example X-ray spectrum (XMM-Newton: EPIC pn)
one temperature blackbody model
Continuum:
one temperature plasma emission model
(XSPEC: “MEKAL”)
Object: AM Herculis
main work stage:
creating consistent
multi-temperature model
5-6 EPIC pn spectra of AM Hercules
Transition to next slide:
to understand the x-ray emission better, we need to understand how the radiation is really produced.
Bad fit: for demonstration purposes only!
Credits: A. Schwope & J. Vogel
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

6. Simple accretion scenario
1994 vanTeeseling - X-ray irradiation of white dwarf atmospheres: The soft X-ray spectrum of AM Herc
Iris Traulsen – Diss., page: 13:
Column accretion onto a magnetic white dwarf. In this simplified view, the material reaches the surface of the white dwarf along the magnetic field lines in a nearly radial symmetric accretion column. In the flow below the shock, it decelerates and cools. Adapted from van Teeseling et al. (1994).
TMax > 107 K
Illustration adapted from
Teeseling et al. 1994
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

7. hydrodynamic equations
Post-shock region
hs << RWD
h = 0
h = hs
h - geometrical height [cm]
Fischer & Beuermann (2001)
1D stationary two-particle-fluid
hydrodynamic equations +
frequency & angle-dependent
radiative transfer
x - column density [g/cm2] dx = - dh
x = 0
x = xs
Shock
g = const.
B = const.
T1, 1
T2, 2
T3, 3 …
Tn-2, n-2
Tn-1, n-1
Tn, n e-
Ion
- Bremsstrahlung (optical thin)
- Cyclotron Radiation (optical thick)
model -> radiation-hydrodynamics
one-dimensional (Width >> hs) -> pill-box shape
- stationary (no time dependence) -> mean properties (no fluctuation)
infinite plane-parallel layers
cooling flows
WD surface
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

8. T +  Distributions 3 main physical parameters: MWD – White Dwarf Mass
B – Magnetic Field of the WD
MFD – Mass Flow Density
(accretion rate per unite area)
Shock - Height
Shock
WD surface
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

9. Magnetic Field Variation
Cyclotron Radiation more efficient
-> faster plasma cooling
-> lower Temperature
-> lower Shock Height
-> higher Volume Density
-> different Spectrum
Shock
WD surface
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

10. Layer + Column Spectra X-ray continuum: Bremsstrahlung
TODO: thicker lines of the layer: Column: 8, Layer: 4
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

11. Various Column Spectra
TODO: MFD: 100 -> 1.0 ; same scale as Slide before: [10^-6,10^+3]
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

12. Example X-ray spectrum (XMM-Newton: EPIC pn)
one temperature blackbody model
Continuum:
one temperature plasma emission model
(MEKAL)
Object: AM Herculis
emission lines
5-6 EPIC pn spectra of AM Hercules
Credits: A. Schwope & J. Vogel
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

13. Example X-ray spectrum (CHANDRA: HETG - HEG)
Object: AM Herculis
Fe XXV
(Helium-like Iron)
Fe XXVI
(Hydrogen-like Iron)
Reprocessed X-ray
Flux [Counts /(sA)]
5-6 EPIC pn spectra of AM Hercules
Transition to next slide:
to understand the x-ray emission better, we need to understand how the radiation is really produced.
Credits: Girish et al. 2007
Wavelength  [Angstroem]
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

14. Synthetic X-ray spectra
for AM Herculis
Fe XXVI
(Hydrogen-like Iron)
Fe XXV
(Helium-like Iron)
- thermal broadening
- no bulk velocity broadening
-> Phase dependent
- no gravitational redshift
- no absorption
TODO: Labeling of the lines!!!, change Title to: „AM Herculis – Iron Lines“
Explain:
no plasma bulk velocity-shift in layer -> no broadening of the total-line (column) ->Phase dependent
- Effective Area was calculated as a mean of HEG between 1,7 and 2,0 Angstroem
Tools: XSPEC with APEC-Model
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

15. Ionization Ratio with Iron
TODO: thicker lines! include Ion.Ratio of Column!
Shock
WD surface
Tools: CHIANTI Database
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

16. Ionization Ratio + T Shock WD surface
TODO: thicker lines! include Ion.Ratio and Mean(T) (weighted by dH) of Column !
Shock
WD surface
Tools: CHIANTI Database
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

17. next work stages further emission line analysis
bulk velocity broadening vs. phase
gravitational redshift
further consistency checks
testing Multi-T-Model with real data
Animation of a MCV:
17sec
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

18. Thank You For Your Attention!
Contributions or Questions?

19. Background - Slides

20. Picture Credits : Mark A. Garlick
MCV
Secondary:
solar like star
hydrogen plasma ball
hydrogen fusion with
Tcore ~ 107 K
PGrav ~ PGas  T
low mass: M = M
long lifetime: > t ~ 1010 years
low TSurface ~ 3500 K
Density ~ 10 g/cm3
late-type
main sequence star
(Secondary)
Picture Credits : Mark A. Garlick
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

21. Picture Credits : Mark A. Garlick
MCV
White Dwarf (Primary):
remnant of a solar like star
degenerated electron gas
PGrav ~ PDeg   (No  T)
Density > 105 g/cm3
MWD = M , Peak at 0.6 M
RWD ~ 1.5 M
elements: no H, mainly C & O
TSurface ~ 104 K
White Dwarf
(Primary)
Picture Credits : Mark A. Garlick
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

22. X-ray spectrum hard x-ray: plasma emission soft x-ray:
bremsstrahlung from the post-shock region
thermal plasma emission fit (“MEKAL”-Model)
soft x-ray:
reprocessed emission from the accretion region
blackbody fit
fits are one-temperature-models
what does this temperature mean?
übergang zur nächsten Folie:
to understand the x-ray emission better, we need to understand how the radiation is really producced.
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

23. Theory hydrodynamic equations: radiative transfer:
two-fluid (ions and electrons separately)
connected by Coulomb interaction
conversation of mass, momentum and energy
electron gas heated by Ekin of the ions
electron gas cooled by radiation
radiative transfer:
frequency and angle-dependent transfer
cyclotron absorption, free-free absorption, electron scattering, no Compton scattering
stationary and one-dimensional
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

24. MFD Variation Shock WD surface Credits: Fischer & Beuermann 2001
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

25. MFD Variation Shock WD surface Credits: Fischer & Beuermann 2001
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

26. WD Mass Variation Shock WD surface Credits: Fischer & Beuermann 2001
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

27. Electron Temperature Shock WD surface 02.07.2010
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

28. Ion Velocity Shock WD surface Credits: Fischer & Beuermann 2001
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

29. Ion Velocity Density: r(x)  1/v(x) Shock WD surface 02.07.2010
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

30. Bremsstrahlung Spectrum
MWD = 0.6 M , B = 30 MG
cyclotron radiation
XMM-Newton
Mass Flow Density
[g/(scm2)]
10-1
100
10+1
10+2
d = 10 pc
D = 108 cm
Credits:
Fischer & Beuermann 2001 IR
optical UV
EUV
X-ray
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

31. Spectral Energy Distribution
XMM-Newton
Optical – UV:
accretion stream
(interstellar absorption)
Soft X-ray:
reprocessed component
(interstellar absorption)
IR – optical:
Secondary Star
1999 Beuermann - Magnetic cataclysmic variables: the state of the art after ROSAT
Iris Traulsen – Diss., page: 17:
Figure 2.6: Spectral energy distribution of AM Her. The dominant components are cyclotron emission in the infrared and optical, UV flux from the heated white-dwarf surface and from the accretion stream (IUE data), a soft X-ray quasi-black body arising from the accretion region (ROSAT data of April 1991), and hard X-ray emission produced in the accretion column (HEAO-1 data). The unabsorbed black body model flux corresponding to the soft X-ray component is marked as a dashed line in addition. From Beuermann (1999).
Hard X-ray:
bremsstrahlung
IR – UV:
Cyclotron radiation
Credits: Beuermann 1999
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

32. Picture Credits : Mark A. Garlick
Origin of radiation
who we see the object? -> due to its radiation.
Picture Credits : Mark A. Garlick
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

33. SKIP: to complicated to explain, important for observers, M_WD-Estimation
TODO: re-plot with CHIANTI-Data, MFD: 1.0 and M_WD- Variation!
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

34. Fe XXVI Hydrogen-like Iron Fe XXV Helium-like Iron
SKIP: to much to explain
Tools: XSPEC with APEC-Model and thermal broadening
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig

35. SKIP: better, to show EW-Dependency on B,MFD and M_WD but this would be to complicated
TODO: inluced: total EW
Shock
WD surface
Tools: CHIANTI-Database
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig