Transcript Folie 1

ESAC Summer Alumni Trainee Meeting 2010
X-ray spectra modeling for
accretion plasma of
magnetic white dwarfs
Speaker:
Origin:
Institute:
Tutor:
Date:
Alexander Kolodzig
Humboldt-Universität, Berlin, Germany
AIP (Astrophysical Institute Potsdam),
Potsdam, Germany
Axel Schwope
02.07.2010
Background Picture Credits : Mark A. Garlick
Magnetic
Cataclysmic Variable
• Terminology:
– accreting magnetic white dwarfs = MCV
– alternative names:
• Polar
• “AM Herculis” - type
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Picture Credits : Mark A. Garlick
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MCV
Roche-lobe overflow
late-type
main sequence star
(Secondary)
• Compact Binary:
– mass ratio: 0.1 - 0.5 MSec./MWD
– period: 80 min - 8.0 hours
– separation: 0.5 - 2.0 R
– accretion rate: 10-12 - 10-8 M /yr
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no accretion disc
White Dwarf
(Primary)
Picture Credits : Mark A. Garlick
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MCV
stagnation region
late-type
main sequence star
(Secondary)
• White Dwarf (WD):
– strong magnetic field (B ≥ 10MG)
– synchronized rotation: PSpin = POrbit
– accretion onto magnetic pole(s)
magnetic field lines
White Dwarf
(Primary)
Shock
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Picture Credits : Mark A. Garlick
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Example X-ray spectrum
(XMM-Newton: EPIC pn)
Object: AM Herculis
one
temperature
blackbody
model
Continuum:
one temperature plasma emission model
(XSPEC: “MEKAL”)
main work stage:
creating consistent
multi-temperature model
Bad fit: for demonstration purposes only!
Credits: A. Schwope & J. Vogel
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Simple accretion scenario
Illustration adapted from
Teeseling et al. 1994
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TMax > 107 K
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Post-shock region
hs << RWD
x=0
h = hs
Shock
T1, 1
T2, 2
e-
eIon
T3, 3
Ion
…
…
e-
Tn-2, n-2
Tn-1, n-1
Ion
e-
- Bremsstrahlung (optical thin)
- Cyclotron Radiation (optical thick)
Tn, n
x = xs
e-
Ion
…
Fischer & Beuermann (2001)
1D stationary two-particle-fluid
hydrodynamic equations
+
Ion
frequency
& angle-dependent
radiative transfer
h=0
WD surface
B = const.
g = const.
h - geometrical height [cm]
x - column density [g/cm2] dx = - dh
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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
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WD surface
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Magnetic Field Variation
Cyclotron Radiation more efficient
-> faster plasma cooling
-> lower Temperature
-> lower Shock Height
-> higher Volume Density
-> different Spectrum
Shock
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WD surface
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Layer + Column Spectra
X-ray continuum: Bremsstrahlung
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Various Column Spectra
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Example X-ray spectrum
(XMM-Newton: EPIC pn)
Object: AM Herculis
emission lines
one
temperature
blackbody
model
Continuum:
one temperature plasma emission model
(MEKAL)
Credits: A. Schwope & J. Vogel
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Example X-ray spectrum
(CHANDRA: HETG - HEG)
Flux [Counts /(sA)]
Fe XXV
(Helium-like Iron)
Credits: Girish et al. 2007
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Object: AM Herculis
Fe XXVI
(Hydrogen-like Iron)
Reprocessed
X-ray
Wavelength  [Angstroem]
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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
Tools: XSPEC with APEC-Model
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Ionization Ratio with Iron
Flux (Fe 26)
Ion.Ratio =
Flux (Fe 25)
Tools: CHIANTI Database
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Shock
WD surface
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Ionization Ratio + T
Tools: CHIANTI Database
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Shock
WD surface
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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:
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17sec
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Thank You For Your Attention!
Contributions or Questions?
e-mail: [email protected]
Background - Slides
MCV
• Secondary:
late-type
main sequence star
(Secondary)
– solar like star
•
•
•
•
hydrogen plasma ball
hydrogen fusion with
Tcore ~ 107 K
PGrav ~ PGas  T
– low mass: M = 0.1 - 0.5 M
• long lifetime: > t ~ 1010 years
• low TSurface ~ 3500 K
• Density ~ 10 g/cm3
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Picture Credits : Mark A. Garlick
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MCV
• White Dwarf (Primary):
– remnant of a solar like star
– degenerated electron gas
• PGrav ~ PDeg   (No  T)
• Density > 105 g/cm3
– MWD = 0.4 - 1.0 M , Peak at 0.6 M
• RWD ~ 1.5 M
– elements: no H, mainly C & O
– TSurface ~ 104 K
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White Dwarf
(Primary)
Picture Credits : Mark A. Garlick
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X-ray spectrum
• hard x-ray: plasma emission
– 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?
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Theory
• hydrodynamic equations:
– 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
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MFD Variation
Shock
WD surface
Credits: Fischer & Beuermann 2001
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MFD Variation
Shock
WD surface
Credits: Fischer & Beuermann 2001
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WD Mass Variation
Shock
WD surface
Credits: Fischer & Beuermann 2001
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Electron Temperature
Shock
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WD surface
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Ion Velocity
Shock
Credits: Fischer & Beuermann 2001
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WD surface
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Ion Velocity
Density: (x)  1/v(x)
Shock
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WD surface
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Bremsstrahlung Spectrum
MWD = 0.6 M , B = 30 MG
d = 10 pc
D = 108 cm
10+2
10+1
cyclotron
radiation
100
XMMNewton
10-1
Credits:
Mass Flow Density
[g/(scm2)]
IR
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optical
Fischer & Beuermann 2001
UV EUV
X-ray
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Spectral Energy
Distribution
Optical – UV:
accretion stream
(interstellar absorption)
Soft X-ray:
reprocessed component
(interstellar absorption)
XMMNewton
IR – optical:
Secondary Star
Hard X-ray:
bremsstrahlung
IR – UV:
Cyclotron radiation
Credits: Beuermann 1999
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Origin of radiation
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Picture Credits : Mark A. Garlick
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Fe XXVI
Hydrogen-like Iron
Fe XXV
Helium-like Iron
Tools: XSPEC with APEC-Model
and thermal broadening
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Tools: CHIANTI-Database
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Shock
X-ray spectra modeling for accretion plasma of MCVs - Alexander Kolodzig
WD surface
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