Transcript pradhan - Harvard-Smithsonian Center for Astrophysics

Atomic Processes, Theory, and Data
For X-Ray Plasmas
Anil Pradhan, Sultana Nahar
Guo-Xin Chen (ITAMP), Franck Delahaye
Justin Oelgoetz, Hong Lin Zhang (LANL)
(www.astronomy.ohio-state.edu/~pradhan)
X-ray Diagnostics For Astrophysical Plasmas
November 15-17, 2004
ITAMP, Harvard-Smithsonian
Center For Astrophysics
Atomic Processes, Theories, and Data
• Processes: Particle Distributions in Lab and
Astro Sources (Lab Astrophysics)
 Resonances and Electron Distribution
Functions in EBIT experiments
• Theories: Electron Impact Excitation
 Close Coupling vs. Distorted Wave
• Data: Opacity Project and Iron Project
 Excitation, Photoionization, Recombination,
A-coefficients
 X-ray Spectral Models
• He-like ions in transient plasmas (e.g. X-Ray
flares)  The Movie !
Relativistic and Non-Relativistic R-matrix Codes For Atomic Processes
Large-scale
calculations
with high precision
and self-consistency
Atomic Data For X-Ray Spectral Diagnostics
• Laboratory Plasmas Sources:
- Electron-Beam-Ion-Traps (EBIT)
- Tokamaks
- Magnetic Z-pinch and other ICF devices
• Astrophysical Sources
- Stellar Coronae
- Active Galactic Nuclei
- Supernova remnants
• Are all these plasma sources the same ?
• Are the line intensities and ratios the same ?
Spectral Formation In Astro and Lab Sources
• Particle Distribution:
- Maxwellian  Most astrophysical cases
- Non-Maxwellian  Tokamaks during heating
phase (ECH, NBI, etc.), ‘runaway electrons’ in highenergy tail
- Gaussian  EBIT (mono-energetic beam)
- Bi-Maxwellian  Electron-ion storage rings
• Radiation Field:
- Stellar UV continuum  Blackbody Planck
Function
- Black Hole accretion  AGN, Non-thermal
power-law L ~ E-a
• Ionization Equilibrium or Non-Eqm:
- Stationary
- Transient (time-dependent)
Benchmarking Laboratory and Astrophysical X-Ray Sources:
Electron Impact Excitation (Chen etal., 2003)
Ne- like
Resonance and relativistic effects
in prominent x-ray transitions
Coupled Channel R-Matrix Theory vs. Distorted Wave
Coupled Channel
• Ab initio treatment of important atomic
processes with the same expansion: Eq.(1)
• Electron impact excitation, radiative transitions,
and a self-consistent and unified treatment of
photoionization and (e + ion) recombination,
including radiative and dielectronic (RR+DR)
 Review: Nahar and Pradhan (2004)
• Significant effects are included
• Infinite series of resonances are considered
Distorted Wave
• Includes only initial and final
channels in Eq. (1); no summation
• Neglects channel coupling
• Resonance states (intermediate
channels) NOT included in
wavefunction expansion
• Limited number of resonances
may be considered in the
isolated resonance approximation
• May not be adequate for highly
charged ions (weak transitions,
resonance effects)
Resonance Effects on the 3F/3C Line Ratio
R-Matrix 3F Collision Strength
Line Ratio vs. Te
Filled Circles – Distorted Wave
Filled Squares - DW
Fe XVII 3F/3C Line Ratio vs. Temperature: Theory and Observations
Chen et.al. (JPB,36,453,2003)
Beiersdorfer et.al., ApJ, 2004
The measured 3F/3C value ~ 0.7 from tokamaks and EBIT agrees with theory
Fe XVII Collision Strengths:
Resonances up to n = 3 and n = 4 complexes
Filled Poiints:
Distorted Wave
Blue: Gaussian
Average
Red: n =3 resonances
Line Ratios and Electron Distribution
Functions (EDF) in X-Ray Sources
• All Fe XVII cross sections averaged over both EDFs –
Maxwellian and Gaussian (Chen and Pradhan 2004)
• Different sets of line ratios computed from
collisional-radiative model including n = 4 levels
• Solution to 3s/3d problem:
3s/3d = (3F+3G+3H) / (3C+3D+3E)
• Line ratios are source-specific
• Tokamak, EBIT, and astrophysical measurements
depend on EDFs
• EBIT results are gaussian; for benchmarking need:
- Precise beam shapes
- Higher resolution (many more energies)
• Oscillations due to distribution of resonances
• Recombination-Cascades
Fe XVII 3s/3d Ratio: Theory and Observations
Chen and Pradhan (2004)
• Maxwellian average – solid line; Gaussian average – solid red line
• Filled Blue – LLNL EBIT; Open Blue – NIST EBIT
• Open red circles – Solar (T~ 4MK); Filled green – Capella (Chandra);
Open green – “
(XMM)
• Extreme left – other measurements
Unified electron-ion recombination (RR+DR):
R-Matrix Theory and Experiments
Gaussian Averaged X-sections
Maxwellian Averaged Rate
Expt
Expt
Theory: Pradhan et.al. (ApJL, 549, L265, 2001)
Expt: Savin et.al. (ApJS, 123, 687, 1999)
Theory
Rates agree to < 20%
R-Matrix Opacity/Iron/RmaX Project Data
(Links From www.astronomy.ohio-state.edu/~pradhan)
•
•
Collisional Data For all Fe ions (also Fe-group)
Radiative Data  Photoionization Cross Sections and
Transition Probablities for most astrophysically abundant
ions, including inner-shell photo-excitation, opacities etc.
• New self-consistent photoionization and unified
(RR+DR) electron-ion recombination cross sections and
rates for over 50 ions (S. Nahar and collaborators), e.g.
for X-ray applications
- Li-, He-like: CIV/CV, OVI/OVII,…..,FeXXIV/FeXXV
- Including total and level-specific recombination rate
coefficients up to n<=10
- Unified recombination cross sections  DR spectrum
• Electronic On-line Database: TIPTOPBASE and
OPSERVER (C. Mendoza and collaborators)
Code XRAD – Theoretical X-ray Absorption Spectrum
• The Opacity Project and Iron Project Data (> 107 lines)
• Ab initio data (theoretical energies, f-values, photoionization xsects, etc.)
Fe L-shell opacity, ~ 1 keV features
• Completeness of atomic data
• General behavior and features
• No detailed fitting
XRAD Simulation of AGN MCG6-15-30
• Code XRAD uses ab initio
XRAD theoretical energies
• No fitting of individual
features
• Vary Te, Ne, Nz
• Overall features obtained
XSPEC
OBS
Code HELINE (Oelgoetz and Pradhan 2001,2004)
Stationary and Transient Spectra of He-like Ions
Time-Dependent Coupled Equations for Level Populations
Collisional Ionization, Recombination, and Photoexcitation
(thermal and non-thermal radiation fields)
Collisional, Photoionized, and Hybrid Plasmas
For Fe XXV the Helium “triplet” becomes a “quartet” with dielectronic satellites
f,i,r
z,x,y,w
The 6.7 keV Ka complex of Fe XXV
Ionization Fractions of Iron In Different Plasma Sources
Black
Body
Non-thermal
Power-Law
Coronal
Eqm.
Log Te
Time-dependent Temperature,
Radiation, and Ionization Fractions
Electron Temperature
Te(t)
Example:
X-Ray
flare in
accretion
disc
around a
Black Hole
Ionization Parameter
U(t) = L / Ne
Ionization Fractions
coll. Ionization
Te(t)
+ Photoionization
U(t)
ASTRO-E2
Hybrid: Te(t) & U(t)
Time (Seconds)
Time Evolution of Transient Plasmas
Collisional
(Lab)
Photoionized
Hybrid
(Astrophysical)
Dielectronic
satellites
dominate at
early times
in collisional
case;
very weak in
photoionized
case.
Recombination
dominates in
all cases at
late times
t = 480 s
t = 1080 s
t = 1320 s
t = 1560 s
t = 1920 s
Spectral
Inversion
z  w
t = 2400 s
Photon Energy (keV)
Time-Dependent Photoionization and Collisional Ionization:
The 6.7 KeV Ka Complex of He-like Fe XXV
(Oelgoetz and Pradhan 2004)
Time-Dependent Photoionization and Collisional Ionization:
The 6.7 KeV Ka Complex of He-like Fe XXV
(Oelgoetz and Pradhan 2004)
w
q
v,u
z
r
y t
PHOTOZN
(U ~ 100)
DOMINATES
AT EARLY
TIMES;
DI-ELEC.
SAT. (DES)
q (1s2s2p)
STRONG
Time-Dependent Photoionization and Collisional Ionization:
The 6.7 KeV Ka Complex of He-like Fe XXV
(Oelgoetz and Pradhan 2004)
w
z
j,r
y
k
x
IONIZN
LAGS
BEHIND
RECOMBN;
SMALL
DES
Time-Dependent Photoionization and Collisional Ionization:
The 6.7 KeV Ka Complex of He-like Fe XXV
(Oelgoetz and Pradhan 2004)
z
x
y
w
SPECTRAL
INVERSION
Z <--> W
DURING
RECOMBN
PHASE AT
LATE
TIMES
Conclusion
•
•
•
•
•
•
The Iron Project and the RmaX Project are providing
large-scale atomic data of high accuracy using the
R-matrix method for electron impact excitation,
photoionization, unified electron-ion recombination,
and transition probabilities in a self-consistent ab
initio formulation
TIPTOPBASE  Electronic database
Spectral diagnostics and interpretation of plasma
conditions my be source-specific
Electron distribution functions need to be known
Relativistic and resonance effects are crucial
Transient X-ray sources require new physical
approximations, independent of global or local
energy balance