On the significance of He-like plasma diagnostics for the study of photoionized media Anabela C.
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Transcript On the significance of He-like plasma diagnostics for the study of photoionized media Anabela C.
On the significance of He-like plasma diagnostics
for the study of photoionized media
Anabela C. Gonçalves 1,2
Olivier Godet 3, Anne-Marie Dumont 1 ,Suzy Collin 1
1 Paris
Observatory (LUTh), France
Observatory (CAAUL), Portugal
3 Leicester University, UK
2 Lisbon Astronomical
X-ray Grating Spectroscopy meeting
Cambridge, July 11-14, 2007
Astrophysical plasmas
Plasmas
Ubiquitous, extremely common, represent 99% of known matter
“Artificial” plasmas: nuclear fusion, spatial propulsion, neon signs, TV
“Natural” plasmas: auroras, solar wind, stellar coronae, nebulae, in AGN
X-ray plasmas cover a wide range in properties: T, nH, NH, x, etc.
X-ray gas can get ionized by
T (K)
controled fusion
inertial
confinement
Collisions (~ keV)
• X-ray bright starburst regions
nebulae
solar winds
thunder
WA
• Stellar coronae
• SNRs
neon
lights
Photoionization (~ eV)
propeler
aurorae
flames
• X-ray binaries
• AGN: BLR, NRL, Warm Absorber
particles/m3
solar core
Plasma Diagnostics in the X-rays
Astrophysical plasma diagnostics
Brickhouse et al. (2000)
Rely on spectroscopy measurements and/or
simulations => compute line-ratios
Conspicuous lines, close in l/Energy =>
minimize calibration errors
High-quality, medium-resolution spectra
(R ≥ 300) => needed to resolve the lines
Gu et al. (2006)
Diagnostics in the X-rays
X-band very rich: many lines from
each ion, many ions from each element
Different ions probe different gas conditions:
H-like, He-like in high-Z and low-Z elements
WA conditions: CV, NVI, OVII (well resolved,
close in E range, easy to use as
diagnostics)
High enough resolution spectra achieved
He-like lines as plasma diagnostics
G(T) = (F+I) / R
R(n) = F / I
Porquet & Dubau (2000)
He-like triplet lines
n=2→1 transitions produce 3 important lines
• Resonance line (R or w)
• Intercombination line (I or x+y)
• Forbidden line (F or z)
G and R diagnostics (Gabriel & Jordan 1969)
G(T) = (F+I)/R = (z+x+y)/w => temperature T
• R line mainly excited by photons, also by
recombinations and by collisions (depend on T)
• F and I lines mainly excited by cascades from
upper levels and by recombination
R(n) = F/I = z/(x+y) => density n
• Collisions (depend on n) depopulate the F level
• Whereas the I level get more populated
Triplet lines appear different in collisional and
photoionized plasmas
(w)
metastable
(x+y)
(z)
G and R applications
G(T) = (F+I) / R
R(n) = F / I
Applications and Complications
G and R used in solar plasma studies (Freeman & Jones 1970; McKenzie et al.
1978,1982)
Then applied to collisional, extra-solar plasmas (Ness et al. 2001; Porquet et al. 2001)
Attempts at photoionized extragalactic plasmas (hybrid/photoionized: Porquet &
Dubau 2000; collisional/photoionized: Bautista & Kallman 2001)
Later, Porquet et al. (2001) added a “photoexcitation” term to their computations
Even when photoexcitation and its effects on the resonant lines taken into account
(e.g.
Sako
2000; Kinkhabwala 2002), or when using performing codes (e.g.
Cloudy,
XSTAR)
Problem:
“Photoionization conditions” = spectrum
due to recombination,
4 K) compatible
Problem:
Radiation
field
assumed
(BB
T~10
with OB
Problem: Thermal
eq. not
consistently
computedexcitation,
with ionization
eq. stars
radiative
cascades,
and collisional
only
Incidence
onnot
Visible-UV
lines,
but none
resonant
lines excitation
Transfer
eq.
solved, not
adequate
to on
model
moderately
thick media
No photoionization/photoexcitation
involved
=>=>
Not
applicable
inin
the
X-ray
absorber/emitter
inin
AGN!
=>
Not
applicable
in
the
X-ray
absorber/emitter
in
AGN!
Not
applicable
the
X-ray
absorber/emitter
AGN!
TITAN photoionization code
TITAN code (Dumont et al. 00; Collin et al. 04; Gonçalves et al 07)
A stationary, photoionization-transfer code developed at Paris Observatory (LUTh)
Code optimized for optically thick media (NH ~> 1022 cm-2), but also thin media
Computes the exact transfer for ~4000 lines (same as Cloudy) and the continuum
Atomic data: H, He, C, N, O, Ne, Mg, Si, S, Fe (UTAs), good He-like description
Assumes a 1D plane-parallel geometry: slab of gas illuminated on one side by an
irradiating X-ray source (flux and SED continuum)
Self-consisting ionization and thermal eq. computation, provides gas structure in
Temperature, density, pressure, ionization
Gives the spectra in transmission, plus emission and reflection in multiple directions
Modes include constant Density, Gaseous Pressure or Total Pressure
Deal with thermal instability, computing models for the hot and cold stable solutions
TITAN photoionization code
Computes the transfer of lines and continuum
No escape probability approximation, but throughout calculations (ALI method)
Gonçalves et al. 2006a
Multi-angle spectra
“normal direction” + 5 cones
(18°, 40°, 60°, 77°, 87°)
computes the transmitted,
reflected and emitted flux
Gonçalves et al. 2006a
OVIII l 18.97
● Chandra data
TITAN model
Can account for P Cyg-like profiles
Can simulate the expected spectrum
in function of the line-of-sight
He-like line-ratios dependency
G(T) = (F+I) / R
R(n) = F / I
G and R depend on a lot of factors…
Optical thickness
• For a very large NH, G reaches a constant value
• Degeneracy: same G value for a small NH and small x, or for a
large NH and large x
• Multiple ion features must be used to disentangle the possibilities
Coupé et al. (2004)
• G varies strongly with NH for a given ionization parameter x
(= L/nH2.D)
• G is very sensitive to microturbulence => NH deduced from G in
turbulent gas would be larger
• R does not depend on microturbulence and abundances
Exact Transfer vs. Escape Probability (EP)
• Large NH: interactions with other ions causing
photon destruction must be taken into account
• Not properly done by EP => exact transfer
photoionization code needed => TITAN
Godet et al. (2004)
Microturbulence
Dumont et al. (2003)
He-like line-ratios dependency
G(T) = (F+I) / R
R(n) = F / I
G and R depend on a lot of factors…
Plasma equilibrium conditions (constant Ptot vs. constant Density)
• Single T for whole medium currently assumed, but T varies along the WA
• Stratification of the WA best explained by gas in constant Total Pressure (e.g. NGC 3783,
Gonçalves et al. 06)
• He-like region T differs from that of the H-like region
• G is different in constant density and constant pressure models
Seyfert 2
F
R
I
He-like line-ratios dependency
G(T) = (F+I) / R
R(n) = F / I
G and R depend on a lot of factors…
Gonçalves & Godet (2007)
Orientation effects
• Know the flux angular-dependence =>
G and R in function of the line-of-sight
• G is extremely sensitive to the l.o.s.
while R does not depend on orientation
• Relative contribution of Reflection,
Emission and Absorption to the
“observed” spectrum depends on
medium size, geometry…
• Type 1 and 2 AGN assume different
geometry => G and R don’t convey the
same information in Sey1 and Sey2!
Some assumptions
Obscuring torus opening angle ~45°
Accretion disk optically thick
Observer located at infinity
Orientation effects: Sey 1 vs. Sey 2
G(T) = (F+I) / R
R(n) = F / I
Orientation effects: Seyfert 1 vs. Seyfert 2
Seyfert 1 with WA (50% of Sey 1)
• Absorbing material on the l.o.s.
reprocesses the primary spectrum
• Also contribution from Emission, the
proportion depends on geometry of
the whole gas
• Example => half contribution from
Emission, half from Absorption
Seyfert 1 without WA (50% of Sey1)
• No absorbing material on the l.o.s.
• The primary source is thus visible
• There is contribution from Emission
from material not on l.o.s.
• Example => half contribution from
Emission, half from primary continuum
Seyfert 1
He-like line-ratios dependency
G(T) = (F+I) / R
R(n) = F / I
Orientation effects: Seyfert 1 vs. Seyfert 2
Seyfert 2s
• Edge-on observer detects some of the
reprocessed primary spectrum => flux
from large opening angles (≥ 45°)
Seyfert 1
• Observed spectrum: contribution from
Emission and Reflection components
• Different scenarios are possible: 50%
reflection and 50% emission; or 90%
reflection and 10% emission, etc.
Seyfert 2
• G is systematically lower in Sey 2, as
the R line is comparatively higher
• This is true for both constant density
and constant Ptot models
• R is not affected by orientation much
Some comments
G(T) = (F+I) / R
R(n) = F / I
More complications than applications?
G and R are particularly tricky to use in the case of thick, photoionized, stratified
media such as the Warm Absorber in AGN
• Because a transfer-photoionization code is needed
• Because the WA is stratified and a single T is not enough to describe the whole medium
• Because Seyfert 1 and Seyfert 2 have different geometry and convey different information
Things we have noticed
Constant Pressure plasma tend to have higher G and R values
In general, Seyfert 2 have higher G than Seyfert 1
R is less affected by orientation effects (because of the resonant line)
Degeneracy: same G may correspond to a high-ionization, constant density medium
in Seyfert 1, or to a low-ionization, constant total pressure medium in Seyfert 2
Unless you know the WA geometry and physics… be careful!
Taking into account multiple spectral features could help disentangle options
Additional slides
Anabela C. Gonçalves
Paris Observatory (LUTh), France
LUTh seminar
Meudon, January the 18th, 2007
He-like line-ratios dependency
G(T) = (F+I) / R
R(n) = F / I
G and R depend on a lot of factors…
Plasma equilibrium conditions (constant Ptot vs. constant Density)
• Single T for whole medium currently assumed, but T varies along the WA
• Stratification of the WA best explained by gas in constant Total Pressure (e.g. NGC 3783,
Gonçalves et al. 06)
• He-like region T differs from that of the H-like region
• G is different in constant density and constant pressure models
Constant Density
Constant Total Pressure
NH=3 1023 cm-2, nH=107 cm-3, x=1000 (U=13.2, Ux= 1.8)
He-like ions
H-like ions
Gonçalves & Godet (2007)
He-like ions
H-like ions
High-, medium-, low-ionization WA
Temperature profiles
G line-ratios, medium-ionization WA
G line-ratios
R line-ratios, medium-ionization WA
R line-ratios
He-like ions atomic model
15 levels
He-like line-ratios dependency
G(T) = (F+I) / R
R(n) = F / I
G and R depend on a lot of factors…
Orientation effects
• G and R do not convey the same information in type 1 or type 2 AGN
• G is extremely sensitive to the observation angle, while R does not depend on
orientation
• G is systematically lower in the case of Seyfert 2s, both in constant density or
constant pressure models
TITAN grids of models
Need for a database of theoretical results
Code has a real potential: unique in dealing with thick media, exact transfer,
thermal instabilities and proper total pressure equilibrium computations
TITAN models compute the exact transfer for ~4000 lines and the continuum
=> long computation times (~30h for constant Ptot model)
TITAN allows for the modeling of regions in total pressure equilibrium, solves
the thermal instabilities => complex models, check for convergence
Several domains of applicability: physical parameters can vary over a large
range => needs quick, first-order estimation of the physical parameters prior
to complete modeling
To compare TITAN physical modeling with other tools, to model and to
simulate X-ray data in XSPEC => need for table FITS models
Opening TITAN to the community
Interoperability with XSPEC
Grid of models converted into XSPEC model tools => easily applicable by a
larger astrophysical community
Scientific applications: theoretical modeling of Active Galactic Nuclei (AGN),
X-ray binaries, Ultraluminous X-ray sources (ULXs), comparison of models
Observational applications: interpretation of high-quality X-ray data from
Chandra, XMM-Newton, Suzaku, …
Instrumental applications: preparation of future X-ray missions (Con-X,
Simbol-X, XEUS,…), data simulation