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), France2 Lisbon Astronomical Observatory (CAAUL), Portugal

3 Leicester University, UK

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, , etc.

X-ray gas can get ionized by Collisions (~ keV)

• X-ray bright starburst regions

• Stellar coronae

• SNRs

Photoionization (~ eV)• X-ray binaries

• AGN: BLR, NRL, Warm Absorber

solar windsnebulae

thunder

inertialconfinement

controled fusion

solar core

neonlights

propeler aurorae flames

particles/m3

T (K)

WA

Brickhouse et al. (2000)

Plasma Diagnostics in the X-rays

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 with Chandra, XMM-Newton, Suzaku, …

Gu et al. (2006)

Astrophysical plasma diagnostics Rely on spectroscopy measurements and/or

simulations => compute line-ratios

Conspicuous lines, close in /Energy => minimize calibration errors

High-quality, medium-resolution spectra (R ≥ 300) => needed to resolve the lines

He-like lines as plasma diagnostics

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

G(T) = (F+I) / RR(n) = F / I

metastable

Porquet & Dubau (2000)

(z)

(x+y)(w)

Problem: “Photoionization conditions” = spectrum due to recombination, radiative cascades, and collisional excitation, only

No photoionization/photoexcitation involved

=> Not applicable in the X-ray absorber/emitter in AGN!

Problem: Radiation field assumed (BB T~104 K) compatible with OB stars

Incidence on Visible-UV lines, but none on resonant lines excitation

=> Not applicable in the X-ray absorber/emitter in AGN!

Problem: Thermal eq. not consistently computed with ionization eq.

Transfer eq. not solved, not adequate to model moderately thick media

=> Not applicable in the X-ray absorber/emitter in AGN!

G and R applications

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)

G(T) = (F+I) / RR(n) = F / I

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)

Can account for P Cyg-like profiles

Can simulate the expected spectrum in function of the line-of-sight

● Chandra data

TITAN model

OVIII 18.97

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

TITAN photoionization code

He-like line-ratios dependency

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

G(T) = (F+I) / RR(n) = F / I

G and R depend on a lot of factors… Optical thickness

• G varies strongly with NH for a given ionization parameter (= L/nH

2.D)

• For a very large NH, G reaches a constant value

• Degeneracy: same G value for a small NH and small , or for a large NH and large

• Multiple ion features must be used to disentangle the possibilities

Microturbulence

• G is very sensitive to microturbulence => NH deduced from G in turbulent gas would be larger

• R does not depend on microturbulence and abundances

Co

up

é et

al.

(200

4)G

od

et e

t al

. (20

04)

Dumont et al. (2003)

He-like line-ratios dependency G(T) = (F+I) / RR(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

I

R

He-like line-ratios dependency

G and R depend on a lot of factors…

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 assumptionsObscuring torus opening angle ~45°

Accretion disk optically thick Observer located at infinity

Gonçalves & Godet (2007)

G(T) = (F+I) / RR(n) = F / I

Orientation effects: Sey 1 vs. Sey 2

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

G(T) = (F+I) / RR(n) = F / I

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

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°)

• Observed spectrum: contribution from Emission and Reflection components

• Different scenarios are possible: 50% reflection and 50% emission; or 90% reflection and 10% emission, etc.

• 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

G(T) = (F+I) / RR(n) = F / I

Seyfert 1

Seyfert 2

Some comments

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

G(T) = (F+I) / RR(n) = F / I

Additional slides

Anabela C. Gonçalves

Paris Observatory (LUTh), France

LUTh seminar Meudon, January the 18 th, 2007

He-like line-ratios dependency

Gonçalves & Godet (2007)

Constant Density Constant Total Pressure

He-like ions He-like ions H-like ionsH-like ions

NH=3 1023 cm-2, nH=107 cm-3, =1000 (U=13.2, Ux= 1.8)

G(T) = (F+I) / RR(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

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

15 levels

He-like ions atomic model

He-like line-ratios dependency

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

G(T) = (F+I) / RR(n) = F / I

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

TITAN grids of models

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

Opening TITAN to the community