X-ray spectroscopy (PDF) - SRON
X-ray spectroscopy (PDF) - SRON
X-ray spectroscopy (PDF) - SRON
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Photoionisation modelling<br />
• Radiation impacts a volume (layer) of gas<br />
• Different interactions of photons with atoms<br />
cause ionisation, recombination, heating &<br />
cooling<br />
• In equilibrium, ionisation state of the plasma<br />
determined by:<br />
– spectral energy distribution incoming radiation<br />
– chemical abundances<br />
– ionisation parameter ξ=L/nr 2 with L ionising<br />
luminosity, n density and r distance from ionising<br />
source; ξ essentially ratio photon density / gas density<br />
Photo-ionisation equilibrium<br />
• Ξ = F ion /nkTc =<br />
ξ/4πckT<br />
• Stable equilibrium<br />
for dT/d Ξ > 0<br />
103<br />
104<br />
Photoionisation models<br />
• Models for transmission<br />
of a thin slab<br />
• Continuum & line<br />
absorption calculated<br />
• slab model: ion columns<br />
independent<br />
• xabs model: ion columns<br />
coupled through<br />
xstar/cloudy runs<br />
• warm model: continuous<br />
distribution of N H (ξ)<br />
Sample spectra<br />
RGS 600 ks, Detmers et al. 2011 (paper III)<br />
Chandra LETGS 180 ks, Ebrero et al. 2011 (paper V)<br />
HST/COS 8-16 ks, Kriss et al. 2011 (paper VI)<br />
XMM-Newton RGS<br />
Chandra LETGS<br />
105<br />
HST/COS<br />
106<br />
Absorption Measure Distribution<br />
Decomposition into separate ξ<br />
Emission measure<br />
Column density<br />
Discrete components<br />
Continuous<br />
distribution<br />
• Early example:<br />
NGC 5548<br />
(Steenbrugge et al. 2003)<br />
• Use column densities Fe<br />
ions from RGS data<br />
• Measured N ion as sum of<br />
separate ξ components<br />
• Need at least 5<br />
components<br />
Ionisation parameter ξ<br />
Temperature<br />
107<br />
108
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