Thermal X-ray radiation (PDF) - SRON

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Table 3.8: Some important iron lines Ion E (keV) transition remark Fexxvi 6.97 2p–1s Lyα Fexxvi 8.21 3p–1s Lyβ Fexxvi 1.29 3p–2s Hα Fexxv 6.70 2p–1s 1 P 1 , resonance line Fexxv 6.67 2p–1s 3 P 2,1 , intercombination line Fexxv 6.63 2s–1s 3 S 1 , forbidden line Fexxv 7.90 3p–1s 1 P 1 Fexxv 1.22 3p–2s 1 P 1 Feii 6.40 2p–1s Kα (from ionisation of Fei) Feii 7.06 3p–1s ”Kβ” (from ionisation of Fei) Feii 0.79 3p–2s ”Lβ” (from ionisation of Fei) 57
3.10 Absorption of X-ray radiation 3.10.1 Continuum versus line absorption X-rays emitted by cosmic sources do not travel unattenuated to a distant observer. This is because intervening matter in the line of sight absorbs a part of the X- rays. With low-resolution instruments, absorption can be studied only through the measurement of broad-band flux depressions caused by continuum absorption. However, at high spectral resolution also absorption lines can be studied, and in fact absorption lines offer more sensitive tools to detect weak intervening absorption systems. We illustrate this in Fig. 3.27. At an Oviii column density of 10 21 m −2 , the absorption edge has an optical depth of 1 %; for the same column density, the core of the Lyα line is already saturated and even for 100 times lower column density, the line core still has an optical depth of 5 %. Figure 3.27: Continuum (left) and Lyα (right) absorption spectrum for a layer consisting of Oviii ions with column densities as indicated. 3.10.2 Continuum absorption Continuum absorption can be calculated simply from the photoionisation cross sections, that we discussed already in Sect. 3.6.7. The total continuum opacity τ cont can be written as τ cont (E) ≡ N H σ cont (E) = ∑ N i σ i (E) (3.81) i i.e, by averaging over the various ions i with column density N i . Accordingly, the continuum transmission T(E) of such a clump of matter can be written as T(E) = exp (−τ cont (E)). For a worked out example see also Sect. 3.10.6. 3.10.3 Line absorption When light from a background source shines through a clump of matter, a part of the radiation can be absorbed. We discussed already the continuum absorption. The transmission in a spectral line at wavelength λ is given by T(λ) = e −τ(λ) (3.82) 58
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High Energy Astrophysics Jelle Kaas
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3.1 Introduction Thermal X-ray radi
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Figure 3.2: The observed X-ray spec
Page 7 and 8: Figure 3.6: X-ray spectrum of the S
Page 9 and 10: series of alkaline spectra). The no
Page 11 and 12: • The first atomic shell (n = 1)
Page 13 and 14: Z El 1s 2s 2p 3s 3p 3d 4s Ground te
Page 15 and 16: m l1 s 1 m l2 s 2 M L M S +1 + +1
Page 17 and 18: 3.3 Energy levels We have seen the
Page 19 and 20: 3.4 Transitions between different l
Page 21 and 22: Figure 3.10: Transitions between a
Page 23 and 24: 3.5 Abundances of the elements With
Page 25 and 26: 3.6 Basic processes In order to be
Page 27 and 28: leading to Here the constant S 0 is
Page 29: 3.6.3 Radiative transition probabil
Page 32 and 33: Figure 3.12: Fluorescence yield as
Page 34 and 35: The formula of Younger While the Lo
Page 36 and 37: 3.6.6 Excitation-Autoionisation In
Page 38 and 39: 3.6.7 Photoionisation Figure 3.20:
Page 40 and 41: 3.6.9 Radiative recombination Radia
Page 42 and 43: 3.6.10 Dielectronic recombination T
Page 44 and 45: 3.7 The ionisation balance In order
Page 46 and 47: of computing time. Therefore one us
Page 48 and 49: 3.8 Continuum emission processes Af
Page 50 and 51: decays back to the 1s orbit by a ra
Page 52 and 53: Inner-shell ionisation The third li
Page 54 and 55: 3.9.3 Line width For most X-ray spe
Page 56 and 57: Table 3.6: The strongest emission l
Page 60 and 61: with τ(λ) = τ 0 ϕ(λ) (3.83) wh
Page 62 and 63: Table 3.9: The most important X-ray
Page 64 and 65: where the hydrogen column density N
Page 66 and 67: source itself. Fortunately, with hi
Page 68 and 69: Figure 3.35: Stability for the ioni
Page 70: Table 3.10: Wavelengths in Å of th
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