Plasmas in the ASCA Bandpass

This page gives some hopefully useful information concering the emission expected from an optically-thin plasma in the ASCA bandpass (~ 0.4-10.0 keV). The emphasis is on how spectral features actually appear after being convoled with the ASCA SIS instrumental response.

An ionization balance calculator (back online)

Raymond-Smith Spectra

These plots show the output of rs_code.for, availble via ftp. See the README file for more details. The expected spectrum (computed in 10 eV bins, roughly the resolution of Astro-E's calorimeter) is plotted in black, along with continuum features plotted in yellow (bremsstrahlung), blue (recombination), and green (2-photon). The spectrum convolved with the ASCA SIS0 response is also shown (plotted in red; note that this response includes the quantum efficiency of the detector which introduces features into the shape of the continuum, most notably an Oxygen absorption edge at ~ 0.5 keV).

0.25 keV	0.65 keV	1.0 keV	2.0 keV	4.0 keV	8.0 keV	16.0 keV

Comparison of Raymond-Smith and MEKAL Code in XSPEC

This plot shows the ratio of a 0.65 keV Raymond-Smith and a 0.65 keV MEKAL plasma, as seen by the ASCA SIS0 (i.e., simulated by XSPEC. The error bars show the stastical errors at high energies, while the statistical error is smaller at lower energies (omitted for clarity).

plot of ratio of R-S and Mekal model spectrum

Line List

This line list was produced by simulating a 0.65 keV Raymond-Smith plasma in XSPEC (using the vray model) where all elemental abund. except for one were set to zero. The resulting spectrum was then fit with a brem + lines model to determine the location, width and intensity of the lines associated with that element. The "intensity" is given in terms of eq. width but this should be treated very cautiously since a brem. is only an approximate fit to the true plasma continuum, and the plasma continuum resulting from a single-element gas differs from that of a gas with typical abundances. For example, the temperature of the brem. typically came out around 0.7 keV, ~ 0.05 keV higher than the input temperature of the plasma.

Note that line intensities are a sensitive function of temperature.

Lines with sigma > 0.01 are marked with a 'b' (i.e., they would appear to be broad to the SIS with sufficient statistics)

Identifications of a given ion state may not be unique... different transitions of different ion states span overlapping energy ranges

N.B. These line identifications are based on the Shull (1981) paper while the spectra were generated with the Raymond-Smith plasma code in XSPEC (in Jan. 1996). This chart needs to be re-done more consistently with a more recent plasma code. However, the line IDs should be approximately correct, particularly for the strong He- and H-like lines.

Energy (keV)	Line ID	EW (eV)
0.51	N7 H-like	16
0.52b	Ar16 Li-like	7
0.57	O7 He-like	14
0.61b	Ca18 Li-like	18
0.65	O8 H-like	298
0.79b	O8 H-like	77
0.81b	Fe16-17-L Na,Ne-like	21
0.90b	Fe18-20-L F,O,N-like	522
0.92	Ne9 He-like	108
0.97b	Some N feature	347
1.03	Ne10 H-like	339
1.11b	Fe20-24-L N-Li-like	509
1.23b	Ne10 H-like	87
1.25b	Some N feature	96
1.35	Mg11 He-like	347
1.44	Fe23-L Be-like	14
1.47	Mg12 H-like	170
1.51	Some N feature	16
1.58	Mg11 He-like	156
1.85	Si13 He-like	959
1.87	Mg12 H-like	11
2.00	Si14 H-like	121
2.19	Si13 He-like	63
2.30b	Si13,14 He,H-like	97
2.45b	S15 He-like	642
2.53	Si14 H-like	10
2.62	S16 H-like	11
2.89	S15 He-like	57
3.04	S15 He-like	40
3.13b	Ar17 He-like	206
3.89b	Ca19 He-like	190
6.50b	Fe-K	1320

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