Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/scisim/release/latest/help/postscript/csim.ps Дата изменения: Wed Jan 12 14:07:05 2005 Дата индексирования: Sat Dec 22 15:33:56 2007 Кодировка: Поисковые слова: zodiacal light

Cosmic Simulator (CSIM) 4.0
Hassan Siddiqui
January 12, 2005
This is a paper version of the CSIM help. If possible, refer to the HTML version, which contains images
and hypertext links.
CSIM forms part of the XMM-Newton Science Simulator SciSim for the XMM-Newton satellite. Its
role is to simulate astrophysical data for subsequent processing by the instrument simulators of the
Science Simulator.
This document contains information specic to CSIM only; for generic information about SciSim, see
the SciSim User Guide.
1

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Contents
1 Overview of CSIM 3
2 Installation 3
3 Getting Started 3
4 General Features 3
4.1 Creating Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1.1 Catalogue Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1.2 Simulating Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1.3 Creating Sources Manually . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2.1 X-ray Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2.2 Optical Sky Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5 Source Properties 6
5.1 Source Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2 Optical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3 Brightness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.4 Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.5 Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6 The Catalogue Data 7
7 Importing Spectra from XSPEC 8
8 Sourcelist le 11
9 Limitations 12

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1 Overview of CSIM
The Cosmic Simulator is the front-end of the Science Simulator and provides astrophysical data for
subsequent processing by the instrument simulators of SciSim.
This document describes version 2 of CSIM. The main addition to this version is the Catalogue Interface.
It is still possible to overlay manually-constructed source elds. The IDL Graphical User Interface of
version 1.0 has been replaced within a Qt-based GUI, of which CSIM features comprise a subset.
The GUI creates an ASCII le containing information about each source in the eld. This le is used by
GSIMand OSIM.
2 Installation
See the catalogue installation notes in the Installation Guide.
The les example capella.qdp, default generic.qdp and default xrb.qdp contain examples of tab-
ulated spectra and are situated in the data/gsim/ directory. These are ASCII les and may be examined
using any text editor.
3 Getting Started
CSIM creates a source le which can be used for simulation runs. A sourcele is of ASCII format and
can be written or modied using either the SciSim GUI or a standard editor.
The OSIM package can use this source le directly. For RSIM and ESIM, the ray generator must rst
be executed, using the source list le as an input. The output of the ray generator may then be piped
to the MSIM module and then to either the RSIM, MSIM, or ESIM simulators. A full simulation can be
executed from the SciSim GUI or via the command line.
To invoke the GUI, the following command can be used :
scisim &
A GUI window is then created. See the SciSim User Guide for details of GUI features.
4 General Features
This section describes the basic features of CSIM, most of which can be accessed from within the SciSim
GUI. For further details of the GUI please refer to the SciSim User Guide.

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4.1 Creating Sources
Three types of sources can be created using CSIM :
1. Catalogue sources
2. Simulated sources
3. Manually-created sources
Catalogue sources are currently provided by the Guide Star Catalogue(GSC), the Tycho Input Cata-
logue(TIC), and the ROSAT WGA catalogue. Articial optical elds can also be created, based on a
galactic number density and spectral distributions. Alternatively, sources can be manually created using
the `EDIT' option.
4.1.1 Catalogue Sources
Catalogue data can be extracted using the `Sources: Catalogue' GUI option. The dialogue provides the
following congurable options:
optical Allows zero or one optical catalogue to be selected.
X-ray Allows zero or one X-ray catalogue to be selected.
radius Denes the circular search region about the spacecraft pointing.
Extract Extracts the desired data from the selected catalogue(s). All previous catalogue-based
sources are removed.
Clear Deletes all catalogue sources previously extracted.
Close Closes the dialogue.
For further information regarding the data itself, see the Catalogue Data section(Sec. 6).
4.1.2 Simulating Sources
Sources can be simulated using the `Sources: Simulated ..' GUI option.
Simulated sources are generated with pseudo-random coordinates, magnitudes and spectral types. The
positions are uniformly distributed within a circular region dened by the parameter radius and the
spacecraft pointing. The magnitudes are distributed using the following star density model based on a
galactic latitude of 50 degrees [1]:
density(B) = 3:04  10 8  B 7:89 (per square degree per magnitude)
A B{V of 0.8 is assumed.
The spectral class distribution (applicable up to V = 8.5), is taken from p. 78 of [2].
The dialogue provides the following congurable options:

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min magn The mininum bound for the magnitude distribution..
max magn The maxinum bound for the magnitude distribution..
Radius Denes the circular region about the s/c pointing within which sources are generated.
Generate Generates the articial eld. All previous simulated sources are removed.
Clear Deletes all simulated sources previously generated.
Close Closes the dialogue.
4.1.3 Creating Sources Manually
This can be done by manipulating the source database via the `Sources:Edit' menu option (see SciSim
User Guide).
4.2 Background
The background model can be dened by selecting the menu option `Sources:Background'. The dialogue
contains the following congurable options:
column The global column density, units of 10 24 HI atoms cm 2 .This is currently only applied to
the X-ray background model.
max magn The maximum bound for the magnitude distribution..
ux The 0.25-12 keV X-ray background ux.
units The units for the ux (photon s 1 mm 2 or eV s 1 mm 2 ).
zodiacal The zodiacal light level.
diuse The diuse light level.
Close Closes the dialogue.
4.2.1 X-ray Background
A simple description of the hard X-ray background is provided, based around a source which emits rays
over a circular region with a radius of 2 degrees, and centred at the spacecraft pointing.
It uses a tabulated spectrum, default xrb.qdp, which is based on observations of the X-ray background
from ASCA data [3]. The model is a power law of photon index 1.4. They measure a ux (corrected to
the XMM-Newton passband of 0.25-12 keV) of approx 1:152  10 3 photon s 1 mm 2 .
This `background source' is automatically created by CSIM, but the ux can be modied by entering
the new value in the ` ux' window situated within the X-ray section of the background dialogue.
4.2.2 Optical Sky Background
The optical sky background (zodiacal or diuse) can be modied by entering the new scaling factor in
either the `zodiacal' or `diuse' windows. These scaling factors are dened in the OSIMdocumentation.

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5 Source Properties
A SciSim source entity has 5 properties: the position of the source in the sky; Optical, which models the
optical counterpart; Brightness, which describes the ux behaviour of the source; Spectrum, the spectral
distribution and Shape, the spatial distribution.
5.1 Source Position
The source direction is stored internally in equatorial coordinates (ra, dec), but can be specied from the
GUI either in (ra,dec) or in terms of a radial oset (deg) and azimuth (deg) with respect to the spacecraft
pointing. The latter pair are converted into the equatorial system. In addition, the position of the source
along the spacecraft's X-axis can be entered. This position is always negative. To represent a source at
an innite distance, `0' should be entered.
5.2 Optical
The optical counterpart of the X-ray source can be specied. At present, there are only stellar represen-
tations. The spectral type (b0, a0, f0, g0, g2, k0 and m0) and the apparent V-magnitude can be changed.
For no optical counterpart, the `none' option should be selected.
5.3 Brightness
The brightness property of the source denes the ux over the energy range over which the source
spectrum is valid, and the temporal behaviour of the source. Two types are provided, Stationary and
Sinusoidal. Sources with the Stationary characteristic emit a constant ux; while the ux from Sinusoidal
sources vary with time. Their parameters are summarized below. Their units are shown in brackets.
Brightness Type Parameters
Stationary Lower energy limit(eV), Upper energy limit(eV), Flux(eV=mm 2 =s
or photon=mm 2 =s)
Sinusoid Lower energy limit, Upper energy limit, Flux, Modulation depth,
period (s), phase Ellipticity, Position Angle
Note that the ux can be expressed in one of two units. The desired units can be selected by clicking the
widget labeled `Units'.
5.4 Spectrum
There are ve spectral types included in CSIM to model photon spectra: Monochrome, Gaussian,
Powerlaw, Powerexp, and XSPEC. These can be selected by clicking on the relevant button on the GUI.
The recommended spectral type for astronomical sources is `XSPEC', as this provides the most exibility.
For spectra of type XSPEC, the spectral distribution is dened in an QDP-type ASCII le, which can
be generated directly from XSPEC (see section7)). Note that interstellar absorption can only be applied
to XSPEC-based spectral types.
The following table summarizes the spectral types and lists their associated parameters :

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Spectral Type Form Parameters
Monochrome P (E) / ф(E E 0 ) Energy (eV)
Gaussian P (E) / exp( (E E0 ) 2
2 ) Energy (eV), standard de-
viation (eV)
PowerLaw P (E) / E  Index , Minimum En-
ergy(eV), Maximum En-
ergy(eV)
PowerExp P (E) / E  exp( E) Power law index, Expo-
nential index, Minimum
Energy, Maximum Energy
XSPEC User dened Name of spectral le
The spectral distributions for Powerlaw and PowerExp types are restricted to an energy band between
the Minimum and Maximum energy values.
When specifying the power law index, the following special cases:
 Uniform in energy: Power law index = 0
 Uniform in wavelength: Power law index = -2
5.5 Shape
The spatial distribution for a source can be selected by clicking on the `TYPE' widget button on the
GUI. CSIM provides three types of spatial distribution { Point, Ellipse and NonUnifEllipse. The model
Point represents a point source in the sky, and Ellipse and NonUnifEllipse describe uniform and gaussian
density distributions respectively, over an elliptical region on the sky. The models and their associated
parameters are summarised below:
Spatial Type Parameters
Point None
Ellipse Inner semi-major axis, Outer semi-major axis, Ellipticity, Position
Angle
NonUnifEllipse Inner semi-major axis, Outer semi-major axis, Ellipticity, Position
Angle, Standard deviation of density distribution
All parameters are specied in degrees.
6 The Catalogue Data
Sources from astronomical catalogues can be accessed using the `Sources: catalogue..' option. See the
SciSim User Guide for further information on GUI-related features.
The optical catalogues provide the position (ra, dec), V-magnitude and whenever available, the stellar
type of a source. The latter is determined from the colour (B-V). The GSC provides B-magnitudes and
no colour information so the stellar classications are determined from the galactic stellar population
distribution [p. 78 of [2]]. , from which the colour and so the B-magnitude is estimated. Approximately
10 % of TIC catalogue sources contain colour information and are therefore classied, the remainder are
assigned an `UNKNOWN' class.

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The WGA catalogue provides the position, ux and whenever possible a spectral model. Approximately
14 % of sources in the WGA catalogue are assigned a number between 1000 and 9998, the remainder are
assigned 9999. This classication is used by CSIM to determine the X-ray spectrum of the source. The
keyword-compound value wga speclist in the conguration le lists the spectral les used by CSIM.
Each le has a numeric label which can run from 0 to 9999. For a given WGA classication number,
CSIM determines the required spectral le using the following scheme :
1. If there is a spectral le in the list with a numeric label equal to the classication number,
ELSE:
2. If there is a spectral le in the list where the last digit is zero, and the rst 3 digits of the
numeric label are equal to the rst 3 digits of the classication number,
ELSE:
3. If there is a spectral le in the list where the last two digits are zero, and the rst 2 digits
of the numeric label are equal to the rst 2 digits of the classication number,
ELSE:
4. If there is a spectral le in the list where the last three digits are zero, and the rst digit of
the numeric label is equal to the rst 1 digits of the classication number,
ELSE:
5. The spectral le null.qdp is assigned to the source.
For example, if the keyword-value wga speclist was assigned the following in the conguration le:
wga_speclist begin
wga_1000.qdp
wga_1234.qdp
wga_3000.qdp
wga_3500.qdp
wga_4000.qdp
wga_4820.qdp
wga_5000.qdp
wga_6000.qdp
wga_7000.qdp
end
Then sources of WGA classes 1234, 4821, 3570, 6951 and 9000 will be assigned wga 1234.qdp, wga 4820.qdp,
wga 3500.qdp, wga 6000.qdp and null.qdp respectively.
7 Importing Spectra from XSPEC
CSIM provides a means by which user-dened spectral distributions can be imported from XSPEC. This
is the `Tabulated' spectrum type. If this type is selected, GSIM will search for the .qdp le specied in
the `File Name' window.

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As an example, a part of a procedure described in the XSPEC Users Document [4] is reproduced here.
The source to be modeled is the elliptical galaxy NGC 4472. This galaxy was observed with BBXRT [5].
The measured ux over the 0.5-4.5 keV passband of the instrument is 6:710 12 erg cm 2 s 1 . The best
t model was a Raymond-Smith, with a temperature range of 0:74  kT  0:98, an abundance range,
in solar units, of 0:09  A  0:46. The column density range was determined to be 5:0  10 20  NH 
3:7  10 21 cm 2 .
To create a spectral le, XSPEC must be invoked.
[27]> xspec
XSPEC 9.00 08:39:54 9-Sep-96
Plot device not set, use "cpd" to set it
Type "help" or "?" for further information
Then the user must specify the parameterized model which closely represents this spectral distribution.
In this case it is a Raymond-Smith (the XSPEC shorthand is `ra') with photoelectric absorption (`wa') :
XSPEC> mo wa ra
The user is then prompted for model parameters. The normalization will be computed later, so a carriage
return is entered at this prompt for the default value.
mo = wabs[1] (raymond[2])
Input parameter value, delta, min, bot, top, and max values for ...
Mod parameter 1 of component 1 wabs nH 10^22
1.000 1.0000E-03 0. 0. 1.0000E+05 1.0000E+06
0.21
Mod parameter 2 of component 2 raymond kT(keV)
1.000 1.0000E-02 8.0000E-03 8.0000E-03 64.00 64.00
0.86
Mod parameter 3 of component 2 raymond Abundanc
1.000 -1.0000E-03 0. 0. 5.000 5.000
0.27
Mod parameter 4 of component 2 raymond Redshift
0. -1.0000E-03 0. 0. 2.000 2.000
Mod parameter 5 of component 2 raymond norm
1.000 1.0000E-02 0. 0. 1.0000E+24 1.0000E+24
---------------------------------------------------------------------------
---------------------------------------------------------------------------
mo = wabs[1] (raymond[2])
Model Fit Model Component Parameter Value
par par comp
1 1 1 wabs nH 10^22 0.210000 +/- 0.
2 2 2 raymond kT(keV) 0.860000 +/- 0.
3 3 2 raymond Abundanc 0.270000 frozen
4 4 2 raymond Redshift 0. frozen
5 5 2 raymond norm 1.00000 +/- 0.

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---------------------------------------------------------------------------
---------------------------------------------------------------------------
3 variable fit parameters
A dummy response matrix must then be created over the XMM-Newton band :
XSPEC> dummy 0.25 12
The correct normalization is then determined over the BBXRT bandpass, by asking XSPEC for the model
ux over that band, assuming the default normalization of 1 :
XSPEC> flux 0.5 4.5
Model flux 0.2913 photons (5.1223E-10 ergs)cm**-2 s**-1 ( 0.500- 4.500)
This is clearly to high. The correct normalization should be approximately 77 times lower. The normal-
ization is reset using the NEWPAR command, followed by the parameter number, followed by the new
value :
XSPEC> newpar 5 0.013
3 variable fit parameters
XSPEC> flux
Model flux 3.7863E-03 photons (6.6590E-12 ergs)cm**-2 s**-1 ( 0.500- 4.500)
The ux over the XMM-Newton bandpass must now be determined. This value, in units of photon cm 2 s 1 ,
should be inserted in the `Flux' window of the GUI, when this source is entered.
XSPEC> flux 0.25 12
Model flux 3.9554E-03 photons (6.8121E-12 ergs)cm**-2 s**-1 ( 0.250- 12.000)
Up to this stage the model has included absorption, so that the observed ux can be estimated. However,
this component is not necessary in the tabulated spectrum as the ray generator has its own absorption
model. Thus, the column should be set to zero:
XSPEC> newpar 1 0
3 variable fit parameters
The XSPEC PLT interface must then be invoked. The graphics device in this example is xwindows (/xw)
XSPEC> cpd /xw
Starting /usr/local/bin/pgxwin_server.
XSPEC> iplot model
PLT>
The model can be saved in QDP format, by using the wdata command :
PLT> wdata test_spectrum

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Finally, exit XSPEC :
PLT> exit
XSPEC> exit
Do you really want to exit (y) y
XSPEC: quit
[22]>
The le test spectrum.qdp should be seen in the current directory.
This le can now be used by the GUI specifying the string test spectrum.qdp in the `File Name'
window (this string may have to be preceeded by the absolute path to the le if the environment variable
$SCISIM PATH is not dened). Remember to include the ux measured over the XMM-Newton bandpass
in the appropriate GUI window, and the column density along the line of sight to the source.
Other examples of tabulated spectra which are available with this package include the XRB model
default xrb.qdp and example capella.qdp which can be found in the $SCISIM DIR/gsim/data direc-
tory. Note that GSIM scans that directory for tabulated les, so to use these examples in simulations
the user need only type in the name of the le in the `File Name' window of the GUI application.
The le example capella.qdp is based on a two-temperature Raymond-Smith model [6] (T 1 = 0:41 keV,
norm 1 = 0:025; T 2 = 2:16 keV, norm 2 = 0:025, with a model abundance of A = 0:1 solar for both
components. A photon ux of 0:1 photons cm 2 s 1 over an energy range of 0.4 { 2.4 keV and a column
density of 3  10 18 cm 2 should be used with this spectrum.
8 Sourcelist le
To save the source data to a permanent le, select the `File : Save sources as..' menu option. The
GUI writes an ASCII le containing spacecraft information and source details This le can be modied
outside of the GUI using a standard editor. Note that running a simulation using GSIM from the GUI
will implicitly create a le tempc containing the current source information. A previously stored source
list can be updated by selecting the `File : Load sources ..' option.
An example le is shown below. It contains two X-ray sources : an x-ray background source (no label),
and a point source with a sinusoidally varying ux and monochromatic spectrum (labelled new). The
optical counterpart to the latter is an a0 star with a magnitude of 15.
# Source list created by scisim
begin
ident CsimData
optical_sky begin
zodiacal 0
diffuse 0
radiusFOV 0.21
background 0
diffSpect diffuse
zodSpect zodiacal
end

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sources begin
begin
dir begin 0 0 end
label new
opt begin a0 15 end
origin 0
ray begin 0 sinusoidal 0.001 p 100 30000 0.3 300 0.15 monochrome 1500 point end
end
end
xraybackground begin
dir begin 0 0 end
label xrb
opt begin NONE 12 end
origin 0
ray begin 0 stationary 1.8e-05 p 250 12000 xspec 0 default_xrb.qdp ellipse 0 2 0 0 end
end
end
9 Limitations
 The absorption feature only acts on sources which contain XSPEC-type spectra.
References
[1] M. Cropper. XMM-OM/MSSL/NT/0015.01, Dec 1991.
[2] M.V. Zombeck. Handbook of Space Astronomy and Astrophysics. Cambridge University Press, 1990.
[3] K. C. Gendreau et al. ASCA Observations of the X-Ray Background. In New Horizon of X-ray
Astronomy, First Results from ASCA, pages 365{371, 1994.
[4] K. A. Arnaud. XSPEC : An X{ray Fitting Package (version 9), Sep 1995.
[5] P. J. Serlemitsos, M. Loewenstein, R. F. Mushotzky, F. E. Marshall, and R. Petre. ApJ, 413:518,
1993.
[6] G. Vacanti. Private communication.