guide to xspec | |||
To begin type: xspec |
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All commands below are entered
at the
XSPEC> prompt. |
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Commands listed in
approximate order of usage. |
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Commands |
Command
Description |
Sample
Command |
Information
Returned after Command execution |
data filename.pha |
Enters data into xspec. Best to
enter data before entering response file. |
data casa_spec.pha |
Brief information about file. |
response filename.rmf or filename.rsp |
Selects response file for data
file. Chandra response files have .rmf extension; EXOSAT response files have .rsp extension. |
response acis.rmf (this file needs to be selected from the list at the Chandar rmf page) |
|
cpd plotting device |
Selects a device to plot the
spectrum. |
cpd /xw |
Graph screen appears with
contact information. |
plot data |
Plots the data file using the
selected device. Good to do after any change to data. |
plot data |
Plot of spectrum appears. |
ignore bad |
Ignores obviously bad data
points in the spectrum. |
ignore bad |
|
ignore value1-value2 |
Removes the range of data points
from the the spectrum data. Can remove a defined range or from one end
of data to a defined point, i.e. first 60 points (**-60) |
ignore 60-100 ignore 60-** ignore **-60 |
|
setplot energy |
Changes x axis values from
Channels to Channel Energy (keV). |
setplot energy |
|
model phabs(spectrum law) |
Attempts to model function based
on one of the three spectrum equations: Powerlaw, Blackbody, Thermal
Bremsstrahlung. Plot data will now show the most current model on the plot with the spectrum. Fit statistics displayed after the default values are entered give an idea of the fit. Reduced chi squared should be close to one and the null hypothesis probability should not be small for a good fit. Usually, fit is not good with default values. |
model phabs(powerlaw) model phabs(bbody) model phabs(bremss) |
Displays prompt to enter
parameter values. Press <Enter> three times to accept all default values. Displays default parameters and fit statistics. |
renorm |
Multiplies entire current model
by a factor calculated from data. Generally gives a better fit. |
renorm |
Displays new parameters and fit
statistics. |
fit |
Attempts to find a lower chi
squared to match data with a better fit. Will only try 10 sets of
values without user telling it to continue. After fit found or user
stops searching, it will display new fit statistics. |
fit |
Displays the sets of values it
attempted and prompts to continue fitting. After searching, displays
new parameters and fit statistics. |
plot data residuals |
Creates a plot of data residuals
beneath the spectrum plot. |
plot data residuals |
|
flux |
Determines the flux of the
object. |
flux |
Displays flux value in photons/cm2/s and in ergs/cm2/s. |