XSPEC User's Guide

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Figure A: The result of the command plot data when the data file in question is
the EXOSAT ME spectrum of the 6s X-ray pulsar 1E1048.1--5937 available
from the HEASARC on-line service
People familiar with EXOSAT ME data will recognize the spectrum to be soft, absorbed and
without an obvious bright iron emission line. We are now ready to fit the data with a model.
Models in XSPEC are specified using the model command, followed by an algebraic expression of
a combination of model components. There are two basic kinds of model components: additive,
which represent X-Ray sources of different kinds. After being convolved with the instrument
response, the components prescribe the number of counts per energy bin (e.g., a bremsstrahlung
continuum); and multiplicative models components, which represent phenomena that modify the
observed X-Radiation (e.g. reddening or an absorption edge). They apply an energy-dependent
multiplicative factor to the source radiation before the result is convolved with the instrumental
response.
More generally, XSPEC allows three types of modifying components: convolutions and
mixing models in addition to the multiplicative type. Since there must be a source, there must be
least one additive component in a model, but there is no restriction on the number of modifying
components. To see what components are available, type model :
XSPEC12>model
Additive Models:
apec bbody bbodyrad bexrav bexriv bknpower
bmc bremss c6mekl c6pmekl c6vmekl cemekl
cevmkl cflow compLS compST compTT compbb