The SXS instrument is the Soft X-ray micro-calorimeter Spectrometer planned for the Japanese ASTRO-H
satellite, scheduled to be launched in 2014. In this paper we describe the X-ray calibration sources used in this
instrument. These sources use light sensitive photo-cathodes to generate electrons, which in turn generate the
X-rays. This design has the unique property to allow for fast discrete pulsations of the generated X-rays. This
enables the energy scale calibration of the instrument simultaneously with astronomical observations, without
adding to the background in the astronomical data. Flight-model sources have been made, and a number of them
have been operating in the past several months to monitor their behaviour. Here we report on the characterisation
and performance of these sources. In addition, we will elaborate on the nature and expected accuracy of the
energy calibration, in relation to the expected stability of the instrument, given the calibration source strength
and its mode of operation.
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