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Q&A: X-ray Astronomy

Q:
NGC 4151
HETG Spectrum
of NGC 4151
Can Chandra calculate red shift data of objects?

A:
Yes. The ability of the transmission gratings on Chandra to make fine distinctions between the energies of the X-rays from an object makes it possible to identify sharp peaks or lines in the spectrum due to ions of oxygen, silicon, iron, etc. if they are present. By comparing the observed energy or wavelength of these peaks with the corresponding values observed in the laboratory, the red shift can be measured.
GRB 991216
ACIS Spectrum
of GRB 991216
A rough measurement (within 5 or 10%) of the red shift can be made with the Advanced CCD Imaging Spectrometer (ACIS) without the gratings. In practice the red shifts determined by Chandra are used as a confirmation of the red shifts measured by optical telescopes. A notable exception is the red shift measured from the X-ray afterglow of the gamma ray burst GRB 991216.


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