http://cxc.harvard.edu/ciao/why/caldb4.1.1_hrma.html
http://web.mit.edu/iachec/meetings/2011/Presentations/Marshall.pdf
http://www.bo.astro.it/gilli/counts.html
http://www.cfa.harvard.edu/hea/genx/
http://hea-www.cfa.harvard.edu/SMARTX/
http://space.mit.edu/cxc/marx/