edit the qpspec parameter file......
source = "marx_beta10_5.qp[ccdid=7]" source qpoe file
region = "c 250 512 100" source region descriptor
bkgd = "none" background qpoe file
bkgdregion = "" bkgd region descriptor
table = "raysm" root name for output files [root_obs.tab, etc.]
(detx = "chipx") type of binning
(dety = "chipy") type of binning
(channels = 4096) number of channels or bins
(binning = "pha") type of binning
NB: If you have few counts, you can cut down the total number of channels by specifying a number smaller than 4096. You can determine the minimum and maximum channel number occupied by photons by inspecting the fits header of the marx2fits output file. The relevant numbers are the T13 parameters (TLMIN13 and TLMAX13) in the header to the binary extension file (can be viewed with the ftools task 'fv' or by unix 'more' or 'less'). TLMAX13 can be larger than 4096, but often you will not loose many photons if you set channels to 1000. If you are using ACIS-I, you will want to either use tdetx,y coordinates or specify a single chip from 0 to 3 (see the MARX handbook, Fig. 14.1). then run qpspec
to produce the 'root_obs.tab' file.