acisabs: Chandra ACIS q.e. decay

This model accounts for the decay in the ACIS quantum efficiency most likely caused by molecular contamination of the ACIS filters. The user needs to supply the number of days between Chandra launch and observation. The acisabs parameters related to the composition of the hydrocarbon and the rate of decay should be frozen and not modified. The present version of acisabs is to be used for the analysis of bare ACIS I and ACIS S data. For the present version of acisabs one must use the standard qe file vN0003 instead of the optional vN0004 file.

Because of the present large uncertainty in the ACIS gain at energies below 350eV we recommend that events in the 0-350eV range be ignored in the spectral analysis until the gain issue is resolved.

acisabs calculates the mass absorption coefficients of the contaminant from atomic scattering factor files provided at

par1 Days between Chandra launch and ACIS observation
par2 Slope of linear quantum efficiency decay
par3 Offset of linear quantum efficiency decay
par4 Number of carbon atoms in hydrocarbon
par5 Number of hydrogen atoms in hydrocarbon
par6 Number of oxygen atoms in hydrocarbon
par7 Number of nitrogen atoms in hydrocarbon