cplinear: a non-physical piecewise-linear model for low count background spectra.

This is a simple non-physical model for low-count background spectra, used by fitting scripts in the ACIS Extract (AE) package. Using this model outside the context of the AE package should be done with extreme caution since it requires a choice on vertex energies and number of segments. AE places the first and last vertices at the lowest and highest energy of the background counts. Intermediate vertices are placed at energies where a background count exists such that each segment covers a similar number of background counts. Any results using this model should cite Broos et al. (2010).

Note that if all the rate parameters in use are thawed then the norm parameter is degenerate and must be frozen. Freezing one of the rate parameters will not work because if that vertex is driven to zero in the fit then the norm will be zero and the other rate parameters infinite.

par1 energy00 (keV)
par2 energy01 (keV)
par3 energy02 (keV)
par4 energy03 (keV)
par5 energy04 (keV)
par6 energy05 (keV)
par7 energy06 (keV)
par8 energy07 (keV)
par9 energy08 (keV)
par10 energy09 (keV)
par11 log_rate00
par12 log_rate01
par13 log_rate02
par14 log_rate03
par15 log_rate04
par16 log_rate05
par17 log_rate06
par18 log_rate07
par19 log_rate08
par10 log_rate09