spex_bk_poisson_error

Set to 0 (default) when background is computed by fit to data in pre- and post-flare intervals. In this case, the background estimate is only as good as the fit to those intervals. The percentage uncertainty should not change when binning over multiple time bins. So average errors rather than combining errors in quadrature (which assumes bk is based on statistics, and error is sqrt(counts)).

Set to 1 when bk is uncoupled (e.g. if you inserted background from a previous orbit) and errors should be summed in quadrature.

(Introduced 9-Dec-2009)