XMM-Newton Science Analysis System


eregionanalyse (especget-1.39.2) [xmmsas_20141104_1833-14.0.0]

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Statistical upper limit

By default this gives the 2-sigma upper limit on the background subtracted source count rate. If the number of counts is small, i.e. there are less than 80 counts in the source region then the Bayesian upper limit is returned (see Kraft, Burrows and Nousek, 1991, ApJ 374, 344). For larger numbers of accounts the returned upper limit is given by:

$$U = ( max((S-B),0) + 2 * \sqrt{ S + B \times (A_{S} / B_{S})^{2} } / exp_tim$$ (3)

Note this number is the upper limit for the count rate in the input source region before centroiding, optimisation or correction for encircled energy.

The significance level of the upper limit may be changed using the ulsig parameter.