XMM-Newton Science Analysis System


eregionanalyse (especget-1.54) [xmmsas_20230412_1735-21.0.0]

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:

  $$U = ( max((S-B*area\_ratio),0) + 2 * \sqrt{ S + B \times area\_ratio^{2} } ) / exp\_tim / eef$$ (3)

where

S = TOTAL counts in source extraction region

B = Counts in background region

area_ratio = area_src_region / area_bgd_region

exp_tim is exposure time at centre of source region

eef is the encircled energy fraction in the source region

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