How to derive flux upper limit

[MattImbr]

Hello,

I am analyzing eROSITA data from the early data release. I was wondering if there is a way to estimate the upper limit of the flux of an undetected source, since from a first look at the eSASS tasks it doesn't seem that there is a task devoted to this. What is the procedure you suggest?

Regards,

Matteo

[TengLiu]

With the task apetool, one could create a flux limit map corresponding to a likelihood threshold (e.g., probability < 4e-6) with a given background map. Note that the apetool result is given in terms of minimum photon counts required by the threshold. It can be converted to flux adopting an ECF. The method of apetool is based on Georgakakis+2008 https://ui.adsabs.harvard.edu/abs/2008M ... G/abstract
If interested in only one source, one could also calculate the flux limit manually using this method without apetool.