follows a $\chi^2$-law with $n$ degrees of freedom for $n$ additional parameters. To evaluate the significance of putative new sources, we compute a two-dimensional residual TS map that tests the hypothesis of a point source with a generic $E^{-2}$ spectrum against the null hypothesis at each point in the sky. The positions where the TS values exceed 25 (corresponding to a significance of more than $4\sigma$) are used as seeds to identify $\gamma$-ray sources in addition to the 3FGL. In that way, we iteratively add eleven sources in the 10° $\times$ 10° region and we fix their spectral parameters to their best-fit values found with `gtlike`. Figure \[fig:TSmap\_all\_sky\] shows the final residual TS map including all the sources. Note that the apparent diffuse residual emission (for which TS$_{\rm{max}}$ $\approx$ 17) disappears above 500 MeV.

![Residual TS map from 300 MeV to 300 GeV of a 10° $\times$ 10° region centered on the SNR and using the PSF3 events. The pixel size is 0.25° and the radio contours of the SNR are overlaid in white. The white circle is an FGES extended source. The white crosses are the 3FGL point sources and the red crosses are the sources added to the 