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tokens: the region. They found that for the region of interest studied here, mostly located outside the Galactic plane, the difference between the standard LAT diffuse model and their refined model is negligible. However, a more complete analysis of the effect of the uncertainties in the background emission model was carried out following Acero et al. ( 2016b ), who used a set of 8 alternative models 3 developed in Ackermann et al. ( 2012 ) by changing some crucial parameters that determine the intensity and distribution of the Galactic gamma-ray emission: the cosmic ray source distribution, the height of the cosmic ray propagation halo and the HI spin temperature. This is important since the standard diffuse emission models distributed for LAT data analysis are optimized for analysis of point sources and compact extended sources (Acero et al. 2016a ), and the analysis must be validated using different models. The estimation of the systematic errors was done as in Acero et al. ( 2016b ) by comparing the source parameters obtained with each alternative model and those with the standard model. The significant detection of G350.6-4.7 (above 15σ for all alternative models considered) gives confidence that the emission is indeed associated to a new extended high-energy source. Systematic errors related to the imperfect knowledge of the effective area were estimated following the LAT team recommendations. 4 Since this uncertainty and the resulting uncertainty from the background model are independent, the total systematic error was obtained by adding them in quadrature. 3 DISCUSSION It is reasonable to attribute the origin of the gamma-rays to the shell of a previously unknown SNR. If located at the distance to the pulsar PSR J1747-4036 (3.4 kpc), the object size would be around 200 pc and the centre of the disc would be located around 250 pc from the plane of the Galaxy. SNRs with diameters of the order of a few degrees are known and a significant number have been seen as extended objects by the LAT (Acero et al. 2016b ). Well-known examples are the Cygnus Loop (Katagiri et al. 2011 ) and RX J0852.0-4622 (Tanaka et al. 2011 ). However, not many SNRs are known to have a diameter greater than 100 pc, although large objects could not have detected due to observational selection effects (Green 1991 ). Dynamic considerations of the expansion and evolution of an SNR can give a physical justification for an upper limit in their size (e.g. Cioffi, McKee Bertschinger 1988 ; Slavin Cox 1993 ). It is possible then that if this new source is an SNR it is much closer than 3.4 kpc and hence unrelated to PSR J1747-4036. This pulsar is classified as a millisecond pulsar (e.g. Abdo et al. 2013 ), and thus if related to the G350.6-4.7, the SNR would also be too old to show a GeV spectrum as the one found here (see e.g. Acero et al. 2016b ). The Cygnus Loop SNR is located at about 540 pc (Blair, Sankrit Raymond 2005 ) and has a diameter of ∼35 pc. If the same physical