3 FIG. 1: (a) Power spectral densities (PSD) normalized by I 2 $_{dc}$, obtained for I$_{dc}$ = 2.6, 2.8, 3 and 3.2 mA with H$_{perp}$ = 5.1 kOe. (b) Schematic of the different forces acting on the vortex core. nant motion is efficient enough to produce competitive passive microwave elements such as high gain resonators [18, 19]. In Fig.1 (a), we display some microwave emission spectra recorded with H$_{perp}$ = + 5.1 kOe at several positive current values. For all I$_{dc}$ , a single peak is observed in the sub-GHz frequency range that is characteristic of the coherent gyrotropic motion of the magnetic vortex core induced by the spin transfer torque [21]. The emission frequency increases with I$_{dc}$ (about 80 MHz/mA) together with a large increase of the peak power spectral density (PSD). The best results have been obtained at large currents ( I$_{dc}$ = 3.2 mA) but still below the threshold above which the MTJ is damaged. At this value, the peak linewidth is only 1.1 MHz and the integrated power is about 5 nW. This is to our knowledge the highest emitted power for STNOs showing similar linewidth. It therefore demonstrates the interest to use the motion of a vortex as microwave source to benefit from the advantages of both the coherency of the vortex gyrotropic motion and the large magnetoresistive signal provided by a MTJ. In most of cases, spin transfer excitations that is focused on the dynamics of a quasi uniform magnetization, is suffering from a lack of comparison with theoretical predictions. The reason comes mainly from the difficulties to accurately take into account the presence of multi-modes, the different sources of spin transfer torques, the role of the Oersted field or of the temperature [23]. An important impact of our work is that we provide a definite comparison and an excellent agreement between experimental data, micromagnetic simula- tions and theoretical predictions. As a matter of fact, we will show that our experiments can