Simulations showing the source and emitter sites. In the image on the left we have applied the criterion that the magnetic field strength converted to frequency must be inside the bandwidth of a single maser site. In the image on the right we have taken into account on top of the bandwidth criterion that the radiation is beamed in a hollow cone with a solid rim. Therefore the emitter is not always visible. The blue arrow depicts the direction towards the observer, its angle corresponds with the inclination of the system. When viewed in Adobe Acrobat Reader these images will appear as gifs, showcasing the fact that the celestial bodies orbit around each other. Only in certain frames the emitter site will be visible. If it is not visible, a single point with magnetic field strength 0 is placed at the origin so it is clear from the colour bar that the emitter site is not visible at this phase. If the embedded animated images do not display correctly, you can alsoaccess them online.