X-ray binaries are systems consisting of a compact object, either a black hole or a neutron star, and a companion star, both orbiting a common centre of mass of the system. When the companion star in an X-ray system is a late-type main sequence star or a white dwarf with mass typically lower than a solar mass, this system is called a low-mass X-ray binary (LMXB). In such a system, the matter from the companion is accreted onto the compact object and forms a rotating disc. During this accretion process, X-rays are generated when the gravitational energy of the in-falling matter is converted into radiation due to viscous processes. However, the observed energy of the X-rays is much higher than the disc emission, which indicates the existence ...