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Neutron stars were predicted by Landau, related to supernovae by Baade and Zwicky, and discovered a quarter century later fifty years ago in the form of pulsars by Hewish et al. Produced by collapse in supernova explosions, these stars have very high magnetic fields of 1012 G, rotate rapidly (with periods ranging from seconds to milliseconds), and are blanketed in a magnetosphere of electron-positron pairs which mostly co-rotates with the star but contains a beam of open lines of force over the magnetic poles, along which particles are accelerated and emit electromagnetic radiation. Particles are accelerated in the gap above the region of the open lines of force, which contains a strong accelerating electric field generated by the magnetic field and the rotation. Stimulated scattering (SS) is an effect as common as a nonlinear frequency shift. In contrast to the frequency shift, at SS the coefficient at a squared module of the amplitude of strong incident wave contains an imaginary part, which is responsible for the arising instability. Each type of stimulated scattering corresponds to its spontaneous analogue. Including as to a surface waves scattering, there has to be the stimulated scattering on them (SS on SW). All kinds of SS had observed in special experiments using powerful sources of radiation (lasers). SS on SW unlike the rest of SS has not been observed in its pure form, although it indirectly manifested itself in the appearance of the surface structures. In nature, any type of SS of the natural origin is still nowhere to be registered. We point out that the SS probably responsible for some forms of radiation in pulsars. The powerful radiation of returned relativistic positrons, extracted from the electron-positron plasma magnetosphere by accelerating electric field and flying toward the star, serves in this case as a source. A specular (mirror) reflection of this radiation in a tilted magnetic field leads to shifts the inter pulses in the Crab Nebula pulsar, detected 20 years ago by Moffet & Hankins [1.2] in the centimeter range, that did not receive any explanation other than that, proposed by S.V.Trofymenko and myself [3] a year ago. Two additional pulse components arise on the same frequencies, and, as well as the shift of the inter pulses, they could be associated with the non-linear reflection in the direction of the diffraction peak on a periodic surface structure excited by the SS [4]. The same mechanism could explain the frequency drift component detected by Hankins, Jones and Eilek [2], which is analyzed in this report. Thus, this is the first case, indicating on the realization of SS in nature. The discussed instability it is a stimulated scattering by the surface waves predicted more than forty years ago (see Refs in [4]) and still nowhere and by no one had been observed. With its help one can hope to obtain information about the surface of the neutron star. The frequency drift of the components is very important in choosing the right theoretical model. Particularly, the coincidence of its directions for both components is an argument in favor of the birefringence of the scattered wave in anisotropic magnetized pulsar plasma. Returned motion of positrons, arising at penetration of accelerating electric field of the gap in the pair plasma, was considered in literature in a connection with heating of the surface by the reverse current. The difference of magnetic field from dipole one, leading in particular to its slope, also was discussed, including with regard to its toroidal component. However, the low-frequency radiation of backflow positrons and reflected radiation from the surface of the pulsar were not considered anywhere until our works.

1. D. Moffett & T. Hankins, ApJ. 468, 779 (1996); astro/ph 9604163.
2. T. Hankins, G. Jones & J. Eilek, Ap J. 802, 130 (2015); arXiv:1502.00677v1 [astro-ph.HE]
3. V. M. Kontorovich & S.V.Trofymenko, arXiv: 1606.02966.
4. V. M. Kontorovich, Low Temperature Physics 42, 672 (2016); arXiv: 1701.02304