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Why is the Microstructure of the Main Pulse and Inter Pulse of the Pulsar in Crab so Strikingly Different?
IX International Conference "SOLITONS, COLLAPSES AND TURBULENCE: Achievements, Developments and Perspectives", Yaroslavl, RF, August 5-9, pp.81-83 (2019)

V.M. Kontorovich

In the remarkable work of Hankins and Ailek*) [1] it was discovered (to the surprise of the authors themselves) the striking difference in the spectra of the MP (main pulse) and of the IP (inter pulse) at microsecond resolution. In particular, a wide frequency range was observed in 81 Conference ?Solitons, collapses and turbulence? (SCT-19) the MP spectra, forming vertical structures, while in the IP spectra at the same frequencies horizontal structures with selected frequencies resembling thezebra structure of solar radio bursts were observed. We offer a possible (partial) answer to this riddle. It consists in, as can be seen from multifrequency measurements (Moffett and Hankins, ApJ, 1996), that in the vicinity of the measurement frequency of the microstructure there is a change in the prevailing mechanisms of radio emission with growing of frequency. The subrelativistic mechanism of radiation with longitudinal acceleration is still valid for the MP (Kontorovich and Flanchik [2]). In this case, a flat in frequency radiation spectrum is formed, which corresponds to the ?vertical? microstructures and terminates (breaks off) at the inverse time of particle acceleration. Acceleration occurs to relativistic velocities from thermal ones in the accelerating electric field increasing from zero on the star?s surface. For the IP this mechanism has already been turned off at the measurement frequency and replaced by another (relativistic) curvature radiation mechanism, which in an inclined magnetic field causes an IP shift (Kontorovich and Trofimenko [3]). Therefore, there are no vertical microstructures in it. We also considered the effect of a logarithmically large acceleration time from thermal to relativistic velocities (Kontorovich and Flanchik, JETP, 2013) to the frequency spectrum break and the possibility of appearance of the separate MPs with vertical structures due to temperature fluctuations in the region of frequencies larger than the average frequency of emission mechanism change. We do not discuss here the micro zebra structure, the explanation of which are devoted various physical scenarios (see Lyutikov, MN RAS, 2007; Ardavan et al, ibidem, 2008; Zheleznyakov et al, Astron. Lett., 2012; Kontorovich, ibidem, 2014) and whose connection with curvature radiation (through bunches or solitons, as example) is not yet clear. In traditional pulsar models the MP and IP should be the same in their observable quantities (such as spectrum, time signature, or dispersion). We were and remain quite surprised that this turns out not to be the case in the Crab pulsar. From J. Eilek and T. Hankins paper [1].