Based on the archive data of the RadioAstron project, we analyze observations of the pulsar B1237+25 carried out with the Arecibo radio telescope on February 26, 2018. The observations were performed at a frequency of 327 MHz in the 16 MHz bandwidth in two polarization channels. We study the fine structure of individual pulses by constructing cross-correlation functions (CCFs) between two polarization channels of the receiver (LCP/RCP). This analysis was carried out separately for five different components of the average profile. No microstructure has been found in the averaged CCFs. However, some individual subpulses exhibit the microstructure. The proportion of such subpulses is about 12%. The time scale of the revealed microstructure is in a range of 0.1–1.0 ms. The intensity distribution of individual pulses over the longitude of the average profile in the flare mode of radio emission (FN), in which the emission is present at all longitudes, is explained by the presence of multipole components of the magnetic field above the polar cap. A peculiar pulse, consisting of ten micropulses of large amplitude (about 2000 Jy) with a duration of about 10 μs, was detected. These micropulses are similar to giant pulses observed in several pulsars. They directly indicate the spark discharge process in the vacuum gap of the polar cap.
Avdeev et al. (Sun,) studied this question.