Unusual features of the millisecond pulsar 1937+21 at 406.9 MHz

Observations of the millisecond pulsar PSR B1937 + 21 acquired in Summer 19 97 with the Medicina cross telescope revealed two interesting features: the existence of long-lived microstructures persisting over several minutes, a nd a close relationship between the pulsar flux and pulse arrival times, du e to refraction on a discrete inhomogeneity. The latter effect, though obse rved earlier at higher frequencies by the Nancay group, is rather peculiar at our low frequency. (C) 2001 MAIK "Nauka/Interperiodica".