Published online by Cambridge University Press: 12 April 2016
The spectra of radio flux from pulsars show deep modulations, over a typical time scale Δtd and frequency scale Δfd. These random diffractive interstellar scintillations are caused by inhomogeneities in the interstellar plasma on scales of 105m to 106m; on occasion there are also refractive modulations caused by very much larger scales. We report here an episode of periodic modulations of the dynamic spectrum of PSR B0834+06 seen in the sequence of observations centered at 408 MHz reported by Gupta et al. (1994 - GRL). There were 12 observations of about 2 hours covering 5 MHz spaced over 14 months. An episode of very fine periodic fringes was detected, though the period 45 kHz in frequency was barely resolved by the 19.5 kHz channel bandwiths; the period in time was about 5 minutes and was fully resolved. The normal Δfd was about 4 MHz (GRL) - ≈90 times the fringe period.