2023MNRAS.523.5934J

We have studied the pulse-to-pulse variability in PSR J1820-0427 and its frequency dependence using high-quality, wide-band observations made with the upgraded Giant Metrewave Radio Telescope (uGMRT; 300-750 MHz) and the Murchison Widefield Array (∼170-200 MHz). The low-frequency data reveal a previously unreported feature in the average profile (at 185 MHz) after accounting for the effects of temporal broadening arising from multipath scattering due to the interstellar medium. We advance a new method for flux density calibration of beamformed data from the uGMRT and use it to measure the single-pulse flux densities across the uGMRT band. Combined with previously published measurements, these flux densities are best fitted with a power-law spectrum with a low-frequency turnover. We also use calibrated flux densities to explore the relationship between pulse-to-pulse variability and the spectral index of individual pulses. Our analysis reveals a large scatter in the single-pulse spectral indices and a general tendency for brighter pulses to show a steepening of the spectral index. We also examine the frequency dependence of the pulse fluence distribution and its relation to the Stochastic Growth Theory.