Studying the nulling, subpulse drifting, and moding in PSR J1921+1948 with the FAST

Abstract

We reported the observations of nulling, subpulse drifting, and moding of radio radiation in pulsar (PSR) B1918+19 at 1250 MHz with the Five-hundred-meter Aperture Spherical radio Telescope. The nulling fraction is 2.6 ± 0.1 per cent and no periodicity of nulling can be seen. We confirmed the existence of three different drift modes (A, B, C) and a disordered mode (N) at 1250 MHz. Unlike the other three modes where the second component of the average pulse profile dominates, the first component of the average pulse profile in mode C is brighter than the other components, the second component shifts forward and the fourth component shifts backward. The bidrifting phenomenon is observed in PSR B1918+19, the drifting of the first and second components is positive, and the drift direction of the fourth component is negative. The drifting rate of the drift bands composed of the first and second components has an obvious evolutionary trend. Mode B has a short duration and no clear trend can be seen. But for mode A, the drift rate of each drift band starts relatively fast, then slows down to a steady state, and finally increases slowly until it enters either null or mode N. Further analysis shows that the emergence and significant variation in the drifting period of multidrifting subpulse emission modes for PSR B1918+19 may be due to the aliasing effect. The interesting subpulse emission phenomenon of PSR B1918+19 at different frequencies provides a unique opportunity to understand the switching mechanism of the multidrift mode of the pulsars.