Single Pulse Emission from PSR B0809+74 at 150 MHz using Polish LOFAR station

TL;DR

This study presents detailed single pulse observations of pulsar B0809+74 at 150 MHz, revealing phenomena like subpulse drifting, nulling, and mode changing, and provides insights into the pulsar's emission mechanisms and magnetic field structure.

Contribution

First detailed single pulse analysis of PSR B0809+74 at 150 MHz using Polish LOFAR, highlighting mode transitions, nulling behavior, and phase variations in drifting.

Findings

Normal drift mode with P3 ≈ 11.1 P observed 96% of the time

Shorter slow-drift mode with P3 ≈ 15.7 P identified

Nulling occurs after mode switching, not before

Abstract

We report the observations of single pulse emission from the pulsar B0809+74 at 150 MHz using the Polish LOFAR station, PL-611. The three major phenomena of subpulse drifting, nulling and mode changing associated with single pulse variations are prominently seen in these observations. The pulsar has a single component conal profile and the single pulses are primarily in the ``normal'' drift mode with periodicity ($P_3$) 11.1$\pm$0.5 $P$ for 96\% of the observing duration, while the shorter duration ``slow-drift'' mode has $P_3$ = 15.7$\pm$1.2 $P$. We were able to measure the phase behaviour associated with drifting from the fluctuation spectral analysis that showed identical linear phase variations across the pulse window for both modes despite their different periodic behaviour. Earlier studies reported that the transitions from the normal state to the slow-drift mode were preceded by the presence of nulling with typical durations of 5 to 10 periods. Our observations however seem to suggest that the transition to nulling follows shortly after the pulsar switches to the slow-drift mode and not at the boundary between the modes, with one instance of complete absence of nulling between mode switching. In addition we also detected a second type of short duration nulls not associated with the mode changing that showed quasi-periodic behaviour with periodicity, $P_N\sim44\pm7$. The variety of features revealed in the single pulse sequence makes PSR B0809+74 an ideal candidate to understand the physical processes in the Partially Screened Gap dominated by non-dipolar magnetic fields.