The ONs and OFFs of Pulsar Radio Emission: Characterizing the Nulling Phenomenon

Abstract Radio emission from pulsars is known to exhibit a diverse range of emission phenomena, among which nulling, where the emission becomes temporarily undetectable, is an intriguing example. Observations suggest nulling is prevalent in many long-period pulsars and thus must be understood to obtain a more comprehensive picture of pulsar emission and its evolution. However, one of the limitations in the observational characterization of nulling is the limited signal-to-noise ratio, which often makes individual pulses difficult to distinguish from noise or from any putative faint emission. Although some of the approaches in the published literature attempt to address this, they lose efficacy when individual pulses appear indistinguishable from noise, and as a result can lead to less accurate measurements. Here, we develop a new method (the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="double-struck">N</mml:mi> </mml:math> sum algorithm) that uses sums of pulses to improve distinguishability from noise, thus measuring the nulling fraction more robustly. The algorithm can be employed to measure nulling fractions in weaker pulsars and can be applied to observations with a limited number of pulses. We compare our method with the recently developed Gaussian mixture modeling approach, using both simulated and real data, and find that our approach yields consistent results for generic and weaker pulsars. We also explore quasiperiodicity in nulling and measure the related parameters for five pulsars, including PSRs J1453−6413, J0950+0755, and J0026−1955, for which these are also the first such measurements. We compare and contrast our analysis of quasiperiodic nulling with previously published work, and explore the use of spin-down energy loss ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mi>E</mml:mi> <mml:mo>̇</mml:mo> </mml:mover> </mml:math> ) to distinguish between different types of modulation behaviour.