On the Apparent Nulls and Extreme Variability of PSR J1107-5907

TL;DR

This study analyzes the emission behavior of PSR J1107-5907 over 10 years, revealing two distinct emission modes, extreme pulse variability, and implications for understanding nulls and the connection between RRATs and pulsars.

Contribution

It provides a detailed characterization of PSR J1107-5907's emission modes and suggests nulls may be weak emissions, bridging the understanding between RRATs and extreme mode pulsars.

Findings

Two emission modes with distinct profiles identified

Nulls may be due to very weak emission rather than cessation

Source likely bridges RRATs and extreme mode pulsars

Abstract

We present an analysis of the emission behaviour of PSR J1107-5907, a source known to exhibit separate modes of emission, using observations obtained over approximately 10 yr. We find that the object exhibits two distinct modes of emission; a strong mode with a broad profile and a weak mode with a narrow profile. During the strong mode of emission, the pulsar typically radiates very energetic emission over sequences of ~200-6000 pulses (~60 s-24 min), with apparent nulls over time-scales of up to a few pulses at a time. Emission during the weak mode is observed outside of these strong-mode sequences and manifests as occasional bursts of up to a few clearly detectable pulses at a time, as well as low-level underlying emission which is only detected through profile integration. This implies that the previously described null mode may in fact be representative of the bottom-end of the pulse intensity distribution for the source. This is supported by the dramatic pulse-to-pulse intensity modulation and rarity of exceptionally bright pulses observed during both modes of emission. Coupled with the fact that the source could be interpreted as a rotating radio transient (RRAT)-like object for the vast majority of the time, if placed at a further distance, we advance that this object likely represents a bridge between RRATs and extreme moding pulsars. Further to these emission properties, we also show that the source is consistent with being a near-aligned rotator and that it does not exhibit any measurable spin-down rate variation. These results suggest that nulls observed in other intermittent objects may in fact be representative of very weak emission without the need for complete cessation. As such, we argue that longer (> 1 h) observations of pulsars are required to discern their true modulation properties.