On the apparent nulls and extreme variability of PSR J1107−5907

Abstract

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