Explore ultra-long period radio pulsars and transients with pulsar emission geometry

ABSTRACT Investigation of 10 ultra-long period radio transients (ULPTs) and pulsars (ULPPs) is conducted using the conventional pulsar emission geometry. The geometry links together the emission height and the pulse width with the obliquity angle, between the magnetic and rotation axes, and the viewing angle, between the rotation axis and the line of sight. Assuming that the ULPTs and ULPPs are pulsars, several emission behaviours can be derived from their known pulse widths and the rotation periods. Then, they are compared with the normal radio pulsars recently discovered using the Five-hundred-meter Aperture Spherical radio Telescope. The results indicate that both the ULPTs and ULPPs show similarities with the normal pulsars in the values of obliquity and viewing angles, suggesting the observed differences between ULPTs+ULPPs and the normal pulsars are not likely due to the emission geometry. The results also show that ULPTs and ULPPs are different from the normal pulsars in the radiation spin-down, and marginally different in the relation of pulse width with the geometric expansion of dipolar field lines. We discuss that ULPTs and ULPPs are not simply slow-rotating pulsars, but may possess a different emission arrangement, which is likely due to the emission being generated from higher heights in the magnetospheres. Alternatively, their observed properties may result from changes in the emission conditions that allow coherent radio bursts at such long periods.