The Square Kilometre Array (SKA)

Abstract:

The SKA telescopes will bring unparalleled sensitivity across a broad radio band, a wide field of view across the Southern sky, and the capacity for sub-arraying, all of which make it the ideal instrument for studying the pulsar magnetosphere. This paper describes the advances that have been made in pulsar magnetosphere physics over the last decade, and details how these have been made possible through the advances of modern radio telescopes, particularly SKA precursors and pathfinders. It explains how the SKA telescopes would transform the field of pulsar magnetosphere physics through a combination of large-scale monitoring surveys and in-depth follow-up observations of unique sources and new discoveries. Finally, it describes how the specific observing opportunities available with the AA* and AA4 configurations will achieve the advances necessary to solve the problem of pulsar radio emission physics in the coming years.

Abstract:

The known population of non-accreting neutron stars is ever growing and currently consists of more than 3500 sources. Pulsar surveys with the SKAO telescopes will greatly increase the known population, adding radio pulsars to every subgroup in the radio-loud neutron star family. These discoveries will not only add to the current understanding of neutron star physics by increasing the sample of sources that can be studied, but will undoubtedly also uncover previously unknown types of sources that will challenge our theories of a wide range of physical phenomena. A broad variety of scientific studies will be made possible by a significantly increased known population of neutron stars, unravelling questions such as: How do isolated pulsars evolve with time; What is the connection between magnetars, high B-field pulsars, and the newly discovered long-period pulsars; How is a pulsar’s spin-down related to its radio emission; What is the nuclear equation of state? Increasing the known numbers of pulsars in binary or triple systems may enable both larger numbers and higher precision tests of gravitational theories and general relativity, as well as probing the neutron star mass distribution. The excellent sensitivity of the SKAO telescopes combined with the wide field of view, large numbers of simultaneous tied-array beams that will be searched in real time, wide range of observing frequencies, and the ability to form multiple sub-arrays will make the SKAO an excellent facility to undertake a wide range of neutron star research. In this paper, we give an overview of different types of neutron stars and discuss how the SKAO telescopes will aid in our understanding of the neutron star population.

Abstract:

This paper presents a comprehensive wideband study of FRB 20240619D focusing on its hyperactivity, rotation measure evolution, and the search for an associated persistent radio source. Using data from the MeerKAT, Murriyang, and Lovell telescopes, we analysed the spectral, temporal, and polarimetric properties of 1539 bursts. Our observations reveal a remarkably high burst rate of 161 bursts per hour in early August above a fluence value of 1.6 Jy ms as well as significant secular variations in rotation measure and diverse polarization characteristics, including high linear polarization fractions and occasional circular polarization. The burst activity also showed frequency dependence with approximately 61 per cent of the total number of bursts detected between 1300 and 1800 MHz. The burst activity of FRB 20240619D ceased abruptly after a period of intense activity lasting approximately 80 d, suggesting an episodic behaviour. Follow-up observations with MeerKAT and Australia Telescope Compact Array did not reveal an associated compact persistent radio source. Altogether, our results highlight the importance of continued long-term monitoring and multiwavelength observations in understanding the emission mechanisms and diversity of progenitor populations of fast radio bursts.

Abstract:

Kilonovae are the scientifically rich—but observationally elusive—optical transient phenomena associated with compact binary mergers. Only a handful of events have been discovered to date, all through multiwavelength (gamma-ray) and multimessenger (gravitational-wave) signals. Given their scarcity, it is important to maximise the discovery possibility of new kilonova events. To this end, we present our follow-up observations of the gravitational-wave signal S250818k—a plausible binary neutron star merger at a distance of 237 ± 62 Mpc. Pan-STARRS tiled 286 and 318 deg2 (32% and 34% of the 90% sky localisation region) within 3 and 7 days of the GW signal, respectively. ATLAS covered 65% of the sky map within 3 days, but with lower sensitivity. These observations uncovered 47 new transients; however, none were deemed to be linked to S250818k. We undertook an expansive follow-up campaign of AT2025ulz, the purported counterpart to S250818k. The griz-band light curve, combined with our redshift measurement (z = 0.0849 ± 0.0003), all indicate that SN2025ulz is a type IIb supernova and thus not the counterpart to S250818k. We rule out the presence of an AT2017gfo-like kilonova within ≈27% of the distance posterior sampled by our Pan-STARRS pointings (≈9.1% across the total 90% 3D sky localisation). We demonstrate that early observations are optimal for probing the distance posterior of the 3D gravitational-wave sky map, and that SN2025ulz was a plausible kilonova candidate for ≲5 days, before ultimately being ruled out.