Since their discovery in the late 1960's the population of known neutron stars has grown to ∼2500. This sample has yielded many surprises and demonstrated that the observational properties of neutron stars are remarkably diverse. The surveys that will be performed with the SKA will produce a further tenfold increase in the number of Galactic neutron stars known. Moreover, the SKA's broad spectral coverage, sub-arraying and multi-beaming capabilities will allow us to characterise these sources with unprecedented efficiency, in turn enabling a giant leap in the understanding of their properties. We review the neutron star population and outline strategies for studying each of the growing number of diverse classes that are populating the "neutron star zoo". Questions that will be addressed by the much larger statistical samples and vastly improved timing efficiency provided by SKA include: (i) the spin period and spin-down rate distributions (and thus magnetic fields) at birth, and the associated information about the supernovae wherein they are formed; (ii) the radio pulsar-magnetar connection; (iii) the link between normal radio pulsars, intermittent pulsars and rotating radio transients; (iv) the slowest possible spin period for a radio pulsar (revealing the conditions at the pulsar death-line); (v) proper motions of pulsars (revealing supernova kick physics); (vi) the mass distribution of neutron stars; (vii) the fastest possible spin period for a recycled pulsar (constraining magnetosphere-accretion disc interactions, gravitational wave radiation and the equation-of-state); (viii) the origin of high eccentricity millisecond pulsars; (ix) the formation channels for recently identified triple systems; and finally (x) how isolated millisecond pulsars are formed. We can also expect that the first phase of the SKA (SKA1), and in particular the full SKA (SKA2), will break new ground unveiling exotic and heretofore unknown systems that will challenge our current knowledge and theories, thus fostering the development of new research areas. Some possibilities for future landmark discoveries representing significant milestones in the astrophysics of compact objects include: (i) sub-millisecond pulsars; (ii) neutron stars born as millisecond pulsars; (iii) neutron stars with masses below 1.1 or above 2.5 M ; (iv) neutron star-black hole binaries; and (v) a triple system containing a pair of neutron stars.Advancing Astrophysics with the Square Kilometre Array
We report on a search for persistent radio emission from the one-off Fast Radio Burst (FRB) 20190714A, as well as from two repeating FRBs, 20190711A and 20171019A, using the MeerKAT radio telescope. For FRB 20171019A we also conducted simultaneous observations with the High Energy Stereoscopic System (H.E.S.S.) in very high energy gamma rays and searched for signals in the ultraviolet, optical, and X-ray bands. For this FRB, we obtain a UV flux upper limit of 1.39 × 10−16erg cm−2 s−1Å−1, X-ray limit of ∼6.6 × 10−14erg cm−2 s−1 and a limit on the very-high-energy gamma-ray flux Φ(E > 120 GeV) < 1.7 × 10−12 erg cm−2 s−1. We obtain a radio upper limit of ∼15μJy beam−1 for persistent emission at the locations of both FRBs 20190711A and 20171019A with MeerKAT. However, we detected an almost unresolved (ratio of integrated flux to peak flux is ∼1.7 beam) radio emission, where the synthesized beam size was ∼ 8″-size with a peak brightness of ∼53 μJy beam−1 at MeerKAT and ∼86 μJy beam−1 at e-MERLIN, possibly associated with FRB 20190714A at z = 0.2365. This represents the first detection of persistent continuum radio emission potentially associated with a (as-yet) non-repeating FRB. If the association is confirmed, one of the strongest remaining distinction between repeaters and non-repeaters would no longer be applicable. A parallel search for repeat bursts from these FRBs revealed no new detections down to a fluence of 0.08 Jy ms for a 1 ms duration burst.
The Gravitational-wave Optical Transient Observer (GOTO) is a wide-field telescope project focused on detecting optical counterparts to gravitational-wave sources. Each GOTO robotic mount holds eight 40 cm telescopes, giving an overall field of view of 40 square degrees. As of 2022 the first two GOTO mounts have been commissioned at the Roque de los Muchachos Observatory on La Palma, Canary Islands, and construction of the second node with two additional 8-telescope mounts has begin at Siding Spring Observatory in New South Wales, Australia. Once fully operational each GOTO mount will be networked to form a robotic, multi-site observatory, which will survey the entire visible sky every two nights and enable rapid follow-up detections of transient sources.
The most massive globular cluster in our Galaxy, Omega Centauri, is an interesting target for pulsar searches, because of its multiple stellar populations and the intriguing possibility that it was once the nucleus of a galaxy that was absorbed into the Milky Way. The recent discoveries of pulsars in this globular cluster and their association with known X-ray sources was a hint that, given the large number of known X-ray sources, there is a much larger undiscovered pulsar population. We used the superior sensitivity of the MeerKAT radio telescope to search for pulsars in Omega Centauri. In this paper, we present some of the first results of this survey, including the discovery of 13 new pulsars; the total number of known pulsars in this cluster currently stands at 18. At least half of them are in binary systems and preliminary orbital constraints suggest that most of the binaries have light companions. We also discuss the ratio between isolated and binaries pulsars and how they were formed in this cluster.
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