A long-period radio transient active for three decades

Several long-period radio transients have recently been discovered, with strongly polarized coherent radio pulses appearing on timescales between tens to thousands of seconds^1,2. In some cases, the radio pulses have been interpreted as coming from rotating neutron stars with extremely strong magnetic fields, known as magnetars; the origin of other, occasionally periodic and less-well-sampled radio transients is still debated³. Coherent periodic radio emission is usually explained by rotating dipolar magnetic fields and pair-production mechanisms, but such models do not easily predict radio emission from such slowly rotating neutron stars and maintain it for extended times. On the other hand, highly magnetic isolated white dwarfs would be expected to have long spin periodicities, but periodic coherent radio emission has not yet been directly detected from these sources. Here we report observations of a long-period (21 min) radio transient, which we have labelled GPM J1839-10. The pulses vary in brightness by two orders of magnitude, last between 30 and 300 s and have quasiperiodic substructure. The observations prompted a search of radio archives and we found that the source has been repeating since at least 1988. The archival data enabled constraint of the period derivative to <3.6 × 10^-13 s s^-1, which is at the very limit of any classical theoretical model that predicts dipolar radio emission from an isolated neutron star.

X-ray astronomy comes of age

The Chandra X-ray Observatory (Chandra) and the X-ray Multi-Mirror Mission (XMM-Newton) continue to expand the frontiers of knowledge about high-energy processes in the Universe. These groundbreaking observatories lead an X-ray astronomy revolution: revealing the physical processes and extreme conditions involved in producing cosmic X-rays in objects ranging in size from a few kilometres (comets) to millions of light years (clusters of galaxies), and particle densities ranging over 20 orders of magnitude. In probing matter under conditions far outside those accessible from Earth, they have a central role in the quest to understand our place in the Universe and the fundamental laws that govern our existence. Chandra and XMM-Newton are also part of a larger picture wherein advances in subarcsecond imaging and high-resolution spectroscopy across a wide range of wavelengths combine to provide a more complete picture of the phenomena under investigation. As these missions mature, deeper observations and larger samples further expand our knowledge, and new phenomena and collaborations with new facilities forge exciting, often unexpected discoveries. This Review provides the highlights of a wide range of studies, including auroral activity on Jupiter, cosmic-ray acceleration in supernova remnants, colliding neutron stars, missing baryons in low-density hot plasma, and supermassive black holes formed less than a billion years after the Big Bang.

Observational diversity of magnetized neutron stars

Young and rotation-powered neutron stars (NSs) are commonly observed as rapidly-spinning pulsars. They dissipate their rotational energy by emitting pulsar wind with electromagnetic radiation and spin down at a steady rate, according to the simple steadily-rotating magnetic dipole model. In reality, however, multiwavelength observations of radiation from the NS surface and magnetosphere have revealed that the evolution and properties of NSs are highly diverse, often dubbed as 'NS zoo'. In particular, many of young and highly magnetized NSs show a high degree of activities, such as sporadic electromagnetic outbursts and irregular changes in pulse arrival times. Importantly, their magnetic field, which are the strongest in the universe, makes them ideal laboratories for fundamental physics. A class of highly-magnetized isolated NSs is empirically divided into several subclasses. In a broad classification, they are, in the order of the magnetic field strength (B) from the highest, 'magnetars' (historically recognized as soft gamma-ray repeaters and/or anomalous x-ray pulsars), 'high-B pulsars', and (nearby) x-ray isolated NSs. This article presents an introductory review for non-astrophysicists about the observational properties of highly-magnetized NSs, and their implications. The observed dynamic nature of NSs must be interpreted in conjunction with transient magnetic activities triggered during magnetic-energy dissipation process. In particular, we focus on how the five fundamental quantities of NSs, i.e. mass, radius, spin period, surface temperature, and magnetic fields, as observed with modern instruments, change with evolution of, and vary depending on the class of, the NSs. They are the foundation for a future unified theory of NSs.