Several Crab-type supernova remnants appear to have very bright non-thermal X-ray cores just around the pulsar or expected pulsar. This X-ray brightness is often not matched by a corresponding increase in radio emission. The best example of this phenomenon is in N157B in the LMC. G21.5−0.9 and possibly 3C 58 also show it while the Crab Nebula and 0540−69.3 do not. Some method to enhance the higher energy particles must be present in these objects.

A systematic X-ray survey of the most energetic rotation-powered pulsars known, based on spin-down energy loss rate, shows that all energetic pulsars with Ė > Ėc ≍ 4 × 1036 ergs s−1 are X-ray-bright, manifest a distinct pulsar wind nebula (PWN), and are associated with a supernova event, with over half residing in shell-like supernova remnants. Below Ėc, the 2–10 keV flux ratio FPWN/FPSR decreases by an order-of-magnitude. This threshold is consistent with the lower limit on the spectral slope γmin ≍ 0.6 observed for rotation-powered pulsars (Gotthelf 2003). The apparent lack of bright PWNe below Ėc suggests a change in the particle injection spectrum and serves as a constraint on emission models for rotation-powered pulsars. Neither a young age nor a high density environment is found to be a sufficient condition for generating a PWN, as often suggested, instead Ė is likely the key parameter in determining the evolution of a rotation-powered pulsar.

I review the observational properties of Soft Gamma Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs), two unusual manifestations of neutron stars. I summarize the reasoning for SGRs being “magnetars,” neutron stars powered by the decay of a very large magnetic field, and the now compelling evidence that SGRs and AXPs are in fact members of the same source class, as predicted uniquely by the magnetar model. I discuss some open issues in the magnetar model, and the prospects for future work.

There are point-like sources in central regions of several supernova remnants which have not been detected outside the X-ray range. The X-ray spectra of these Central Compact Objects (CCOs) have thermal components with blackbody temperatures of 0.2–0.5 keV and characteristic sizes of 0.3-3 km. Most likely, the CCOs are neutron stars born in supernova explosions. We overview their observational properties, emphasizing the Chandra data, and compare them with magnetars.

During 2002–2003 the number of IR-identified counterparts to the Anomalous X-ray Pulsars (AXPs) has grown to four (4U 0142+61, IE 2259+586, IE 1048.1−5937 and RXS J170849−400910) out of the six objects (plus two candidates) known in this class. More importantly, some new common characteristics have been identified, such as IR variability, IR flattening in the broad-band energy spectrum, X-ray spectral variability as a function of pulse phase (which are not predicted by the magnetar model), and X-ray bursts (which cannot be explained in terms of standard accretion models). We present the results obtained from an extensive multi-wavelength observational campaign carried out with the NTT and CFHT for the optical/IR bands, and XMM and Chandra (plus BeppoSAX archival data) in X-rays. Based on these results and those reported in the literature, the IR-to-X-ray emission of AXPs is compared.

The detection of optical/infrared counterparts to Anomalous X-ray Pulsars (AXPs) has greatly increased our understanding of these systems. Models for the AXP phenomenon were based upon their X-ray emission, and all but the magnetar model made predictions for the optical/infrared that have now been falsified. With detections in hand, detailed studies of the optical/infrared to X-ray flux ratios, variability, and the spectral energy distributions have become possible. We present new data on two AXPs taken with Keck and Magellan, and compare the results with predictions made in the context of the magnetar model, in which the emission is due to ion currents flowing in the ≳ 1014G magnetosphere of young neutron stars.

PSRs J1847–0130 and J1718–37184 have inferred surface dipole magnetic fields greater than those of any other known pulsars and well above the “quantum critical field” above which some models predict radio emission should not occur. These fields are similar to those of the anomalous X-ray pulsars (AXPs), which growing evidence suggests are “magnetars”. The lack of AXP-like X-ray emission from these radio pulsars (and the non-detection of radio emission from the AXPs) creates new challenges for understanding pulsar emission physics and the relationship between these classes of apparently young neutron stars.

We review the evolution of the Crab pulsar's rotational history during the past 35 years. Representing 3.7% of the pulsar's age, it is possible to estimate the likely development of the magnetic field and characteristic age much better than previously. The increasing magnetic field of this pulsar and of other young pulsars, most dramatically the Vela pulsar, raises the interesting possibility that these objects might evolve into magnetars. We discuss the observational case for such a proposal, but note that the origin of these field enhancements may be associated with glitch activity. However, it is understood no better than the origin of the magnetar fields, but may be one and the same.

The detection of pulsed radio emission and first results of the investigations from the anomalous X-ray pulsar (AXP) 1E 2259+586 and the AXP candidate RX J1308.6+2127 at the frequency 111 MHz are presented.

The electromagnetic fields of magnetodipole radiation can penetrate to the conducting matter of a neutron star crust and create there electric currents and tangential magnetic fields of high magnitude. The solution obtained here has the form of surface magnetic field discontinuities propagating through the crust to the core. This model explains the phenomena of magnetars — Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars.

A principal candidate for quiescent non-thermal gamma-ray emission from magnetars is resonant inverse Compton scattering in the strong fields of their magnetospheres. This paper outlines expectations for such emission, formed from non-thermal electrons accelerated in a pulsar-like polar cap potential upscattering thermal X-rays from the hot stellar surface. The resultant spectra are found to be strikingly flat, with fluxes and strong pulsation that could be detectable by GLAST.

A new model is proposed to explain the main properties of anomalous X-ray pulsars and soft gamma-ray repeaters, in terms of drift waves in the vicinity of the light cylinder of a neutron star with a surface magnetic field ∼ 1012 G.

The discovery of deep spectral features in the X-ray spectrum of 1E 1207.4–5209 has pushed this Isolated Neutron Star (INS) out of the chorus line, since no other INS has shown significant features in its X-ray continuum. On 2002 Aug, XMM-Newton devoted a two-orbit target-of-opportunity observation to this target, with the aim of better understanding the nature of such spectral features using much improved statistics. Indeed, the 260 ksec observation yielded 360 000 photons from 1E 1207.4–5209, allowing for a very sensitive study of the temporal and spectral behavior of this object.

We have carried out an H I survey towards X-ray central compact objects (CCOs) inside supernova remnants (SNRs), which shows that many of them are placed within local H I minimA. The nature of these minima is not clear, but the most likely explanation is that the CCOs have evacuated the neighboring gas. This survey also allowed us to detect a weak, diffuse radio nebula inside the SNR G266.2−1.2, probably created by the winds of its associated CCO.

The nearby compact object RX J1856.5−3754 may be a paradigm for the vast majority of neutron stars. Its spectral energy distribution lacks any non-thermal continuua or lines. Study of the thermal surface has provided insights into the surface and interior properties of neutron stars. We report on attempts to model the spectrum. Non-magnetic heavy metal atmospheres reproduce the overall spectral energy distribution, but not the lack of absorption lines.

I describe recent high-resolution X-ray spectroscopy of surface emission from nearby, thermally emitting neutron stars. I focus on RX J0720.4−3125, RX J1308.6+2127 and RX J1605.3+3249, all of which have similar temperature, but differ in the presence and strength of absorption features in their spectrA. I discuss possible causes for the absorption we see in two sources, and conclude that it may be proton cyclotron line absorption, but weakened due to the strong-field quantum electrodynamics effect of vacuum resonance mode conversion.

The properties of neutron and strange matter stars are discussed from global and observational perspectives. The global features, i.e., the mass-radius relation, the moment of inertia, and the binding energy, of these objects can be understood by examination of the few known relevant analytic solutions to Einstein's equations. A close connection exists between neutron star radii and the density dependence of the isospin dependence of strong interactions, i.e., the nuclear symmetry energy. Interestingly, a similar relation has been found to exist between the symmetry energy and the neutron skin thickness of neutron-rich nuclei, the object of a new generation of laboratory experiments, although these are 1018 times smaller. Recent observations of neutron star masses and radiation radii are summarized. The status of these observations as predictors of nuclear force properties is examined. The combination of observations, laboratory experiments, and theory is an extremely powerful tool for both nuclear physics and nuclear astrophysics.

The structure of cold and hot dense matter at subnuclear densities is investigated by quantum molecular dynamics simulations. The phase diagrams obtained show that the density of the phase boundaries between the different nuclear structures decreases with increasing temperature due to the thermal expansion of the nuclear matter region.

The reason we need the terms “strange”, “bare” and“solid” before quark stars is presented concisely, although some fundamental issues are not certain. Observations favoring these stars are introduced.

Within the realms of possibility of solid quark matter, we fitted the 500 ks Chandra LETG/HRC data for RX J1856.5−3754 with a phenomenological spectral model, and found that the electric conductivity of quark matter on the stellar surface is about > 1.2 × 1018 s−1.