Central Compact Objects (CCOs) are a handful of soft X-ray sources located close to the centers of Supernova Remnants and supposed to be young, radio-quiet Isolated Neutron Stars (INSs). A clear understanding of their physics would be crucial in order to complete our view of the birth properties of INSs. We will review the phenomenologies of CCOs, underlining the most important, recent results, and we will discuss the possible relationships of such sources with other classes of INSs.

Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts of long (greater than two seconds) duration are produced by the core-collapse of massive stars1, and those of short (less than two seconds) duration by the merger of compact objects, such as two neutron stars2. A third class of events with hybrid high-energy properties was identified3, but never conclusively linked to a stellar progenitor. The lack of bright supernovae rules out typical core-collapse explosions4-6, but their distance scales prevent sensitive searches for direct signatures of a progenitor system. Only tentative evidence for a kilonova has been presented7,8. Here we report observations of the exceptionally bright GRB 211211A, which classify it as a hybrid event and constrain its distance scale to only 346 megaparsecs. Our measurements indicate that its lower-energy (from ultraviolet to near-infrared) counterpart is powered by a luminous (approximately 1042 erg per second) kilonova possibly formed in the ejecta of a compact object merger.

It is shown that Ton 256 (z = 0.131) and PKS 2251+11 (z = 0.323) are associated with galaxies of essentially the same redshift, thus implying that these objects are at cosmological distances. The nature of Ton 256 is questionable, and it is argued that it represents a transition between Seyfert galaxies and QSOs. There is no doubt that PKS 2251+11 is a bona fide QSO; it is bright (M = -24.7), blue (B - V = 0.20, U - B = -0.84), has a starlike image under high resolution, and is a strong radio source. A peculiar emission structure near PKS 2251+11 is also discussed.

We use the dynamics of a galaxy, set up initially at a constant proper distance from an observer, to derive and illustrate two counter-intuitive general relativistic results. Although the galaxy does gradually join the expansion of the universe (Hubble flow), it does not necessarily recede from us. In particular, in the currently favored cosmological model, which includes a cosmological constant, the galaxy recedes from the observer as it joins the Hubble flow, but in the previously favored cold dark matter model, the galaxy approaches, passes through the observer, and joins the Hubble flow on the opposite side of the sky. We show that this behavior is consistent with the general relativistic idea that space is expanding and is determined by the acceleration of the expansion of the universe -- not a force or drag associated with the expansion itself. We also show that objects at a constant proper distance will have a nonzero redshift; receding galaxies can be blueshifted and approaching galaxies can be redshifted.

We present a multi-wavelength study of Extremely Red Objects (EROs) employing deep RIzJHK photometry of a 8.5'x8.5' region to identify 68 EROs with R-K>5.3 and K10^23 W/Hz at z>1 or a SFR of >25Mo/yr. We detect radio emission from 21 EROs at >12.6uJy and resolve a third of these with our 1.6'' FWHM beam. The SEDs of most of these radio EROs are consistent with dust-reddened starbursts at z~1. At z~1 the radio luminosities of these EROs indicate far-infrared luminosities of L_FIR>10^12 Lo, meaning half are ultraluminous infrared galaxies. We conclude that >16+/-5% of EROs with K1. We also photometrically classify the EROs to investigate the mix of dusty/active and evolved/passive systems in the radio-undetected EROs. We suggest that at least 30%, and perhaps up to ~60%, of all EROs with R-K>5.3 and K1. The SFD in this optically faint (R>26) population is rho^* (0.1-100Mo)=0.11+/-0.03 Mo/yr/Mpc^3, comparable to that in H-alpha emitting galaxies at z~1, and greater than that in UV-selected samples at these epochs. This support the claim of a strong increase in obscured star formation at high redshifts. Using the observed counts of the radio-detected EROs we model the break in the K-band number counts of all EROs at K~19-20 and propose that the passive ERO class dominates the total population in a narrow range around K~20, with dusty EROs dominating at fainter magnitudes. [Abridged]

We report the observational analyses and theoretical interpretations of unusually red galaxies in the Subaru Deep Field (SDF). A careful analysis of the SDF data revealed a population with unusually red near-infrared (NIR) colors of J-K>~3-4, with a higher confidence than the previous SDF result. Their surface number density drastically increases at K>~22 and becomes roughly the same as that of dusty starburst galaxies detected by submillimeter observations in recent years. These colors are even redder than the known population of the extremely red objects (EROs) and are too red to be explained as passively evolving elliptical galaxies, which are the largest population of EROs. Hence, these hyper extremely red objects should be considered as a distinct population from EROs. We discuss several possible interpretations of these enigmatic objects, and we show that these red NIR colors, the K-band and submillimeter flux, and the surface number density are quantitatively best explained by primordial elliptical galaxies reddened by dust and still in the starburst phase of their formation at z~3. Partially based on the data corrected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Radio positions of the three sources have been determined with the two 90-foot antennas working as an interferometer with an r.m.s. accuracy in both co-ordinates better than 10 seconds of arc. Direct photographs show that a starlike object exists within the error rectangle at each of the source positions. Exceedingly faint wisps of nebulosity are associated with the stars in 3C 48 and 3C 196. The observations are incomplete for 3C 286 in this regard. Photoelectric photometry of the stars shows each to have quite peculiar color indices, most closely resembling the colors of old novae or possibly white dwarfs, but we are not suggesting identification with these types of stars. Photometry of 3C 48 through 13 months shows the star to be variable by at least AV = 0W4. The radio flux appears to be constant. Optical spectra for 3C 48 show several very broad emission features, the most intense at X 3832 being unidentified. Spectra by Schmidt of 3C 196 and 3C 286 show other unusual features. The radio structure of the three radio stars is similar in that each has an unresolved core of <1" diameter. However, 3C 196 and 3C 286 show halos of 12" and 20", respectively, while no radio halo has been detected for 3C 48. it is shown that the radiant flux in the optical region can be computed from the radio-flux data and the theory of synchrotron radiation for 3C 48 and 3C 196, but not for 3C 286. This, together with other arguments, suggests that the optical as well as the radio flux could be due to the synchrotron mechanism, but the arguments are not conclusive. We have used the assumption of minimum total energy to compute the energy in relativistic particles and magnetic field required by the synchrotron mechanism to explain the observed emission. The magnetic field in each of the core components is near 0.1 gauss and depends mainly on the assumed angular size of the emitting region. The total energy in the core components is near 10 ergs. The rate of radiation is such that the energy in relativistic electrons must be replaced in a time scale of a few years if the value of the magnetic field determined in this way is correct. These calculations are based on a distance of 100pcs. The frequency of occurrence of radio stars is examined, and they are estimated to comprise from 5 to 10 per cent of sources in the 3C catalogue. The percentage is likely to be less for fainter sources. Rough limits have been estimated for the mean distances of these radio stars. A mean distance of approximately 100 pc is suggested if these objects are in the Galaxy. Evidence obtained since this paper was written suggests that 3C 48 has a large redshift of z = 0.3675 (Greenstein and Matthews 1963); thus these objects may be associated with a distant galaxy. The absolute magnitude of the starlike objects is M = -24.3, which is much brighter than any other known galaxy. As a radio source, 3C 48 is not very different from other identified sources. The emitted flux is the same as 3C 295 and Cygnus A, but the emitting volume is much less. The faint nebulosity does not resemble a galaxy, and it also is brighter than a normal galaxy. if caused by an explosion in the past and expanding at the velocity of light, its age would be > 1.8 X 10 years. The synchrotron lifetime calculated in the normal manner is much shorter than that inferred from the extent of the faint nebulosity. Thus either the magnetic field must be much lower than calculated, or high-energy electrons must be supplied continuously.