We present high spatial resolution optical imaging and polarization observations of the PSR B0540−69.3 and its highly dynamical pulsar wind nebula (PWN) performed with Hubble Space Telescope, and compare them with X-ray data obtained with the Chandra X-ray Observatory. In particular, we have studied the bright region south-west of the pulsar where a bright 'blob' is seen in 1999. In a recent paper by De Luca et al. it was argued that the 'blob' moves away from the pulsar at high speed. We show that it may instead be a result of local energy deposition around 1999, and that the emission from this then faded away rather than moved outward. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-'blob' orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the 'blob' position, faster orthogonal to the pulsar-'blob' direction than along this axis of orientation. This could indicate that the pulsar-'blob' orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an [S II]-to-[O III]-ratio map, and comparing this to optical continuum and X-ray emission maps. We argue, through modelling, that the high [S II]/[O III] ratio is not due to time-dependent photoionization caused by possible rapid X-ray emission variations in the 'blob' region. We have also created a multiwavelength energy spectrum for the 'blob' position showing that one can, to within 2σ , connect the optical and X-ray emission by a single power law. The slope of that power law (defined from F ν = ν −α ν ) would be α ν = 0.74 ± 0.03, which is marginally different from the X-ray spectral slope alone with α ν = 0.65 ± 0.03. A single power law for most of the PWN is, however, not be possible. We obtain best power-law fits for the X-ray spectrum if we include 'extra' oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20-25 M range, i.e. in the upper mass range for progenitors of Type IIP supernovae.

The Vela and Geminga pulsars are rotation powered neutron stars, which have been identified in various spectral domains, from the near-infrared to hard $\gamma$-rays. In the near-infrared they exhibit tentative emission excesses, as compared to the optical range. To check whether these features are real, we analysed archival mid-infrared broadband images obtained with the Spitzer Space Telescope in the 3.6--160 $\mu$m range and compared them with the data in other spectral domains. In the 3.6 and 5.8 $\mu$m bands we detected at $\sim$ (4--5)$\sigma$ significance level a point-like object, that is likely to be the counterpart of the Vela pulsar. Its position coincides with the pulsar at < 0.4 arcsec 1$\sigma$-accuracy level. Combining the measured fluxes with the available multiwavelength spectrum of the pulsar shows a steep flux increase towards the infrared, confirming the reality of the near-infrared excess reported early, and, hence, the reality of the suggested mid-infrared pulsar identification. Geminga is also identified, but only at a marginal 2$\sigma$ detection level in one 3.6 $\mu$m band. This needs a farther confirmation by deeper observations, while the estimated flux is also compatible with the near-infrared Geminga excess. The detection of the infrared excess is in contrast to the Crab pulsar, where it is absent, but is similar to the two magnetars, 4U 0142+61 and 1E 2259+586, showing similar features. We discuss X-ray irradiated fall-back discs around the pulsars, unresolved pulsar nebula structures, and pulsar magnetospheres as possible origins of the excesses. We note also possible infrared signatures of an extended tail behind Geminga and of the Vela plerion radio lobes.Comment: 16 pages, 9 figures, 2 table

For samples of the Ce 1-x Gd x O 2-y system prepared by the Pechini route and promoted with Pt, the mobility and reactivity of lattice oxygen were found to correlate with the density of surface and bulk anion vacancies.

We have analyzed archival XMM-Newton and Chandra observations of the γ-ray radioquiet pulsar J1826−1256 and its pulsar wind nebula. The pulsar spectrum can be described by a power-law model with a photon index Γ ≈ 1. We find that the nebular spectrum softens with increasing distance from the pulsar, implying synchrotron cooling. The empirical interstellar absorption-distance relation gives a distance of ≈ 3.5 kpc to J1826−1256. We also discuss the nebula geometry and association between the pulsar, the very high energy source HESS J1826−130, the supernova remnant candidate G18.45−0.42 and the open star cluster Bica 3.

Context. G292.0+1.8 is the Cas A-like supernova remnant containing the young pulsar PSR J1124-5916, which powers a compact torus-like pulsar wind nebula with a jet visible in X-rays. Aims. We have performed deep optical observations of the pulsar field to detect the optical counterpart of the pulsar and its nebula. Methods. The observations were carried out using the direct imaging mode of FORS2 at the ESO VLT/UT1 telescope in the V, R, and I bands. We also analyzed archival images obtained with the Chandra/ACIS-I, ACIS-S, and HRC-S in X-rays. Results. In all three optical bands we detect a faint elliptical nebulosity, whose brightness peak and center position are consistent at a sub-arcsecond level with the X-ray position of the pulsar. The field is densely packed with background stars, but after subtraction of these stars the morphology of the object and the orientation of its major axis appear to be in a good agreement with the brightest inner part of the pulsar nebula torus region seen almost edge on in X-rays. Within the nebulosity we do not resolve any point-like optical object that could be identified with the pulsar and estimate its contribution to the observed nebulosity flux as < ∼ 20%. Extracting the X-ray spectrum from the physical region equivalent to the optical source position and extent and combining that with the measured optical fluxes, we compile a tentative multi-wavelength spectrum of the inner part of the nebula. Within uncertainties of the interstellar extinction towards G292.0+1.8 it is reminiscent of either the Crab or PSR B540-69 and J0205+6449 pulsar wind nebula spectra. Conclusions. The position, morphology, and spectral properties of the detected nebulosity suggest that it is the likely optical counterpart of the pulsar plus its wind nebula system in G292.0+1.8. Higher spatial resolution optical observations and the extension of the broad-band spectrum of the proposed counterpart candidate towards the IR and UV are necessary to confirm its origin.