A. Danilenko

The Vela and Geminga pulsars in the mid-infrared

The Vela and Geminga pulsars are rotation powered neutron stars, which have been identified in various spectral domains, from the near-infrared to hard -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 �m range and compared them with the data in other spectral domains. In the 3.6 and 5.8 �m bands we detected at � (4–5)� 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: 00 4 1�-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� detection level in one 3.6 �m band. This needs a farther confirmation by deeper observations, while the estimated flux is also compatible with the nearinfrared 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.

Possible optical counterpart of PSR J1357−6429

Context. PSR J1357−6429 is a Vela-like radio pulsar that has been recently detected in X-rays and γ-rays. It powers a compact taillike X-ray pulsar wind nebula and X-ray-radio plerion associated with an extended TeV source HESS J1356−645. Aims. We present our deep optical observations with the Very Large Telescope to search for an optical counterpart of the pulsar and its nebula. Methods. The observations were carried out using a direct imaging mode in the V, R ,a ndI bands. We also analysed archival X-ray data obtained with Chandra and XMM-Newton. Results. In all three optical bands, we detect a point-like source with V = 27.3 ± 0.3, R = 25.52 ± 0.07, and I = 24.13 ± 0.05, whose position is within the 1σ error circle of the X-ray position of the pulsar, and whose colours are distinct from those of ordinary stars. We consider it as a candidate optical counterpart of the pulsar. If it is indeed the counterpart, its 5σ offset from the radio pulsar position, measured about 9 yr earlier, implies that the transverse velocity of the pulsar is in the range of 1600–2000 km s −1 at the distance of 2–2.5 kpc, making it the fastest moving pulsar known. The direction of the estimated proper motion coincides with the extension of the pulsar’s X-ray tail, suggesting that this is a jet. The tentative optical luminosity and efficiency of the pulsar are similar to those of the Vela pulsar, which also supports the optical identification. However, the candidate undergoes an unusually steep dereddened flux increase towards the infrared with a spectral index αν ∼ 5, that is not typical of optical pulsars. It implies a strong double-knee spectral break in the pulsar emission between the optical and X-rays. The reasons for the spectral steepness are unclear. It may be caused by a nebula knot projected onto the jet and strongly overlapping with the pulsar, as observed for the Crab, where the knot has a significantly steeper spectrum than the pulsar. We find no other signs of the pulsar nebula in the optical. Alternatively, the detected source may be a faint AGN, that has not yet been seen at other wavelengths. Conclusions. The position and peculiar colours of the detected source suggest that it is an optical counterpart of the pulsar. Further high spatial-resolution infrared observations can help to verify its real nature.

The G292.0+1.8 pulsar wind nebula in the mid-infrared

G292.0+1.8 is a Cas A-like supernova remnant that contains the young pulsar PSR J1124-5916 powering a compact torus-like pulsar wind nebula visible in X-rays. A likely counterpart to the nebula has been detected in the optical VRI bands. To confirm the counterpart candidate nature, we examined archival mid-infrared data obtained with the Spitzer Space Telescope. Broad-band images taken at 4.5, 8, 24, and 70 microns were analyzed and compared with available optical and X-ray data. The extended counterpart candidate is firmly detected in the 4.5 and 8 micron bands. It is brighter and more extended in the bands than in the optical, and its position and morphology agree well with the coordinates and morphology of the torus-like pulsar wind nebula in X-rays. The source is not visible in 24 and 70 micron images, which are dominated by bright emission from the remnant shell and filaments. We compiled the infrared fluxes of the nebula, which probably contains a contribution from an unresolved pulsar in its center, with the optical and X-ray data. The resulting unabsorbed multiwavelength spectrum is described by power laws of significantly steeper slope in the infrared-optical than in X-rays, implying a double-knee spectral break between the optical and X-rays. The 24 and 70 microns flux upper limits suggest a second break and a flatter spectrum at the long wavelength limit. These features are common to two other pulsar wind nebulae associated with the remnants B0540-69.3 and 3C 58 and observed in all three ranges. The position, morphology, and spectral properties of the detected source allow us to comfirm that it is the infrared-optical counterpart to both the pulsar and its wind nebula system in the G292.0+1.8 supernova remnant.

Near-infrared observations of PSR J1357−6429

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6429 is a young radio pulsar that was detected in X-rays and

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Constraining the parameters of the pulsar wind nebula DA 495 and its pulsar with Chandra and XMM–Newton

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Observations of the

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