Vela Pulsar Wind Nebula Research Articles

A search for variability of hard X-ray emission from the Vela pulsar wind nebula

Observations of hard X-ray emission from the Vela pulsar wind nebula (PWN) with the ISGRI camera aboard INTEGRAL gamma-ray observatory have been analysed with the aim to search for possible flux variability on scales from weeks to years, which could be caused by short-term evolution of pulsar wind structures similar to those governing sharp flares and flux depressions observed in the sub-GeV emission of the Crab PWN. No statistically significant flux depressions or flares have been found in none of the considered energy ranges: 20-50 keV, 50-100 keV, and 100-200 keV, however some hints of flux instability can be seen in the former two bands. If the variability of the pulsar wind termination surface or instabilities of turbulent magnetic field in the nebula predicted by a number of PWN models indeed influence the synchrotron spectrum of such objects, the variability of the 1-30 MeV emission from the Vela PWN could be checked with the next generation of gamma-ray facilities, like eASTROGAM or HERMES.

On Dynamics and Spectra of Fine Spatial Structures in the Vela Pulsar Wind Nebula

Evolution of X-ray surface brightness and spectra of fine spatial structures in the Vela pulsar wind nebula (PWN) are studied. Variability of morphology and the spectrum of a small-scale structure at the base of the southern jet of the nebula – a bright transverse bar is investigated for the first time. The size of the bar located within 4″–5″ from the Vela pulsar is ∼ 4.5″ × 1.5″. It is shown that brightness, shapes, and positions of the bar and the southern jet base vary on the timescale of 1–2 weeks, the bar can disappear and emerge again within 10 days. The power-law photon index of the jet base is much harder than that of the bar, 1.20 ± 0.12 vs 1.65 ± 0.15. The latter index is close to 1.6, a typical value for synchrotron emission of electrons accelerated at an ultrarelativistic shock. We speculate that bright blobs seen on both sides of the southern jet base may have the same nature as the bright blobs in the Crab PWN, which are believed to mark the position of the termination shock of the pulsar wind.

Suzaku Detection of Diffuse Hard X-Ray Emission outside Vela X

Abstract Vela X is a large, 3 $^{\circ}$$\times$ 2 $^{\circ}$ , radio-emitting pulsar wind nebula (PWN) powered by the Vela pulsar in the Vela supernova remnant. Using four Suzaku/XIS observations pointed just outside Vela X, we have found hard X-ray emission extending throughout the fields of view. The hard X-ray spectra are well represented by a power-law. The photon index was measured to be constant at $\Gamma$$\sim$ 2.4, similar to that of the southern outer part of Vela X. The power-law flux decreases with increasing distance from the pulsar. These properties lead us to propose that the hard X-ray emission is associated with the Vela PWN. The larger X-ray extension found in this work strongly suggests that distinct populations of relativistic electrons form the X-ray PWN and Vela X, as was recently inferred from multiwavelength spectral modeling of Vela X.

Detection of Gamma-Ray Emission from the Vela Pulsar Wind Nebula with AGILE

Pulsars are known to power winds of relativistic particles that can produce bright nebulae by interacting with the surrounding medium. These pulsar wind nebulae are observed by their radio, optical, and x-ray emissions, and in some cases also at TeV (teraelectron volt) energies, but the lack of information in the gamma-ray band precludes drawing a comprehensive multiwavelength picture of their phenomenology and emission mechanisms. Using data from the AGILE satellite, we detected the Vela pulsar wind nebula in the energy range from 100 MeV to 3 GeV. This result constrains the particle population responsible for the GeV emission and establishes a class of gamma-ray emitters that could account for a fraction of the unidentified galactic gamma-ray sources.

The hard X-ray emission from the Vela pulsar wind nebula

We present the results of a preliminary spectral analysis performed on the BeppoSAX and XMM observations of the Vela plerion. The broad energy range covered by the instruments on board the two observatories allows an evaluation of the spectral parameters of the high energy emission model and provides an indication on the morphology of the source emission above 10 keV. We confirm the softening of the PWN spectrum (3–10 keV band) at distances greater than 4′ from the pulsar and estimate the diameter of the high energy (>10 keV) emission region to be on the order of 25′–30′.

Vela X at 31 GHz

We present observations of the Vela X region at 31 GHz using the Cosmic Background Imager (CBI). We find a strong compact radio source (59 × 41, FWHM) about the Vela pulsar, which we associate with the Vela pulsar wind nebula (PWN) recently discovered at lower radio frequencies. The CBI's 4' resolution for a 45' field of view allows the PWN to be studied in the large-scale context of Vela X. Filamentary structure in Vela X, which stands out in lower frequency maps, is very low level at 31 GHz. By combining the 10 CBI channels, which cover 26-36 GHz, and 8.4 GHz archive data, we study the spectral energy distribution (SED) of the PWN and the brightest filaments. Our results show that the spectral index α (Fν ∝ να) of the PWN is flat, or even marginally positive, with a value of α = 0.10 ± 0.06, while the Vela X filamentary structure has a negative spectral index of α = -0.28 ± 0.09. The SED inhomogeneity observed in Vela X suggests different excitation processes between the PWN and the filaments. We investigate whether the PWN's flat spectrum is a consequence of variability or truly reflects the SED of the object. We also investigate the nature of the Vela X filamentary structure. A faint filament crosses the PWN with its tangent sharing the same position angle as the PWN major axis, suggesting that it might be an extension of the PWN itself. The SED and bulk morphology of Vela X are similar to those of other well-studied plerions, suggesting that it might be powered by the pulsar. The peak of the PWN at 31 GHz is 80'' ± 20'' southwest of the peak at 8.4 GHz. This shift is confirmed by comparing the 31 GHz CBI image with higher resolution 5 GHz Australia Telescope Compact Array observations and is likely to be due to SED variations within the PWN.