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Register a new userSimultaneous Fitting of the Spectral Energy Density, Energy-dependent Size, and X-ray Spectral Index vs. Radius of The Young Pulsar Wind Nebula PWN G0.9+0.1
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We have constructed and calibrated a spherically-symmetric, spatially-dependent particle transport and emission code for young pulsar wind nebulae (PWNe). This code predicts the spectral energy distribution (SED) of the radiation spectrum at different positions in a PWN, thus yielding the surface brightness vs. radius and hence the nebular size as function of energy. It also predicts the X-ray spectral index at different radii from the central pulsar, depending on the nebular B-field profile and particle transport properties. We apply the code to PWN G0.9+0.1 and fit these three functions concurrently, thus maximizing the constraining power of the data. We use a Markov-chain-Monte-Carlo (MCMC) method to find best-fit parameters with accompanying errors. This approach should allow us to better probe the spatial behaviour of the bulk-particle motion, the $B$-field and diffusion coefficient, and break degeneracies between different model parameters. Our model will contribute to interpreting results by the future Cherenkov Telescope Array (CTA) that will yield many more discoveries plus morphological details of very-high-energy Galactic PWNe.
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We present a study of the composite supernova remnant G0.9+0.1 based on observations by XMM-Newton. The EPIC spectrum shows diffuse X-ray emission from the region corresponding to the radio shell. The X-ray spectrum of the whole Pulsar Wind Nebula is well fitted by an absorbed power-law model with a photon index Gamma ~ 1.9 and a 2-10 keV luminosity of about 6.5 X 10^34 d^2_10 erg s^-1 (d_10 is the distance in units of 10 kpc). However, there is a clear softening of the X-ray spectrum with distance from the core, which is most probably related to the finite lifetime of the synchrotron emitting electrons. This is fully consistent with the plerionic interpretation of the Pulsar Wind Nebula, in which an embedded pulsar injects energetic electrons into its surrounding region. At smaller scales, the eastern part of the arc-like feature, which was first revealed by Chandra observations, shows indications of a hard X-ray spectrum with a corresponding small photon index (Gamma=1.0 +- 0.7), while the western part presents a significantly softer spectrum (Gamma=3.2 +- 0.7). A possible explanation for this feature is fast rotation and subsequent Doppler boosting of electrons: the eastern part of the torus has a velocity component pointing towards the observer, while the western part has a velocity component in the opposite direction pointing away from the observer.
We model the morphology and spectrum of a pulsar wind nebula using a leptonic emission code. This code is a time-dependent, multi-zone model that investigates the changes in the particle spectrum as they traverse the nebula. We calculate the synchrotron and inverse Compton emissivities at different positions in the nebula, obtaining the surface brightness versus the radius, and also the size of the nebula as a function of energy. We incorporate a time and spatially-dependent $B$-field, spatially-dependent bulk particle speed implying convection and adiabatic losses, diffusion, as well as radiative losses. We calibrate our new model using two independent models. We then apply the model to PWN G0.9+0.1 and show that simultaneously fitting the spectral energy distribution and the energy-dependent source size may lead to constraints on several model parameters pertaining to the spatial properties of the PWN.
We present observations with the Chandra X-ray Observatory of the pulsar wind nebula (PWN) within the supernova remnant G0.9+0.1. At Chandras high resolution, the PWN has a clear axial symmetry; a faint X-ray point source lying along the symmetry axis possibly corresponds to the pulsar itself. We argue that the nebular morphology can be explained in terms of a torus of emission in the pulsars equatorial plane and a jet directed along the pulsar spin axis, as is seen in the X-ray nebulae powered by other young pulsars. A bright clump of emission within the PWN breaks the axisymmetry and may correspond to an intermediate-latitude feature in the pulsar wind.
In the last decade ground-based Imaging Atmospheric Cherenkov Telescopes have discovered roughly 30 pulsar wind nebulae at energies above 100 GeV. We present first results from a leptonic emission code that models the spectral energy density of a pulsar wind nebula by solving the Fokker-Planck transport equation and calculating inverse Compton and synchrotron emissivities. Although models such as these have been developed before, most of them model the geometry of a pulsar wind nebula as that of a single sphere. We have created a time-dependent, multi-zone model to investigate changes in the particle spectrum as the particles diffuse through the pulsar wind nebula, as well as predict the radiation spectrum at different positions in the nebula. We calibrate our new model against a more basic previous model and fit the observed spectrum of G0.9+0.1, incorporating data from the High Energy Stereoscopic System as well as radio and X-ray experiments.
Taking advantage of more than 11 years of Fermi-LAT data, we perform a new and deep analysis of the pulsar wind nebula (PWN) HESS J1825-137. Combining this analysis with recent H.E.S.S. results we investigate and constrain the particle transport mechanisms at work inside the source as well as the system evolution. The PWN is studied using 11.6 years of Fermi-LAT data between 1 GeV and 1 TeV. In particular, we present the results of the spectral analysis and the first energy-resolved morphological study of the PWN HESS J1825-137 at GeV energies, which provide new insights into the gamma-ray characteristics of the nebula. An optimised analysis of the source returns an extended emission region larger than 2$^{circ}$, corresponding to an intrinsic size of about 150 pc, making HESS J1825-137 the most extended gamma-ray PWN currently known. The nebula presents a strong energy dependent morphology within the GeV range, moving from a radius of $sim1.4^circ$ below 10 GeV to a radius of $sim$0.8$^circ$ above 100 GeV, with a shift in the centroid location. Thanks to the large extension and peculiar energy-dependent morphology, it is possible to constrain the particle transport mechanisms inside the PWN HESS J1825-137. Using the variation of the source extension and position, as well as the constraints on the particle transport mechanisms, we present a scheme for the possible evolution of the system. Finally, we provide an estimate of the electron energy density and we discuss its nature in the PWN and TeV halo-like scenario.
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