A wind nebula generating extended X-ray emission was recently detected surrounding Swift J1834.9-0846. This is the first magnetar for which such a wind nebula was found. Here, we investigate whether ...there is a plausible scenario where the pulsar wind nebula (PWN) can be sustained without the need of advocating for additional sources of energy other than rotational. We do this by using a detailed radiative and dynamical code that studies the evolution of the nebula and its particle population in time. We find that such a scenario indeed exists: Swift J1834.9-0846's nebula can be explained as being rotationally powered, as all other known PWNe are, if it is currently being compressed by the environment. The latter introduces several effects, the most important of which is the appearance of adiabatic heating, being increasingly dominant over the escape of particles as reverberation goes by. The need of reverberation naturally explains why this is the only magnetar nebula detected and provides estimates for Swift 1834.9-0846's age.
We numerically study the radiative properties of the reverberation phase of pulsar wind nebulae. Reverberation brings a significant evolution in a short period of time. We show that even the Crab ...Nebula, associated with the more energetic pulsar of the sample that we consider, has a period in its future time evolution where the X-ray luminosity will exceed the spin-down power at the time. In fact, all of the nebulae in our sample are expected to have a period of radio, X-ray, and GeV superefficiency, and most will also have a period of TeV superefficiency. We analyze and characterize these superefficient phases.
The Pierre Auger collaboration has provided a compelling indication for a possible correlation between the arrival directions of ultrahigh-energy cosmic rays and nearby starburst galaxies. Herein we ...show how the latest large-scale modeling of starburst galaxies is compatible with the cosmic rays producing the anisotropy signal being accelerated at the terminal shock of superwinds.
ABSTRACT
In this work, we present a leptonic, time‐dependent model of pulsar wind nebulae (PWNe). The model seeks a solution for the lepton distribution function considering the full ...time‐energy‐dependent diffusion‐loss equation. The time‐dependent lepton population is balanced by injection, energy losses and escape. We include synchrotron, inverse‐Compton (IC; with the cosmic‐microwave background as well as with IR/optical photon fields), self‐synchrotron Compton, and bremsstrahlung processes, all devoid of any radiative approximations. With this model in place we focus on the Crab nebula as an example and present its time‐dependent evolution. Afterwards, we analyse the impact of different approximations made at the level of the diffusion‐loss equation, as can be found in the literature. Whereas previous models ignored the escape term, e.g. with the diffusion‐loss equation becoming advective, others approximated the losses as catastrophic, so that the equation has only time derivatives. Additional approximations are also described and computed. We study what the impact of these approaches is on the determination of the PWN evolution. In particular, we find the time‐dependent deviation of the multi‐wavelength spectrum and the best‐fitting parameters obtained with the complete and the approximate models.
ABSTRACT This work presents a methodological approach to generate realistic γ-ray light curves of pulsars, resembling reasonably well the observational ones observed by the Fermi-Large Area Telescope ...(Fermi-LAT) instrument, fitting at the same time their high-energy spectra. The theoretical light curves are obtained from a spectral and geometrical model of the synchro-curvature emission. Despite our model relying on a few effective physical parameters, the synthetic light curves present the same main features observed in the observational γ-ray light-curve zoo, such as the different shapes, variety in the number of peaks, and a diversity of peak widths. The morphological features of the light curves allow us to statistically compare the observed properties. In particular, we find that the proportion of the number of peaks found in our synthetic light curves is in agreement with the observational one provided by the third Fermi-LAT pulsar catalogue. We also found that the detection probability due to beaming is much higher for orthogonal rotators (approaching 100 per cent) than for small inclination angles (less than 20 per cent). The small variation in the synthetic skymaps generated for different pulsars indicates that the geometry dominates over timing and spectral properties in shaping the γ-ray light curves. This means that geometrical parameters such as the inclination angle can be in principle constrained by γ-ray data alone independently of the specific properties of a pulsar. At the same time, we find that γ-ray spectra seen by different observers can slightly differ, opening the door to constraining the viewing angle of a particular pulsar.
ABSTRACT
In this work, we introduce the use of the differential geometry Frenet–Serret equations to describe a magnetic line in a pulsar magnetosphere. These equations, which need to be solved ...numerically, fix the magnetic line in terms of their tangent, normal, and binormal vectors at each position, given assumptions on the radius of curvature and torsion. Once the representation of the magnetic line is defined, we provide the relevant set of transformations between reference frames; the ultimate aim is to express the map of the emission directions in the star corotating frame. In this frame, an emission map can be directly read as a light curve seen by observers located at a certain fixed angle with respect to the rotational axis. We provide a detailed step-by-step numerical recipe to obtain the emission map for a given emission process, and give a set of simplified benchmark tests. Key to our approach is that it offers a setting to achieve an effective description of the system’s geometry together with the radiation spectrum. This allows to compute multifrequency light curves produced by a specific radiation process (and not just geometry) in the pulsar magnetosphere, and intimately relates with averaged observables such as the spectral energy distribution.
ABSTRACT
We report on a detailed spectral characterization of the non-thermal X-ray emission for a large sample of gamma-ray pulsars in the second Fermi Large Area Telescope catalogue. We outline the ...criteria adopted for the selection of our sample, its completeness, and critically describe different approaches to estimate the spectral shape and flux of pulsars. We perform a systematic modelling of the pulsars’ X-ray spectra using archival observations with XMM–Newton, Chandra, and NuSTAR and extract the corresponding non-thermal X-ray spectral distributions. This set of data is made available online and is useful to confront with predictions of theoretical models.
ABSTRACT
The detected high-energy pulsars’ population is growing in number, and thus, having agile and physically relevant codes to analyse it consistently is important. Here, we update our existing ...synchro-curvature radiation model by including a better treatment of the particle injection, particularly where the large pitch angle particles dominate the spectra, and by implementing a fast and accurate minimization technique. The latter allows a large improvement in computational cost, needed to test model enhancements, and to apply the model to a larger pulsar population. We successfully fit the sample of pulsars with X-ray and gamma-ray data. Our results indicate that, for every emitting particle, the spatial extent of their trajectory where the pitch angle is large and most of the detected X-ray radiation is produced is a small fraction of the light cylinder. We also confirm with this new approach that synchrotron radiation is not negligible for most of the gamma-ray pulsars detected. In addition, with the results obtained, we argue that J0357+3205 and J2055+2539 are MeV pulsar candidates and are suggested for exhaustive observations in this energy band.
The potato yellow vein disease, caused by the potato yellow vein virus (PYVV), is a limiting potato disease in northern South America. The virus can be transmitted either by the greenhouse whitefly ...(GWF),
(Westwood) (Hemiptera: Aleyrodidae), or through vegetative propagules, such as infected tubers. Recently, GWF populations have been spotlighted as one of the main drivers of PYVV re-emergence, and consequently, PYVV management has been predominantly directed toward vector control, which is heavily based on insecticide use. However, the drivers of the PYVV outbreaks as well as the contribution of GWF populations on the spread of PYVV among potato crops are still not completely understood. This study aims to assess the role of the GWF as a driver of the PYVV epidemic in the potato-producing areas in Colombia, one of the countries more severely affected by the PYVV epidemic, and whose geography allows the study of the spatial association between the vector and the disease epidemic across a wide altitude range. The geographical clusters where the PYVV epidemic is concentrated, as well as those of farms affected by the GWF were identified using a novel spatial epidemiology approach. The influence of altitude range on the association between PYVV and
was also assessed. We found a relatively poor spatial association between PYVV epidemic and the presence of the GWF, especially at altitudes above 3,000 m above mean sea level. Furthermore, GWF populations could only explain a small fraction of the extent of the PYVV epidemic in Colombia. Movement of infected seed tubers might be the main mechanism of dispersion, and could be a key driver for the PYVV infection among potato crops. Agricultural policies focused on improving quality of seed tubers and their appropriate distribution could be the most efficient control intervention against PYVV dispersion.
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