We study the transport of high-energy particles in pulsar wind nebulae (PWN) using three-dimensional magnetohydrodynamic (MHD) and test-particle simulations, as well as a Fokker–Planck particle ...transport model. The latter includes radiative and adiabatic losses, diffusion, and advection on the background flow of the simulated MHD nebula. By combining the models, the spatial evolution of flux and photon index of the X-ray synchrotron emission is modelled for the three nebulae G21.5−0.9, the inner regions of Vela, and 3C 58, thereby allowing us to derive governing parameters: the magnetic field strength, average flow velocity, and spatial diffusion coefficient. For comparison, the nebulae are also modelled with the semi-analytic Kennel & Coroniti model but the Porth et al. model generally yields better fits to the observational data. We find that high velocity fluctuations in the turbulent nebula (downstream of the termination shock) give rise to efficient diffusive transport of particles, with average Péclet number close to unity, indicating that both advection and diffusion play an important role in particle transport. We find that the diffusive transport coefficient of the order of ∼ 2 × 1027(L
s/0.42 Ly) cm2 s− 1 (L
s is the size of the termination shock) is independent of energy up to extreme particle Lorentz factors of γp ∼ 1010.
Mass loading of bow shock pulsar wind nebulae Morlino, G; Lyutikov, M; Vorster, M
Monthly notices of the Royal Astronomical Society,
12/2015, Letnik:
454, Številka:
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We investigate the dynamics of bow shock nebulae created by pulsars moving supersonically through a partially ionized interstellar medium. A fraction of interstellar neutral hydrogen atoms ...penetrating into the tail region of a pulsar wind will undergo photoionization due to the ultraviolet light emitted by the nebula, with the resulting mass loading dramatically changing the flow dynamics of the light leptonic pulsar wind. Using a quasi-1D hydrodynamic model of both non-relativistic and relativistic flow, and focusing on scales much larger than the stand-off distance, we find that if a relatively small density of neutral hydrogen, as low as 10−4 cm−3, penetrate inside the pulsar wind, this is sufficient to strongly affect the tail flow. Mass loading leads to the fast expansion of the pulsar wind tail, making the tail flow intrinsically non-stationary. The shapes predicted for the bow shock nebulae compare well with observations, both in Hα and X-rays.
Many women receiving antenatal care in public health services in Cape Town choose bilateral tubal ligation as their preferred method of postpartum contraception during their antenatal course. If the ...sterilisation does not occur immediately, these women are discharged on an alternative form of contraception and, ideally, an interval date for bilateral tubal ligation is arranged.
To assess the access to tubal ligation services in the Metro West area of Cape Town, South Africa, in women who request permanent contraception following delivery, looking specifically at the number of women requesting bilateral tubal ligation who receive the procedure intrapartum, immediately postpartum or as an interval procedure. Other objectives included determining the reproductive outcomes if bilateral tubal ligation was not performed, investigating the alternative forms of contraception provided and to study the demographics of the population requesting bilateral tubal ligation as a form of contraception.
The study was conducted as a cross-sectional observational study collecting data over a period of 3 months, from June 2019 to August 2019. Maternity case records for deliveries between June 2019 and August 2019 from four facilities were reviewed. The facilities, representing all levels of care, were Vanguard Midwife Obstetric Unit, Wesfleur Hospital (district hospital), New Somerset Hospital (regional hospital), Groote Schuur Hospital (tertiary hospital).
There were 260 women who requested tubal ligation as their choice of contraception. Only 50% of these received a tubal ligation. Of the 131 tubal ligations performed, 2 were interval sterilisations. Ninety-one percent (120/131) of the tubal ligations were done at the time of caesarean section. Of the 129 women who received alternative forms of contraception, 13 women had a recurrent pregnancy.
The study suggests that only 50% of women requesting tubal ligation as form of contraception actually end up receiving the procedure. Alternative forms of contraception are widely used and relied upon, but not without risks of recurrent pregnancy. Interval tubal ligation was not easily accessed by those women who were referred for the procedure.
Public theology or kingdom theology? Thoughts on the social relevance of Reformed Theology. This article investigated the metatheoretical assumptions of the contemporary discourse about Public ...Theology. The investigation attended to the historical roots of the movement to understand the notion of defining theology as a mere social programme where the principles are sought in a contextual reading from the context of the reader – thus a reading ‘from below’. Although a clear definition of Public Theology is not possible at this stage of the discourse due to a variety of fundamental ideas promoted by the various exponents of Public Theology, certain dualisms can be discerned in the presentations by public theologians. This investigation presented Kingdom Theology, developed in the classic Reformed tradition as a corrective to the dualisms in Public Theology. The research found that Kingdom Theology is better equipped to address social wrongs and to seek socio-political justice.Contribution The investigation presented the Kingdom Theology of the classic Reformed tradition as a corrective to the notion of Public Theology and indicated that the ethic Kingdom Theology can address the totality of life and the social order fundamentally, and is not inhibited by contexts, temporality and historic spaces.
A possible way to calculate particle spectra as a function of position in pulsar wind nebulae is to solve a Fokker-Planck transport equation. This paper presents numerical solutions to the transport ...equation with the processes of convection, diffusion, adiabatic losses, and synchrotron radiation included. In the first part of the paper, the steady-state version of the transport equation is solved as a function of position and energy. This is done to distinguish the various effects of the aforementioned processes on the solutions to the transport equation. The second part of the paper deals with a time-dependent solution to the transport equation, specifically taking into account the effect of a moving outer boundary. The paper highlights the fact that diffusion can play a significant role in reducing the amount of synchrotron losses, leading to a modification in the expected particle spectra. These modified spectra can explain the change in the photon index of the synchrotron emission as a function of position. The solutions presented in this paper are not limited to pulsar wind nebulae, but can be applied to any similar central source system, e.g., globular clusters.
Following an eruptive accretion event in NGC 6334I-MM1, flares in the various maser species, including water masers, were triggered. We report the observed relative proper motion of the highly ...variable water masers associated with the massive star-forming region, NGC 6334I. High velocity H2O maser proper motions were detected in five maser clusters, CM2-W2 (bow-shock structure), MM1-W1, MM1-W3, UCHII-W1, and UCHII-W3. The overall average of the derived relative proper motion is 85 km s−1. This mean proper motion is in agreement with the previous results from VLA multiepoch observations. Our position as well as the velocity variance and covariance matrix analyses of the maser proper motions show its major axis to have a position angle of −79 4, cutting through the dust cavity around MM1B and being aligned in the northwest-southeast direction. We interpret this as the axis of the jet driving the CM2 shock and the maser motion. The complicated proper motions in MM1-W1 can be explained by the combined influence of the MM1 northeast-southwest bipolar outflow, the CS(6−5) north-south collimated bipolar outflow, and the radio jet. The relative proper motions of the H2O masers in UCHII-W1 are likely not driven by the jets of the MM1B protostar but by MM3-UCHII. Overall, the post-accretion burst relative proper motions of the H2O masers trace shocks of jet motion.
A spatially independent model that calculates the time evolution of the electron spectrum in a spherically expanding pulsar wind nebula (PWN) is presented, allowing one to make broadband predictions ...for the PWN's non-thermal radiation. The source spectrum of electrons injected at the termination shock of the PWN is chosen to be a broken power law. In contrast to previous PWN models of a similar nature, the source spectrum has a discontinuity in intensity at the transition between the low- and high-energy components. To test the model, it is applied to the young PWN G21.5 - 0.9, where it is found that a discontinuous source spectrum can model the emission at all wavelengths better than a continuous one. The model is also applied to the unidentified sources HESS J1427 - 608 and HESS J1507 - 622. Parameters are derived for these two candidate nebulae that are consistent with the values predicted for other PWNe. For HESS J1427 - 608, a present day magnetic field of B sub(age) = 0.4 mu G is derived. As a result of the small present day magnetic field, this source has a low synchrotron luminosity, while remaining bright at GeV/TeV energies. It is therefore possible to interpret HESS J1427 - 608 within the ancient PWN scenario. For the second candidate PWN HESS J1507 - 622, a present day magnetic field of B sub(age) = 1.7 mu G is derived. Furthermore, for this candidate PWN a scenario is favored in the present paper in which HESS J1507 - 622 has been compressed by the reverse shock of the supernova remnant.
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