Modelling of self-similar cylindrical shock wave in radiating magnetogasdynamics,I

Self-similar flows of a perfect gas behind a cylindrical blast wave with radiation heat flux in the presence of an azimuthal magnetic field have been investigated. The effects of radiation flux and magnetic field together on the other flow variables have been studied in the region of interest. The magnetic field and density distribution vary as an inverse power of radial distance from the axis of symmetry. The electrical conductivity of the gas is taken to be infinite. The total energy of the flow between the inner expanding surface and the shock is assumed to be constant. We also have supposed the gas to be grey and opaque and the shock to be transparent and isothermal.     

Self-similar propagation of axisymmetric radiative magnetogasdynamic shocks with increasing energy,II

In this paper self-similar solutions have been investigated for the propagation of axisymmetric radiative gasdynamic shocks caused by an explosion into an inhomogeneous ideal gas permeated by a current free azimuthal magnetic field. The effects of radiation flux and magnetic field together have been seen in the region of interest on the other flow variables. The total energy of the flow between the inner expanding surface and the shock is taken to be dependent on shock radius obeying a power law. The radiative pressure and energy have been neglected.     

An exact similarity solution in radiation magneto-gas-dynamics for the flows behind a spherical shock wave

An exact similarity solution for a spherical magnetogasdynamic shock is obtained in the case when radiation energy, radiation pressure and radiative heat flux are important. The total energy of the shock wave increase with time. We have shown that due to the magnetic field the flow variables are considerably changed. Also, due to increases in radiation pressure number the radiation flux is increased.     

Spherical mhd shock waves under the action of monochromatic radiation

Self-similar MHD shock waves have been studied under the action of monochromatic radiation into a non-uniform stellar atmosphere with a constant intensity on unit area. It has been assumed that the radiation flux moves through the gas. Variation of flow variables have heen shown in tables for two different cases.     

Self-similar problem with increasing energy in radiative magneto-gas dynamics

In the present paper self-similar solutions have been investigated for the propagation of piston driven, radiative gas-dynamic shocks into an inhomogeneous ideal gas permeated by a current free azimuthal magnetic field for spherical symmetry. The effects of radiation flux and magnetic field together have been seen in the region of interest on the other flow variables. The total energy of the flow between the piston and the shock is taken to be dependent on the shock radius obeying a power law. The radiative pressure and energy have been neglected. This problem is more general than the others done so far. The word piston implies some means to drive plasma radially onwards.     

Similarity solution for the propagation of shock waves with varying strength in radiating medium

A model of similarity solution for the propagation of shock waves produced on account of an instantaneous release of energy in an inhomogeneous medium with the effect of radiation has been discussed. The disturbances of the medium are headed by a shock of variable strength. The variations of flow variables have been discussed for the different values of strength of the shock.     

Self-similar model of magnetohydrodynamic radiative shock waves with increasing density

The magnetohydrodynamic model of shock waves has been discussed in an atmosphere with gravitation and radiation. The disturbance is headed by a strong shock of increasing density. The medium ahead of the shock is assumed to be inhomogeneous and at rest. Variation of magnetic field radiation flux, and other flow variables are given in tabular form.     

Magnetogasdynamic cylindrical shock wave model in an optically thin atmosphere

Similarity solutions for one-dimensional unsteady isothermal flow of a perfect gas behind a magnetogasdynamic shock wave including the effects of thermal radiation has been investigated in a uniform thin atmosphere. The flow is caused by an expanding piston and the total energy of the flow is assumed to be constant. Radiation pressure and energy have been neglected in comparison to radiation heat flux and the gas is assumed to be grey and opaque.     

The Project for Intercomparison of Land-surface Parameterization Schemes (PILPS) phase 2(c) Red-Arkansas River basin experiment:: 2. Spatial and temporal analysis of energy fluxes

The energy components of sixteen Soil-Vegetation Atmospheric Transfer (SVAT) schemes were analyzed and intercompared using 10 years of surface meteorological and radiative forcing data from the Red-Arkansas River basin in the Southern Great Plains of the United States. Comparisons of simulated surface energy fluxes among models showed that the net radiation and surface temperature generally had the best agreement among the schemes. On an average (annual and monthly) basis, the estimated latent heat fluxes agreed (to within approximate estimation errors) with the latent heat fluxes derived from a radiosonde-based atmospheric budget method for slightly more than half of the schemes. The sensible heat fluxes had larger differences among the schemes than did the latent heat fluxes, and the model-simulated ground heat fluxes had large variations among the schemes. The spatial patterns of the model-computed net radiation and surface temperature were generally similar among the schemes, and appear reasonable and consistent with observations of related variables, such as surface air temperature. The spatial mean patterns of latent and sensible heat fluxes were less similar than for net radiation, and the spatial patterns of the ground heat flux vary greatly among the 16 schemes. Generally, there is less similarity among the models in the temporal (interannual) variability of surface fluxes and temperature than there is in the mean fields, even for schemes with similar mean fields.     

Propagation of spherical shock waves in an exponential medium with radiation heat flux

In this paper propagation of spherical shock waves with radiation heat flux is considered in an exponentially increasing medium. The shock wave moves with variable velocity and the total energy of the wave is variable. For different values of radiation parameter, the numerical solution has been made and the nature of the field variables are illustrated by the tables.     

Correlations between the peak flux density and the position angle of inner-jet in three blazars

We aim to investigate the relation between the long-term flux density and the position angle (PA) evolution of inner-jet in blazars. We have carried out the elliptic Gaussian model-fit to the ‘core’ of 50 blazars from 15 GHz VLBA data, and analyzed the variability properties of three blazars from the model-fit results. Diverse correlations between the long-term peak flux density and the PA evolution of the major axis of the ‘core’ have been found in ～20 % of the 50 sources. Of them, three typical blazars have been analyzed, which also show quasi-periodic flux variations of a few years (T). The correlation between the peak flux density and the PA of inner-jet is positive for S5 0716+714, and negative for S4 1807+698. The two sources cannot be explained with the ballistic jet models, the non-ballistic models have been analyzed to explain the two sub-luminal blazars. A correlation between the peak flux density and the PA (with a T/4 time lag) of inner-jet is found in [HB89] 1823+568, this correlation can be explained with a ballistic precession jet model. All the explanations are based mainly on the geometric beaming effect; physical flux density variations from the jet base would be considered for more complicated situations in future, which could account for the no or less significance of the correlation between the peak flux density and the PA of inner-jet in the majority blazars of our sample.     

MHD free-convection flow of an elasto-viscous fluid past an infinite vertical plate

A theoretical model of shock wave propagation in a self-gravitating radiative magneto-hydrodynamic medium has been studied. The effects of the magnetic field, radiation, and gravitation have been discussed separately. The results discussed depend upon the numerical variations of flow variables behind the shock.     

In-situ observations of the latitudinal gradients of the solar wind parameters during 1976 and 1977

Interplanetary observations from Helios 1, Helios 2, and IMP-8 spacecraft during 1976 and 1977, namely the early portion of solar cycle 21, have been used to investigate the latitudinal gradients of the solar wind parameters with respect to the angular displacement from the current sheet inferred from synoptic HAO white-light maps of the solar corona at 1.75 solar radii. A latitudinal belt of ±25 deg around the current sheet has been investigated. Large gradients for solar wind flow speed, proton density and temperature have been found. Smoother gradients were also found for particle flux, kinetic, gravitational and thermal energy density flux. All these gradients revealed to become smoother going towards the solar cycle's maximum. Neither latitudinal nor temporal variations were identified for magnetic and thermal energy density. A remarkable result of this study is that the momentum flux density and the total energy flux density which other authors found to be independent of any longitudinal stream structure were also found to be independent of any latitudinal structure. Moreover, these two parameters did not show any temporal variation during the period of interest.     

The generation of ionization-shock front oscillations by a variable radiation flux

The effect of a time-varying radiation flux incident on an ionization front on the generation of ionization-shock front oscillations in the interstellar medium is analyzed analytically and numerically. We take into account both variations in the flux of ionizing radiation directly from the source that produces the ionization front and the absorption of energetic photons by the post-front plasma. Based on our calculations, we show that the time dependence of the radiation flux can be an additional factor (apart from small inhomogeneities in the interstellar medium) that contributes to the amplification of oscillations and to the kinetic energy input to the observed turbulent motions in H II regions.     

Can self-organized critical accretion disks generate a log-normal emission variability in AGN?

Active Galactic Nuclei (AGN), such as Seyfert galaxies, quasars, etc., show light variations in all wavelength bands, with various amplitude and in many time scales. The variations usually look erratic, not periodic nor purely random. Many of these objects also show lognormal flux distribution and RMS–flux relation and power law frequency distribution. So far, the lognormal flux distribution of black hole objects is only observational facts without satisfactory explanation about the physical mechanism producing such distribution in the accretion disk. One of the most promising models based on cellular automaton mechanism has been successful in reproducing PSD (Power Spectral Density) of the observed objects but could not reproduce lognormal flux distribution. Such distribution requires the existence of underlying multiplicative process while the existing SOC models are based on additive processes. A modified SOC model based on cellular automaton mechanism for producing lognormal flux distribution is presented in this paper. The idea is that the energy released in the avalanche and diffusion in the accretion disk is not entirely emitted instantaneously as in the original cellular automaton model. Some part of the energy is kept in the disk and thus increase its energy content so that the next avalanche will be in higher energy condition and will release more energy. The later an avalanche occurs, the more amount of energy is emitted to the observers. This can provide multiplicative effects to the flux and produces lognormal flux distribution.     

The spectra of radiation and relativistic electrons formed by Compton scattering at non-zero particle fluxes

The formation of steady-state spectra of radiation or particles by Compton scattering is discussed for the case when the flux from the source is present. Power-law distributions, or those characterized by a power-law asymptotic behaviour, can appear under these conditions.The power indices and normalizations have been found as well as the flux directions for the electron and photon distributions in two cases. The first case is that of differential energy transfer over the electron spectrum (interaction with soft radiation). For the case of integrated transfer, relations have been found between the indices.The possibility of a power-law electron spectrum (with an index =2) has been shown for scattering by equilibrium radiation (the black-body background included).     

Empirical Modeling of Radiative <Emphasis Type="Italic">versus</Emphasis> Magnetic Flux for the Sun-as-a-Star

We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles. We use two different statistical methods to determine the underlying nature of these flux – flux relationships. First, we use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second, we use signal theory to examine the flux – flux relationships for a temporal component. We find that a well-defined temporal component exists and accounts for some of the variance in the data. This temporal component arises because active regions with high magnetic-field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux density. In most cases, the model reconstructions can account for 85 – 90% of the variability of the radiative flux from the chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures of solar and stellar variability.     

Timing and spectral properties of the X-ray emission from the blazar 1ES 1426+428

Most of the extragalactic sources from which very-high-energy (VHE, E > 10¹¹ eV) gamma-ray fluxes have been detected belong to the category of high-energy peaked BL Lacertae objects (HBLs)—the sources in which the synchrotron radiation peaks in the UV or X-ray band. They often have higher X-ray luminosities than the VHE gamma-ray energy output, which makes them the most valuable objects for studying the characteristic spectral and temporal variations in the region of the synchrotron peak of the spectral energy distribution. The blazar 1ES 1426+428 belonging to this category is a target of many multiwavelength studies, both orbital and ground-based ones. The properties of its X-ray emission have also been investigated using RXTE/PCA, XMM-Newton, and SWIFT observations. Archival PCA/RXTE data with a total exposure time in 2002 and 2004 of ≈120^h and the most recent available background and calibration files have been used. The extracted light curves of 1ES 1426+428 in the 2.9–24 keV energy band have shown an intense flaring activity on various time scales. Analysis of the observational data has also confirmed the spectral hardening with increasing X-ray intensity typical of blazars. The flaring state of the object is also characterized by a flat spectrum, which steepens with decreasing flux. The previously detected evidence of a spectral hysteresis in a separate flare has also been confirmed. Observations of 1ES 1426+428 with the SWIFT/XRT telescope and the EPIC instrument onboard XMM-Newton have revealed several intermediate-intensity flares in the 1.5–12 keV energy band with flux variations reaching a factor of 2, while analysis of the light curves has revealed a correlation between two components of the X-ray emission from the object.     

Modeled soft X-ray solar irradiances

Solar soft X-rays have historically been inaccurately modeled in both relative variations and absolute magnitudes by empirical solar extreme ultraviolet (EUV) irradiance models. This is a result of the use of a limited number of rocket data sets which were primarily associated with the calibration of the AE-E satellite EUV data set. In this work, the EUV91 solar EUV irradiance model has been upgraded to improve the accuracy of the 3.0 to 5.0 nm relative irradiance variations. The absolute magnitude estimate of the flux in this wavelength range has also been revised upwards. The upgrade was accomplished by first digitizing the SOLRAD 11 satellite 4.4 to 6.0 nm measured energy flux data set, then extracting and extrapolating a derived 3.0 to 5.0 nm photon flux from these data, and finally by performing a correlation between these derived data and the daily and 81-day mean 10.7 cm radio flux emission using a multiple linear regression technique. A correlation coefficient of greater than 0.9 was obtained between the dependent and independent data sets. The derived and modeled 3.0 to 5.0 nm flux varies by more than an order of magnitude over a solar cycle, ranging from a flux below 1×10⁸ to a flux greater than 1×10⁹ photons cm^–2 s^–1. Solar rotational (27-day) variations in the flux magnitude are a factor of 2. The derived and modeled irradiance absolute values are an order of magnitude greater than previous values from rocket data sets related to the calibration of the AE-E satellite.     

A model for GRB jets

By using relativistic, axisymmetric, ideal MHD, we examine the motion of the baryon/e^±/ photon fluid that emanates from a stellar-mass compact object/debris-disk system (a common outcome of many progenitor models). We prove that the motion can be described as a frozen pulse, which permits the study of each shell of the pancake-shaped outflow using steady-state equations. The ejected energy flux is dominated by the electromagnetic (Poynting) contribution, but it can also have a non negligible e^±/radiation (thermal fireball)component. We demonstrate, through exact self-similar solutions, that the flow is first thermally and subsequently magnetically accelerated up to equipartition between kinetic and Poynting fluxes, i.e., ～ 50% of the total energy is converted into baryonic kinetic energy. The electromagnetic forces also collimate the flow, reaching a cylindrical structure asymptotically.