Fast transients in the form of spiky radio bursts have been observed in solar flares events, emitting at different ranges in frequency. These dynamical phenomena show up as high brightness temperature increments with short durations of the order of milliseconds. In this work, we present results of the analysis of some properties of radio spike events observed at frequencies between 0.01 and 8.4 GHz, as reported in different studies. We analyze the relation of the duration, bandwidth, emitted flux, polarization and drift rate of the radio spikes with its observational frequency. Also, we analyze its correlation with other energetic solar events.

Electrons accelerated in the corona during solar activity give rise to radio emission events that can be observed over a wide range of frequencies. Among different finer-scale structures in the dynamic spectra observed in the radio range, fast transients with extents of some milliseconds known as solar radio spikes are observed accompaning the background continuum emission. Fundamental to the generation of radio spikes is a propagating electron beam and following its evolution allows us to understand the physical processes occurring in the solar corona. With the use of a numerical Fokker-Planck code we follow a previous numerical study to simulate the propagation of an electron beam pulse injected in a small region at the top of a magnetic field and outwards the solar corona under typical flare conditions. It was found that in large ambient densities of 10(10) cm(-3) at the injection point, Coulomb collision effects have an important effect on the propagation of the electrons, causing that the injected electrons thermalize faster in a time of 0.1 and 0.4 s for an electron distribution with a low-energy cut off of 16 and 7 keV respectively and a spectral index of 3. For a tenous ambient medium of density 10(9) cm(-3) thermalization occurs only for an electron distribution with smaller low-energy cut off (7 keV) with a duration of approximate to 1.5 s, while for a larger low-energy cut off (16 keV) the loss of accelerated electrons is very slow, regardles of the spectral index (3, 7). The electron loss time by Coulomb collisions, which depends on the low boundary ambient density, might be an important parameter that influences the generation of radio spikes due to the formation of instabilities in the corona. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

Simulation of fluid dynamics using the Smoothed-Particle Hydrodynamics (SPH) technique, has many applications in areas such as engineering, video games, animation, and graphics. In many of these cases, the values of the SPH parameters employed, such as the number of particles used in the simulation, the SPH kernel length and the values of additional parameters, are not discussed. In this work we optimize the SPH parameters by means of metaheuristic algorithms, using SPH-simulations of five very representative fluid-dynamics test problems. For this purpose, a fitness function based on the exact solution of the test problems analyzed is proposed. We provide optimized parameters that can be applied to real-world and real-time applications and suggest a method to choose these parameters based on the initial conditions in the computational domain. Furthermore, we compare the Univariate Marginal Distribution Algorithm (UMDA), the Univariate Boltzmann Marginal Distribution Algorithm (BUMDA), and Differential Evolution (DE) in terms of their performance in this optimization task. Through statistical analysis it is determined that UMDA is superior, and its convergence to the optimum parameters is examined.

We report continuum GMRT observations aimed to explore the behaviour of the jet associated with IRAS 16547-4247 at very low frequencies (325 MHz and 610 MHz). The obtained maps reveal an elongated morphology in the SE-NW direction. In addition, the 610 MHz map shows three knots associated to the elongated morphology that seems to correspond to the triple radio source identified as the jet seen at higher frequencies. However, at 325 MHz, although an elongated morphology is also observed, only two knots appear in the map. By comparing our knot positions at both frequencies with a precessing jet model used in a previous work, we find that the knots fall closely to the wiggling path and, hence, they likely represent shocks of the material of the precessing jet with the medium. Only the nature of the southern most knot detected at 325 MHz remains unclear. Besides, we found that the whole emission of the lobes is non-thermal down to very low frequencies and that the possible associated emission mechanisms work differently in both lobes, causing the discrepancies observed between frequencies. To explain these discrepancies we investigate mechanisms such as synchrotron radiative losses in a magnetic field of similar to 0.5 mG in the shocks and find this possibility unlikely to occur. Alternatively, we invoke jet interaction with an inhomogeneous medium as the most probable scenario.

We compiled observations of solar radio spikes (RSs) reported in the literature. The compilation spans a wide range in frequency from 0.01 MHz to 8.4 GHz. We also compiled available information of energetic solar events that may be related to RSs. Using this compilation, though the RS events are associated with other energetic solar events, we show that there is no clear preference to any particular type of solar event. We study the dependence of the duration, bandwidth, emitted flux, polarization and drift rate of the RSs with its observational frequency.

Estimation of Distribution Algorithms (EDAs) maintain and iteratively update a probabilistic model to tackle optimization problems. The Boltzmann Probability Distribution Function (Boltzmann-PDF) provides advantages when used in energy based EDAs. However, direct sampling from the Boltzmann-PDF to update the probabilistic model is unpractical, and several EDAs employ an approximation to the Boltzmann-PDF by means of a Gaussian distribution that is usually derived by the minimization of the Kullback-Leibler divergence (KL-divergence) computed between the Gaussian and the Boltzmann-PDFs. The KL-divergence measure is not symmetric, and this causes the Gaussian approximation to fail at correctly modeling the target function for the EDAs, because the parameters of the Gaussian are not optimally estimated. In this paper, we derive an approximation to the Boltzmann-PDF using Jeffreys' divergence (a symmetric measure) in lieu of the KL-divergence and thus improve the performance of the optimization algorithm. Our approach is termed Symmetric-approximation Energy-based Estimation of Distribution (SEED) algorithm. The SEED algorithm is experimentally compared under a univariate approach against two other EDAs (UMDAc and BUMDA) on several benchmark optimization problems. The results show that the SEED algorithm is more effective and more efficient than the other algorithms.

Smooth particle hydrodynamics (SPH) is a mesh free numerical method for solving hydrodynamical equations. For its functioning, the method uses; one integer-domain parameter (the total number of particles) and three real domain parameters (smoothing parameters and artificial viscosity). For a given problem (geometry and initial conditions) these parameters can be tuned to reduce the computational cost and improve the accuracy of the solutions. Optimized values of the SPH parameters using the evolutionary algorithms, Differential Evolution (DE) and Boltzmann Univariate Marginal Distribution Algorithm (BUMDA) are obtained for different Sod shock tube test problems. Comparison of the numerical solution of the physical variables with that of the exact solution shows that this optimization strategy can be used to make an initial guess of the SPH parameters based on the initial conditions of the simulation domain. The performance of the two algorithms are statistically compared.

Se presentan resultados de la aplicacion de tecnicas de deep learning al problema de identificacion de radio fuentes gigantes (GRSs) presentes en el catalogo NVSS. Se hizo un pre procesamiento de las imagenes para la deteccion de estas fuentes y posteriormente realizar su clasificacion, para esto se implemento una red neuronal convolucional basada en el modelo VGG la cual se entreno con el catalogo NVSS. El tamano del conjunto de entrenamiento fue de 1616 imagenes astronomicas distribuidas en 16 categorias. De nuestro analisis, encontramos que nuestro metodo es efectivo con una precision de 87%.

We have used optical V and R band observations from the Massive Compact Halo Object (MACHO) project on a sample of 59 quasars behind the Magellanic clouds to study their long term optical flux and colour variations. These quasars, lying in the redshift range of 0.2 < z < 2.8 and having apparent V band magnitudes between 16.6 and 20.1 mag, have observations ranging from 49 to 1353 epochs spanning over 7.5 yr with frequency of sampling between 2 to 10 days. All the quasars show variability during the observing period. The normalised excess variance (Fvar) in V and R bands are in the range 0.2% < FVvar < 1.6% and 0.1% < FRvar < 1.5% respectively. In a large fraction of the sources, Fvar is larger in the V band compared to the R band. From the z-transformed discrete cross-correlation function analysis, we find that there is no lag between the V and R band variations. Adopting the Markov Chain Monte Carlo (MCMC) approach, and properly taking into account the correlation between the errors in colours and magnitudes, it is found that the majority of sources show a bluer when brighter trend, while a minor fraction of quasars show the opposite behaviour. This is similar to the results obtained from another two independent algorithms, namely the weighted linear least squares fit (FITEXY) and the bivariate correlated errors and intrinsic scatter regression (BCES). However, the ordinary least squares (OLS) fit, normally used in the colour variability studies of quasars, indicates that all the quasars studied here show a bluer when brighter trend. It is therefore very clear that the OLS algorithm cannot be used for the study of colour variability in quasars.

We measure carbon radio recombination line (RRL) emission at 5.3 GHz toward four HII regions with the Green Bank Telescope (GBT) to determine the magnetic field strength in the photodissociation region (PDR) that surrounds the ionized gas. Roshi (2007) suggests that the non-thermal line widths of carbon RRLs from PDRs are predominantly due to magneto-hydrodynamic (MHD) waves, thus allowing the magnetic field strength to be derived. We model the PDR with a simple geometry and perform the non-LTE radiative transfer of the carbon RRL emission to solve for the PDR physical properties. Using the PDR mass density from these models and the carbon RRL non-thermal line width we estimate total magnetic field strengths of B 100-300 micro Gauss in W3 and NGC6334A. Our results for W49 and NGC6334D are less well constrained with total magnetic field strengths between B 200-1000 micro Gauss. HI and OH Zeeman measurements of the line-of-sight magnetic field strength (B_los), taken from the literature, are between a factor of 0.5-1 of the lower bound of our carbon RRL magnetic field strength estimates. Since |B_los| <= B, our results are consistent with the magnetic origin of the non-thermal component of carbon RRL widths.

Narrowband radio bursts with durations of the order of milliseconds, called spikes, are known to be associated with solar flares. In order to understand the particle beams responsible for the radio spike phenomena, evolution of electron beam pulses injected from a solar flare region into the corona is studied. Numerical integration of the Fokker–Planck (FP) equation is used to follow the evolution of the electron beam pulse. The simulations show that the short duration pulses lose most of their energy within a second of propagation into the corona. Electron beam with a small low energy cut off is thermalized faster than that with a high low energy cut off.

We made a direct, quantitative comparison between theoretical and observed density profiles of the planetary nebula NGC 6826. For this, we observed the optically thin (CO)-C-13 (J=1-0) and (CO)-C-13(J=2-1) rotational transition lines at a projected radial distance from the central star of 60 '' and 75 ''. The line strengths and ratios observed at the inner point, and the upper limits observed at the outer point, are consistent with density profiles predicted by mass-loss histories computed from our evolution models when non-LTE radiative transfer and the conditions of collisional excitation in the envelope are taken into account.

The dependence of the turnover frequency on the linear size is presented for a sample of Gigahertz Peaked Spectrum and Compact Steep Spectrum radio sources derived from complete samples. The dependence of the luminosity of the emission at the peak frequency with the linear size and the peak frequency is also presented for the galaxies in the sample. The luminosity of the smaller sources evolve strongly with the linear size. Optical depth effects have been included to the 3D model for the radio source of Kaiser to study the spectral turnover. Using this model, the observed trend can be explained by synchrotron self-absorption. The observed trend in the peak-frequency-linear-size plane is not affected by the luminosity evolution of the sources.

We present images of C110$\alpha$ and H110$\alpha$ radio recombination line (RRL) emission at 4.8 GHz and images of H166$\alpha$, C166$\alpha$ and X166$\alpha$ RRL emission at 1.4 GHz, observed toward the starforming region NGC 2024. The 1.4 GHz image with angular resolution $\sim$ 70\arcsec\ is obtained using VLA data. The 4.8 GHz image with angular resolution $\sim$ 17\arcsec\ is obtained by combining VLA and GBT data. The similarity of the LSR velocity (10.3 \kms\) of the C110$\alpha$ line to that of lines observed from molecular material located at the far side of the \HII\ region suggests that the photo dissociation region (PDR) responsible for C110$\alpha$ line emission is at the far side. The LSR velocity of C166$\alpha$ is 8.8 \kms. This velocity is comparable with the velocity of molecular absorption lines observed from the foreground gas, suggesting that the PDR is at the near side of the \HII\ region. Non-LTE models for carbon line forming regions are presented. Typical properties of the foreground PDR are $T_{PDR} \sim 100$ K, $n_e^{PDR} \sim 5$ \cmthree, $n_H \sim 1.7 \times 10^4$ \cmthree, path length $l \sim 0.06$ pc and those of the far side PDR are $T_{PDR} \sim$ 200 K, $n_e^{PDR} \sim$ 50 \cmthree, $n_H \sim 1.7 \times 10^5$ \cmthree, $l \sim$ 0.03 pc. Our modeling indicates that the far side PDR is located within the \HII\ region. We estimate magnetic field strength in the foreground PDR to be 60 $\mu$G and that in the far side PDR to be 220 $\mu$G. Our field estimates compare well with the values obtained from OH Zeeman observations toward NGC 2024.

We model the carbon recombination line (CRL) emission from the photodissociation region (PDR) surrounding the ultracompact (UC) H ii region W48A. Our modelling shows that the inner regions (A(V) similar to 1) of the C ii layer in the PDR contribute significantly to the CRL emission. Using models spanning over a large range of parameters that are typical for the environments of UCH ii regions, we explore the dependence of the line ratios of CRL emission on the density of the PDR and on the far-ultraviolet radiation incident in the region. We find that it is possible to constrain the density of the PDR by observing a suitable set of CRLs. If the neutral density in the PDR is high ( greater than or similar to 10(7) cm(-3)), then the CRL emission is bright at high frequencies ( greater than or similar to 20 GHz), and the absorption lines from such regions can be detected at low frequencies ( less than or similar to 10 GHz). By modelling CRL observations towards W48A, we can show that the UCH ii region is embedded in a molecular cloud with a density of about 4 x 10(7) cm(-3).

We present observations carried out with the TRAM 30m telescope in Sierra Nevada, Spain, of the halo of NGC 6826, a young planetary nebula. We obtain information of the cool Asymptotic Giant Branch stellar mass by means of a comparison with a density profile from a 1.25 M-circle dot mass-loss history obtained from stellar evolution models paired with a mass loss prescription from dust-driven wind models.

We present the results of our optical monitoring campaign of the X-ray source H 0507+164, a low luminosity Seyfert 1.5 galaxy at a redshift z = 0.018. Spectroscopic observations were carried out during 22 nights in 2007, from the 21 of November to the 26 of December. Photometric observations in the R-band for 13 nights were also obtained during the same period. The continuum and broad line fluxes of the galaxy were found to vary during our monitoring period. The R-band differential light curve with respect to a companion star also shows a similar variability. Using cross correlation analysis, we estimated a time delay of 3.01 days (in the rest frame), of the response of the broad H-beta line fluxes to the variations in the optical continuum at 5100 angstroms. Using this time delay and the width of the H-beta line, we estimated the radius for the Broad Line Region (BLR) of 2.53 x 10^{-3} parsec, and a black hole mass of 9.62 x 10^{6} solar mass.

Light curves of the continuum at 5100 angstrom and H beta line are obtained from spectroscopic monitoring observations of the Seyfert 1.5 galaxy H 0507+164. The mass of the black hole is calculated based on cross-correlation analysis of these light curves.