Sofia University

About: Sofia University is a education organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Large Hadron Collider & Laser. The organization has 8533 authors who have published 15730 publications receiving 306320 citations. The organization is also known as: University of Sofia & BFUS.

Variability of the blazar 4C 38.41 (B3 1633+382) from GHz frequencies to GeV energies

Abstract: Context. After years of modest optical activity, the quasar-type blazar 4C 38.41 (B3 1633+382) experienced a large outburst in 2011, which was detected throughout the entire electromagnetic spectrum, renewing interest in this source.Aims. We present the results of low-energy multifrequency monitoring by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) consortium and collaborators, as well as those of spectropolarimetric/spectrophotometric monitoring at the Steward Observatory. We also analyse high-energy observations of the Swift and Fermi satellites. This combined study aims to provide insights into the source broad-band emission and variability properties.Methods. We assemble optical, near-infrared, millimetre, and radio light curves and investigate their features and correlations. In the optical, we also analyse the spectroscopic and polarimetric properties of the source. We then compare the low-energy emission behaviour with that at high energies.Results. In the optical-UV band, several results indicate that there is a contribution from a quasi-stellar-object (QSO) like emission component, in addition to both variable and polarised jet emission. In the optical, the source is redder-when-brighter, at least for R ≳ 16. The optical spectra display broad emission lines, whose flux is constant in time. The observed degree of polarisation increases with flux and is higher in the red than the blue. The spectral energy distribution reveals a bump peaking around the U band. The unpolarised emission component is likely thermal radiation from the accretion disc that dilutes the jet polarisation. We estimate its brightness to be R QSO ~ 17.85–18 and derive the intrinsic jet polarisation degree. We find no clear correlation between the optical and radio light curves, while the correlation between the optical and γ -ray flux apparently fades in time, likely because of an increasing optical to γ -ray flux ratio. Conclusions. As suggested for other blazars, the long-term variability of 4C 38.41 can be interpreted in terms of an inhomogeneous bent jet, where different emitting regions can change their alignment with respect to the line of sight, leading to variations in the Doppler factor δ . Under the hypothesis that in the period 2008–2011 all the γ -ray and optical variability on a one-week timescale were due to changes in δ , this would range between ~7 and ~21. If the variability were caused by changes in the viewing angle θ only, then θ would go from ~2.6° to ~5°. Variations in the viewing angle would also account for the dependence of the polarisation degree on the source brightness in the framework of a shock-in-jet model.

No polarization–Expected Values of Climate Change Impacts among European Forest Professionals and Scientists

Abstract: The role of values in climate-related decision-making is a prominent theme of climate communication research. The present study examines whether forest professionals are more driven by values than scientists are, and if this results in value polarization. A questionnaire was designed to elicit and assess the values assigned to expected effects of climate change by forest professionals and scientists working on forests and climate change in Europe. The countries involved covered a north-to-south and west-to-east gradient across Europe, representing a wide range of bio-climatic conditions and a mix of economic–social–political structures. We show that European forest professionals and scientists do not exhibit polarized expectations about the values of specific impacts of climate change on forests in their countries. In fact, few differences between forest professionals and scientists were found. However, there are interesting differences in the expected values of forest professionals with regard to climate change impacts across European countries. In Northern European countries, the aggregated values of the expected effects are more neutral than they are in Southern Europe, where they are more negative. Expectations about impacts on timber production, economic returns, and regulatory ecosystem services are mostly negative, while expectations about biodiversity and energy production are mostly positive.

Raman and infrared-active phonons in hexagonal HoMnO3 single crystals: magnetic ordering effects

Abstract: Polarized first- and second-order Raman scattering and infrared reflection spectra of hexagonal HoMnO3 single crystals in the temperature range 10–300 K are reported. Based on the symmetry analysis and comparison with the results of lattice dynamics calculations the observed lines are assigned to the lattice eigenmodes. The magnetic ordering of Mn ions, which occurs below TN = 76 K, is shown to affect Raman- and infrared-active phonons, which modulate Mn–O–Mn bonds and, consequently, the Mn–Mn exchange interaction.

Image of the Janis-Newman-Winicour naked singularity with a thin accretion disk

Abstract: We study the optical appearance and the apparent radiation flux of a geometrically thin and optically thick accretion disk around the static Janis-Newman-Winicour naked singularity. We confine ourselves to the astrophysically most relevant case, when the solution possesses a photon sphere, assuming that the radiation emitted by the disk is described by the Novikov-Thorne model. The observable images closely resemble the visual appearance of the Schwarzschild black hole, as only quantitative differences are present. For the Janis-Newman-Winicour solution the accretion disk appears smaller, and its emission is characterized by a higher peak of the radiation flux. In addition, the most significant part of the radiation is concentrated in a closer neighborhood of the flux maximum. The results are obtained independently by two alternative methods, consisting of a semianalytical scheme using the spherical symmetry of the spacetime, and a fully numerical ray-tracing procedure valid for any stationary and axisymmetric spacetime.