We present the updated empirical radio surface-brightness-to-diameter (? ? D) relation for supernova remnants (SNRs) in our Galaxy. Our original calibration sample of Galactic SNRs with independently determined distances (Pavlovic et al. 2013, hereafter Paper I) is reconsidered and updated with data which became available in the past two years. The orthogonal fitting procedure and probability-density-function-based (PDF) method are applied to the calibration sample in the log? ? logD plane. Non-standard orthogonal regression keeps the ??D and D?? relations invariant within estimated uncertainties. Our previous Monte Carlo simulations verified that the slopes of the empirical ??D relation should be determined by using the orthogonal regression, because of its good performances for data sets with severe scatter. The updated calibration sample contains 65 shell SNRs. 6 new Galactic SNRs are added to the sample from Paper I, one is omitted and distances are changed for 10 SNRs. The slope derived is here slightly steeper (? ? 5.2) than the ??D slope in Paper I (? ? 4.8). The PDF method relies on data points density maps which can provide more reliable calibrations that preserve more information contained in the calibration sample. We estimate distances to five new faint Galactic SNRs discovered for the first time by Canadian Galactic Plane Survey, and obtained distances of 2.3, 4.0, 1.3, 2.9 and 4.7 kiloparsecs for G108.5+11.0, G128.5+2.6, G149.5+3.2, G150.8+3.8 and G160.1?1.1, respectively. The updated empirical relation is used to estimate distances of 160 shell Galactic SNRs and new results change their distance scales up to 15 per cent, compared to the results from Paper I. The PDF calculation can provide even few times higher or lower values in comparison with the orthogonal fit, as it uses a totally different approach. However, on average, this difference is 32, 24 and 18 per cent for mode, median and mean distances. [Projekat Ministarstva nauke Republike Srbije, br. 176005: Emission nebulae: structure and evolution?. B.V. also acknowledges financial support through the Project i br. 176021: Visible and invisible matter in nearby galaxies: theory and observations]

The published version of this article contained a computational error in the calculation of the mass accretion rate J 0 (mass current crossing the shock surface in units of M yr −1 ) at redshift z 0 of the galactic cluster to which we normalize our models of structure formation cosmic rays. The mass accretion rate J 0 was calculated using Pavlidou & Fields (2006):where Ω b = 0.04 is the baryonic matter energy density parameter, ρ c,0 is the critical density at the present epoch, c s,1 is the adiabatic sound speed of the pre-shocked material, δ s is the overdensity in which the accretor is located, and r v is the virial radius of the accretor. The Mach number of the accretion shock is M. We chose to normalize to Coma cluster, so the correct value of the accretion rate for this cluster is J 0 = 417.86 M yr −1 . This value is an order of magnitude lower than the value used in the published version of the paper. This does not change our main conclusion that structure formation cosmic rays can make an important contribution to the Left: all components shown separately-blazars (solid line), normal star-forming galaxies based on two limiting cases given in Fields et al. (2010; red dash dotted line represents luminosity evolution and blue dash dot dotted line represents density evolution), and structure formation cosmic-ray contribution calculated as in the published article, but with the corrected value for J 0 , normalized to the Coma cluster gamma-ray flux limit, with initial gas mass parameter = 0, for three different source models derived in Pavlidou & Fields (2006; long dashed, Model 1; short dashed, Model 2; dotted line, Model 3). Top panel shows structure formation cosmic-ray spectra derived using spectral index α γ = 2.1 and bottom panel α γ = 2.7. Right: the combined contribution of all components where different curves reflect different normal galaxy emission models (thick red curves, luminosity evolution; thin blue curves, density evolution) and different structure formation cosmic-ray emission models (three different line types correspond to the same models as on the top panel).

We present observations of a portion of the nearby spiral galaxy IC342 using narrow band [SII] and Hα filters. These observations were carried out in November 2011 with the 2m RCC telescope at Rozhen National Astronomical Observatory in Bulgaria. In this paper we report coordinates, diameters, Hα and [SII] fluxes for 203 HII regions detected in two fields of view in IC342 galaxy. The number of detected HII regions is 5 times higher than previously known in these two parts of the galaxy.

For more than a decade now the complete origin of the diffuse gamma-ray emission background (EGRB) has been unknown. Major components like unresolved star-forming galaxies (making < ∼ 50% of the EGRB) and blazars ( < ∼ 23%), have failed to explain the entire background observed by Fermi. Another, though subdominant, contribution is expected to come from the process of large-scale structure formation. The growth of structures is accompanied by accretion and merger shocks, which would, with at least some magnetic field present, give rise to a population of structure-formation cosmic rays (SFCRs). Though expected, this cosmic-ray population is still hypothetical and only very weak limits have been placed to their contribution to the EGRB. The most promising insight into SFCRs was expected to come from Fermi -LAT observations of clusters of galaxies, however, only upper limits and no detection have been placed. Here, we build a model of gamma-ray emission from large-scale accretion shocks implementing a source evolution calibrated with the Fermi -LAT cluster observation limits. Though our limits to the SFCR gamma-ray emission are weak (above the observed EGRB) in some case, in others, some of our models can provide a good fit to the observed EGRB. More importantly, we show that these largescale shocks could still give an important contribution to the EGRB, especially at high energies. Future detections of cluster gamma-ray emission would help place tighter constraints on our models and give us a better insight into large-scale shocks forming around them.

Accretion of gas during the large scale structure formation has been thought to give rise to shocks that can accelerate cosmic rays. This process then results in an isotropic extragalactic gamma-ray emission contributing to the extragalactic gamma-ray background observed by the Fermi -LAT. Unfortunately this emission has been difficult to constrain and thus presents an uncertain foreground to any attempts to extract potential dark matter signal. Recently, IceCube has detected high-energy isotropic neutrino flux which could be of an extragalactic origin. In general, neutrinos can be linked to gamma rays since cosmic-ray interactions produce neutral and charged pions where neutral pions decay into gamma rays, while charged pions decay to give neutrinos. By assuming that isotropic high-energy IceCube neutrinos are entirely produced by cosmic rays accelerated in accretion shocks during the process of structure formation, we obtain the strongest constraint to the gamma-ray emission from large scale structure formation (strong) shocks and find that they can make at best ∼ 20% of the extragalactic gammaray background, corresponding to neutrino flux with spectral index α ν = 2, or ∼ 10% for spectral index α ν = 2.46. Since typical objects where cosmic rays are accelerated in accretion shocks are galaxy clusters, observed high-energy neutrino fluxes can then be used to determine the gamma-ray emission of a dominant cluster type and constrain acceleration efficiency, and thus probe the process of large scale structure formation.

By applying a method of virtual quanta we derive formulae for relativistic non-thermal bremsstrahlung radiation from relativistic electrons as well as from protons and heavier particles with power-law momentum distribution N (p)dp = kp −q dp. We show that emission which originates from an electron scattering on an ion, represents the most significant component of relativistic non-thermal bremsstrahlung. Radiation from an ion scattering on electron, known as inverse bremsstrahlung, is shown to be negligible in overall non-thermal bremsstrahlung emission. These results arise from theory refinement, where we introduce the dependence of relativistic kinetic energy of an incident particle, upon the energy of scattered photon. In part, it is also a consequence of a different mass of particles and relativistic effects.

Abstract. Recently, the modified equipartition calculation for supernova remnants (SNRs) has been derived by Arbutina et al. (2012). Their formulae can be used for SNRs with the spectral indices between 0.5 < α < 1. Here, by using approximately the same analytical method, we derive the equipartition formulae useful for SNRs with spectral index α = 0.5. These formulae represent next step upgrade of Arbutina et al. (2012) derivation, because among 30 Galactic SNRs with available observational parameters for the equipartition calculation, 16 have spectral index α = 0.5. For these 16 Galactic SNRs we calculated the magnetic field strengths which are approximately 40 per cent higher than those calculated by using Pacholczyk (1970) equipartition and similar to those calculated by using Beck & Krause (2005) (2005) revised equipartition formula for α = 0.5. Applying our formula yields to magnetic field strengths which are approximately 40 % higher than those calculated by using classical approach derived by Pacholczyk (1970). This is mostly because we were using a wider interval of integration than standard Pacholczyk interval of 10 MHz − 10 GHz.The Web application for calculation of the magnetic field strengths of SNRs for the spectral indices 0.5 < α < 1 is available at http://poincare.matf.bg.ac.rs/~arbo/ eqp/ and value α = 0.578 should be used instead of α = 0.5.