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We present observations of the nearby tidal dwarf galaxy Holmberg IX in M81 galaxy group in narrow band [SII] and H$alpha$ filters, carried out in March and November 2008 with the 2m RCC telescope at NAO Rozhen, Bulgaria. Our search for resident supernova remnants (identified as sources with enhanced [SII] emission relative to their H$alpha$ emission) in this galaxy yielded no sources of this kind, besides M&H 10-11 or HoIX X-1. Nevertheless, we found a number of objects with significant H$alpha$ emission that probably represent uncatalogued HII regions.

It has recently been reported that some of the flux density values for an evolved supernova remnant (SNR) HB 3 (G132.7$+$1.3) are not accurate enough. In this work we therefore revised the analysis of the possible thermal emission at radio frequencies from this SNR using the recently published, corrected flux density values. A model including the sum of non-thermal (purely synchrotron) and thermal (bremsstrahlung) components is applied to fit the integrated radio spectrum of this SNR. The contribution of thermal component to the total volume emissivity at $1 mathrm{GHz}$ is estimated to be $approx37 \%$. The ambient density is also estimated to be $napprox 9 mathrm{cm}^{-3}$ for $mathrm{T}=10^{4} mathrm{K}$. Again we obtained a relatively significant presence of thermal emission at radio frequencies from the SNR, which can support interaction between SNR HB 3 and adjacent molecular cloud associated with the mbox{H,{sc ii}} region W3. Our model estimates for thermal component contribution to total volume emissivity at $1 mathrm{GHz}$ and ambient density are similar to those obtained earlier ($approx40 \%$, $approx10 mathrm{cm^{-3}}$). It is thus obvious that the corrected flux density values do not affect the basic conclusions.

We determined the shock speed in the Galactic supernova remnant Cygnus Loop, using the proper motion of its optical filaments and the latest estimate of its distance. The proper motion was measured by comparing Hα images of the remnant observed in two epochs: 1993 (Kitt Peak National Observatory) and 2018/2019 (National Astronomical Observatory Rozhen and Astronomical Station Vidojevica). We derived shock speed for 35 locations along different filaments, which is twice as much as in earlier studies of the north-eastern part of the Cygnus Loop. For the first time, we have measured the shock speed of the radiative filaments in this region. Three of the analyzed locations where we measured the proper motion of filaments are radiative, based on their presence in [SII] images from the second epoch. The other filaments are non-radiative. The speed we obtained for the non-radiative filaments is in the range of 240{650 km s-1, with an estimate for the uncertainty of 70 km s-1. These values are mostly in agreement with previous studies. The radiative filaments have lower speeds of 100-160 ±70 km s-1, which is in agreement with the assumption that they are older in evolutionary terms. This clear distinction between the speed of the two types of filaments proves that [SII] emission can be used for identifying radiative filaments in supernova remnants.

We present detection of 64 Hii regions, three superbubbles and two optical supernova remnant (SNR) candidates in the nearby irregular galaxy NGC 2366. The SNR candidates were detected by applying [S ii]/Hα ratio criterion to observations made with the 2-m RCC telescope at Rozhen National Astronomical Observatory in Bulgaria. In this paper we report coordinates, diameters, Hα and [S ii] fluxes for detected objects across the two fields of view in the NGC 2366 galaxy. Using archival XMM-Newton observations we suggest possible X-ray counterparts of two optical SNR candidates. Also, we discard classification of two previous radio SNR candidates in this galaxy since they appear to be background galaxies. [ABSTRACT FROM AUTHOR]

In this paper, the integrated continuum radio spectrum of supernova remnant (SNR) W44 was analyzed up to 70 GHz by testing different emission models that can be responsible for its particular shape. The observations by the Planck space telescope made it possible to analyze the high frequency part of radio emission from SNRs. Although the quality of radio continuum spectrum (a high scatter of data points at same frequencies) prevents us to make definite conclusions, the possibility of spinning the dust emission detection towards this remnant is emphasized. In addition, a concave-down feature due to synchrotron losses can not be definitely dismissed by the present knowledge of the integrated radio continuum spectrum of this SNR. [ABSTRACT FROM AUTHOR]

In this paper we present the updated empirical radio surface- brightness-to-diameter (Σ-D) relation for Galactic supernova remnants (SNRs) calibrated using 110 SNRs with reliable distances. We apply orthogonal fitting procedure and kernel density smoothing in the Σ ¡ D plane and compare the results with the latest theoretical Σ - D relations derived from simulations of radio evolution of SNRs. We argue that the best agreement between the empirical and simulated Σ ¡ D relations is achieved if the mixed-morphology SNRs and SNRs of both, low brightness and small diameter, are filtered out from the calibration sample. The distances to 5 newly discovered remnants and 27 new candidates for shell SNRs are estimated from our full and filtered calibration samples. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 176005: Emission nebulae: structure and evolution]