In this paper we present the most up-to-date list of nearby galaxies with optically detected supernova remnants (SNRs). We discuss the contribution of the H{alpha} flux from the SNRs to the total H{alpha} flux and its influence on derived star format
ion rate (SFR) for 18 galaxies in our sample. We found that the contribution of SNRs flux to the total H{alpha} flux is 5 $pm$ 5 per cent. Due to the observational selection effects, the SNRs contamination of SFRs derived herein represents only a lower limit.
We present a method for distance calibration without using standard fitting procedures. Instead we use random resampling to reconstruct the probability density function (PDF) of calibration data points in the fitting plane. The resulting PDF is then
used to estimate distance-related properties. The method is applied to samples of radio surface brightness to diameter (Sigma-D) data for the Galactic supernova remnants (SNRs) and planetary nebulae (PNe), and period-luminosity (PL) data for the Large Magellanic Cloud (LMC) fundamental mode classical Cepheids. We argue that resulting density maps can provide more accurate and more reliable calibrations than those obtained by standard linear fitting procedures. For the selected sample of the Galactic SNRs, the presented PDF method of distance calibration results in a smaller average distance fractional error of up to $approx 16$ percentage points. Similarly, the fractional error is smaller for up to $approx 8$ and $approx 0.5$ percentage points, for the samples of Galactic PNe and LMC Cepheids, respectively. In addition, we provide a PDF-based calibration data for each of the samples.
We present observations of the portion of the nearby spiral galaxy IC342 using narrow band [SII] and H$alpha$ filters. These observations were carried out in November 2011 with the 2m RCC telescope at Rozhen National Astronomical Observatory in Bulga
ria. In this paper we report coordinates, diameters, H$alpha$ 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.
The equipartition or minimum-energy calculation is a well-known procedure for estimating magnetic field strength and total energy in the magnetic field and cosmic ray particles by using only the radio synchrotron emission. In one of our previous pape
rs we have offered a modified equipartition calculation for supernova remnants (SNRs) with spectral indices 0.5<alpha <1. Here we extend the analysis to SNRs with alpha =0.5 and alpha =1.
In this paper we present new empirical radio surface brightness-to-diameter ({Sigma} - D) relations for supernova remnants (SNRs) in our Galaxy. We also present new theoretical derivations of the {Sigma} - D relation based on equipartition or on cons
tant ratio between cosmic rays and magnetic field energy. A new calibration sample of 60 Galactic SNRs with independently determined distances is created. Instead of (standard) vertical regression, used in previous papers, different fitting procedures are applied to the calibration sample in the log {Sigma} - log D plane. Non-standard regressions are used to satisfy the requirement that values of parameters obtained from the fitting of {Sigma} - D and D - {Sigma} relations should be invariant within estimated uncertainties. We impose symmetry between {Sigma} - D and D - {Sigma} due to the existence of large scatter in both D and {Sigma}. Using four fitting methods which treat {Sigma} and D symmetrically, different {Sigma} - D slopes {beta} are obtained for the calibration sample. Monte Carlo simulations verify that the slopes of the empirical {Sigma} - D relation should be determined by using orthogonal regression, because of its good performance for data sets with severe scatter. The slope derived here ({beta} = 4.8) is significantly steeper than those derived in previous studies. This new slope is closer to the updated theoretically predicted surface brightness-diameter slope in the radio range for the Sedov phase. We also analyze the empirical {Sigma} - D relations for SNRs in the dense environment of molecular clouds and for SNRs evolving in lower-density interstellar medium. Applying the new empirical relation to estimate distances of Galactic SNRs results in a dramatically changed distance scale.
In this paper, we investigate the possibility of significant production of thermal bremsstrahlung radiation at radio continuum frequencies that could be linked to some Galactic supernova remnants (SNRs). The main targets for this investigation are SN
Rs expanding in high density environments. There are several indicators of radio thermal bremsstrahlung radiation from SNRs, such as a flattening at higher frequencies and thermal absorption at lower frequencies intrinsic to an SNR. In this work we discuss the radio continuum properties of 3 SNRs that are the best candidates for testing our hypothesis of significant thermal emission. In the case of SNRs IC443 and 3C391, thermal absorption has been previously detected. For IC443, the contribution of thermal emission at 1 GHz, from our model fit is 3-57%. It is similar to the estimate obtained from the thermal absorption properties (10-40% at 1 GHz). In the case of the 3C391 the conclusions are not so clear. The results from our model fit (thermal emission contribution of 10-25% at 1 GHz) and results obtained from the low frequency absorption (thermal contribution of 0.15-7% at 1 GHz) do not overlap. For the SNR 3C396 we suggest that if previously detected thermal absorption could be intrinsic to the SNR then the thermal emission (<47% at 1 GHz from our model fit) could be significant enough to shape the radio continuum spectrum at high frequencies. Polarization observations for these SNRs can constrain the strength of a thermal component. Reliable observations at low frequencies (<100 MHz) are needed as well as more data at high radio frequencies (>1 GHz), in order to make stronger conclusions about the existence of radio thermally active SNRs.
Determination of the magnetic field strength in the interstellar medium is one of the most complex tasks of contemporary astrophysics. We can only estimate the order of magnitude of the magnetic field strength by using a few very limited methods. Bes
ides Zeeman effect and Faraday rotation, the equipartition or the minimum-energy calculation is a widespread method for estimating magnetic field strength and energy contained in the magnetic field and cosmic ray particles by using only the radio synchrotron emission. Despite of its approximate character, it remains a useful tool, especially when there is no other data about the magnetic field in a source. In this paper we give a modified calculation which we think is more appropriate for estimating magnetic field strengths and energetics in supernova remnants (SNRs). Finally, we present calculated estimates of the magnetic field strengths for all Galactic SNRs for which the necessary observational data are available. The web application for calculation of the magnetic field strength of SNRs is available at http://poincare.matf.bg.ac.rs/~arbo/eqp/.
The radio surface brightness-to-diameter ({Sigma} - D) relation for supernova remnants (SNRs) in the starburst galaxy M82 is analyzed in a statistically more robust manner than in the previous studies that mainly discussed sample quality and related
selection effects. The statistics of data fits in log {Sigma} - log D plane are analyzed by using vertical (standard) and orthogonal regressions. As the parameter values of D - {Sigma} and {Sigma} - D fits are invariant within the estimated uncertainties for orthogonal regressions, slopes of the empirical {Sigma} - D relations should be determined by using the orthogonal regression fitting procedure. Thus obtained {Sigma} - D relations for samples which are not under severe influence of the selection effects could be used for estimating SNR distances. Using the orthogonal regression fitting procedure {Sigma} - D slope {beta} approx 3.9 is obtained for the sample of 31 SNRs in M82. The results of implemented Monte Carlo simulations show that the sensitivity selection effect does not significantly influence the slope of M82 relation. This relation could be used for estimation of distances to SNRs that evolve in denser interstellar environment, with number denisty up to 1000 particles per cm3 .
An analysis of the relation between radio surface brightness and diameter, so-called Sigma-D relation, for planetary nebulae (PNe) is presented: i) the theoretical Sigma-D relation for the evolution of bremsstrahlung surface brightness is derived; ii
) contrary to the results obtained earlier for the Galactic supernova remnant (SNR) samples, our results show that the updated sample of Galactic PNe does not severely suffer from volume selection effect - Malmquist bias (same as for the extragalactic SNR samples) and; iii) we conclude that the empirical Sigma-D relation for PNe derived in this paper is not useful for valid determination of distances for all observed PNe with unknown distances.
