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ABSTRACT: 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 constant 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.
10/2012;
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ABSTRACT: 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 SNRs 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.
07/2012;
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ABSTRACT: We present observations of the HI tidal arm near dwarf galaxy NGC 3077
(member of the M81 galaxy group) in narrow band [SII] and H_alpha filters.
Observations were carried out in March 2011 with the 2m RCC telescope at NAO
Rozhen, Bulgaria. Our search for possible supernova remnant candidates
(identified as sources with enhanced [SII] emission relative to their H_alpha
emission) in this region yielded no sources of this kind. Nevertheless, we
found a number of objects with significant H_alpha emission that probably
represent uncatalogued, low brightness HII regions.
12/2011;
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ABSTRACT: 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. Besides 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/.
11/2011;
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ABSTRACT: 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 .
06/2010;
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B. Arbutina
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ABSTRACT: This editorial provides results of research on the Serbian Astronomical Journal citation. We give full information on citation for the last three years, and the impact factors calculated for the period 2003-2009.
Serbian Astronomical Journal. 01/2010;
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ABSTRACT: 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.
Serbian Astronomical Journal. 01/2009;
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ABSTRACT: 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. Comment: 4 pages, 2 figures
04/2007;
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ABSTRACT: In this paper we present a brief discussion of the magnetic field (H)
evolution in supernova remnant (SNRs). Evolution models generally assume
H ∝ D-δ. Knowing δ would be particularly
important in the study of the radio surface brightness to diameter
(Σ -D) relation for SNRs, since it would allow us to compare
different theoretical models for the radio evolution.
Publications de l'Observatoire Astronomique de Beograd. 04/2006; 80:95-97.
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ABSTRACT: During the last couple of decades of work on the Σ–D (radio surface brightness to diameter) relation for supernova remnants (SNRs), it has been generally accepted that no single Σ–D relation can be constructed for all SNRs. However, it may still be possible to construct the relations for some classes of SNRs. In our previous paper we analysed Σ–D relation(s) for remnants in the dense environments of molecular clouds. The aim of this paper is to examine, in the same context, a class of oxygen-rich SNRs, and to extend the analysis to remnants evolving in lower-density interstellar media, namely Balmer-dominated SNRs. We have obtained good relations with certain similarities to our previous findings – similarities that emphasize, again, the role of ambient density in the evolution of SNRs.
Monthly Notices of the Royal Astronomical Society 05/2005; 360(1):76 - 80. · 4.90 Impact Factor
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ABSTRACT: We discuss the L–D correlation (possible dependence of radio luminosity on linear diameter) for supernova remnants (SNRs) in order to see whether the Σ–D relation actually exists and whether determination of SNR distances on the basis of the Σ–D relation is possible. We do not find any significant correlation, except for the M82 starburst galaxy for which a good Σ–D relation does exist. Finally, we suggest that a similar relation might exist for Galactic SNRs associated with large molecular clouds, indicating once again that the density of the SNR environment is probably the crucial parameter in SNR evolution.
Monthly Notices of the Royal Astronomical Society 02/2004; 350(1):346 - 350. · 4.90 Impact Factor
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ABSTRACT: We present an extended analysis of the relation between radio surface brightness and diameter – the so-called $\Sigma-D$ relation for planetary nebulae (PNe). We revise our previous derivation of the theoretical $\Sigma-D$ relation for the evolution of bremsstrahlung surface brightness in order to include the influence of the fast wind from the central star. Different theoretical forms are derived: $\Sigma\propto D^{-1}$ for the first and second phases of evolution and $\Sigma\propto D^{-3}$ for the final stage of evolution. Also, we analyzed several different Galactic PN samples. All samples are influenced by severe selection effects, but the Malmquist bias seems to be less influential here than in the supernova remnant (SNR) samples. We derived empirical $\Sigma-D$ relations for 27 sample sets using 6 updated PN papers from which an additional 21 new sets were extracted. Twenty four of these have a trivial form of $\beta\approx2$. However, we obtain one empirical $\Sigma-D$ relation that may be useful for determining distances to PNe. This relation is obtained by extracting a recent nearby ($<$1 kpc) Galactic PN sample.
http://dx.doi.org/10.1051/0004-6361/200809494.
