arXiv subjects

D. Urošević

Publications and source records attributed to D. Urošević.

28 records · Page 2Linked to original sources

arXiv2014

Multi-frequency study of a new Fe-rich supernova remnant in the Large Magellanic Cloud, MCSNR J0508-6902

We present a detailed radio, X-ray and optical study of a newly discovered Large Magellanic Cloud (LMC) supernova remnant (SNR) which we denote MCSNR J0508-6902. Observations from the Australian Telescope Compact Array (ATCA) and the $\textit{XMM-Newton}$ X-ray observatory are complemented by deep H$α$ images and Anglo Australian Telescope AAOmega spectroscopic data to study the SNR shell and its shock-ionisation. Archival data at other wavelengths are also examined. The remnant follows a filled-in shell type morphology in the radio-continuum and has a size of $\sim$74 pc $\times$ 57 pc at the LMC distance. The X-ray emission exhibits a faint soft shell morphology with Fe-rich gas in its interior $-$ indicative of a Type Ia origin. The remnant appears to be mostly dissipated at higher radio-continuum frequencies leaving only the south-eastern limb fully detectable while in the optical it is the western side of the SNR shell that is clearly detected. The best-fit temperature to the shell X-ray emission ($kT = 0.41^{+0.05}_{-0.06}$ keV) is consistent with other large LMC SNRs. We determined an O/Fe ratio of $<21$ and an Fe mass of 0.5-1.8$~M_{\odot}$ in the interior of the remnant, both of which are consistent with the Type Ia scenario. We find an equipartition magnetic field for the remnant of $\sim$28 $μ$G, a value typical of older SNRs and consistent with other analyses which also infer an older remnant.

astro-ph.HE↗

arXiv2013

Multifrequency study of SNR J0533-7202, a new supernova remnant in the LMC

We present a detailed study of Australia Telescope Compact Array (ATCA) observations of a newly discovered Large Magellanic Cloud (LMC) supernova remnant (SNR), SNR J0533-7202. This object follows a horseshoe morphology, with a size 37 pc x 28 pc (1-pc uncertainty in each direction). It exhibits a radio spectrum with the intrinsic synchrotron spectral index of alpha= -0.47+-0.06 between 73 and 6 cm. We report detections of regions showing moderately high fractional polarisation at 6 cm, with a peak value of 36+-6% and a mean fractional polarisation of 12+-7%. We also estimate an average rotation measure across the remnant of -591 rad m^-2. The current lack of deep X-ray observation precludes any conclusion about high-energy emission from the remnant. The association with an old stellar population favours a thermonuclear supernova origin of the remnant.

astro-ph.GA↗

arXiv2012

Radio-Continuum Observations Of Small, Radially Polarised Supernova Remnant J0519-6902 In The Large Magellanic Cloud

We report on new Australian Telescope Compact Array (ATCA) observations of SNR J0519-6902. The Supernova Remnant (SNR) is small in size (~8 pc) and exhibits a typical SNR spectrum of alpha = -0.53 +- 0.07, with steeper spectral indices found towards the northern limb of the remnant. SNR J0519-6902 contains a low level of radially orientated polarisation at wavelengths of 3 & 6 cm, which is characteristic of younger SNRs. A fairly strong magnetic field was estimated of ~171 microG. The remnant appears to be the result of a typical Type Ia supernovae, sharing many properties as another small and young Type Ia LMC SNR, J0509-6731.

astro-ph.GA↗

arXiv2011

Spectra of HB 21 supernova remnant: Evidence of spectra flattening at the low frequencies

We use observations of the continuum radio emission at 1420, 820, 408, 34.5 and 22 MHz to estimate the mean brightness temperatures of the HB 21 supernova remnant (SNR) at five frequencies. We also presented mean spectral index of HB 21. The spectra of HB 21 are estimated for mean temperatures versus frequency for 1420, 820, 408, 34.5 and 22 MHz. We also presented $T-T$ plots of three frequency pairs: between 1420--34.5, 1420--22, 34.5--22 MHz. We noticed flatter spectral indices at frequencies below 408 MHz. Probably this is due to the absorption by thermal plasma at low frequencies.

astro-ph.GA↗

arXiv2011

The brightness temperatures of the main Galactic radio-loops at 22 MHz

The average brightness temperatures and surface brightnesses at 22 MHz are derived for the four main Galactic radio-continuum loops (Loops I, II, III and IV, hereafter radio-loops). Also the radio-continuum spectra for the radio-loops are presented. Adding the average brightness temperatures at 22 MHz derived here with the average brightness temperatures derived from spectra published previously at 408, 820 and 1420 MHz we obtained clearly non-thermal spectral indices for all radio-loops. Our derived spectral indices are slightly shallower than those measured by previous works.

astro-ph.GA↗

arXiv2011

Temperature, brightness and spectral index of the Cygnus radio loop

The estimated brightness of the Cygnus loop supernova remnant (SNR) at 2720, 1420, 820, 408 and 34.5 MHz are presented. The observations of the continuum radio emission are used to calculate the mean brightness temperatures and surface brightnesses of this loop at the five frequencies in wide spectral range, using the method we have previously developed for large radio loops. The spectrum for mean temperatures versus frequency between the five frequencies is estimated and the spectral index of Cygnus loop is also obtained. Also, from our results can be concluded that Cygnus loop evolves in the low density environment and the initial energy of supernova explosion was relatively low. The obtained results confirm non-thermal origin of the Cygnus radio loop and show that our method is applicable to almost all remnants.

astro-ph.GA↗

arXiv2009

The Monoceros radio loop: temperature, brightness, spectral index and distance

In this paper we estimated the temperatures and brightnesses of the Monoceros radio loop at 1420, 820 and 408 MHz. Linear spectrum is estimated for mean temperatures versus frequency between 1420, 820 and 408 MHz. The spectral index of Monoceros loop is also obtained. The brightness temperatures and surface brightnesses of the loop are computed using data taken from radio-continuum surveys at the three frequencies. The spectral index of the loop is also obtained from $T-T$ plots between 1420 - 820, 1420 - 408 and 820 - 408 MHz. The obtained results confirm non-thermal origin of the Monoceros radio loop.

astro-ph.GA↗

arXiv2009

The Sigma - D relation for planetary nebulae

We present an extended analysis of the relation between radio surface brightness and diameter -- the so-called $Σ-D$ relation for planetary nebulae (PNe). We revise our previous derivation of the theoretical $Σ-D$ 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: $Σ\propto D^{-1}$ for the first and second phases of evolution and $Σ\propto D^{-3}$ for the final stage of evolution. Also, we analyzed several different Galactic PN samples. All samples are influenced by severe selection effects, but Malmquist bias seems to be less influential here than in the supernova remnant (SNR) samples. We derived empirical $Σ-D$ 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 $β\approx 2$. However, we obtain one empirical $Σ-D$ relation that may be useful for determining distances to PNe. This relation is obtained by extracting a recent nearby (< 1 kpc) Galactic PN sample.

astro-ph.SR↗

arXiv2008

An analysis of the possible thermal emission at radio frequencies from an evolved supernova remnant HB 3 (G132.7 + 1.3): revisited

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. In this work we revised an analysis of the possible thermal emission at radio frequencies from the SNR HB 3 using the recently published, corrected, flux density values. A model including a sum of non-thermal (purely synchrotron) and thermal (bremsstrahlung) component is applied for fitting integrated radio spectrum of the SNR. The contribution of thermal component in total volume emissivity at $1 \mathrm{GHz}$ was estimated to be $\approx37 %$. The ambient density was also estimated to be $n\approx 9 \mathrm{cm}^{-3}$ for the $\mathrm{T}=10^{4} \mathrm{K}$. Again, we obtained the relatively significant presence of thermal emission at radio frequencies from the SNR so we could support interaction between SNR HB 3 and adjacent molecular cloud associated with the 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 clear that the corrected flux density values do not change the basic conclusions.

astro-ph↗

arXiv2008

The Brightness of the Galactic Radio Loops at 1420 MHz: Some Indications for the Existence of Loops V and VI

In this article we use 1420 MHz data to demonstrate the likely reality of Galactic radio Loops V and VI. We further estimate distances and spectral indices for both these and the four main radio loops. In the cases of Loops I - IV, radio spectral indices are calculated from the mean brightnesses at 1420 and 820/404 MHz. The spectral indices of Loops V and VI are obtained from $T - T$ plots between 1420 and 408 MHz. Using the supernova remnant (SNR) hypothesis for the origin of radio loops, distances are calculated from the surface brightnesses and the angular diameters at 1420 MHz. We also study how results for brightnesses and distances of radio loops agree with current theories of SNR evolution. For this purpose, the ambient density and initial explosion energy of the loops are discussed. We also discuss applications of different $Σ- D$ relations. The results obtained confirm a non-thermal origin and nearby locations for the Galactic radio loops. Therefore, we have indications that they are very old SNRs that evolve in low ambient densities, with high initial explosion energies.

astro-ph↗