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D. Onić

Publications and source records attributed to D. Onić.

8 recordsLinked to original sources
arXiv2026

The radio emission from radiative filaments of Cygnus Loop

The Galactic supernova remnant (SNR) Cygnus Loop emerges as an ideal laboratory for analyzing the different radiation mechanisms, as well as the particle acceleration mechanisms at different types of shocks. In order to determine radio spectral indices of non-radiative and radiative filaments in Cygnus Loop, we observed previously optically analyzed filaments with the Karl G. Jansky Very Large Array (VLA). At 1 and 5 GHz, we detected only radiative filaments in the field of view. Non-radiative optical filaments are also present, but were not detected in radio. Contrary to the expected non-thermal spectral slopes characteristic of SNRs, we instead observed spectral slopes characteristic of the thermal radiation mechanism from the radiative filaments in Cygnus Loop. These evolutionary older parts of Cygnus Loop radiate at radio frequencies predominantly via the thermal bremsstrahlung mechanism, and in that sense their emission more closely resembles the radio emission of HII regions rather than the radio emission of SNRs.

astro-ph.HE↗
arXiv2019

Updated radio $Σ-D$ relation for Galactic supernova remnants -- II

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 $Σ-D$ 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.

astro-ph.GA↗
arXiv2019

Revealing the nature of central emission nebulae in the dwarf galaxy NGC 185

In this paper we present new optical observations of the galaxy NGC 185 intended to reveal the status of supernova remnants (SNRs) in this dwarf companion of the Andromeda galaxy. Previously, it was reported that this galaxy hosts one SNR. Our deep photometric study with the 2m telescope at Rozhen National Astronomical Observatory using narrow-band H$α$ and [SII] filters revealed complex structure of the interstellar medium in the center of the galaxy. To confirm the classification and to study the kinematics of the detected nebulae, we carried out spectroscopic observations using the SCORPIO multi-mode spectrograph at the 6m telescope at the Special Astrophysical Observatory of the Russian Academy of Science, both in low- and high-resolution modes. We also searched the archival X-ray and radio data for counterparts of the candidate SNRs identified by our optical observations. Our observations imply the presence of one more SNR, one possible HII region previously cataloged as part of an SNR, and the presence of an additional source of shock ionization in one low-brightness PN. We detected enhanced [SII]/H_alpha and [NII]/H_alpha line ratios, as well as relatively high (up to 90 km s$^{-1}$) expansion velocities of the two observed nebulae, motivating their classification as SNRs (with diameters of 45 pc and 50 pc), confirmed by both photometric and spectral observations. The estimated electron density of emission nebulae is 30 - 200 cm$^{-3}$. Archival XMM-Newton observations indicate the presence of an extended, low-brightness, soft source in projection of one of the optical SNRs, whereas the archival VLA radio image shows weak, unresolved emission in the center of NGC 185.

astro-ph.GA↗
arXiv2019

Murchison Widefield Array and XMM-Newton observations of the Galactic supernova remnant G5.9+3.1

In this paper we discuss the radio continuum and X-ray properties of the so-far poorly studied Galactic supernova remnant (SNR) G5.9+3.1. We present the radio spectral energy distribution (SED) of the Galactic SNR G5.9+3.1 obtained with the Murchison Widefield Array (MWA). Combining these new observations with the surveys at other radio continuum frequencies, we discuss the integrated radio continuum spectrum of this particular remnant. We have also analyzed an archival XMM-Newton observation, which represents the first detection of X-ray emission from this remnant. The SNR SED is very well explained by a simple power-law relation. The synchrotron radio spectral index of G5.9+3.1, is estimated to be 0.42$\pm$0.03 and the integrated flux density at 1GHz to be around 2.7Jy. Furthermore, we propose that the identified point radio source, located centrally inside the SNR shell, is most probably a compact remnant of the supernova explosion. The shell-like X-ray morphology of G5.9+3.1 as revealed by XMM-Newton broadly matches the spatial distribution of the radio emission, where the radio-bright eastern and western rims are also readily detected in the X-ray while the radio-weak northern and southern rims are weak or absent in the X-ray. Extracted MOS1+MOS2+PN spectra from the whole SNR as well as the north, east, and west rims of the SNR are fit successfully with an optically thin thermal plasma model in collisional ionization equilibrium with a column density N_H~0.80x$10^{22}$ cm$^{-2}$ and fitted temperatures spanning the range kT~0.14-0.23keV for all of the regions. The derived electron number densities n_e for the whole SNR and the rims are also roughly comparable (ranging from ~$0.20f^{-1/2}$ cm$^{-3}$ to ~$0.40f^{-1/2}$ cm$^{-3}$, where f is the volume filling factor). We also estimate the swept-up mass of the X-ray emitting plasma associated with G5.9+3.1 to be ~$46f^{-1/2}M_{\odot}$.

astro-ph.GA↗
arXiv2019

Optical observations of the nearby galaxy NGC 2366 through narrowband H$α$ and SII filters. Supernova remnants status

We present detection of 67 HII regions and two optical supernova remnant (SNR) candidates in the nearby irregular galaxy NGC 2366. The SNR candidates were detected by applying [SII]/H$α$ 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, H$α$ and [SII] fluxes for detected objects across the two fields of view in 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.

astro-ph.GA↗
arXiv2015

On the integrated continuum radio spectrum of supernova remnant W44 (G34.7-0.4): new insights from Planck

In this paper, the integrated continuum radio spectrum of supernova remnant (SNR) W44 was analyzed up to 70 GHz, testing the different emission models that can be responsible for its particular shape. The observations by the Planck space telescope made 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 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.

astro-ph.HE↗
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↗