134 research outputs found
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 was estimated to be . The ambient
density was also estimated to be for the
. 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 and ambient density
are similar to those obtained earlier (, ). It is clear that the corrected flux density values do not
change the basic conclusions.Comment: 6 pages, 1 figur
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.Comment: 12 pages, 5 tables, 11 figures. Accepted for publication in RevMexA
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 plots between 1420 - 820, 1420 - 408 and 820 - 408 MHz. The
obtained results confirm non-thermal origin of the Monoceros radio loop.Comment: 9 pages, 7 tables, 5 figures. Accepted for publication in Astron.
Nach
An Analysis of the Broadband (22-3900 MHz) Radio Spectrum of HB3 (G132.7+1.3): The Detection of Thermal Radio Emission from an Evolved Supernova Remnant?
We present an analysis of the broadband radio spectrum (from 22 to 3900 MHz)
of the Galactic supernova remnant (SNR) HB3 (G132.7+1.3). Published
observations have revealed that a curvature is present in the radio spectrum of
this SNR, indicating that a single synchrotron component appears is
insufficient to adequately fit the spectrum. We present here a fit to this
spectrum using a combination of a synchrotron component and a thermal
bremsstrahlung component. We discuss properties of this latter component and
estimate the ambient density implied by the presence of this component to be n
\~ 10 cm^-3. We have also analyzed extracted X-ray spectra from archived {\it
ASCA} GIS observations of different regions of HB3 to obtain independent
estimates of the density of the surrounding interstellar medium (ISM). From
this analysis, we have derived electron densities of 0.1-0.4 f^-1/2 cm^-3 for
the ISM for the three different regions of the SNR, where f is the volume
filling factor. By comparing these density estimates with the estimate derived
from the thermal bremsstrahlung component, we argue that the radio thermal
bremsstrahlung emission is emitted from a thin shell enclosing HB3. The
presence of this thermal bremsstrahlung component in the radio spectrum of HB3
suggests that this SNR is in fact interacting with an adjacent molecular cloud
associated with the HII region W3. By extension, we argue that the presence of
thermal emission at radio wavelengths may be a useful tool for identifying
interactions between SNRs and molecular clouds, and for estimating the ambient
density near SNRs using radio continuum data.Comment: 5 pages, 2 figures, accepted for ApJ
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.Comment: 10 pages 7 figures, submitted to Serbian Astronomical Journa
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.Comment: 11 pages, 2 tables, 9 figures. Accepted for publication in Open
Astronomy Journa
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 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)
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. 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.Comment: 15 pages, 14 figures, accepted for publication in A&
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