63 research outputs found
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
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&
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 0.420.03 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 cm 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 ~ cm to ~ cm, 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 ~.Comment: Accepted for publication in A&
Galactic and Extragalactic Samples of Supernova Remnants: How They Are Identified and What They Tell Us
Supernova remnants (SNRs) arise from the interaction between the ejecta of a
supernova (SN) explosion and the surrounding circumstellar and interstellar
medium. Some SNRs, mostly nearby SNRs, can be studied in great detail. However,
to understand SNRs as a whole, large samples of SNRs must be assembled and
studied. Here, we describe the radio, optical, and X-ray techniques which have
been used to identify and characterize almost 300 Galactic SNRs and more than
1200 extragalactic SNRs. We then discuss which types of SNRs are being found
and which are not. We examine the degree to which the luminosity functions,
surface-brightness distributions and multi-wavelength comparisons of the
samples can be interpreted to determine the class properties of SNRs and
describe efforts to establish the type of SN explosion associated with a SNR.
We conclude that in order to better understand the class properties of SNRs, it
is more important to study (and obtain additional data on) the SNRs in galaxies
with extant samples at multiple wavelength bands than it is to obtain samples
of SNRs in other galaxiesComment: Final 2016 draft of a chapter in "Handbook of Supernovae" edited by
Athem W. Alsabti and Paul Murdin. Final version available at
https://doi.org/10.1007/978-3-319-20794-0_90-
Radio emission from Supernova Remnants
The explosion of a supernova releases almost instantaneously about 10^51 ergs
of mechanic energy, changing irreversibly the physical and chemical properties
of large regions in the galaxies. The stellar ejecta, the nebula resulting from
the powerful shock waves, and sometimes a compact stellar remnant, constitute a
supernova remnant (SNR). They can radiate their energy across the whole
electromagnetic spectrum, but the great majority are radio sources. Almost 70
years after the first detection of radio emission coming from a SNR, great
progress has been achieved in the comprehension of their physical
characteristics and evolution. We review the present knowledge of different
aspects of radio remnants, focusing on sources of the Milky Way and the
Magellanic Clouds, where the SNRs can be spatially resolved. We present a brief
overview of theoretical background, analyze morphology and polarization
properties, and review and critical discuss different methods applied to
determine the radio spectrum and distances. The consequences of the interaction
between the SNR shocks and the surrounding medium are examined, including the
question of whether SNRs can trigger the formation of new stars. Cases of
multispectral comparison are presented. A section is devoted to reviewing
recent results of radio SNRs in the Magellanic Clouds, with particular emphasis
on the radio properties of SN 1987A, an ideal laboratory to investigate
dynamical evolution of an SNR in near real time. The review concludes with a
summary of issues on radio SNRs that deserve further study, and analyzing the
prospects for future research with the latest generation radio telescopes.Comment: Revised version. 48 pages, 15 figure
ATCA Study of Small Magellanic Cloud Supernova Remnant 1E 0102.2-7219
We present new and archival Australia Telescope Compact Array and Atacama
Large Millimeter/submillimeter Array data of the Small Magellanic Cloud
supernova remnant 1E 0102.2-7219 at 2100, 5500, 9000, and 108000 MHz; as well
as Hi data provided by the Australian Square Kilometre Array Pathfinder. The
remnant shows a ring-like morphology with a mean radius of 6.2 pc. The 5500 MHz
image reveals a bridge-like structure, seen for the first time in a radio
image. This structure is also visible in both optical and X-ray images. In the
9000 MHz image we detect a central feature that has a flux density of 4.3 mJy
but rule out a pulsar wind nebula origin, due to the lack of significant
polarisation towards the central feature with an upper limit of 4 per cent. The
mean fractional polarisation for 1E 0102.2-7219 is 7 +- 1 and 12 +- 2 per cent
for 5500 and 9000 MHz, respectively. The spectral index for the entire remnant
is -0.61 +- 0.01. We estimate the line-of-sight magnetic field strength in the
direction of 1E 0102.2-7219 of ~44 microG with an equipartition field of 65 +-
5 microG. This latter model, uses the minimum energy of the sum of the magnetic
field and cosmic ray electrons only. We detect an Hi cloud towards this remnant
at the velocity range of ~160-180 km s-1 and a cavity-like structure at the
velocity of 163.7-167.6 km s-1. We do not detect CO emission towards 1E
0102.2-7219
EMU Detection of a Large and Low Surface Brightness Galactic SNR G288.8-6.3
We present the serendipitous detection of a new Galactic Supernova Remnant
(SNR), G288.8-6.3 using data from the Australian Square Kilometre Array
Pathfinder (ASKAP)-Evolutionary Map of the Universe (EMU) survey. Using
multi-frequency analysis, we confirm this object as an evolved Galactic SNR at
high Galactic latitude with low radio surface brightness and typical SNR
spectral index of . To determine the magnetic field
strength in SNR G288.8-6.3, we present the first derivation of the
equipartition formulae for SNRs with spectral indices . The
angular size is 1.\!^\circ 8\times 1.\!^\circ 6 (107.\!^\prime 6 \times
98.\!^\prime 4) and we estimate that its intrinsic size is pc which
implies a distance of kpc and a position of pc above the
Galactic plane. This is one of the largest angular size and closest Galactic
SNRs. Given its low radio surface brightness, we suggest that it is about 13000
years old.Comment: Accepted for publication in The Astrophysical Journa
AMI observations of northern supernova remnants at 14-18 GHz
We present observations between 14.2 and 17.9 GHz of 12 reported supernova
remnants (SNRs) made with the Arcminute Microkelvin Imager Small Array (AMI
SA). In conjunction with data from the literature at lower radio frequencies,
we determine spectra of these objects. For well-studied SNRs (Cas A, Tycho's
SNR, 3C58 and the Crab Nebula), the results are in good agreement with spectra
based on previous results. For the less well-studied remnants the AMI SA
observations provide higher-frequency radio observations than previously
available, and better constrain their radio spectra. The AMI SA results confirm
a spectral turnover at ~11 GHz for the filled-centre remnant G74.9+1.2. We also
see a possible steepening of the spectrum of the filled-centre remnant
G54.1+0.3 within the AMI SA frequency band compared with lower frequencies. We
confirm that G84.9+0.5, which had previously been identified as a SNR, is
rather an HII region and has a flat radio spectrum.Comment: 12 pages, 24 figures, accepted MNRA
A Statistical Study of Galactic SNRs using the PMN Survey
The Parkes-MIT-NRAO (PMN) radio survey has been used to generate a quasi
all-sky study of Galactic Supernova Remnants (SNRs) at a common frequency of
4.85 GHz. We present flux densities estimated for the sample of 110 Southern
Galactic SNRs (up to Dec = - 65 deg.) observed with the Parkes 64-m radio
telescope and an additional sample of 54 from the Northern PMN (up to Dec = +64
deg.) survey undertaken with the Green Bank 43-m (20 SNRs) and 91-m (34 SNRs)
radio telescopes. Out of this total sample of 164 selected SNRs (representing
71% of the 231 known SNRs in the Green catalogue) we consider 138 to provide
reliable estimates of flux density and surface brightness distribution. This
sub-sample represents those SNRs which fall within carefully chosen selection
criteria which minimises the effects of the known problems in establishing
reliable fluxes from the PMN survey data. Our selection criteria are based on a
judicious restriction of source angular size and telescope beam together with
careful evaluation of fluxes on a case by case basis. This gives confidence in
the newly derived PMN fluxes when the selection criteria are respected. We find
a sharp drop off in the flux densities for Galactic SNRs beyond 4 Jy and then a
fairly flat distribution from 5-9 Jy, a slight decline and a further flat
distribution from 9-20 Jy though the numbers of SNR in each Jy bin are low. We
also re-visit the contentious Sigma-D relation to determine a new power law
index for a sub-sample of shell type SNRs which yields beta= -2.2 +/- 0.6. This
new evaluation of the Sigma-D relation, applied to the restricted sample,
provides new distance estimates and their Galactic scale height distribution.
We find a peak in the SNR distribution between 7-11 kpc with most restricted to
+/- 100 pc Galactic scale height.Comment: 14 pages, 7 figures. Accepted for publishing in Astrophysics and
Space Scienc
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