3,297 research outputs found
20 cm VLA Radio-Continuum Study of M31 - Images and Point Source Catalogues DR2: Extraction of a supernova remnant sample
We present Data Release 2 of the Point Source Catalogue created from a series
of previously constructed radio-continuum images of M31 at lambda=20 cm (nu=1.4
GHz) from archived VLA observations. In total, we identify a collection of 916
unique discrete radio sources across the field of M31. Comparing these detected
sources to those listed by Gelfand et al. (2004) at lambda=92 cm, the spectral
index of 98 sources has been derived. The majority (73%) of these sources
exhibit a spectral index of alpha <-0.6, indicating that their emission is
predominantly non-thermal in nature, which is typical for background objects
and Supernova Remnants (SNRs). Additionally, we investigate the presence of
radio counterparts for some 156 SNRs and SNR candidates, finding a total of
only 13 of these object in our images within a 5 arcsec search area. Auxiliary
optical, radio and X-ray catalogs were cross referenced highlighting a small
population of SNR and SNR candidates common to multi-frequency domains
Newly confirmed and high quality candidate Galactic SNRs uncovered from the AAO/UKST HAlpha survey
We present a catalogue of 18 new Galactic supernova remnants (SNRs) uncovered
in the optical regime as filamentary emissions and extended nebulosities on
images of the Anglo Australian Observatory/United Kingdom Schmidt Telescope
(AAO/UKST) HAlpha survey of the southern Galactic plane. Our follow-up spectral
observations confirmed classical optical SNR emission lines for these 18
structures via detection of very strong [SII] at 6717 and 6731A relative to
HAlpha ([SII]/HAlpha> 0.5). Morphologically, 10 of these remnants have
coherent, extended arc or shell structures, while the remaining objects are
more irregular in form but clearly filamentary in nature, typical of optically
detected SNRs.
In 11 cases there was a clear if not complete match between the optical and
radio structures with H filamentary structures registered inside and along the
presumed radio borders. Additionally, ROSAT X-ray sources were detected inside
the optical/radio borders of 11 of these new remnants and 3 may have an
associated pulsar.
The multi-wavelength imaging data and spectroscopy together present strong
evidence to confirm identification of 18 new, mostly senile Galactic SNRs. This
includes G288.7-6.3, G315.1+2.7 and G332.5-5.6, identified only as possible
remnants from preliminary radio observations. We also confirm existence of
radio quiet but optically active supernova remnants.Comment: In original form 21 pages, 29 figures Accepted for MNRA
SMC SMP 24: A newly radio-detected planetary nebula in the small magellanic cloud
In this paper we report new radio-continuum detection of an extragalactic PN:
SMC SMP 24. We show the radio-continuum image of this PN and present the
measured radio data. The newly reduced radio observations are consistent with
the multi-wavelength data and derived parameters found in the literature. SMC
SMP 24 appear to be a young and compact PN, optically thick at frequencies
below 2 GHz.Comment: accepted for publication in Serbian Astronomical Journa
A ROSAT PSPC X-Ray Survey of the Small Magellanic Cloud
We present the results of a systematic search for point-like and moderately
extended soft (0.1-2.4 keV) X-ray sources in a raster of nine pointings
covering a field of 8.95 deg^2 and performed with the ROSAT PSPC between
October 1991 and October 1993 in the direction of the Small Magellanic Cloud.
We detect 248 objects which we include in the first version of our SMC
catalogue of soft X-ray sources. We set up seven source classes defined by
selections in the count rate, hardness ratio and source extent. We find five
high luminosity super-soft sources (1E 0035.4-7230, 1E 0056.8-7146, RX
J0048.4-7332, RX J0058.6-7146 and RX J0103-7254), one low-luminosity super-soft
source RX J0059.6-7138 correlating with the planetary nebula L357, 51 candidate
hard X-ray binaries including eight bright hard X-ray binary candidates, 19
supernova remnants, 19 candidate foreground stars and 53 candidate background
active galactic nuclei (and quasars). We give a likely classification for ~60%
of the catalogued sources. The total count rate of the detected point-like and
moderately extended sources in our catalogue is 6.9+/-0.3 s^-1, comparable to
the background subtracted total rate from the integrated field of ~6.1+/-0.1
s^-1.Comment: Accepted by A&AS, 13 pages, 2 Postscript figure
Radio-continuum study of Large Magellanic Cloud Supernova Remnant J0509-6731
We present a detailed study of Australia Telescope Compact Array (ATCA)
observations ( = 20, 13, 6 & 3~cm) of supernova remnant (SNR)
J0509--6731 in the Large Magellanic Cloud (LMC). The remnant has a ring
morphology with brightened regions towards the south-western limb. We also find
a second brightened inner ring which is only seen in the radio-continuum. The
SNR is almost circular, with a diameter ranging from 7 to 8~pc, and a steep
radio spectral index between 36 and 3~cm of , which is
characteristic of younger SNRs. We also report detection of radially orientated
polarisation across the remnant at 6~cm, with a mean fractional polarisation
level of ~(26~~13)%. We find the magnetic field (168~G)
and ( ~W
m~Hz~sr , 7.35~pc) to be consistent with other young
remnants
Radio-continuum detections of Galactic Planetary Nebulae I. MASH PNe detected in large-scale radio surveys
We present an updated and newly compiled radio-continuum data-base for MASH
PNe detected in the extant large scale "blind" radio-continuum surveys (NVSS,
SUMSS/MGPS-2 and PMN) and, for a small number of MASH PNe, observed and
detected in targeted radio-continuum observations. We found radio counterparts
for approximately 250 MASH PNe. In comparison with the percentage of previously
known Galactic PNe detected in the NVSS and MGPS-2 radio-continuum surveys and
according to their position on the flux density-angular diameter and the radio
brightness temperature evolutionary diagrams we conclude, unsurprisingly, that
the MASH sample presents the radio-faint end of the known Galactic PNe
population. Also, we present radio-continuum spectral properties of a small
sub-sample of MASH PNe located in the strip between declinations -30arcdeg and
-40arcdeg, that are detected in both the NVSS and MGPS-2 radio surveys.Comment: 13 figures and 7 tables, accepted for publication in MNRA
Physical Properties of the Supernova Remnant Population in the Small Magellanic Cloud
The X-ray emission from a supernova remnant is a powerful diagnostic of the
state of its shocked plasma. The temperature and the emission measure are
related to the energy of the explosion, the age of the remnant, and the density
of the surrounding medium. Here we present the results of a study of the
remnant population of the Small Magellanic Cloud. Progress in X-ray
observations of remnants has resulted in a sample of 20 remnants in the Small
Magellanic Clound with measured temperatures and emission measures. We apply
spherically symmetric supernova remnant evolution models to this set of
remnants, to estimate ages, explosion energies, and circumstellar medium
densities. The distribution of ages yields a remnant birthrate of 1/1200
yr. The energies and densities are well fit with log-normal distributions, with
means of 1.6 erg and 0.14 cm, and 1 dispersions
of a factor of 1.87 in energy and 3.06 in density, respectively.Comment: 23 pages, 5 figures, accepted for publication in The Astrophysical
Journa
XMM-Newton study of 30 Dor C and a newly identified MCSNR J0536-6913 in the Large Magellanic Cloud
Aims: We present a study of the superbubble (SB) 30 Dor C and the newly
identified MCSNR J0536-6913 in the LMC. Methods: All available XMM-Newton data
(exposure times of 420 ks EPIC-pn, 556 ks EPIC-MOS1, 614 ks EPIC-MOS2) were
used to characterise the thermal X-ray emission in the region. An analysis of
the non-thermal X-rays is also presented and discussed in the context of
emission mechanisms previously suggested in the literature. These data are
supplemented by X-ray data from Chandra, optical data from the MCELS, and radio
data from ATCA and MOST. Results: The brightest thermal emission was found to
be associated with a new supernova remnant, MCSNR J0536-6913. X-ray spectral
analysis of MCSNR J0536-6913 suggested an ejecta-dominated remnant with lines
of O, Ne, Mg, and Si, and a total 0.3-10 keV luminosity of ~8E+34 erg/s. Based
on derived ejecta abundance ratios, we determined the mass of the stellar
progenitor to be either ~18 M_sun or as high as >40 M_sun, though the spectral
fits were subject to assumptions (e.g., uniform temperature and well-mixed
ejecta). The thermal emission from the SB exhibited enrichment by alpha-process
elements, evidence for a recent core-collapse SNR interaction with the SB
shell. We detected non-thermal X-ray emission throughout 30 Dor C, with the
brightest regions being highly correlated with the H-alpha and radio shells. We
created a non-thermal spectral energy distribution for the north-eastern shell
of 30 Dor C which was best-fit with an exponentially cut-off synchrotron model.
Conclusions: Thermal X-ray emission from 30 Dor C is very complex, consisting
of a large scale SB emission at the eastern shell wall with the brightest
emission due to MCSNR J0536-6913. The fact that the non-thermal spectral energy
distribution of the SB shell was observed to roll-off is further evidence that
the non-thermal X-rays from 30 Dor C are synchrotron in origin.Comment: 22 pages, 21 figures, accepted for publication in Astronomy and
Astrophysic
Evidence of molecular adaptation to extreme environments and applicability to space environments
This is initial study of a gene signatures responsible for adapting
microscopic life to the life in extreme Earth environments. We present a
results on ID of the clusters of COGs common to several hyperthermophiles and
exclusion of those common to a mesophile: E.coli.K12, will yield a group of
proteins possibly involved in adaptation to life under extreme T. Methanogens
stand out as the only group of organisms that have species capable of growth at
0C (M.frigidum and M.burtonii) and 110C (M.kandleri). Not all the components of
heat adaptation can be attributed to novel genes, the chaperones known as heat
shock proteins stabilize the enzymes under elevated temperature. Highly
conserved chaperons found in bacteria and eukaryots are not present in
hyperthermophilic Archea, rather, they have a unique chaperone TF55. Our aim is
to use software which we specifically developed for extremophile genome
comparative analyses in order to search for additional novel genes involved in
hyperthermophile adaptation. The following hyperthermophile genomes
incorporated in our software were used for these studies: M.jannaschii,
M.kandleri, A.fulgidus and 3 species of Pyrococcus. Common genes were annotated
and grouped according to their roles in cellular processes when information was
available and proteins not previously implicated in the heat-adaptation of
hyperthermophiles were identified. Additional experimental data is needed in
order to learn more about these proteins. To address a non-gene based
components of thermal adaptation, all sequenced extremophiles were analysed for
their GC contents and aminoacid hydrophobicity. We develop a prediction model
for optimal growth temperature.Comment: 6 pages, 1 figure, To be published in Serbian Astronomical Journa
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