200 research outputs found
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
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
Mechanical properties of several newly produced RAFM steels with Tungsten content in the range of 2 wt%
The contribution of ENEA together with Rina-CSM to the Eurofusion programme \u201cWPMAT-Advanced Seels\u201d deals with the development of innovative RAFM steels able to withstand the critical temperatures typical of the different operational environments foreseen for the blanket of the first DEMO reactor. The optimization of the chemical composition and the Thermo Mechanical Treatment for these materials should be done according to the blanket operating temperatures that are related to two possible working conditions: the WCLL-BB (Water Cooled Lead Lithium Breeding Blanket) or the H(D)CLL-BB (Helium (Dual) Cooled Lead Lithium Breeding Blanket). On the one hand the \u201cwater-cooling\u201d option implies a minimum irradiation temperature for the blanket material in the range of 280\u2013350 \ub0C. On the other hand, the \u201chelium-cooled\u201d and the \u201cdual-coolant\u201d solutions imply an operating temperature for the blanket material in the range of 650 \ub0C. Therefore in the first case the target is the improvement of the toughness of the martensitic alloys; whilst concerning the second scenario the target is the development of more creep resistant martensitic steels, suitable to tolerate such a high operating temperature. In both the cases the Tungsten content plays a key role, both in terms of solid solution hardening and influence on the DBTT. Two alloys aimed at fulfilling the specifications for the two DEMO operating conditions, both with increased Tungsten content respect to Eurofer, have been produced and characterized. The mechanical properties of these two alloys are hereby reported and discussed
Multifrequency radio observations of SNR J0536-6735 (N 59B) with associated pulsar
We present a study of new Australian Telescope Compact Array (ATCA)
observations of supernova remnant, SNR J0536-6735. This remnant appears to
follow a shell morphology with a diameter of D=36x29 pc (with 1 pc uncertainty
in each direction). There is an embedded Hii region on the northern limb of the
remnant which made various analysis and measurements (such as flux density,
spectral index and polarisation) difficult. The radio-continuum emission
followed the same structure as the optical emission, allowing for extent and
flux density estimates at 20 cm. We estimate a surface brightness for the SNR
at 1 GHz of 2.55x10^-21 W m^-2 Hz^-1 sr^-1. Also, we detect a distinctive
radio-continuum point source which confirms the previous suggestion of this
remnant being associated with a pulsar wind nebulae (PWN). The tail of this
remnant isn't seen in the radio-continuum images and is only seen in the
optical and X-ray images.Comment: 10 pages 4 figures, accepted for publication in SA
Development of innovative steels and thermo-mechanical treatments for DEMO high operating temperature blanket options
Among the options currently taken into account for the realization of the first DEMO reactor there are the "helium-cooled" and the "dual coolant" breeding blanket. Therefore the high temperature (650 °C) behavior of the proposed innovative martensitic alloys should be improved, namely the frame of the hereby reported activities is the development of martensitic alloys more resistant to creep, suitable to tolerate such a high operating temperature. In order to improve the high temperature mechanical properties, concerning the alloy design strategies, two alternative routes are proposed; the effect of Nitrogen and Tungsten increase are taken into account as well as the addition of carbo-nitride forming elements, like Vanadium, combined with the "ausforming" thermo-mechanical treatments. Two alloys have been designed and a special thermo-mechanical treatment on Eurofer 97-2 is proposed. The "ausforming" treatment, consisting in a sort of hot-working at a lower temperature with respect to the austenitization one after the austenitization stage, is aimed at the achievement of a beneficial dislocation "pinning" at high temperature due to carbide precipitation. Generally the improvement of tensile properties is associated to the hardening of the steel due to dislocation network and precipitation effects. This hardening is accompanied by a DBTT increase to markedly higher values with respect to Standard Eurofer. The proposed materials should be, in any case, at least room temperature ductile in order to undergo safe manufacturing and assembling processes. Therefore the issue of the DBTT increase has been taken into account by tuning the tempering temperature adequately. The two variations from chemical composition of Eurofer 97 have been casted and the thermo-mechanical treatments have been selected by means of SEM and hardness measurements to tune grain size and precipitation of carbides. The outcomes of the preliminary mechanical characterization (tensile, creep and impact tests) will be discussed in this paper. Keywords: EUROFER 97, RAFM steels, Thermo-mechanical treatment, Ausforming, Tensile, Creep, Charp
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
Multifrequency Radio Observations of a SNR in the LMC. The Case of SNR J0527-6549 (DEM l204)
We present a detailed study and results of new Australia Telescope Compact
Array (ATCA) observations of supernova remnant, SNR J0527-6549. This Large
Magellanic Cloud (LMC) ob ject follows a typical supernova remnant (SNR)
horseshoe morphology with a diameter of D=(66x58)+-1 pc which is among the
largest SNRs in the LMC. Its relatively large size indicates older age while a
steeper than expected radio spectral index of aplha=-0.92+-0.11 is more typical
for younger and energetic SNRs. Also, we report detections of regions with a
high order of polarization at a peak value of ~54+-17% at 6 cm.Comment: 9 Pages, 6 figures, accepted for publication in SA
XMM-Newton observation of SNR J0533-7202 in the Large Magellanic Cloud
Aims. We present an X-ray study of the supernova remnant SNR J0533-7202 in
the Large Magellanic Cloud (LMC) and determine its physical characteristics
based on its X-ray emission. Methods. We observed SNR J0533-7202 with
XMM-Newton (flare-filtered exposure times of 18 ks EPIC-pn and 31 ks
EPIC-MOS1/MOS2). We produced X-ray images of the SNR, performed an X-ray
spectral analysis, and compared the results to multi-wavelength studies.
Results. The distribution of X-ray emission is highly non-uniform, with the
south-west region brighter than the north-east. The X-ray emission is
correlated with the radio emission from the remnant. We determine that this
morphology is likely due to the SNR expanding into a non-uniform ambient medium
and not an absorption effect. We estimate the size to be 53.9 (\pm 3.4) x 43.6
(\pm 3.4) pc, with the major axis rotated ~64 degrees east of north. We find no
spectral signatures of ejecta and infer that the X-ray plasma is dominated by
swept-up interstellar medium. Using the spectral fit results and the Sedov
self-similar solution, we estimate an age of ~17-27 kyr, with an initial
explosion energy of (0.09-0.83) x 10^51 erg. We detected an X-ray source
located near the centre of the remnant, namely XMMU J053348.2-720233. The
source type could not be conclusively determined due to the lack of a
multi-wavelength counterpart and low X-ray counts. We find that it is likely
either a background active galactic nucleus or a low-mass X-ray binary in the
LMC. Conclusions. We detected bright thermal X-ray emission from SNR J0533-7202
and determined that the remnant is in the Sedov phase of its evolution. The
lack of ejecta emission prohibits us from typing the remnant with the X-ray
data. Therefore, the likely Type Ia classification based on the local stellar
population and star formation history reported in the literature cannot be
improved upon.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Development of innovative materials and thermal treatments for DEMO water cooled blanket
One of the options currently taken into account for the realization of the first DEMO reactor is the "water-cooled lanket". This option implies an irradiation temperature for the blanket material in the range of 280–350 °C. Therefore, in light of the under irradiation behaviour of EUROFER, namely of the DBTT shift toward high temperature due to the low irradiation temperature embrittlement, the target of the hereby reported activities is the development of much tougher alloys, to try to tolerate the embrittlement due to the low irradiation temperature. We report in this paper the work done to optimize the toughness of Eurofer 97, increasing the normalizing temperature and maintaining a small grain size using multiple normalizing treatments. We report also the mechanical behaviour of two 9Cr1WTa type alloys, produced and tested with the same aim to find alloys more resistant to embrittlement at low irradiation temperature. Keywords: EUROFER 97, RAFM steels, Microstructure, Heat treatment, Tensile, Charpy, KLS
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