2,542 research outputs found
Suzaku View of the Supernova Remnant RCW 86: X-Ray Studies of Newly-Discovered Fe-Rich Ejecta
We report on results of imaging and spectral analysis of the supernova
remnant (SNR) RCW 86 observed with Suzaku. The SNR is known to exhibit K-shell
emission of low ionized Fe, possibly originating from supernova ejecta. We
revealed the global distribution of the Fe-rich plasma in the entire remnant,
for the first time; the Fe-K emission was clearly detected from the west,
north, and south regions, in addition to the X-ray brighter shells of southwest
and northeast, where the presence of the Fe-rich ejecta has already been
reported. The spectrum of each region is well represented by a three-component
model consisting of low- and high-temperature thermal plasmas and a non-thermal
emission. The lower-temperature component, with elemental abundances of near
the solar values, likely originates from the forward shocked interstellar
medium, while the Fe-rich ejecta is described by the hotter plasma. From the
morphologies of the forward and reverse shocks in the west region, the total
ejecta mass is estimated to be 1-2M_sun for the typical explosion energy of ~ 1
x 10^{51} erg. The integrated flux of the Fe-K emission from the entire SNR
roughly corresponds to a total Fe mass of about 1M_sun. Both of these estimates
suggest a Type Ia supernova origin of this SNR. We also find possible evidence
of an Fe-rich clump located beyond the forward-shock front in the north rim,
which is reminiscent of ejecta knots observed in the Tycho and Vela SNRs.Comment: Published by PAS
N49: the first robust discovery of a recombining plasma in an extra galactic supernova remnant
Recent discoveries of recombining plasmas (RPs) in supernova remnants (SNRs)
have dramatically changed our understanding of SNR evolution. To date, a dozen
of RP SNRs have been identified in the Galaxy. Here we present Suzaku deep
observations of four SNRs in the Large Magellanic Cloud (LMC), N49, N49B, N23,
and DEM L71, for accurate determination of their plasma state. Our uniform
analysis reveals that only N49 is in the recombining state among them, which is
the first robust discovery of a RP from an extra-galactic SNR. Given that RPs
have been identified only in core-collapse SNRs, our result strongly suggests a
massive star origin of this SNR. On the other hand, no clear evidence for a RP
is confirmed in N23, from which detection of recombination lines and continua
was previously claimed. Comparing the physical properties of the RP SNRs
identified so far, we find that all of them are categorized into the
"mixed-morphology" class and interacting with surrounding molecular clouds.
This might be a key to solve formation mechanisms of the RPs.Comment: 8 pages, 4 figures, Accepted for publication in Ap
Asymmetric Ejecta Distribution in SN 1006
We present the results from deep X-ray observations (~400 ks in total) of SN
1006 by the X-ray astronomy satellite Suzaku. The thermal spectrum from the
entire supernova remnant (SNR) exhibits prominent emission lines of O, Ne, Mg,
Si, S, Ar, Ca, and Fe. The observed abundance pattern in the ejecta components
is in good agreement with that predicted by a standard model of Type Ia
supernovae (SNe). The spatially resolved analysis reveals that the distribution
of the O-burning and incomplete Si-burning products (Si, S, and Ar) is
asymmetric, while that of the C-burning products (O, Ne, and Mg) is relatively
uniform in the SNR interior. The peak position of the former is clearly shifted
by 5' (~3.2 pc at a distance of 2.2 kpc) to the southeast from the SNR's
geometric center. Using the SNR age of ~1000 yr, we constrain the velocity
asymmetry (in projection) of ejecta to be ~3100 km/s. The abundance of Fe is
also significantly higher in the southeast region than in the northwest region.
Given that the non-uniformity is observed only among the heavier elements (Si
through Fe), we argue that SN 1006 originates from an asymmetric explosion, as
is expected from recent multi-dimensional simulations of Type Ia SNe, although
we cannot eliminate the possibility that an inhomogeneous ambient medium
induced the apparent non-uniformity. Possible evidence for the Cr K-shell line
and line broadening in the Fe K-shell emission is also found.Comment: 11 pages, 12 figures, 4 tables, formatted using emulateapj.cls.
Accepted for publication in Ap
Naturalness and lepton number/flavor violation in inverse seesaw models
We introduce three right-handed neutrinos and three sterile neutrinos, and
consider an inverse seesaw mechanism for neutrino mass generation. From
naturalness point of view, their Majorana masses should be small, while it
induces a large neutrino Yukawa coupling. Then, a neutrinoless double beta
decay rate can be enhanced, and a sizable Higgs mass correction is inevitable.
We find that the enhancement rate can be more than ten times compared with a
standard prediction from light neutrino contribution alone, and an analytic
form of heavy neutrino contributions to the Higgs mass correction. In addition,
we numerically analyze the model, and find almost all parameter space of the
model can be complementarily searched by future experiments of neutrinoless
double beta decay and conversion.Comment: 19 pages, 6 figures: version accepted for publication in JHE
Multiple-point principle with a scalar singlet extension of the Standard Model
We suggest a scalar singlet extension of the standard model, in which the
multiple-point principle (MPP) condition of a vanishing Higgs potential at the
Planck scale is realized. Although there have been lots of attempts to realize
the MPP at the Planck scale, the realization with keeping naturalness is quite
difficult. Our model can easily achieve the MPP at the Planck scale without
large Higgs mass corrections. It is worth noting that the electroweak symmetry
can be radiatively broken in our model. In the naturalness point of view, the
singlet scalar mass should be of or less. We also
consider right-handed neutrino extension of the model for neutrino mass
generation. The model does not affect the MPP scenario, and might keep the
naturalness with the new particle mass scale beyond TeV, thanks to accidental
cancellation of Higgs mass corrections.Comment: 17 pages, 6 figures, version accepted for publication in PTE
Bosonic seesaw mechanism in a classically conformal extension of the Standard Model
We suggest the so-called bosonic seesaw mechanism in the context of a
classically conformal extension of the Standard Model with two
Higgs doublet fields. The symmetry is radiatively broken via the
Coleman-Weinberg mechanism, which also generates the mass terms for the two
Higgs doublets through quartic Higgs couplings. Their masses are all positive
but, nevertheless, the electroweak symmetry breaking is realized by the bosonic
seesaw mechanism. Analyzing the renormalization group evolutions for all model
couplings, we find that a large hierarchy among the quartic Higgs couplings,
which is crucial for the bosonic seesaw mechanism to work, is dramatically
reduced toward high energies. Therefore, the bosonic seesaw is naturally
realized with only a mild hierarchy, if some fundamental theory, which provides
the origin of the classically conformal invariance, completes our model at some
high energy, for example, the Planck scale. We identify the regions of model
parameters which satisfy the perturbativity of the running couplings and the
electroweak vacuum stability as well as the naturalness of the electroweak
scale.Comment: 5 pages, 2 figures, published version in PL
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