712 research outputs found
Constraining the Age and Distance of the Galactic Supernova Remnant G156.2+5.7 by H-alpha Expansion Measurements
We present deep H-alpha images of portions of the X-ray bright but optically
faint Galactic supernova remnant G156.2+5.7, revealing numerous and delicately
thin nonradiative filaments which mark the location of the remnant's forward
shock. These new images show that these filaments have a complex structure not
visible on previous lower resolution optical images. By comparing H-alpha
images taken in 2004 at the McDonald Observatory and in 2015-2016 at the Kiso
Observatory, we set a stringent 1-sigma upper limit of expansion to be 0.06
arcsec/yr. This proper motion, combined with a shock speed of 500 km/s inferred
from X-ray spectral analyses, gives a distance of > 1.7 kpc. In addition, a
simple comparison of expansion indices of several SNRs allows us to infer the
age of the remnant to be a few 10,000 yr old. These estimates are more
straightforward and reliable than any other previous studies, and clearly rule
out a possibility that G156.2+5.7 is physically associated with part of the
Taurus-Auriga cloud and dust complex at a distance of 200-300 pc.Comment: 16 pages, 5 figures, accepted for publication in The Astrophysical
Journa
A New Insight into Electron Acceleration Properties from Theoretical Modeling of Double-Peaked Radio Light Curves in Core-Collapse Supernovae
It is recognized that some core-collapse supernovae (SNe) show a
double-peaked radio light curve within a few years since the explosion. A shell
of circumstellar medium (CSM) detached from the SN progenitor has been
considered to play a viable role in characterizing such a re-brightening of
radio emission. Here, we propose another mechanism that can give rise to the
double-peaked radio light curve in core-collapse SNe. The key ingredient in the
present work is to expand the model for the evolution of the synchrotron
spectral energy distribution (SED) to a generic form, including fast and slow
cooling regimes, as guided by the widely-accepted modeling scheme of gamma-ray
burst afterglows. We show that even without introducing an additional CSM
shell, the radio light curve would show a double-peaked morphology when the
system becomes optically thin to synchrotron self-absorption at the
observational frequency during the fast cooling regime. We can observe this
double-peaked feature if the transition from fast cooling to slow cooling
regime occurs during the typical observational timescale of SNe. This situation
is realized when the minimum Lorentz factor of injected electrons is initially
large enough for the non-thermal electrons' SED to be discrete from the thermal
distribution. We propose SN 2007bg as a special case of double-peaked radio SNe
that can be explained by the presented scenario. Our model can serve as a
potential diagnostic for electron acceleration properties in SNe.Comment: 16 pages, 8 figures, submitted to Ap
The NEDD8 system is essential for cell cycle progression and morphogenetic pathway in mice
NEDD8/Rub1 is a ubiquitin (Ub)-like molecule that covalently ligates to target proteins through an enzymatic cascade analogous to ubiquitylation. This modifier is known to target all cullin (Cul) family proteins. The latter are essential components of Skp1/Cul-1/F-box protein (SCF)–like Ub ligase complexes, which play critical roles in Ub-mediated proteolysis. To determine the role of the NEDD8 system in mammals, we generated mice deficient in Uba3 gene that encodes a catalytic subunit of NEDD8-activating enzyme. Uba3−/− mice died in utero at the periimplantation stage. Mutant embryos showed selective apoptosis of the inner cell mass but not of trophoblastic cells. However, the mutant trophoblastic cells could not enter the S phase of the endoreduplication cycle. This cell cycle arrest was accompanied with aberrant expression of cyclin E and p57Kip2. These results suggested that the NEDD8 system is essential for both mitotic and the endoreduplicative cell cycle progression. β-Catenin, a mediator of the Wnt/wingless signaling pathway, which degrades continuously in the cytoplasm through SCF Ub ligase, was also accumulated in the Uba3−/− cytoplasm and nucleus. Thus, the NEDD8 system is essential for the regulation of protein degradation pathways involved in cell cycle progression and morphogenesis, possibly through the function of the Cul family proteins
Passive mode-locking and terahertz frequency comb generation in resonant-tunneling-diode oscillator
Optical frequency combs in the terahertz frequency range are long-awaited frequency standards for spectroscopy of molecules and high-speed wireless communications. However, a terahertz frequency comb based on a low-cost, energy-efficient, and room-temperature-operating device remains unavailable especially in the frequency range of 0.1 to 3 THz. In this paper, we show that the resonant-tunneling-diode (RTD) oscillator can be passively mode-locked by optical feedback and generate a terahertz frequency comb. The standard deviation of the spacing between the comb lines, i.e., the repetition frequency, is reduced to less than 420 mHz by applying external bias modulation. A simulation model successfully reproduces the mode-locking behavior by including the nonlinear capacitance of RTD and multiple optical feedback. Since the mode-locked RTD oscillator is a simple semiconductor device that operates at room temperature and covers the frequency range of 0.1 to 2 THz (potentially up to 3 THz), it can be used as a frequency standard for future terahertz sensing and wireless communications
Cyclic arrays of five pyrenes on one rim of a planar chiral pillar[5]arene
Spatial arrangement of multiple planar chromophores is an emerging strategy for molecule-based chiroptical materials via easy and systematic synthesis. We attached five pyrene planes to a chiral macrocycle, pillar[5]arene, producing a set of chiroptical molecules in which pyrene-derived absorption and emission were endowed with dissymmetry by effective transfer of chiral information. The chiroptical response was dependent on linker structures and substituted patterns because of variable interactions between pyrene units. One of these hybrids showed larger dissymmetry factor and response wavelength (g[lum] = 7.0 × 10⁻³ at ca. 547 nm) than reported pillar[5]arene-based molecules using the pillar[5]arene cores as parts of photo-responsive π-conjugated units
Constraining the Age and Distance of the Galactic Supernova Remnant G156.2+5.7 by H A Expansion Measurements
We present deep Hα images of portions of the X-ray bright, but optically faint, Galactic supernova remnant G156.2+5.7, revealing numerous and delicately thin non-radiative filaments, which mark the location of the remnant\u27s forward shock. These new images show that these filaments have a complex structure not visible on previous lower resolution optical images. By comparing Hα images taken in 2004 at the McDonald Observatory and in 2015–2016 at the Kiso Observatory, we set a stringent 1σ upper limit of expansion to be 0.06 arcsec/yr. This proper motion, combined with a shock speed of 500 km s−1, inferred from X-ray spectral analyses, gives a distance of \u3e 1.7 kpc. In addition, a simple comparison of expansion indices of several supernova remnants allows us to infer the age of the remnant to be a few tens of thousands years old. These estimates are more straightforward and reliable than any other previous studies, and clearly rule out the possibility that G156.2+5.7 is physically associated with part of the Taurus–Auriga cloud and dust complex at a distance of 200–300 pc
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