1,510 research outputs found
The Probable Detection of SN 1923A: The Oldest Radio Supernova?
Based upon the results of VLA observations, we report the detection of two
unresolved radio sources that are coincident with the reported optical position
of SN 1923A in M83. For the source closest to the SN position, the flux density
was determined to be 0.30 +/- 0.05 mJy at 20 cm and 0.093 +/- 0.028 mJy at 6
cm. The flux density of the second nearby source was determined to be 0.29 +/-
0.05 at 20 cm and 0.13 +/- 0.028 at 6 cm. Both sources are non-thermal with
spectral indices of alpha = -1.0 +/- 0.30 and -0.69 +/- 0.24, respectively. SN
1923A has been designated as a Type II-P. No Type II-P (other than SN 1987A)
has been detected previously in the radio. The radio emission from both sources
appears to be fading with time. At an age of approximately 68 years when we
observed it, this would be the oldest radio supernova (of known age) yet
detected
Lawrence O’B. Branch letter in which he discusses military intelligence and notes his confidence of defending his current position. January 22, 1862; New Bern, N.C.
Branch led the forces at the subsequent Battle of New Bern. In this letter he writes I feel a conviction that if the enemy shall come up hence, I will beat him off. Branch also mentions the comings and going of two or three officers.https://digitalcommons.wofford.edu/littlejohnmss/1219/thumbnail.jp
The Environments of Supernovae in Post-Refurbishment Hubble Space Telescope Images
The locations of supernovae in the local stellar and gaseous environment in
galaxies contain important clues to their progenitor stars. Access to this
information, however, has been hampered by the limited resolution achieved by
ground-based observations. High spatial resolution Hubble Space Telescope (HST)
images of galaxy fields in which supernovae had been observed can improve the
situation considerably. We have examined the immediate environments of a few
dozen supernovae using archival post-refurbishment HST images. Although our
analysis is limited due to signal-to-noise ratio and filter bandpass
considerations, the images allow us for the first time to resolve individual
stars in, and to derive detailed color-magnitude diagrams for, several
environments. We are able to place more rigorous constraints on the masses of
these supernovae. A search was made for late-time emission from supernovae in
the archival images, and for the progenitor stars in presupernova images of the
host galaxies. We have detected SN 1986J in NGC 891 and, possibly, SN 1981K in
NGC 4258. We have also identified the progenitor of the Type IIn SN 1997bs in
NGC 3627. By removing younger resolved stars in the environments of SNe Ia, we
can measure the colors of the unresolved stellar background and attribute these
colors generally to an older, redder population. HST images ``accidentally''
caught the Type Ia SN 1994D in NGC 4526 shortly after its outburst; we measure
its brightness. Finally, we add to the statistical inferences that can be made
from studying the association of SNe with recent star-forming regions.Comment: 20 pages, 29 figures, to appear in A
Simulation of semi-arid biomass plantations and irrigation using the WRF-NOAH model – a comparison with observations from Israel
A 10 × 10 km irrigated biomass plantation was simulated in an arid
region of Israel to simulate diurnal energy balances during the summer of
2012 (JJA). The goal is to examine daytime horizontal flux gradients between
plantation and desert. Simulations were carried out within the coupled
WRF-NOAH atmosphere/land surface model. MODIS land surface data was adjusted
by prescribing tailored land surface and soil/plant parameters, and by
adding a controllable sub-surface irrigation scheme to NOAH. Two model cases
studies were compared – Impact and Control. Impact simulates the irrigated plantation.
Control simulates the existing land surface, where the predominant land surface is
bare desert soil. Central to the study is parameter validation against land
surface observations from a desert site and from a 400 ha Simmondsia chinensis (jojoba)
plantation. Control was validated with desert observations, and Impact with Jojoba
observations. Model evapotranspiration was validated with two
Penman–Monteith estimates based on the observations.
Control simulates daytime desert conditions with a maximum deviation for surface 2 m air temperatures (T2)
of 0.2 °C, vapour pressure deficit (VPD) of 0.25 hPa, wind
speed (U) of 0.5 m s−1, surface radiation (Rn) of 25 W m−2,
soil heat flux (G) of 30 W m−2 and 5 cm soil temperatures (ST5) of
1.5 °C. Impact simulates irrigated vegetation conditions with a maximum deviation for T2 of 1–1.5 °C,
VPD of 0.5 hPa, U of 0.5 m s−1, Rn of 50 W m−5,
G of 40 W m−2 and ST5 of 2 °C.
Latent heat curves in Impact correspond closely with Penman–Monteith estimates,
and magnitudes of 160 W m−2 over the plantation are usual. Sensible heat
fluxes, are around 450 W m−2 and are at least 100–110 W m−2
higher than the surrounding desert. This surplus is driven by reduced albedo
and high surface resistance, and demonstrates that high evaporation rates
may not occur over Jojoba if irrigation is optimized. Furthermore, increased
daytime T2 over plantations highlight the need for hourly as well as daily
mean statistics. Daily mean statistics alone may imply an overall cooling
effect due to surplus nocturnal cooling, when in fact a daytime warming
effect is observed
Cosmology with X-ray Cluster Baryons
X-ray cluster measurements interpreted with a universal baryon/gas mass
fraction can theoretically serve as a cosmological distance probe. We examine
issues of cosmological sensitivity for current (e.g. Chandra X-ray Observatory,
XMM-Newton) and next generation (e.g. Con-X, XEUS) observations, along with
systematic uncertainties and biases. To give competitive next generation
constraints on dark energy, we find that systematics will need to be controlled
to better than 1% and any evolution in f_gas (and other cluster gas properties)
must be calibrated so the residual uncertainty is weaker than (1+z)^{0.03}.Comment: 6 pages, 5 figures; v2: 13 pages, substantial elaboration and
reordering, matches JCAP versio
Electronic Raman scattering in YBCO and other superconducting cuprates
Superconductivity induced structures in the electronic Raman spectra of
high-Tc superconductors are computed using the results of ab initio LDA-LMTO
three-dimensional band structure calculations via numerical integrations of the
mass fluctuations, either in the whole 3D Brillouin zone or limiting the
integrations to the Fermi surface. The results of both calculations are rather
similar, the Brillouin zone integration yielding additional weak structures
related to the extended van Hove singularities. Similar calculations have been
performed for the normal state of these high-Tc cuprates. Polarization
configurations have been investigated and the results have been compared to
experimental spectra. The assumption of a simple d_(x^2-y^2)-like gap function
allows us to explain a number of experimental features but is hard to reconcile
with the relative positions of the A1g and B1g peaks.Comment: 14 pages, LaTeX (RevTeX), 5 PostScript figures, uses multicol.sty,
submitted to PR
Extinction and the Radial Distribution of Supernova Properties in Their Parent Galaxies
We use a Monte Carlo technique and assumed spatial distributions of dust and
supernova (SN) progenitors in a simple model of a characteristic SN--producing
disk galaxy to explore the effects of extinction on the radial distributions of
SN properties in their parent galaxies. The model extinction distributions and
projected radial number distributions are presented for various SN types. Even
though the model has no core-collapse SNe within three kpc of the center, a
considerable fraction of the core-collapse SNe are projected into the inner
regions of inclined parent galaxies owing to their small vertical scale height.
The model predicts that because of extinction, SNe projected into the central
regions should on average appear dimmer and have a much larger magnitude
scatter than those in the outer regions. In particular, the model predicts a
strong deficit of bright core-collapse events inside a projected radius of a
few kpc. Such a deficit is found to be present in the observations. It is a
natural consequence of the characteristic spatial distributions of dust and
core-collapse SNe in galaxies, and it leads us to offer an alternative to the
conventional interpretation of the Shaw effect.Comment: 14 pages, 4 figure
Tycho Brahe's 1572 supernova as a standard type Ia explosion revealed from its light echo spectrum
Type Ia supernovae (SNe Ia) are thermonuclear explosions of white dwarf stars
in close binary systems. They play an important role as cosmological distance
indicators and have led to the discovery of the accelerated expansion of the
Universe. Among the most important unsolved questions are how the explosion
actually proceeds and whether accretion occurs from a companion or via the
merging of two white dwarfs. Tycho Brahe's supernova of 1572 (SN 1572) is
thought to be one of the best candidates for a SN Ia in the Milky Way. The
proximity of the SN 1572 remnant has allowed detailed studies, such as the
possible identification of the binary companion, and provides a unique
opportunity to test theories of the explosion mechanism and the nature of the
progenitor. The determination of the yet unknown exact spectroscopic type of SN
1572 is crucial to relate these results to the diverse population of SNe Ia.
Here we report an optical spectrum of Tycho Brahe's supernova near maximum
brightness, obtained from a scattered-light echo more than four centuries after
the direct light of the explosion swept past Earth. We find that SN 1572
belongs to the majority class of normal SNe Ia. The presence of a strong Ca II
IR feature at velocities exceeding 20,000 km/s, which is similar to the
previously observed polarized features in other SNe Ia, suggests asphericity in
SN 1572.Comment: 15 pages, 3 figures - accepted for publication in Natur
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