16,217 research outputs found
Experimental Issues for Precision Electroweak Physics at a High-Luminosity Z Factory
We discuss the ultimate precision for ALR, and therefore for the weak mixing
angle, at a high-luminosity Linear Collider. Drawing on our experience at the
SLC, and considering various machine parameter sets for the NLC and for TESLA,
it emerges that a compromise between peak luminosity and precision will be a
likely outcome. This arises due to the severe requirements on the uncertainty
in the luminosity weighted collision energy (Ecm). We consider the cases with
and without a polarized positron beam.Comment: Submitted to LCWS2000 (Linear Collider Workshop 20000), Fermilab,
10-24-200
Balmer-Dominated Shocks Exclude Hot Progenitors for Many Type Ia Supernovae
The evolutionary mechanism underlying Type Ia supernova explosions remains
unknown. Recent efforts to constrain progenitor models based on the influence
that their high energy emission would have on the interstellar medium (ISM) of
galaxies have proven successful. For individual remnants, Balmer-dominated
shocks reveal the ionization state of hydrogen in the immediately surrounding
gas. Here we report deep upper limits on the temperature and luminosity of the
progenitors of four Type Ia remnants with associated Balmer filaments: SN 1006,
0509-67.5, 0519-69.0, and DEM L71. For SN 1006, existing observations of helium
line emission in the diffuse emission ahead of the shock provide an additional
constraint on the helium ionization state in the vicinity of the remnant. Using
the photoionization code Cloudy, we show that these constraints exclude any
hot, luminous progenitor for SN 1006, including stably hydrogen or helium
nuclear-burning white dwarfs, as well as any Chandrasekhar-mass white dwarf
accreting matter at yr via a disk. For
0509-67.5, the Balmer emission alone rules out any such white dwarf accreting
yr. For 0519-69.0 and DEM L71, the inferred
ambient ionization state of hydrogen is only weakly in tension with a recently
hot, luminous progenitor, and cannot be distinguished from e.g., a relatively
higher local Lyman continuum background, without additional line measurements.
Future deep spectroscopic observations will resolve this ambiguity, and can
either detect the influence of any luminous progenitor or rule out the same for
all resolved SN Ia remnants.Comment: 9 pages, 3 figures, 1 table. Accepted for publication in Ap
Work and reversibility in quantum thermodynamics
It is a central question in quantum thermodynamics to determine how
irreversible is a process that transforms an initial state to a final
state , and whether such irreversibility can be thought of as a useful
resource. For example, we might ask how much work can be obtained by
thermalizing to a thermal state at temperature of an
ambient heat bath. Here, we show that, for different sets of resource-theoretic
thermodynamic operations, the amount of entropy produced along a transition is
characterized by how reversible the process is. More specifically, this entropy
production depends on how well we can return the state to its original
form without investing any work. At the same time, the entropy
production can be linked to the work that can be extracted along a given
transition, and we explore the consequences that this fact has for our results.
We also exhibit an explicit reversal operation in terms of the Petz recovery
channel coming from quantum information theory. Our result establishes a
quantitative link between the reversibility of thermodynamical processes and
the corresponding work gain.Comment: 14 page
The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005
On 2004 December 27, a highly-energetic giant flare was recorded from the
magnetar candidate SGR 1806-20. In the months preceding this flare, the
persistent X-ray emission from this object began to undergo significant
changes. Here, we report on the evolution of key spectral and temporal
parameters prior to and following this giant flare. Using the Rossi X-ray
Timing Explorer, we track the pulse frequency of SGR 1806-20 and find that the
spin-down rate of this SGR varied erratically in the months before and after
the flare. Contrary to the giant flare in SGR 1900+14, we find no evidence for
a discrete jump in spin frequency at the time of the December 27th flare
(|dnu/nu| < 5 X 10^-6). In the months surrounding the flare, we find a strong
correlation between pulsed flux and torque consistent with the model for
magnetar magnetosphere electrodynamics proposed by Thompson, Lyutikov &
Kulkarni (2002). As with the flare in SGR 1900+14, the pulse morphology of SGR
1806-20 changes drastically following the flare. Using the Chandra X-ray
Observatory and other publicly available imaging X-ray detector observations,
we construct a spectral history of SGR 1806-20 from 1993 to 2005. The usual
magnetar persistent emission spectral model of a power-law plus a blackbody
provides an excellent fit to the data. We confirm the earlier finding by
Mereghetti et al. (2005) of increasing spectral hardness of SGR 1806-20 between
1993 and 2004. Contrary to the direct correlation between torque and spectral
hardness proposed by Mereghetti et al., we find evidence for a sudden torque
change that triggered a gradual hardening of the energy spectrum on a timescale
of years. Interestingly, the spectral hardness, spin-down rate, pulsed, and
phase-averaged of SGR 1806-20 all peak months before the flare epoch.Comment: 37 pages, 8 figures, 8 tables. Accepted for publication in ApJ. To
appear in the Oct 20 2006 editio
No hot and luminous progenitor for Tycho's supernova
Type Ia supernovae have proven vital to our understanding of cosmology, both
as standard candles and for their role in galactic chemical evolution; however,
their origin remains uncertain. The canonical accretion model implies a hot and
luminous progenitor which would ionize the surrounding gas out to a radius of
10--100 parsecs for 100,000 years after the explosion. Here we
report stringent upper limits on the temperature and luminosity of the
progenitor of Tycho's supernova (SN 1572), determined using the remnant itself
as a probe of its environment. Hot, luminous progenitors that would have
produced a greater hydrogen ionization fraction than that measured at the
radius of the present remnant (3 parsecs) can thus be excluded. This
conclusively rules out steadily nuclear-burning white dwarfs (supersoft X-ray
sources), as well as disk emission from a Chandrasekhar-mass white dwarf
accreting yr (recurrent novae). The lack of a
surrounding Str\"omgren sphere is consistent with the merger of a double white
dwarf binary, although other more exotic scenarios may be possible.Comment: 17 pages, 2 figures, including supplementary information. Original
accepted manuscript (before copyediting/formatting by Nature Astronomy
Probing the birth of fast rotating magnetars through high-energy neutrinos
We investigate the high-energy neutrino emission expected from newly born
magnetars surrounded by their stellar ejecta. Protons might be accelerated up
to 0.1-100 EeV energies possibly by, e.g., the wave dissipation in the winds,
leading to hadronic interactions in the stellar ejecta. The resulting PeV-EeV
neutrinos can be detected by IceCube/KM3Net with a typical peak time scale of a
few days after the birth of magnetars, making the characteristic soft-hard-soft
behavior. Detections would be important as a clue to the formation mechanism of
magnetars, although there are ambiguities coming from uncertainties of several
parameters such as velocity of the ejecta. Non-detections would also lead to
useful constraints on the scenario.Comment: 5 pages, 3 figures, accepted for publication in PR
- âŠ