3,630 research outputs found
Constraints on primordial magnetic fields from CMB distortions in the axiverse
Measuring spectral distortions of the cosmic microwave background (CMB) is
attracting considerable attention as a probe of high energy particle physics in
the cosmological context, since PIXIE and PRISM have recently been proposed. In
this paper, CMB distortions due to resonant conversions between CMB photons and
light axion like particles (ALPs) are investigated, motivated by the string
axiverse scenario which suggests the presence of a plenitude of light axion
particles. Since these resonant conversions depend on the strength of
primordial magnetic fields, constraints on CMB distortions can provide an upper
limit on the product of the photon-ALP coupling constant g and the comoving
strength of primordial magnetic fields B. Potentially feasible constraints from
PIXIE/PRISM can set a limit g B < 10^{-16} GeV^{-1} nG for ALP mass, m_\phi <
10^{-14} eV. Although this result is not a direct constraint on g and B, it is
significantly tighter than the product of the current upper limits on g and B.Comment: 8 pages, 3 figure
Asymptotic behavior of the mean square displacement of the Brownian parametric oscillator near the singular point
A parametric oscillator with damping driven by white noise is studied. The
mean square displacement (MSD) in the long-time limit is derived analytically
for the case that the static force vanishes, which was not treated in the past
work \cite{tashiro07}. The formula is asymptotic but is applicable to a general
periodic function. On the basis of this formula, some periodic functions
reducing MSD remarkably are proposed
On Spectral and Temporal Variability in Blazars and Gamma Ray Bursts
A simple model for variability in relativistic plasma outflows is studied, in
which nonthermal electrons are continuously and uniformly injected in the
comoving frame over a time interval dt. The evolution of the electron
distribution is assumed to be dominated by synchrotron losses, and the energy-
and time-dependence of the synchrotron and synchrotron self-Compton (SSC)
fluxes are calculated for a power-law electron injection function with index s
= 2. The mean time of a flare or pulse measured at photon energy E with respect
to the onset of the injection event varies as E^{-1/2} and E^{-1/4} for
synchrotron and SSC processes, respectively, until the time approaches the
limiting intrinsic mean time (1+z)dt/(2 D), where z is the redshift and D is
the Doppler factor. This dependence is in accord with recent analyses of blazar
and GRB emissions, and suggests a method to discriminate between external
Compton and SSC models of high-energy gamma radiation from blazars and GRBs.
The qualititative behavior of the X-ray spectral index/flux relation observed
from BL Lac objects can be explained with this model. This demonstrates that
synchrotron losses are primarily responsible for the X-ray variability behavior
and strengthens a new test for beaming from correlated hard X-ray/TeV
observations.Comment: 10 pages, 2 figures, accepted for publication in Astrophysical
Journal Letters; uses aaspp4.sty, epsf.st
Leading Effects in Hadroproductions of Lambda_c and D From Constituent Quark-Diquark Cascade Picture
We discuss the hadroproductions of Lambda_c, Lambda_c bar, D and D bar in the
framework of the constituent quark-diquark cascade model taking into account
the valence quark annihilation. The spectra of Lambda_c and Lambda_c bar in pA,
Sigma^-A and pi^-A collisions are well explained by the model using the values
of parameters used in hadroproductions of D and D bar. It is shown that the
role of valence diquark in the incident baryon is important for D bar
productions as well as for Lambda_c production.Comment: 11 pages, 5 figures, v2:some explanations added, references added,
typos corrected, v3: top margin change
Time-evolution of Peak Energy and Luminosity Relation within Pulses for GRB 061007: Probing Fireball Dynamics
We perform a time-resolved spectral analysis of bright, long Gamma-ray burst
GRB 061007 using Suzaku/WAM and Swift/BAT. Thanks to the large effective area
of the WAM, we can investigate the time evolution of the spectral peak energy,
Et_peak and the luminosity Lt_iso with 1-sec time resolution, and we find that
luminosity Lt_iso with 1-sec time resolution, and we find that the
time-resolved pulses also satisfy the Epeak-Liso relation, which was found for
the time-averaged spectra of other bursts, suggesting the same physical
conditions in each pulse. Furthermore, the initial rising phase of each pulse
could be an outlier of this relation with higher Et_peak value by about factor
2. This difference could suggest that the fireball radius expands by a factor
of 2-4 and/or bulk Lorentz factor of the fireball is decelerated by a factor of
4 during the initial phase, providing a new probe of the fireball dynamics in
real time.Comment: 21 pages, 16 figures, accepted for publication in PAS
The unusual thickness dependence of superconductivity in -MoGe thin films
Thin films of -MoGe show progressively reduced 's as the
thickness is decreased below 30 nm and the sheet resistance exceeds 100
. We have performed far-infrared transmission and reflection
measurements for a set of -MoGe films to characterize this weakened
superconducting state. Our results show the presence of an energy gap with
ratio in all films studied, slightly higher
than the BCS value, even though the transition temperatures decrease
significantly as film thickness is reduced. The material properties follow
BCS-Eliashberg theory with a large residual scattering rate except that the
coherence peak seen in the optical scattering rate is found to be strongly
smeared out in the thinner superconducting samples. A peak in the optical mass
renormalization at is predicted and observed for the first time
Multiwavelength observation from radio through very-high-energy Gamma-ray of OJ 287 during the 12-year cycle flare in 2007
We performed simultaneous multiwavelength observations of OJ 287 with the
Nobeyama Millimeter Array for radio, the KANATA telescope and the KVA telescope
for optical, the Suzaku satellite for X-ray and the MAGIC telescope for very
high energy (VHE) gamma-ray in 2007. The observations were conducted for a
quiescent state in April and in a flaring state in November-December. We
clearly observed increase of fluxes from radio to X-ray bands during the
flaring state while MAGIC could not detect significant VHE gamma-ray emission
from the source. We could derive an upper limit (95% confidence level) of 1.7%
of the Crab Nebula flux above 150 GeV from about 41.2 hours of the MAGIC
observation. A simple SSC model suggests that the observed flaring activity
could be caused by evolutions in the distribution of the electron population
rather than changes of the magnetic field strength or Doppler beaming factor in
the jet.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
Molecular genetic and physical analysis of gas vesicles in buoyant enterobacteria.
Different modes of bacterial taxis play important roles in environmental adaptation, survival, colonization and dissemination of disease. One mode of taxis is flotation due to the production of gas vesicles. Gas vesicles are proteinaceous intracellular organelles, permeable only to gas, that enable flotation in aquatic niches. Gene clusters for gas vesicle biosynthesis are partially conserved in various archaea, cyanobacteria, and some proteobacteria, such as the enterobacterium, Serratia sp. ATCC 39006 (S39006). Here we present the first systematic analysis of the genes required to produce gas vesicles in S39006, identifying how this differs from the archaeon Halobacterium salinarum. We define 11 proteins essential for gas vesicle production. Mutation of gvpN or gvpV produced small bicone gas vesicles, suggesting that the cognate proteins are involved in the morphogenetic assembly pathway from bicones to mature cylindrical forms. Using volumetric compression, gas vesicles were shown to comprise 17% of S39006 cells, whereas in Escherichia coli heterologously expressing the gas vesicle cluster in a deregulated environment, gas vesicles can occupy around half of cellular volume. Gas vesicle production in S39006 and E. coli was exploited to calculate the instantaneous turgor pressure within cultured bacterial cells; the first time this has been performed in either strain.The authors would like to thank Professor Tony Walsby (Emeritus, Bristol university) for advice, technical help and donation of the pressure nephelometry and volumetric calculation apparatus. We would also like to thank Alison Drew for technical support and Chin Mei Lee and Andrew Day for critical reading. REM and GPCS were supported through the BBSRC (Grant ID BB/K001833/1). YT was supported by a Scientific Research Fellowship from the Japan Society for the Promotion of Sciences (JSPS) and JPR was supported by a Herschel Smith Post Doctoral Fellowship while at Cambridge University.This is the final version of the article. It first appeared from Wiley via https://doi.org/10.1111/1462-2920.1320
The XMM-Newton Detection of Diffuse Inverse Compton X-rays from Lobes of the FR-II Radio Galaxy 3C98
The XMM-Newton observation of the nearby FR-II radio galaxy 3C 98 is
reported. In two exposures on the target, faint diffuse X-ray emission
associated with the radio lobes was significantly detected, together with a
bright X-ray active nucleus, of which the 2 -- 10 keV intrinsic luminosity is
(4 -- 8) \times 10^{42} erg s-1. The EPIC spectra of the northern and southern
lobes are reproduced by a single power law model modified by the Galactic
absorption, with a photon index of 2.2-0.5+0.6 and 1.7-0.6+0.7 respectively.
These indices are consistent with that of the radio synchrotron spectrum, 1.73
+- 0.01 The luminosity of the northern and southern lobes are measured to be
8.3-2.6+3.3 \times 10^{40} erg s-1 and 9.2-4.3+5.7 \times 10^{40} erg s-1,
respectively, in the 0.7 -- 7 keV range. The diffuse X-ray emission is
interpreted as an inverse-Compton emission, produced when the
synchrotron-emitting energetic electrons in the lobes scatter off the cosmic
microwave background photons. The magnetic field in the lobes is calculated to
be about 1.7 \mu G, which is about 2.5 times lower than the value estimated
under the minimum energy condition. The energy density of the electrons is
inferred to exceed that in the magnetic fields by a factor of 40 -- 50.Comment: 23 pages, 7 figures. Accepted for publication in the Astrophysical
Journa
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