2,973 research outputs found
Parameter constraints in a near-equipartition model with multi-frequency \emph{NuSTAR}, \emph{Swift} and \emph{Fermi-LAT} data from 3C 279
Precise spectra of 3C 279 in the 0.5-70 keV range, obtained during two epochs
of
\emph{Swift} and \emph{NuSTAR} observations, are analyzed using a
near-equipartition model. We apply a one-zone leptonic model with a
three-parameter log-parabola electron energy distribution (EED) to fit the
\emph{Swift} and \emph{NuSTAR} X-ray data, as well as simultaneous optical and
\emph{Fermi}-LAT -ray data. The Markov Chain Monte Carlo (MCMC)
technique is used to search the high-dimensional parameter space and evaluate
the uncertainties on model parameters. We show that the two spectra can be
successfully fit in near-equipartition conditions, defined by the ratio of the
energy density of relativistic electrons to magnetic field
being close to unity. In both spectra, the observed X-rays are dominated by
synchrotron-self Compton photons, and the observed rays are dominated
by Compton scattering of external infrared photons from a surrounding dusty
torus.
Model parameters are well constrained. From the low state to the high state,
both the curvature of the log-parabola width parameter and the synchrotron peak
frequency significantly increase. The derived magnetic fields in the two states
are nearly identical (\ G), but the Doppler factor in the high state is
larger than that in the low state (28 versus 18). We derive that
the gamma-ray emission site takes place outside the broad-line region, at
0.1 pc from the black hole, but within the dusty torus. Implications
for 3C 279 as a source of high-energy cosmic-rays are discussed.Comment: accepted by MNRA
The consistency test on the cosmic evolution
We propose a new and robust method to test the consistency of the cosmic
evolution given by a cosmological model. It is realized by comparing the
combined quantity r_d^CMB/D_V^SN, which is derived from the comoving sound
horizon r_d from cosmic microwave background (CMB) measurements and the
effective distance D_V derived from low-redshift Type-Ia supernovae (SNe Ia)
data, with direct and independent r_d/D_V obtained by baryon acoustic
oscillation (BAO) measurements at median redshifts. We apply this test method
for the Lambda-CDM and wCDM models, and investigate the consistency of the
derived value of r_d/D_V from Planck 2015 and the SN Ia data sets of Union2.1
and JLA (z<1.5), and the r_d/D_V directly given by BAO data from
six-degree-field galaxy survey (6dFGS), Sloan Digital Sky Survey Data Release 7
Main Galaxy Survey (SDSS-DR7 MGS), DR11 of SDSS-III, WiggleZ and Ly-alpha
forecast surveys from Baryon Oscillation Spectroscopic Data (BOSS) DR-11 over
0.1<z<2.36. We find that r_d^CMB/D_V^SN for both non-flat Lambda-CDM and flat
wCDM models with Union2.1 and JLA data are well consistent with the BAO and CMB
measurements within 1-sigma CL. Future surveys will further tight up the
constraints significantly, and provide stronger test on the consistency.Comment: 11 pages, 5 figures, 4 tables. Version accepted by PR
Multifunctional Bracts in the Dove Tree Davidia involucrata (Nyssaceae:Cornales)
Although there has been much experimental work on floral traits that are under selection from mutualists and antagonists, selection by abiotic environmental factors on flowers has been largely ignored. Here we test whether pollen susceptibility to rain damage could have played a role in the evolution of the reproductive architecture of Davidia involucrata, an endemic in the mountains of western China. Flowers in this tree species lack a perianth and are arranged in capitula surrounded by large (up to 10 cm#5 cm) bracts that at anthesis turn from green to white, losing their photosynthetic capability. Flowers are nectarless, and pollen grains are presented on the recurved anther walls for 5–7 days. Flower visitors, and likely pollinators, were mainly pollen-collecting bees from the genera Apis, Xylocopa, Halictus, and Lasioglossum. Capitula with natural or white paper bracts attracted significantly more bees per hour than capitula that had their bracts removed or replaced by green paper. Experimental immersion of pollen grains in water resulted in rapid loss of viability, and capitula with bracts lost less pollen to rain than did capitula that had their bracts removed, suggesting that the bracts protect the pollen from rain damage as well as attracting pollinators
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