5,425 research outputs found
Evidence for Nonlinear X-ray Variability from the Broad-line Radio Galaxy 3C 390.3
We present analysis of the light curve from the ROSAT HRI monitoring
observations of the broad-line radio galaxy 3C 390.3. Observed every three days
for about 9 months, this is the first well sampled X-ray light curve on these
time scales. The flares and quiescent periods in the light curve suggest that
the variability is nonlinear, and a statistical test yields a detection with >6
sigma confidence. The structure function has a steep slope ~0.7, while the
periodogram is much steeper with a slope ~2.6, with the difference partially
due to a linear trend in the data. The non-stationary character of the light
curve could be evidence that the variability power spectrum has not turned over
to low frequencies, or it could be an essential part of the nonlinear process.
Evidence for X-ray reprocessing suggests that the X-ray emission is not from
the compact radio jet, and the reduced variability before and after flares
suggests there cannot be two components contributing to the X-ray short term
variability. Thus, these results cannot be explained easily by simple models
for AGN variability, including shot noise which may be associated with flares
in disk-corona models or active regions on a rotating disk, because in those
models the events are independent and the variability is therefore linear. The
character of the variability is similar to that seen in Cygnus X-1, which has
been explained by a reservoir or self-organized criticality model. Inherently
nonlinear, this model can reproduce the reduced variability before and after
large flares and the steep PDS seen generally from AGN. The 3C 390.3 light
curve presented here is the first support for such models to explain AGN
variability on intermediate time scales from a few days to months.Comment: 10 pages using (AASTeX) aaspp4.sty and 3 Postscript figures.
Astrophysical Journal Letters, in pres
Integrated photonic quantum gates for polarization qubits
Integrated photonic circuits have a strong potential to perform quantum
information processing. Indeed, the ability to manipulate quantum states of
light by integrated devices may open new perspectives both for fundamental
tests of quantum mechanics and for novel technological applications. However,
the technology for handling polarization encoded qubits, the most commonly
adopted approach, is still missing in quantum optical circuits. Here we
demonstrate the first integrated photonic Controlled-NOT (CNOT) gate for
polarization encoded qubits. This result has been enabled by the integration,
based on femtosecond laser waveguide writing, of partially polarizing beam
splitters on a glass chip. We characterize the logical truth table of the
quantum gate demonstrating its high fidelity to the expected one. In addition,
we show the ability of this gate to transform separable states into entangled
ones and vice versa. Finally, the full accessibility of our device is exploited
to carry out a complete characterization of the CNOT gate through a quantum
process tomography.Comment: 6 pages, 4 figure
Mycotoxins and Other Secondary Metabolites Produced in vitro by Penicillium paneum Frisvad and Penicillium roqueforti Thom Isolated from Baled Grass Silage in Ireland
Detection of circumstellar material in a normal Type Ia Supernova
Type Ia supernovae are thought to be thermonuclear explosions of accreting
white dwarfs that reach a critical mass limit. Despite their importance as
cosmological distance indicators, the nature of their progenitors has remained
controversial. Here we report the detection of circumstellar material in a
normal Type Ia supernova. The expansion velocities, densities and dimensions of
the circumstellar envelope indicate that this material was ejected from the
progenitor system. The relatively low expansion velocities appear to favor a
progenitor system where a white dwarf accretes material from a companion star
which is in the red-giant phase at the time of explosion.Comment: 25 pages, 7 figures. Accepted for publication in Science. Full
resolution version at
http://www.hq.eso.org/~fpatat/science/sn06X/preprint.pdf . The original paper
can be found at http://www.sciencemag.org/cgi/content/abstract/114300
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