1,965 research outputs found
The X-ray Jet in Centaurus A: Clues on the Jet Structure and Particle Acceleration
We report detailed studies of the X-ray emission from the kpc scale jet in
the nearest active galaxy, Cen A. 41 compact sources were found within the jet,
13 of which were newly identified. We construct the luminosity function for the
detected jet-knots and argue that the remaining emission is most likely to be
truly diffuse, rather than resulting from the pile-up of unresolved faint
knots. The transverse jet profile reveals that the extended emission has the
intensity peak at the jet boundaries. We note that limb-brightened jet
morphologies have been observed previously at radio frequencies in some jet
sources, but never so clearly at higher photon energies. Our result therefore
supports a stratified jet model, consisting of a relativistic outflow including
a boundary layer with a velocity shear. In addition, we found that the X-ray
spectrum of the diffuse component is almost uniform across and along the jet.
We discuss this spectral behavior within a framework of shock and stochastic
particle acceleration processes. We note some evidence for a possible spectral
hardening at the outer sheath of the jet. Due to the limited photon statistics
of the present data, further deep observations of Cen A are required to
determine the reality of this finding, however we note that the existence of
the hard X-ray features at outer jet boundaries would provide an important
challenge to theories for the evolution of ultra-relativistic particles within
the jets.Comment: 27page, 8 figures, ver2, accepted for publication in the Ap
On the Interaction of the PKS B1358-113 Radio Galaxy with the Abell 1836 Cluster
[abridged] Here we present the analysis of multifrequency data gathered for
the FRII radio galaxy PKS B1358-113, hosted in the brightest cluster galaxy of
Abell 1836. The galaxy harbors one of the most massive black holes known to
date and our analysis of the optical data reveals that this black hole is only
weakly active. Based on new Chandra and XMM-Newton X-ray observations and
archival radio data we derive the preferred range for the jet kinetic
luminosity erg s. This is above the values
implied by various scaling relations proposed for radio sources in galaxy
clusters, being instead very close to the maximum jet power allowed for the
given accretion rate. We constrain the radio source lifetime as
Myrs, and the total amount of deposited jet energy \,ergs. The detailed analysis of the X-ray data provides indication for
the presence of a bow-shock driven by the expanding radio lobes into the Abell
1836 cluster environment, with the corresponding Mach number . This,
together with the recently growing evidence that powerful FRII radio galaxies
may not be uncommon in the centers of clusters at higher redshifts, supports
the idea that jet-induced shock heating may indeed play an important role in
shaping the properties of clusters, galaxy groups, and galaxies in formation.
We speculate on a possible bias against detecting jet-driven shocks in poorer
environments, resulting from an inefficient electron heating at the shock
front, combined with a relatively long electron-ion equilibration timescale.Comment: Version accepted to Ap
No Tradeoff between Coherence and Sub-Poissonianity for Heisenberg-Limited Lasers
The Heisenberg limit to laser coherence -- the number of
photons in the maximally populated mode of the laser beam -- is the fourth
power of the number of excitations inside the laser. We generalize the previous
proof of this upper bound scaling by dropping the requirement that the beam
photon statistics be Poissonian (i.e., Mandel's ). We then show that the
relation between and sub-Poissonianity () is win-win, not a
tradeoff. For both regular (non-Markovian) pumping with semi-unitary gain
(which allows ), and random (Markovian) pumping with
optimized gain, is maximized when is minimized.Comment: This is a companion letter to the manuscript entitled "Optimized
Laser Models with Heisenberg-Limited Coherence and Sub-Poissonian Beam Photon
Statistics", arxiv:2208.14082. 6 pages, 2 figure
Optimized Laser Models with Heisenberg-Limited Coherence and Sub-Poissonian Beam Photon Statistics
Recently it has been shown that it is possible for a laser to produce a
stationary beam with a coherence (quantified as the mean photon number at
spectral peak) which scales as the fourth power of the mean number of
excitations stored within the laser, this being quadratically larger than the
standard or Schawlow-Townes limit [1]. Moreover, this was analytically proven
to be the ultimate quantum limit (Heisenberg limit) scaling under defining
conditions for CW lasers, plus a strong assumption about the properties of the
output beam. In Ref. [2], we show that the latter can be replaced by a weaker
assumption, which allows for highly sub-Poissonian output beams, without
changing the upper bound scaling or its achievability. In this Paper, we
provide details of the calculations in Ref. [2], and introduce three new
families of laser models which may be considered as generalizations of those
presented in that work. Each of these families of laser models is parameterized
by a real number, , with corresponding to the original models. The
parameter space of these laser families is numerically investigated in detail,
where we explore the influence of these parameters on both the coherence and
photon statistics of the laser beams. Two distinct regimes for the coherence
may be identified based on the choice of , where for , each family of
models exhibits Heisenberg-limited beam coherence, while for , the
Heisenberg limit is no longer attained. Moreover, in the former regime, we
derive formulae for the beam coherence of each of these three laser families
which agree with the numerics. We find that the optimal parameter is in fact
, not .Comment: This is a companion manuscript to the letter entitled "No Tradeoff
between Coherence and Sub-Poissonianity for Heisenberg-Limited Lasers",
arxiv:2208.14081. 22 pages, 11 figure
Maximum Likelihood Estimation in Gaussian Chain Graph Models under the Alternative Markov Property
The AMP Markov property is a recently proposed alternative Markov property
for chain graphs. In the case of continuous variables with a joint multivariate
Gaussian distribution, it is the AMP rather than the earlier introduced LWF
Markov property that is coherent with data-generation by natural
block-recursive regressions. In this paper, we show that maximum likelihood
estimates in Gaussian AMP chain graph models can be obtained by combining
generalized least squares and iterative proportional fitting to an iterative
algorithm. In an appendix, we give useful convergence results for iterative
partial maximization algorithms that apply in particular to the described
algorithm.Comment: 15 pages, article will appear in Scandinavian Journal of Statistic
Casimir effect for tachyonic fields
In this paper we examine Casimir effect in the case of tachyonic field, which
is connected with particles with negative four-momentum square. We consider
here only the case of one dimensional, scalar field. In order to describe
tachyonic field, we use the absolute synchronization scheme preserving Lorentz
invariance. The renormalized vacuum energy is calculated by means of Abel-Plana
formula. Finaly, the Casimir energy and Casimir force as the functions of
distance are obtained. In order to compare the resulting formula with the
standard one, we calculate the Casimir energy and Casimir force for massive,
scalar field.Comment: 7 pages, 9 figure
On QBF Proofs and Preprocessing
QBFs (quantified boolean formulas), which are a superset of propositional
formulas, provide a canonical representation for PSPACE problems. To overcome
the inherent complexity of QBF, significant effort has been invested in
developing QBF solvers as well as the underlying proof systems. At the same
time, formula preprocessing is crucial for the application of QBF solvers. This
paper focuses on a missing link in currently-available technology: How to
obtain a certificate (e.g. proof) for a formula that had been preprocessed
before it was given to a solver? The paper targets a suite of commonly-used
preprocessing techniques and shows how to reconstruct certificates for them. On
the negative side, the paper discusses certain limitations of the
currently-used proof systems in the light of preprocessing. The presented
techniques were implemented and evaluated in the state-of-the-art QBF
preprocessor bloqqer.Comment: LPAR 201
Small-scale anisotropy of cosmic rays above 10^19eV observed with the Akeno Giant Air Shower Array
With the Akeno Giant Air Shower Array (AGASA), 581 cosmic rays above 10^19eV,
47 above 4 x 10^19eV, and 7 above 10^20eV are observed until August 1998.
Arrival direction distribution of these extremely high energy cosmic rays has
been studied. While no significant large-scale anisotropy is found on the
celestial sphere, some interesting clusters of cosmic rays are observed. Above
4 x 10^19eV, there are one triplet and three doublets within separation angle
of 2.5^o and the probability of observing these clusters by a chance
coincidence under an isotropic distribution is smaller than 1 %. Especially the
triplet is observed against expected 0.05 events. The cos(\theta_GC)
distribution expected from the Dark Matter Halo model fits the data as well as
an isotropic distribution above 2 x 10^19eV and 4 x 10^19eV, but is a poorer
fit than isotropy above 10^19eV. Arrival direction distribution of seven
10^20eV cosmic rays is consistent with that of lower energy cosmic rays and is
uniform. Three of seven are members of doublets above about 4 x 10^19eV.Comment: 40 pages, 12 figure, AASTeX *** Authors found a typo on Table 2 --
Energy of event 94/07/06 **
Particle-unstable nuclei in the Hartree-Fock theory
Ground state energies and decay widths of particle unstable nuclei are
calculated within the Hartree-Fock approximation by performing a complex
scaling of the many-body Hamiltonian. Through this transformation, the wave
functions of the resonant states become square integrable. The method is
implemented with Skyrme effective interactions. Several Skyrme parametrizations
are tested on four unstable nuclei: 10He, 12O, 26O and 28O.Comment: 5 pages, LaTeX, submitted to Phys. Rev. Let
Permutable entire functions satisfying algebraic differential equations
It is shown that if two transcendental entire functions permute, and if one
of them satisfies an algebraic differential equation, then so does the other
one.Comment: 5 page
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