5,968 research outputs found
Nuclear magnetic octupole moment and the hyperfine structure of the states of the Ba ion
The hyperfine structure of the long-lived and levels of
Ba ion is analyzed. A procedure for extracting relatively unexplored
nuclear magnetic moments is presented. The relevant electronic matrix
elements are computed in the framework of the ab initio relativistic many-body
perturbation theory. Both the first- and the second-order (in the hyperfine
interaction) corrections to the energy levels are analyzed. It is shown that a
simultaneous measurement of the hyperfine structure of the entire
fine-structure manifold allows one to extract without contamination
from the second-order corrections. Measurements to the required accuracy should
be possible with a single trapped barium ion using sensitive techniques already
demonstrated in Ba experiments.Comment: Phys Rev A in pres
Eliminating artefacts in polarimetric images using deep learning
Polarization measurements done using Imaging Polarimeters such as the Robotic Polarimeter are very sensitive to the presence of artefacts in images. Artefacts can range from internal reflections in a telescope to satellite trails that could contaminate an area of interest in the image. With the advent of wide-field polarimetry surveys, it is imperative to develop methods that automatically flag artefacts in images. In this paper, we implement a Convolutional Neural Network to identify the most dominant artefacts in the images. We find that our model can successfully classify sources with 98 per cent true positive and 97 per cent true negative rates. Such models, combined with transfer learning, will give us a running start in artefact elimination for near-future surveys like WALOP
Optical polarisation variability of radio loud narrow line Seyfert 1 galaxies. Search for long rotations of the polarisation plane
Narrow line Seyfert 1 galaxies (NLSy1s) constitute the AGN subclass
associated with systematically smaller black hole masses. A few radio loud ones
have been detected in MeV -- GeV energy bands by Fermi and evidence for the
presence of blazar-like jets has been accumulated. In this study we wish to
quantify the temporal behaviour of the optical polarisation, fraction and
angle, for a selected sample of radio loud NLSy1s. We also search for rotations
of the polarisation plane similar to those commonly observed in blazars. We
have conducted R-band optical polarisation monitoring of a sample of 10 RL
NLSy1s 5 of which have been previously detected by Fermi. The dataset includes
observations with the RoboPol, KANATA, Perkins and Steward polarimeters. In the
cases where evidences for long rotations of the polarisation plane are found,
we carry out numerical simulations to assess the probability that they are
caused by intrinsically evolving EVPAs instead of observational noise. Even our
moderately sampled sources show indications of variability, both in
polarisation fraction and angle. For the four best sampled objects in our
sample we find multiple periods of significant polarisation angle variability.
In the two best sampled cases, namely J1505+0326 and J0324+3410, we find
indications for three long rotations. We show that although noise can induce
the observed behaviour, it is much more likely that the apparent rotation is
caused by intrinsic evolution of the EVPA. To our knowledge this is the very
first detection of such events in this class of sources. In the case of the
largest dataset (J0324+3410) we find that the EVPA concentrates around a
direction which is at 49.3\degr to the 15-GHz radio jet implying a projected
magnetic field at an angle of 40.7\degr to that axis.Comment: Accepted for publication in section 2. Astrophysical processes of
Astronomy and Astrophysic
Measurement of Lande g factor of 5D5/2 state of BaII with a single trapped ion
We present the first terrestrial measurement of the Lande g factor of the
5D5/2 state of singly ionized barium. Measurements were performed on single
Doppler-cooled 138Ba+ ions in a linear Paul trap. A frequency-stabilized fiber
laser with nominal wavelength 1.762 um was scanned across the 6S1/25D5/2
transition to spectroscopically resolve transitions between Zeeman sublevels of
the ground and excited states. From the relative positions of the four narrow
transitions observed at several different values for the applied magnetic
field, we find a value of 1.2020+/-0.0005 for g of 5D5/2.Comment: 3 figure
Coherent Excitation of the 6S1/2 to 5D3/2 Electric Quadrupole Transition in 138Ba+
The electric dipole-forbidden, quadrupole 6S1/2 5D3/2 transition in Ba+
near 2051 nm, with a natural linewidth of 13 mHz, is attractive for potential
observation of parity non-conservation, and also as a clock transition for a
barium ion optical frequency standard. This transition also offers a direct
means of populating the metastable 5D3/2 state to measure the nuclear magnetic
octupole moment in the odd barium isotopes. Light from a diode-pumped, solid
state Tm,Ho:YLF laser operating at 2051 nm is used to coherently drive this
transition between resolved Zeeman levels in a single trapped 138Ba+ ion. The
frequency of the laser is stabilized to a high finesse Fabry Perot cavity at
1025 nm after being frequency doubled. Rabi oscillations on this transition
indicate a laser-ion coherence time of 3 ms, most likely limited by ambient
magnetic field fluctuations.Comment: 5 pages, 5 figure
Hyperfine and Optical Barium Ion Qubits
State preparation, qubit rotation, and high fidelity readout are demonstrated
for two separate \baseven qubit types. First, an optical qubit on the narrow
6S to 5D transition at 1.76 m is implemented. Then,
leveraging the techniques developed there for readout, a ground state hyperfine
qubit using the magnetically insensitive transition at 8 GHz is accomplished
Temporal response to harmonic driving in electroconvection
The temporal evolution of the spatially periodic electroconvection (EC)
patterns has been studied within the period of the driving ac voltage by
monitoring the light intensity diffracted from the pattern. Measurements have
been carried out on a variety of nematic systems, including those with negative
dielectric and positive conductivity anisotropy, exhibiting "standard EC"
(s-EC), those with both anisotropies negative exhibiting "non-standard EC"
(ns-EC), as well as those with the two anisotropies positive. Theoretical
predictions have been confirmed for stationary s-EC and ns-EC patterns.
Transitions with Hopf bifurcation have also been studied. While traveling had
no effect on the temporal evolution of dielectric s-EC, traveling conductive
s-EC and ns-EC patterns exhibited a substantially altered temporal behavior
with a dependence on the Hopf frequency. It has also been shown that in
nematics with both anisotropies positive, the pattern develops and decays
within an interval much shorter than the period, even at relatively large
driving frequencies.Comment: 19 pages, 5 figure
Radio jet emission from GeV-emitting narrow-line Seyfert 1 galaxies
We studied the radio emission from four radio-loud and gamma-ray-loud
narrow-line Seyfert 1 galaxies. The goal was to investigate whether a
relativistic jet is operating at the source, and quantify its characteristics.
We relied on the most systematic monitoring of such system in the cm and mm
radio bands which is conducted with the Effelsberg 100 m and IRAM 30 m
telescopes and covers the longest time-baselines and the most radio frequencies
to date. We extract variability parameters and compute variability brightness
temperatures and Doppler factors. The jet powers were computed from the light
curves to estimate the energy output. The dynamics of radio spectral energy
distributions were examined to understand the mechanism causing the
variability. All the sources display intensive variability that occurs at a
pace faster than what is commonly seen in blazars. The flaring events show
intensive spectral evolution indicative of shock evolution. The brightness
temperatures and Doppler factors are moderate, implying a mildly relativistic
jet. The computed jet powers show very energetic flows. The radio polarisation
in one case clearly implies a quiescent jet underlying the recursive flaring
activity. Despite the generally lower flux densities, the sources appear to
show all typical characteristics seen in blazars that are powered by
relativistic jets.Comment: Accepted for publication in 4 - Extragalactic astronomy of Astronomy
and Astrophysic
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