1,607 research outputs found
Signatures of restarted activity in core-dominated, triple radio sources selected from the FIRST survey
Signatures of the re-occurrence of activity in radio-loud AGNs, indicated
either by the so-called double-double or X-shaped structures, have been
observed in a number of radio sources. All such objects known to date have
linear sizes of the order of a megaparsec. A number of the sources that are
appreciably more compact than this, but that exhibit hints of a past phase of
activity, were found in the VLA FIRST survey. Their structures show symmetric
relic lobes straddling relatively bright, unresolved cores. Observations of the
cores of 15 such structures with MERLIN at 5 GHz have shown that four of them
are doubles or core-jets on the subarcsecond scale. Misalignments of \Delta PA
\ga 30 degr. between the axis of the inner structure and the line connecting
the fitted maxima of the arcminute-scale relic lobes are clearly visible in
three of the four sources. From these results, we can infer that a rapid
repositioning of the central engine in each of these three radio sources is the
most plausible interpretation of the observed morphology and that a merger is
most likely the original cause of such a repositioning. In the case of TXS
1033+026, the optical image extracted from the SDSS archives clearly suggests
that two objects separated by only 2.7 kpc (projected onto the sky plane) are
indeed merging. The inner parts of TXS 0818+214 and TXS 1312+563 could be
interpreted as double-lobed, and consequently, these sources could be of the
double-double type; but further multifrequency observations are necessary to
provide support for such an interpretation.Comment: 9 pages, 5 figures, matches the version printed in Astronomy &
Astrophysics, very minor correction of Table
A survey of Low Luminosity Compact sources and its implication for evolution of radio-loud AGNs. I. Radio data
We present a new sample of Compact Steep Spectrum (CSS) sources with radio
luminosity below 10^26 W/Hz at 1.4 GHz called the low luminosity compact (LLC)
objects. The sources have been selected from FIRST survey and observed with
MERLIN at L-band and C-band. The main criterion used for selection was
luminosity of the objects and approximately one third of the CSS sources from
the new sample have a value of radio luminosity comparable to FRIs. About 80%
of the sources have been resolved and about 30% of them have weak extended
emission and disturbed structures when compared with the observations of higher
luminosity CSS sources. We studied correlation between radio power and linear
size, and redshift with a larger sample that included also published samples of
compact objects and large scale FRIIs and FRIs. The low luminosity compact
objects occupy the space in radio power versus linear size diagram below the
main evolutionary path of radio objects. We suggest that many of them might be
short-lived objects, and their radio emission may be disrupted several times
before becoming FRIIs. We conclude that there exists a large population of
short-lived low luminosity compact objects unexplored so far and part of them
can be precursors of large scale FRIs.Comment: 19 pages, 5 figures, 3 tables, MNRAS in pres
RSFQ devices with selective dissipation for quantum information processing
We study the possibility to use frequency dependent damping in RSFQ circuits
as means to reduce dissipation and consequent decoherence in RSFQ/qubit
circuits. We show that stable RSFQ operation can be achieved by shunting the
Josephson junctions with an circuit instead of a plain resistor. We derive
criteria for the stability of such an arrangement, and discuss the effect on
decoherence and the optimisation issues. We also design a simple flux generator
aimed at manipulating flux qubits
Origin of the complex radio structure in BAL QSO 1045+352
We present new more sensitive high-resolution radio observations of a compact
broad absorption line (BAL) quasar, 1045+352, made with the EVN+MERLIN at 5
GHz. They allowed us to trace the connection between the arcsecond structure
and the radio core of the quasar. The radio morphology of 1045+352 is dominated
by a knotty jet showing several bends. We discuss possible scenarios that could
explain such a complex morphology: galaxy merger, accretion disk instability,
precession of the jet and jet-cloud interactions. It is possible that we are
witnessing an ongoing jet precession in this source due to internal
instabilities within the jet flow, however, a dense environment detected in the
submillimeter band and an outflowing material suggested by the X-ray absorption
could strongly interact with the jet. It is difficult to establish the
orientation between the jet axis and the observer in 1045+352 because of the
complex structure. Nevertheless taking into account the most recent inner radio
structure we conclude that the radio jet is oriented close to the line of sight
which can mean that the opening angle of the accretion disk wind can be large
in this source. We also suggest that there is no direct correlation between the
jet-observer orientation and the possibility of observing BALs.Comment: 8 pages, 3 figures, accepted for publication in Ap
Quantifying modeling uncertainties when combining multiple gravitational-wave detections from binary neutron star sources
With the increasing sensitivity of gravitational-wave detectors, we expect to observe multiple binary neutron-star systems through gravitational waves in the near future. The combined analysis of these gravitational-wave signals offers the possibility to constrain the neutron-star radius and the equation of state of dense nuclear matter with unprecedented accuracy. However, it is crucial to ensure that uncertainties inherent in the gravitational-wave models will not lead to systematic biases when information from multiple detections are combined. To quantify waveform systematics, we perform an extensive simulation campaign of binary neutron-star sources and analyse them with a set of four different waveform models. Based on our analysis with about 38 simulations, we find that statistical uncertainties in the neutron-star radius decrease to ( at credible interval) but that systematic differences between currently employed waveform models can be twice as large. Hence, it will be essential to ensure that systematic biases will not become dominant in inferences of the neutron-star equation of state when capitalizing on future developments
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