1,975 research outputs found
A Markov Chain Monte Carlo approach for measurement of jet precession in radio-loud active galactic nuclei
© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Jet precession can reveal the presence of binary systems of supermassive black holes. The ability to accurately measure the parameters of jet precession from radio-loud AGN is important for constraining the binary supermassive black hole population, which are expected as a result of hierarchical galaxy evolution. The age, morphology, and orientation along the line of sight of a given source often result in uncertainties regarding jet path. This paper presents a new approach for efficient determination of precession parameters using a 2D MCMC curve-fitting algorithm which provides us a full posterior probability distribution on the fitted parameters. Applying the method to Cygnus A, we find evidence for previous suggestions that the source is precessing. Interpreted in the context of binary black holes leads to a constraint of parsec scale and likely sub-parsec orbital separation for the putative supermassive binary.Peer reviewe
Surrender your market! Do the G5 countries use World Bank Trade Conditionality to promote Trade?
In this paper we investigate whether the design of World Bank conditionality, namely the extent of trade liberalization conditions, is influenced by the commercial motives of the Bank’s five major shareholders. Using a newly available dataset on World Bank conditionality we analyze the conditionality design of more than 870 projects over the 1981 – 2010 period. Our results suggest that countries of commercial interest for Germany have, on average, more trade liberalization conditions attached to their loans, indicating a trade promotion strategy. For the US, on the other hand, our results show that trading partners receive significantly fewer trade conditions. This suggests protection of the own bilateral trading relations from competition that would arise in the case of more open markets
3D Hydrodynamic Simulations of Large-Scale Precessing Jets : Radio Morphology
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society] ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. The final published version is available at: https://doi.org/10.1093/mnras/staa3020.The prospect of relativistic jets exhibiting complex morphologies as a consequence of geodetic precession has long been hypothesised. We have carried out a 3D hydrodynamics simulation study varying the precession cone angle, jet injection speed and number of turns per simulation time. Using proxies for the radio emission we project the sources with different inclinations to the line of sight to the observer. We find that a number of different precession combinations result in characteristic `X' shaped sources which are frequently observed in radio data, and some precessing jet morphologies may mimic the morphological signatures of restarting radio sources. We look at jets ranging in scale from tens to hundreds of kiloparsecs and develop tools for identifying known precession indicators of point symmetry, curvature and jet misalignment from the lobe axis and show that, based on our simulation sample of precessing and non-precessing jets, a radio source that displays any of these indicators has a 98% chance of being a precessing source.Peer reviewe
Activity Dependent Branching Ratios in Stocks, Solar X-ray Flux, and the Bak-Tang-Wiesenfeld Sandpile Model
We define an activity dependent branching ratio that allows comparison of
different time series . The branching ratio is defined as . The random variable is the value of the next signal given
that the previous one is equal to , so . If
, the process is on average supercritical when the signal is equal to
, while if , it is subcritical. For stock prices we find
within statistical uncertainty, for all , consistent with an ``efficient
market hypothesis''. For stock volumes, solar X-ray flux intensities, and the
Bak-Tang-Wiesenfeld (BTW) sandpile model, is supercritical for small
values of activity and subcritical for the largest ones, indicating a tendency
to return to a typical value. For stock volumes this tendency has an
approximate power law behavior. For solar X-ray flux and the BTW model, there
is a broad regime of activity where , which we interpret as an
indicator of critical behavior. This is true despite different underlying
probability distributions for , and for . For the BTW model the
distribution of is Gaussian, for sufficiently larger than one, and
its variance grows linearly with . Hence, the activity in the BTW model
obeys a central limit theorem when sampling over past histories. The broad
region of activity where is close to one disappears once bulk dissipation
is introduced in the BTW model -- supporting our hypothesis that it is an
indicator of criticality.Comment: 7 pages, 11 figure
New mechanisms for forming multiple hotspots in radio jets
Hotspots of radio galaxies are regions of shock-driven particle acceleration.
Multiple hotspots have long been identified as potential indicators of jet
movement or precession. Two frequent explanations describe a secondary hotspot
as either the location of a prior jet termination point, or a deflected
backflow-driven shock: the so-called Dentist's Drill and Splatter Spot models.
We created high-resolution simulations of precessing jets with a range of
parameters. In addition to the existing mechanisms, our results show three
additional mechanisms for multiple hotspot formation: (1) the splitting of a
large terminal hotspots into passive and active components; (2) jet stream
splitting resulting in two active hotspots; (3) dynamic multiple hotspot
complexes that form as a result of jet termination in a turbulent cocoon,
linked here to rapid precession. We show that these distinct types of multiple
hotspots are difficult to differentiate in synthetic radio maps, particularly
hotspot complexes which can easily be mistaken for the jet itself. We discuss
the implication for hypothesised binary supermassive black hole systems where
jet precession is a key component of the morphology, and show a selection of
potential precession candidates found using the LOFAR Two-Metre Sky Survey Data
Release 2 (LoTSS DR2).Comment: 14 pages, 10 figure
Spatial competition and price formation
We look at price formation in a retail setting, that is, companies set
prices, and consumers either accept prices or go someplace else. In contrast to
most other models in this context, we use a two-dimensional spatial structure
for information transmission, that is, consumers can only learn from nearest
neighbors. Many aspects of this can be understood in terms of generalized
evolutionary dynamics. In consequence, we first look at spatial competition and
cluster formation without price. This leads to establishement size
distributions, which we compare to reality. After some theoretical
considerations, which at least heuristically explain our simulation results, we
finally return to price formation, where we demonstrate that our simple model
with nearly no organized planning or rationality on the part of any of the
agents indeed leads to an economically plausible price.Comment: Minor change
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