3,833 research outputs found
Assessing luminosity correlations via cluster analysis: Evidence for dual tracks in the radio/X-ray domain of black hole X-ray binaries
[abridged] The radio:X-ray correlation for hard and quiescent state black
hole X-ray binaries is critically investigated in this paper. New observations
of known sources, along with newly discovered ones, have resulted in an
increasingly large number of outliers lying well outside the scatter about the
quoted best-fit relation. Here, we employ and compare state of the art data
clustering techniques in order to identify and characterize different data
groupings within the radio:X-ray luminosity plane for 18 hard and quiescent
state black hole X-ray binaries with nearly simultaneous multi-wavelength
coverage. Linear regression is then carried out on the clustered data to infer
the parameters of a relationship of the form {ell}_{r}=alpha+beta {ell}_x
through a Bayesian approach (where {ell} denotes log lum). We conclude that the
two cluster model, with independent linear fits, is a significant improvement
over fitting all points as a single cluster. While the upper track slope
(0.63\pm0.03) is consistent, within the errors, with the fitted slope for the
2003 relation (0.7\pm0.1), the lower track slope (0.98\pm0.08) is not
consistent with the upper track, nor it is with the widely adopted value of
~1.4 for the neutron stars. The two luminosity tracks do not reflect systematic
differences in black hole spins as estimated either from reflection, or
continuum fitting method. These results are insensitive to the selection of
sub-samples, accuracy in the distances, and to the treatment of upper limits.
Besides introducing a further level of complexity in understanding the
interplay between synchrotron and Comptonised emission from black hole X-ray
binaries, the existence of two tracks in the radio:X-ray domain underscores
that a high level of caution must be exercised when employing black hole
luminosity relations for the purpose of estimating a third parameter, such as
distance or mass.Comment: MNRAS, in press (10 pages, 7 figures
No evidence for black hole spin powering of jets in X-ray binaries
In this paper we take the reported measurements of black hole spin for black
hole X-ray binaries, and compare them against measurements of jet power and
speed across all accretion states in these systems. We find no evidence for any
correlation between the properties of the jets and the reported spin
measurements. These constraints are strongest in the hard X-ray state, which is
associated with a continuous powerful jet. We are led to conclude that one or
more of the following is correct: (i) the calculated jet power and speed
measurements are wrong, (ii) the reported spin measurements are wrong, (iii)
there is no strong dependence of the jet properties on black hole spin. In
addition to this lack of observational evidence for a relation between black
hole spin and jet properties in stellar mass black holes, we highlight the fact
that there appear to be at least three different ways in which the jet power
and/or radiative efficiency from a black hole X-ray binary may vary, two of
which are certainly independent of spin because they occur in the same source
on relatively short timescales, and the third which does not correlate with any
reported measurements of black hole spin. We briefly discuss how these findings
may impact upon interpretations of populations of active galactic nuclei in the
context of black hole spin and merger history.Comment: Accepted for publication in MNRA
The declining representativeness of the British party system, and why it matters
In a recent article, Michael Laver has explained âWhy Vote-Seeking Parties May Make Voters Miserableâ. His model shows that, while ideological convergence may boost congruence between governments and the median voter, it can reduce congruence between the party system and the electorate as a whole. Specifically, convergence can increase the mean distance between voters and their nearest party. In this article we show that this captures the reality of todayâs British party system. Policy scale placements in British Election Studies from 1987 to 2010 confirm that the pronounced convergence during the past decade has left the Conservatives and Labour closer together than would be optimal in terms of minimising the policy distance between the average voter and the nearest major party. We go on to demonstrate that this comes at a cost. Respondents who perceive themselves as further away from one of the major parties in the system tend to score lower on satisfaction with democracy. In short, vote-seeking parties have left the British party system less representative of the ideological diversity in the electorate, and thus made at least some British voters miserable
The first accurate parallax distance to a black hole
Using astrometric VLBI observations, we have determined the parallax of the
black hole X-ray binary V404 Cyg to be 0.418 +/- 0.024 milliarcseconds,
corresponding to a distance of 2.39 +/- 0.14 kpc, significantly lower than the
previously accepted value. This model-independent estimate is the most accurate
distance to a Galactic stellar-mass black hole measured to date. With this new
distance, we confirm that the source was not super-Eddington during its 1989
outburst. The fitted distance and proper motion imply that the black hole in
this system likely formed in a supernova, with the peculiar velocity being
consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred
to exist in this system is less than 1.4 AU at 22 GHz. Astrometric observations
of a larger sample of such systems would provide useful insights into the
formation and properties of accreting stellar-mass black holes.Comment: Accepted for publication in ApJ Letters. 6 pages, 2 figure
The MeV spectral tail in Cyg X-1 and optically-thin emission of jets
We study the average X-ray and soft gamma-ray spectrum of Cyg X-1 in the hard
spectral state, using data from INTEGRAL. We compare these results with those
from CGRO, and find a good agreement. Confirming previous studies, we find the
presence of a high-energy MeV tail beyond a thermal-Comptonization spectrum;
however, the tail is much softer and weaker than that recently published by
Laurent et al. In spite of this difference, the observed high-energy tail could
still be due to the synchrotron emission of the jet of Cyg X-1, as claimed by
Laurent et al.
To test this possibility, we study optically-thin synchrotron and
self-Compton emission from partially self-absorbed jets. We develop formalisms
for calculating both emission of the jet base (which we define here as the
region where the jet starts its emission) and emission of the entire jet. We
require the emission to match that observed at the turnover energy. The
optically thin emission is dominated by that from the jet base, and it has to
become self-absorbed within it at the turnover frequency. We find this implies
the magnetic field strength at the jet base of B_0 prop. to z_0^4, where z_0 is
the distance of the base from the black-hole centre. The value of B_0 is then
constrained from below by the condition that the self-Compton emission is below
an upper limit in the GeV range, and from above by the condition that the
Poynting flux does not exceed the jet kinetic power. This yields B_0 of the
order of ~10^4 G and the location of the jet base at ~10^3 gravitational radii.
Using our formalism, we find the MeV tail can be due to jet synchrotron
emission, but this requires the electron acceleration at a rather hard
power-law index, p~1.3-1.6. For acceleration indices of p> 2, the amplitude of
the synchrotron component is much below that of MeV tail, and its origin is
likely to be due to hybrid Comptonization in the accretion flow.Comment: MNRAS, in press, 13 page
Distribution patterns of three sodium channel mutations associated with pyrethroid resistance in Rhipicephalus (Boophilus) microplus populations from North and South America, South Africa and Australia
AbstractResistance to synthetic pyrethroids (SP) in the cattle tick Rhipicephalus (Boophilus) microplus is widespread throughout its distribution area. Three single nucleotide substitutions identified in Domains II and III of the sodium channel gene of R. (B.) microplus are known to be associated with target site pyrethroid resistance. We developed a multiplex PCR using allele-specific primers to amplify wild type or mutated genotypes of the three mutations simultaneously. This assay was used to screen tick samples originating from Brazil, Argentina, Mexico, South Africa and Australia whose phenotype to flumethrin and cypermethrin had been determined by the use of the Larval Tarsal test (LTT) or the Larval Packet Test (LPT). These mutations were found to have distinct geographical distributions and result in different resistance phenotypes. The L64I Domain II mutation conferring resistance to several SP compounds was found in all the Brazilian, Argentinean and Australian populations and in one South African population, with frequencies between 38% and 100% in flumethrin and cypermethrin resistant populations. In contrast, this mutation was not found in samples from Mexico, while the Domain III mutation was found exclusively in this country. The G72V Domain II flumethrin-specific mutation was found in a single Australian population, with a very low resistant allele frequency (3%). The homozygous resistant RR genotype of the L64I Domain II mutation correlated significantly with the survival rates at the discriminating doses of flumethrin and cypermethrin. This survey shows the widespread distribution of the L64I Domain II mutation and provides evidence of its geographic separation from the Domain III mutation
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