Flow Equations and Normal Ordering

In this paper we consider flow-equations where we allow a normal ordering which is adjusted to the one-particle energy of the Hamiltonian. We show that this flow converges nearly always to the stable phase. Starting out from the symmetric Hamiltonian and symmetry-broken normal ordering nearly always yields symmetry breaking below the critical temperature.Comment: 7 page

Jets from X-ray Binaries to Active Galactic Nuclei

It is generally believed that active galactic nuclei (AGN) and black hole X-ray binaries (XRBs) have a similar central engine and that they could be described with a unified model. However, up to now such a model has not been fully established. In this thesis we present a symbiotic disk/jet model for both classes. Energy and mass conservation can be used to derive scaling laws for the emission of a jet. This allows us to identify the main parameters of the system: the mass of the central black hole and the accretion rate. We follow the idea that the spectral energy distributions (SEDs) of all weakly accreting black holes are probably jet dominated while highly accreting black holes are thermally dominated. Thus, the developedmodel can be used to argue for a unifying view of all weakly accreting black holes: a unification of XRBs and AGN. We classify the zoo of AGN in jet and disk dominated sources and test our unification schemeof weakly accreting sources by establishing a universal radio/X-ray correlation for XRBs and AGN. Our model is further tested by exploring the phenomenon of ultra-luminous X-ray sources (ULXs) which are bright off-nucleus X-ray point sources. If the central engine of XRBS and AGN is indeed similar, there should be a stellar analogue of a blazar (a blazar is an AGN with its relativistic jet pointing towards the observer). We show that these microblazars can indeed explain the known population of ULXs. As thedetection of a compact radio core at the positions of the ULX would strongly support this explanation, we have monitored a sample of ULXs to search for radio flares and continuous emission. We interpret the non-detections in the context of the universal radio/X-ray correlation. Finally we investigate if the complex timing behavior of accreting black holes is in agreement with ourjet model. The power law in the spectrum created by synchrotron emission originates mainly from one area in the jet. Thus, the power law in the SED can only vary in intensity and spectral index. Such a pivoting power law can be used to explain the Fourier time lags and other statistical properties of XRBs. Thus, our disk/jet model is in agreement with the observations and connects stellar mass XRBs to the supermassive AGN

Compact radio emission in Ultraluminous X-ray sources

We present results from our studies of radio emission from selected Ultraluminous X-ray (ULX) sources, using archival Giant Metrewave Radio Telescope (GMRT) data and new European VLBI Network (EVN) observations. The GMRT data are used to find possible faint radio emission from ULX sources located in late-type galaxies in the Chandra Deep Fields. No detections are found at 235, 325 and 610 MHz, and upper limits on the radio flux densities at these frequencies are given. The EVN observations target milliarcsecond-scale structures in three ULXs with known radio counterparts (N4449- X1, N4088-X1, and N4861-X2). We confirm an earlier identification of the ULX N4449-X1 with a supernova remnant and obtain the most accurate estimates of its size and age. We detect compact radio emission for the ULX N4088-X1, which could harbour an intermediate mass black hole (IMBH) of 10^5 M\odot accreting at a sub-Eddington rate. We detect a compact radio component in the ULX N4861-X2, with a brightness temperature > 10^6 K and an indication for possible extended emission. If the extended structure is confirmed, this ULX could be an HII region with a diameter of 8.6 pc and surface brightness temperature \geq 10^5 K. The compact radio emission may be coming from a ~ 10^5 M\odot black hole accreting at 0.1M_Edd.Comment: 5 pages, 6 figures. Accepted for publication in the Astronomische Nachrichte

More evidence for extinction of activity in galaxies

This Research Note amends an article in which we showed that radio-loud quasars can become radio-quiet. Exploring the analogy between galactic nuclei and X-ray binaries (XRB), we pointed out there that this transition in quasars could be identified with a switch from low/hard to high/soft state in microquasars. Here, we present the evidence that traces of past occurrences of this kind of phenomena can be found in normal but once active galaxies. Based on the properties of a few such "post-active" galaxies that are representative for a much wider group, it has been argued that they have reached the evolutionary stages when their nuclei, which were radio-loud in the past, now, mimicking the behaviour of XRBs, remain in the intermediate state on their way towards quiescence or even have already entered the quiescent state. It follows that the full evolutionary track of XRBs can be mapped onto the evolution of galaxies. The above findings are in line with those reported recently for IC 2497, a galaxy that 70,000 years ago or less hosted a quasar but now appears as a normal one. This scenario stems from the presence of Hanny's Voorwerp, a nebulous object in its vicinity excited by that QSO in the epoch when IC 2497 was active. The post-active galaxies we deal with here are accompanied by extremely weak and diffuse relic radio lobes that were inflated during their former active period. These relics can be regarded as radio analogues of Hanny's Voorwerp.Comment: 10 pages, 6 figures, A&A in pres

A high-reproducibility and high-accuracy method for automated topic classification

Much of human knowledge sits in large databases of unstructured text. Leveraging this knowledge requires algorithms that extract and record metadata on unstructured text documents. Assigning topics to documents will enable intelligent search, statistical characterization, and meaningful classification. Latent Dirichlet allocation (LDA) is the state-of-the-art in topic classification. Here, we perform a systematic theoretical and numerical analysis that demonstrates that current optimization techniques for LDA often yield results which are not accurate in inferring the most suitable model parameters. Adapting approaches for community detection in networks, we propose a new algorithm which displays high-reproducibility and high-accuracy, and also has high computational efficiency. We apply it to a large set of documents in the English Wikipedia and reveal its hierarchical structure. Our algorithm promises to make "big data" text analysis systems more reliable.Comment: 23 pages, 24 figure

1.4 GHz on the Fundamental Plane of Black Hole Activity

The fundamental plane of black hole activity is an empirical relationship between the OIII/X-ray luminosity depicting the accretion power, the radio luminosity as a probe of the instantaneous jet power and the mass of the black hole. For the first time, we use the 1.4 GHz FIRST radio luminosities on the optical fundamental plane, to investigate whether or not FIRST fluxes can trace nuclear activity. We use a SDSS-FIRST cross-correlated sample of 10149 active galaxies and analyse their positioning on the optical fundamental plane. We focus on various reasons that can cause the discrepancy between the observed FIRST radio fluxes and the theoretically expected core radio fluxes, and show that that FIRST fluxes are heavily contaminated by non-nuclear, extended components and other environmental factors. We show that the subsample of 'compact sources', which should have negligible lobe contribution, statistically follow the fundamental plane when corrected for relativistic beaming, while all the other sources lie above the plane. The sample of LINERs, which should have negligible lobe and beaming contribution, also follow the fundamental plane. A combined fit of the low-luminosity AGN and the X-ray binaries, with the LINERs, results in the relation log L$_R$ = 0.77 log L$_{OIII}$ + 0.69 log M. Assuming that the original fundamental plane relation is correct, we conclude that 1.4 GHz FIRST fluxes do not trace the pure 'core' jet and instantaneous nuclear activity in the AGN, and one needs to be careful while using it on the fundamental plane of black hole activity.Comment: 10 pages, 5 figures, accepted for publication by MNRA

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

Radio observations of NGC 6388: an upper limit on the mass of its central black hole

We present the results of deep radio observations with the Australia Telescope Compact Array (ATCA) of the globular cluster NGC 6388. We show that there is no radio source detected (with a r.m.s. noise level of 27 uJy) at the cluster centre of gravity or at the locations of the any of the Chandra X-ray sources in the cluster. Based on the fundamental plane of accreting black holes which is a relationship between X-ray luminosity, radio luminosity and black hole mass, we place an upper limit of 1500 M_sun on the mass of the putative intermediate-mass black hole located at the centre of NGC 6388. We discuss the uncertainties of this upper limit and the previously suggested black hole mass of 5700 M_sun based on surface density profile analysis.Comment: 6 pages, 2 figures, accepted for publication in MNRA

Statistics of Natural Movements Are Reflected in Motor Errors

Humans use their arms to engage in a wide variety of motor tasks during everyday life. However, little is known about the statistics of these natural arm movements. Studies of the sensory system have shown that the statistics of sensory inputs are key to determining sensory processing. We hypothesized that the statistics of natural everyday movements may, in a similar way, influence motor performance as measured in laboratory-based tasks. We developed a portable motion-tracking system that could be worn by subjects as they went about their daily routine outside of a laboratory setting. We found that the well-documented symmetry bias is reflected in the relative incidence of movements made during everyday tasks. Specifically, symmetric and antisymmetric movements are predominant at low frequencies, whereas only symmetric movements are predominant at high frequencies. Moreover, the statistics of natural movements, that is, their relative incidence, correlated with subjects' performance on a laboratory-based phase-tracking task. These results provide a link between natural movement statistics and motor performance and confirm that the symmetry bias documented in laboratory studies is a natural feature of human movement. </jats:p

Three episodes of jet activity in the FRII radio galaxy B0925+420

We present Very Large Array images of a "Double-Double Radio Galaxy", a class of objects in which two pairs of lobes are aligned either side of the nucleus. In this object, B0925+420, we discover a third pair of lobes, close to the core and again in alignment with the other lobes. This first-known "Triple-Double" object strongly increases the likelihood that these lobes represent mutiple episodes of jet activity, as opposed to knots in an underlying jet. We model the lobes in terms of their dynamical evolution. We find that the inner pair of lobes is consistent with the outer pair having been displaced buoyantly by the ambient medium. The middle pair of lobes is more problematic - to the extent where an alternative model interpreting the middle and inner "lobes" as additional bow shocks within the outer lobes may be more appropriate - and we discuss the implications of this on our understanding of the density of the ambient medium.Comment: Accepted for publication in MNRAS. Figure 2 is best viewed in colou