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

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

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

a global study of x ray binaries

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Radio jets from stellar tidal disruptions

A star that passes too close to a massive black hole will be torn apart by tidal forces. The flare of photons emitted during the accretion of the stellar debris is predicted to be observable and candidates of such events have been observed at optical to X-ray frequencies. If a fraction of the accreted material is fed into a jet, tidal flares should be detectable at radio frequencies too, thus comprising a new class of rare radio transients. Using the well-established scaling between accretion power and jet luminosity and basic synchrotron theory, we construct an empirically-rooted model to predict the jet luminosity for a time-dependent accretion rate. We apply this model to stellar tidal disruptions and predict the snapshot rate of these events. For a small angle between the observer and the jet, our model reproduces the observed radio flux of the tidal flare candidate GRB 110328A. We find that future radio surveys will be able to test whether the majority of tidal disruptions are accompanied by a jet.Comment: Accepted for publication in MNRAS letter

Radio spectra of bright compact sources at z>4.5

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.High-redshift quasars are important to study galaxy and active galactic nuclei (AGN) evolution, test cosmological models, and study supermassive black hole growth. Optical searches for high-redshift sources have been very successful, but radio searches are not hampered by dust obscuration and should be more effective at finding sources at even higher redshifts. Identifying high-redshift sources based on radio data is, however, not trivial. Here we report on new multi-frequency Giant Metrewave Radio Telescope (GMRT) observations of eight z>4.5 sources previously studied at high angular resolution with very long baseline interferometry (VLBI). Combining these observations with those from the literature, we construct broad-band radio spectra of all 30 z>4.5 sources that have been observed with VLBI. In the sample we found flat, steep and peaked spectra in approximately equal proportions. Despite several selection effects, we conclude that the z>4.5 VLBI (and likely also non-VLBI) sources have diverse spectra and that only about a quarter of the sources in the sample have flat spectra. Previously, the majority of high-redshift radio sources were identified based on their ultra-steep spectra (USS). Recently a new method has been proposed to identify these objects based on their megahertz-peaked spectra (MPS). Neither method would have identified more than 18% of the high-redshift sources in this sample. More effective methods are necessary to reliably identify complete samples of high-redshift sources based on radio data.Peer reviewedFinal Published versio

Using the Fundamental Plane of Black Hole Activity to Distinguish X-ray Processes from Weakly Accreting Black Holes

The fundamental plane of black hole activity is a relation between X-ray luminosity, radio luminosity, and black hole mass for hard state Galactic black holes and their supermassive analogs. The fundamental plane suggests that, at low-accretion rates, the physical processes regulating the conversion of an accretion flow into radiative energy could be universal across the entire black hole mass scale. However, there is still a need to further refine the fundamental plane in order to better discern the radiative processes and their geometry very close to the black hole, in particular the source of hard X-rays. Further refinement is necessary because error bars on the best-fit slopes of the fundamental plane are generally large, and also the inferred coefficients can be sensitive to the adopted sample of black holes. In this work, we regress the fundamental plane with a Bayesian technique. Our approach shows that sub-Eddington black holes emit X-ray emission that is predominantly optically thin synchrotron radiation from the jet, provided that their radio spectra are flat or inverted. X-ray emission dominated by very radiatively inefficient accretion flows are excluded at the >3\sigma\ level. We also show that it is difficult to place FR I galaxies onto the fundamental plane because their X-ray jet emission is highly affected by synchrotron cooling. On the other hand, BL Lac objects fit onto the fundamental plane. Including a uniform subset of high-energy peaked BL Lac objects from the SDSS, we find sub-Eddington black holes with flat/inverted radio spectra follow log L_x=(1.45\pm0.04)log L_R-(0.88\pm0.06)\logM_{BH}-6.07\pm1.10, with \sigma_{int}=0.07\pm0.05 dex. Finally, we discuss how the effects of synchrotron cooling of jet emission from the highest black hole masses can bias fundamental plane regressions, perhaps leading to incorrect inferences on X-ray radiation mechanisms.Comment: 23 pages, 8 figures, 3 tables. Accepted for publication in MNRA

What are the megahertz peaked-spectrum sources?

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record [MNRAS (July 1, 2016) 459: 2455-2471. First published online April 7, 2016] is available online at: doi: 10.1093/mnras/stw799Megahertz peaked-spectrum (MPS) sources have spectra that peak at frequencies below 1 GHz in the observer's frame and are believed to be radio-loud active galactic nuclei (AGN). We recently presented a new method to search for high-redshift AGN by identifying unusually compact MPS sources. In this paper, we present European VLBI Network (EVN) observations of 11 MPS sources which we use to determine their sizes and investigate the nature of the sources with ~10 mas resolution. Of the 11 sources, we detect nine with the EVN. Combining the EVN observations with spectral and redshift information, we show that the detected sources are all AGN with linear sizes smaller than 1.1 kpc and are likely young. This shows that low-frequency colour-colour diagrams are an easy and efficient way of selecting small AGN and explains our high detection fraction (82%) in comparison to comparable surveys. Finally we argue that the detected sources are all likely compact symmetric objects and that none of the sources are blazars.Peer reviewe

Dwarf nova-type cataclysmic variable stars are significant radio emitters

We present 8–12 GHz radio light curves of five dwarf nova (DN) type cataclysmic variable stars (CVs) in outburst (RX And, U Gem, and Z Cam), or superoutburst (SU UMa and YZ Cnc), increasing the number of radio-detected DN by a factor of 2. The observed radio emission was variable on time-scales of minutes to days, and we argue that it is likely to be synchrotron emission. This sample shows no correlation between the radio luminosity and optical luminosity, orbital period, CV class, or outburst type; however, higher cadence observations are necessary to test this, as the measured luminosity is dependent on the timing of the observations in these variable objects. The observations show that the previously detected radio emission from SS Cyg is not unique in type, luminosity (in the plateau phase of the outburst), or variability time-scales. Our results prove that DN, as a class, are radio emitters in outburst

Short Timescale Evolution of the Polarized Radio Jet during V404 Cygni's 2015 Outburst

We present a high time resolution, multi-frequency linear polarization analysis of Very Large Array (VLA) radio observations during some of the brightest radio flaring (~1 Jy) activity of the 2015 outburst of V404 Cygni. The VLA simultaneously captured the radio evolution in two bands (each with two 1 GHz base-bands), recorded at 5/7 GHz and 21/26 GHz, allowing for a broadband polarimetric analysis. Given the source's high flux densities, we were able to measure polarization on timescales of ~13 minutes, constituting one of the highest temporal resolution radio polarimetric studies of a black hole X-ray binary (BHXB) outburst to date. Across all base-bands, we detect variable, weakly linearly polarized emission (<1%) with a single, bright peak in the time-resolved polarization fraction, consistent with an origin in an evolving, dynamic jet component. We applied two independent polarimetric methods to extract the intrinsic electric vector position angles and rotation measures from the 5 and 7 GHz base-band data and detected a variable intrinsic polarization angle, indicative of a rapidly evolving local environment or a complex magnetic field geometry. Comparisons to the simultaneous, spatially-resolved observations taken with the Very Long Baseline Array at 15.6 GHz, do not show a significant connection between the jet ejections and the polarization state.Comment: 24 pages, 9 figures, accepted by MNRA