Black Hole Variability 2010

International workshop for PhD students

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List of participants

Bachetti, Matteo
Other (ie Alien)
CESR

Belloni, Tomaso
Faculty
INAF/OAB
Low-Frequency Variability in X-Ray Binaries
I will review the major properties of fast time variability in the X-ray emission from X-ray binaries. In addition to kHz QPOs in NS LMXB, there is a whole wealth of observables at frequency below a few tens of Hz, which has been successfully tied both to the high-frequency features and to the multiwavelength properties. This variability takes the form of broad noise components and quasi-periodic oscillations. In addition, I will present the current observational status of high-frequency QPOs in black-hole binaries, one of the most elusive signals in X-ray astronomy and will examine the prospects for future instruments.
Casella, Piergiorgio
Post-doc
University of Southampton
Beyond X-ray timing: fast multi-wavelength variability from jets in X-ray binaries
The frontiers of high time resolution Astrophysics are rapidly expanding, moving from the traditional X-ray Astronomy to more and more wavelengths. The study of X-ray variability in X-ray binaries has represented - and still is - one of the most powerful tools to study the accretion flow in the vicinity of compact objects. During the last decade, the advent of new instrumentation has opened a new exciting window, allowing the study of multi-wavelength fast variable emission from X-ray binaries. In particular, newly available optical and infrared detectors with fast readout modes now allow us to detect fast-variable emission from relativistic jets. This field is at its dawn, but it is already showing its large potential. I will quickly review the state of the art, and describe how this type of data already allows us to put quantitative constraints to the properties of the jet and its connection with the accretion flow.
Chen, Tao
PhD student
SAp/CEA
Timing properties of the black hole candidate XTE J1752-223 during the initial hard state of its 2009-2010 outburst
We report the analysis of RXTE/PCA observations of the 2009-2010 outburst of the black hole candidate XTE J1752-223. We focus on the initial hard state of the source and present the timing analysis of the observations from October 28, 2009 to January 29, 2010. The power spectra of individual observations are well represented by two broad Lorentzians, with no obvious QPO. The width of both Lorentzians clearly evolves with time. However, while one of the two features has a rather steady power over the period of interest, the second one shows a clear decrease of its power with time. We also study the spectral evolution of the source over the same time. The source spectra are well represented by an absorbed power law, an Iron line and a reflection component. We discover a strong correlation of the power of one of the Lorentzian with the photon spectral index. This may suggest a link between the origin of the broad band variability and the material at the origin of the power law emission.
Chun, Yoon Young
PhD student
Sabanci Univ.

Curran, Peter
Post-doc
MSSL/UCL

De Marco, Barbara
Post-doc
University of Bologna - INAF/IASF

Dincer, Tolga
PhD student
Sabanci University

Done, Chris
Faculty
University of Durham
Spectra and variability properties of accretion flows
I will outline how the changes in spectra and power spectra can be understood in the truncated disc/hot inner flow model. I will give examples of how this works in both neutron stars and black hole binaries, and then talk about how to scale these models up to the supermassive black holes in AGN
Egron, Elise
PhD student
Università di Cagliari

Emmanoulopoulos, Dimitrios
Post-doc
University of Southampton
Probing quantum-gravity effects through blazar variability studies at very high energies
Einstein’s postulate that “Light always propagates through a vacuum at a definite velocity, c, which is independent of the state of motion of the emitting body” (Lorenz invariance).Although, in the framework of special relativity there is no fundamental length-scale associated with such an invariance, quantum effects at Planck scales are expected (not yet proven) to strongly affect the nature of space time causing deviations from this invariance. Such violations can be tested by measuring time-lags between very high energy photons emitted simultaneously from distant astrophysical sources, expressing possible variations of photon speed as a function of energy. Blazars are ideal sources for such studies due to their variability properties at VHE (up to few TeV). Cross-correlation analysis techniques can be used in order to set constraints on the energy scale of the speed of light.
Heil, Lucy
PhD student
University of Leicester
The RMS-Flux relation in Black hole X-ray Binaries
The X-ray timing properties of accreting compact objects provide an opportunity to study changes in the accretion flow and its properties very close to the accreting source. Among the more recent discoveries in this area is that of a simple linear scaling of rms variability amplitude and flux -- the power spectrum is shifted to higher amplitudes during periods of high flux such that the rms over a frequency band scales with flux. This effect has been seen in several AGN (Seyfert 1 galaxies), one Neutron star (NS) X-ray binary (SAX J1808.4-3658) and a few Galactic black hole X-ray binaries (BH XRBs), notably Cygnus X-1. The prevalence of this relation would seem to indicate it is common and basic property of accretion onto compact objects (or, at least, luminous black holes and NSs). This simple rms-flux relation explains and predicts several observational properties such as millisecond flares in XRBs, the lognormal distribution of fluxes, and prolonged periods of low flux in AGN. It also has important consequences for models of the variability process: the linearity of the rms-flux relation over a wide range of time scales rules out simple shot noise models (which rely on each shot being independent), but are naturally explained by models that involve fluctuations propagating through the accretion flow and modulating the flow (and hence fluctuations) produced at different radii. In order to test the ubiquity of the linear rms-flux relation, and its dependence on timescale, energy, source state, and so on we have analysed most of the data available in the RXTE archive for 9 BH XRBs (2077 observations), the majority of which showed a clear rms-flux relation. This is an indicator that a linear rms-flux relation is indeed a common property of BH XRBs. Most of the observations have been taken when the sources are in outburst, the relation has been observed in a range of different states and variability levels. We have compared the gradient (k) and the x-intercept (C) over the course of these outbursts and observe not only clear differences in these parameters dependent on spectral hardness, but also striking similarities between different sources. By taking the average of the rms and flux in each observation it is also possible to study the long term rms-flux relation, this long term relationship shows changes and distinct patterns relating to hardness over the course of the outburst. We will also discuss the energy and frequency dependence of this relation in individual observations. Finally, we will discuss an analysis of the rms-flux properties of an Ultra-Luminous X-ray source (ULX) and the ubiquity of the rms-flux relation in accreting black holes of all scales.
Hiemstra, Beike
PhD student
Kapteyn astronomical Institute
X-ray variability of GRO J1655-40 in the soft state
We present the results of the soft-state X-ray variability studies of the black hole transient GRO J1655-40. Opposite to the hard-state, the soft-state variability is not well-studied, and will therefore be a relevant contribution in the understanding of X-ray variability with respect to the accretion states. We study the soft-state QPOs and compare their characteristics with the different classes that are known for the hard state.
Ingram, Adam
PhD student
University of Durham
Low frequency QPOs: a precession model in the context of mass accretion rate fluctuations
Although it has been known for over 20 years, there is still no consensus in the literature as to the origin of the low frequency Quasi-Periodic Oscillations (QPOs) observed in the PSD of X-ray binaries. I describe a model that associates the QPO with Lense-Thirring precession of the hot inner flow and show how this process is effected by fluctuations in mass accretion rate. I then show that this model, in addition to producing the observed frequencies, predicts the observed shape, harmonic structure and evolution of the PSD.
Kalamkar, Maithili
PhD student
Astronomical Institute, University of Amsterdam, Netherlands
Aperiodic variability study of the accreting millisecond pulsar IGR J17511-3057
IGR J17511-3057 is one of the thirteen Accreting Millisecond Pulsars discovered so far. It is a very peculiar source as it appears to exhibit kHz QPOs while in the Extreme Island State. If the kHz QPOs are to be believed, the frequency difference between the kHz QPOs is inconsistent with being equal to spin frequency of 244.8 Hz which is the case for slow rotators. Instead, it is close to half the spin frequency, the case for fast rotators. The source plays a very important role in testing the existing models for the origin of QPOs. We will discuss the results of the aperiodic variability study of this source.
Kolehmainen, Mari
PhD student
Durham University

Maccarone, Tom
Faculty
University of Southampton
The bispectrum and other higher order statistics
I will present a discussion of the bispectrum, a higher moment of the Fourier spectrum, and the Fourier domain equivalent of the three-point correlation function. This statistic is of use for understanding the strength of non-linear variability components in a power spectrum. I will show some results for Cygnus X-1 and GRS 1915+105, which show coupling between variability components on different timescales, including coupling between "noise" and QPO components. I will also discuss some other statistical tests that go beyond the standard power spectrum.
McHardy, Ian
Faculty
University of Southampton
Black Hole Timing Unification
To complement earlier talks on X-ray binaries states, I will begin by discussing states, as defined by timing, to AGN and show how AGN also display the rms-flux relationship. I will discuss how characteristic timescales, which can be extracted from powerspectra, scale with mass and accretion rate for all accreting objects and discuss possible origins for this timescale. I will show how these timescales relate, perhaps somewhat puzzlingly, to properties of the optical broad line region in AGN. I will show how the same timing properties seem to apply to the relativistically beamed AGN as well as to the non-beamed Seyfert galaxies, implying a similar origin for the variations. If time permits, I will show how some of the disc perturbations seen in binaries might be apparent in the optical variability properties of AGN.
Mendez, Mariano
Faculty
University of Groningen
Heterodyning kilohertz quasi-periodic oscillations
Kilohertz quasi-periodic oscillations (kHz QPOs) are appealing because their high-frequencies (up to ~1200 Hz) suggest variability very close to a compact object. E.g., 1200 Hz is the orbital frequency 5 km above the surface of a 1.4 solar mass, 10-km neutron star. Because some kHz QPOs are very coherent, there are tricks one can play with them to try and enhance hidden signals in the data. I will show applications of a variation of a well-known technique used in electronics, heterodyning (we called this shift-and-add), both for power spectra and cross spectra.
Middleton, Matthew
Post-doc
University of Durham
Challenging times: a re-analysis of NGC5408 X-1
Quasi-periodic oscillations (QPOs) are frequently observed in galactic black holes (GBHs) and have now been observed in a high mass accretion rate AGN. These prominent features are seen to scale tentatively with mass allowing crude mass estimates to be made, assuming the analogous feature is correctly identified. This can be achieved by accurately determining the position of the feature relative to breaks in the power spectrum, by flux spectral analysis and by more involved temporal analysis such as lag, rms and covariance spectra. We present a re-analysis of two deep XMM-Newton observations of the ultraluminous X-ray source NGC 5408 X-1, that strongly suggests that the ~10 mHz signal may in fact be analogous to the Ultra Low Frequency QPOs seen in the most extreme GBHs. We discuss the consequences of this result for the presence of an intermediate-mass black hole in this source.
Munoz Darias, Teo
Post-doc
INAF/OAB
Beyond X-ray timing: using reprocessing to map the geometry of X-ray binaries
The advent of new instrumentation during the last decade has made possible to extend high time resolution studies to optical and infrared wavelenghts. Contemporarily, high-excitation emission lines have been used to constrain orbital parameters in active low mass X-ray binaries. They are the result of X-ray reprocessing in the different sites of the binary, particularly in the outer accretion disc and the inner hemisphere of the companion star. I will report on a novel technique, echo-tomography, which uses time-delays between correlated X-ray/optical fast variability (0.1-1s) to map the binary geometry in active low mass X-ray binaries. I will present the different optical instruments that allow us to perform high-time resolution observations, as well as the results we have obtained during the last few years in several observing campaings.
Reis, Rubens
PhD student
Institute of Astronomy

Sanna, Andrea
PhD student
University of Goningen, Kapteyn Astronomical Insitute
Study of the properties of kHz QPOs in the transient source XTE J1701-462
XTE J1701-462 is a unique transient neutron star LMXB, since it is the only system so far that went through Z and Atoll phases during an outburst. Interestingly, kilohertz quasi-periodic oscillations (kHz QPOs) have been detected in both phases making possible, for the first time, to test ideas that properties of kHz QPOs reflect either space-time structure around the NS or properties of the accretion flow. Here I present a detailed analysis of the kHz QPOs of J1701-462 in the Z and Atoll phase that shows that kHz QPOs features are influenced more by the properties of the accretion flow than by the geometry of the space-time close to the compact object.
Soleri, Paolo
Post-doc
Kapteyn Astronomical Institute, University of Groningen
Disentangling the complicated phenomenology of the neutron star X-ray binary Cir X-1
Cir X-1 is a peculiar neutron star X-ray binary. The source follows complicated patters in an X-ray hardness-intensity diagram and features distinctive and rapidly variable power density spectra (PDS). The complexity of its variability prevented a clear understanding of the system for many years. Although the presence of a neutron star in the binary has been ascertained with the detection of type-I X-ray bursts and of kHz quasi-periodic oscillations (QPOs) in the PDS, its phenomenology is still puzzling and unique when compared to other neutron star systems. In fact, its classification as either a "Z'' or an "atoll" source (neutron stars accreting at near-Eddington or relatively low rates, respectively) is still a matter of debate. Here I present the results of X-ray observations of Cir X-1 performed with the Rossi X-ray timing explorer satellite in October 2000 and December 2002. I identified typical Z source behaviour in the power density spectra as well as characteristic Z patterns drawn in an X-ray hardness-intensity diagram. Power spectra typical of bright atoll sources have also been identified at orbital phases after the periastron passage, while orbital phases before the periastron passage are characterized by power spectra that are typical neither of Z nor of atoll sources. I will describe the analysis that I carried out, focussing on the techniques that I used to disentangle the complicated phenomenology of this source.
Stiele, Holger
Post-doc
INAF Brera

Uttley, Phil
Faculty
University of Southampton
X-ray spectral-timing: methods and interpretation
Fourier spectral-timing techniques can show how the variations at different energies are related, in terms of their amplitudes, correlations and time-delays between the variations in each band. I will discuss these techniques, show how they can be applied, and give some tips as to how the signal-to-noise in the outputs can be optimised over what is normally obtained. I will also show how we can interpret these results with a few real examples, focussing on the evidence for intrinsic disc variability and X-ray reverberation in accreting black hole systems.
Vaughan, Simon
Faculty
University of Leicester
Black hole variability from limited data
I will discuss power spectrum estimation via the periodogram. Although this is among the oldest and most widely-used of time series tools, it requires considerable care and attention to avoid being misled by periodogram data. I will discuss several of these issues, and in particular discuss power spectrum estimation from limited data of the kind one might obtain from AGN and ULXs, and long-timescale series of XRBs. I will give some attention to the problem of identifying (or testing for) periodicities in short, noisy time series. I will then discuss methods for simulating 'realistic' time series data - essentially the inverse of the above problem - and how these can be put to good use in data analysis. In the last part of the talk I will introduce some aspects of the analysis of time series from non-linear processes, and how one may include non-linearities in time series simulation.
Walton, Dom
PhD student
Institute of Astronomy, Cambridge

Wilkinson, Tony
PhD student
University of Southampton

Zoghbi, Abderahmen
PhD student
Intitute of Astronomy, Cambridge
Modelling soft lags in AGN
Recent XMM-Newton observations of the NLS1 1H0707 has shown a significant soft lag between 0.3-1 and 1-4 keV. This is the first reverberation from the inner few gravitational radii of the black hole. Most of the radiation originate within few gravitational radii of the black hole. Detailed modeling of the lag and broad iron K line emission in this extreme object is enabling us to map the geometry of the accretion system very close to the event horizon where light bending effects are at work.