Accretion flow instabilities:

Registered participants

1. Abolmasov, Pavel: "Microlensing evidence for supercritical accretion in quasars" - P. Abolmasov and N. I. Shakura [poster] Show abstract
   Microlensing by the stellar population of lensing galaxies provides an important opportunity to spatially resolve the accretion disks in strongly lensed quasars. Disk sizes estimated this way are generally larger than the standard Shakura-Sunyaev accretion disk model predicts. Analysing the observational data on microlensing variability allows to suggest that some fraction of lensed quasars (primarilly, smaller-mass objects) are accreting in super-Eddington regime. Super-Eddington accretion manifests itself in formation of an optically-thick envelope scattering the radiation formed in the disk. This makes the apparent disk size larger and practically independent on wavelength. In the framework of our model, it is possible to make self-consistent estimates of mass accretion rates and black hole masses for the cases when both de-amplified fluxes and radii are available.
2. Abramowicz, Marek
3. Antonyuk, Oksana: "Peculiarity of the outburst activity of the SU UMa dwarf novae V 1504 Cyg and NY Ser over several supercycles" [poster] Show abstract
   We present the result of long-term study of SU UMa dwarf novae V 1504 Cyg and NY Ser in 2000-2009 yrs based on the CCD photometry carried out in the Crimean Astrophysical Observatory and on the available Kepler data. The peculiarity of the supercycles and cycles variations, differences among normal outbursts, "magnitude-color" diagrams of normal outbursts and appearing of positive superhums at normal outbursts are considered.
4. Bagińska, Patrycja: "Testing accretion disc instabilities in X-ray binaries" [poster] Show abstract
   We study RXTE observations of the sample of black hole binaries, which possess X-ray novae outbursts in their light curves. Typically, one outburst occurs in collected light curves, with total duration from 30 up to 400 days. The shape of outburst can be very regular fast rise and exponential decay (FRED) characteristic for ionization disc instability, or irregular suggesting that, beside FRED, additional flickering occurs. We compare observed time scales with those obtained from model computations done by Janiuk et al. 2002. The model calculates time dependent evolution of ionization instability in an accretion disk around black hole, assuming simple viscosity parametrization. By comparing data to model we want to exam if observed outburst are really caused by ionization disk instability in selected objects.
5. Balman, Solen: "X-ray Observations of Dwarf Novae in quiescence and outburst" Show abstract
   Diversity of the X-ray observations of dwarf nova are still not fully understood. I will review the X-ray spectral characteristics of dwarf novae during the quiescence which in general explained by cooling flow models. The outburst spectra show dichotomy as in SWIFT observations of GW Lib and RXTE observations of SS Cyg or WW Cet or SU Uma. These different behaviour will be discussed in the light of DIM and the characteristics of the aperiodic variability in dwarf novae systems. I will also review nature of aperiodic time variability of brightness of dwarf novae. I show that lightcurves (chosen from XMM-Newton data) of dwarf novae systems in UV and X-ray energy bands demonstrate band limited noise, which can be described in the framework of the model of propagating fluctuations. The frequency of the break indicates inner disk truncation with a range of radii (10-3)e+9 cm. I will demonstrate that the RXTE and optical (RTT150) data of SS Cyg in outburst and quiescence reveal that the inner disk radius moves towards the white dwarf and receeds as the outburst declines to quiescence. Cross-correlations between the simultaneous UV and X-ray light curves find time lags in the X-rays of 96-181 sec consistent with travel time of matter from a truncated inner disc to the white dwarf surface. This suggests that dwarf noave and other plausible nonmagnetic systems have truncated accretion discs indicating that the disks may be partially evaporated and the accretion may occur through coronal flows in the disk.
6. Barret, Didier: "Future X-ray observatories in the European context" Show abstract
   I will present the LOFT and ATHENA X-ray observatories that are being considered for implementation in the science program of the European Space Agency, focussing on their capabilities to study accretion disk physics.
7. Bąkowska, Karolina: "November 2010 superoutburst of HT Cas" [poster] Show abstract
   TBD
8. Blaes, Omer: "MRI Simulations and the Thermal-Viscous Instability" Show abstract
   TBD
9. Cannizzo, John: "The Thermal-Viscous Limit Cycle Model in Dwarf Novae" Show abstract
   I present a historical overview of the model, from its inception to the present. I discuss the development of different aspects of the model, and connections with observation. I end with results from Kepler of several short period dwarf novae which now have amassed > 2 yrs of data, and discuss the implications of these high fidelity data for the limit cycle model.
10. Chashkina, Anna: "Black hole spin evolution in different accretion regimes" [poster] Show abstract
    It is shown that while standard disk accretion has the potential of spinning a black hole up to a ~1, radiatively inefficient regimes produce slower rotators. This may account for the small spin parameters of quiet supermassive black holes and the accretors in X-ray novae.
11. Ciesielski, Adam
12. Czerny, Bożena
13. Godet, Olivier: "Constraining the accretion flow evolution around the best intermediate mass black hole candidate HLX-1 in the galaxy ESO 243-49" Show abstract
    Ultra Luminous X-ray sources (ULXs) are off-nuclear sources with X-ray luminosities greater than 3x1039 erg/s. Their nature is still highly debated. Possible explanations invoke sub-Eddington accretion around an intermediate mass black hole (IMBH) or super-Eddington or critical accretion around a stellar mass BH. Even if most ULXs are unlike ly to be IMBH, the most luminous ULXs are still promising IMBH candidates. In this talk, I will focus on the most luminous ULX detected so far and the best IMBH candidate, HLX-1, in the galaxy ESO 243-49. After a brief overview on t he unique properties of HLX-1, I will discuss the spectral constraints on both the evolution of the accretion flow and the BH mass we derived using physically-motivated accretion disk models and multi-epoch and multi-instrument X- ray spectra. Finally, I will discuss these results along with other observational constraints on the nature of the source.
14. Hameury, Jean-Marie
15. Hryniewicz, Krzysztof: "Accretion disk in a weak emission lines quasar" [poster] Show abstract
    Weak emission lines quasars are quasars which are radio-quiet and X-ray weak AGN. They spectrum has normal accretion disk-like continuum but weak emission lines. To resolve puzzle of one of its kind we have fitted accretion disk continuum and its emission lines and have done photoionization simulations. We show that values of physical parameters of line emitting gas are similar to those of accretion disk atmosphere. We conclude that this object maybe representative of a quasar in phase of developing broad line region.
16. Jamrozy, Marek: "Recurrent activity in extragalactic radio sources" Show abstract
    One of the most interesting issues in our understanding of active galactic nuclei (AGNs) is the duration of their active phase and whether such activity is episodic. The morphology and spectra of extended radio emission from radio galaxies contain information on the history of their central AGN. They thus provide a unique opportunity to study the time scales of the AGN's duty cycles. The most striking examples of AGNs with recurrent jet activity are the double-double radio sources which contain two or more pairs of lobes. In this presentation I show some recent examples and summarize results on recurrent activity in radio galaxies.
17. Janiuk, Agnieszka: "Radiation pressure instability in the accreting black hole systems" Show abstract
    There has been a long standing concern regarding the standard accretion disk model, that the disk is both thermally and viscously unstable when radiation pressure is dominant (Lightman & Eardley 1974). This occurs in the inner regions of the disk around a ten solar mass black hole, when its luminosity exceeds ≥3×10³⁷ ergs/s. X-ray binaries can typically exceed this luminosity which is substantially smaller than than the Eddington limit of ≈10³⁹ergs/s. For AGNs, harboring 10⁷M_☉ black holes, the disk should be unstable for luminosities exceeding  ≥5×10⁴³ ergs/s significantly less than the Eddington limit of ≈10⁴⁵ergs/s. Thus, for typical black hole binaries and AGNs, the standard accretion disk is unstable. However, in the soft state, where the luminosity could be even higher than the hard one, there is a soft thermal-like emission indicating that the standard disk somehow survives the instability. Moreover, time-dependent numerical evolution of the unstable disk, shows that instead of the disk getting transformed to a hot one, it undergoes cyclic behavior, which result in large amplitude oscillations in luminosity.These large variations in luminosity have sometimes been observed, however only in very few sources. I will review the observational support for the radiation pressure driven cyclic behaviour of the accreting sources, as well as the theoretically discussed methods that are used to stabilize the disks at high accretion rates.
18. Katysheva, Natalia: "PR Her - a new cataclysmic variable of a WZ Sge-type" [poster] - S.Yu. Shugarov, N.A. Katysheva Show abstract
    We present multicolor CCD photometry during superoutburst of a new cataclysmic variable PR Herculis, bursted on November 22, 2011, and was classified as a new WZ Sge-type system. The analysis of our data revealed the presence of early and ordinary superhumps with the period close to 0.055 d. The common light curve of superoutburst was constructed and the duration of superoutburst was estimated. The evolution of superhumps profiles, its amplitude and the superhump period, connected with the changes in accretion disc around the white dwarf, is analysed. Two-colour diagrams together with the superoutburst evolutionary tracks of PR Her are presented.
19. King, Andrew: "Disc instability in soft X-ray transients" Show abstract
    TBD
20. Kluźniak, Włodzimierz "Thermal stability of accretion disks with delayed heating" Show abstract
    MHD simulations of Hirose et al 2009 suggest that radiation-pressure dominated disks may be stable against thermal perturbations. The question of thermal stability of alpha disks is revisited under the assumption of a time offset between fluctuations in torque and in heating. Under certain conditions, as found by Ciesielski, Wielgus et al. 2012, and others, a delay in heating may stabilise the accretion disk.
21. Knigge, Christian: "Disc stability vs. close binary evolution" Show abstract
    TBD
22. Kotko, Iwona
23. Krzemiński, Wojciech
24. Kunert-Bajraszewska, Magdalena "Intermittent activity of radio-loud BAL quasar 1045+352" Show abstract
    The radio morphology of compact steep spectrum (CSS) broad absorption line (BAL) quasar 1045+352 is dominated by the strong radio jet resolved into many sub-components and changing the orientation during propagation in the central regions of the host galaxy. We discuss possible scenarios explaining such complex morphology: galaxy merger, accretion disc instability, precession of the jet and jet-cloud interactions. It is possible that we are whitnessing in this source an ongoing jet precession due to internal instabilities within the jet flow, however, a dense environment detected in the submillimeter band and an outflowing material suggested by the X-ray absorption can strongly interact with the jet.
25. Lasota-Hirszowicz, Jean-Pierre
26. Malanchev, Konstantin: "Non-stationary disk accretion in Soft X-ray transients" - K. Malanchev, A. Meshcheryakov, N. Shakura. Show abstract
    In this work light curves of soft X-ray transients are studied. We assume that on the first stage of disk accretion all the hydrogen is ionized and the disk size is constant. The zone of partically ionized hydrogen appears on the outer edge of the disk 30÷70 days after X-ray maximum. Convection, appeared in this zone, increases viscosity parameter and accretion rate. In this case secondary peak appears on the light curve. On the next stage of accretion the edge between neutral hydrogen and completely ionized hydrogen moves to the inner edge of the disk. Fitting both X-ray and optical light curves of X-ray transient one could determine a coupe of parameters of this object: alpha parameter value before and after the secondary peak, mass of black hole and its Kerr parameter.
27. Mazur, Grzegorz
28. Meyer, Friedrich
29. Meyer-Hoffmeister, Emmi
30. Mikołajewska, Joanna
31. Nikolajuk, Marek: "Low covering factor of the BLR in weak emission-line quasars" - M. Nikolajuk and R. Walter Show abstract
    We probe the nature of weak emission-line quasars (WLQs) by comparing the Baldwin effect (BEff) in WLQs and normal quasars (QSOs). 83 high- and intermediate-redshift (z > 1.66) WLQs were selected from SDSS and Chandra observations. We compare the parameters of WLQs with these of ~230 normal quasars observed by BQS, SDSS and Chandra. We analyse the influence of the Eddington ratio, and the X-ray to optical luminosity ratio on the BEff. The weakness or even absence of emission-lines in WLQs does not seem to be caused by their extremely soft ionising continuum but by low covering factor of their broad line region (BLR). The ratios of the covering factors of high-ionisation line and low-ionisation line are lover. It shows the deficit of the BLR in WLQ. If the reactivation scenario is presented in WLQ, this low gas covering factor may simply be a result of an instability in the accretion disk.
32. Ohsuga, Ken
33. Osaki, Yoji: "A brief history of the disk instability model for the dwarf nova outburst" Show abstract
    I review a history of the research on the outburst mechanism of dwarf novae, in particularly on the disk instability model, from my personal point of view. By starting from the research in the 1960s when cataclysmic variable stars were established to be special types of close binary systems, I discuss my proposal of 1974 for a working hypothesis of the dwarf nova outburst, now known as the disk instability model, and its fierce dispute in late 1970s with the mass-transfer burst model first proposed by Bath in 1973.　I then deal with the thermal viscous instability proposed in early 1980s as a physical explanation for the disk instability. Finally, I discuss the thermal-tidal instability model (abbreviated the TTI model) for the superoutburst and superhump phenomenon of the SU UMa-type dwarf novae and a unification model based on the TTI model for the dwarf nova outbursts.
34. Otulakowska-Hypka, Magdalena: "IX Draconis - a curious ER UMa-type dwarf nova" Show abstract
    TBD
35. Pimentel, Claiton
36. Ramsay, Gavin: "Outbursts in AM CVn binaries" Show abstract
    AM CVn binaries have orbital periods between 5 - 70 mins and composed of a degenerate star accreting from a degenerate (or semi degenerate) star. Their accretion flows are devoid of hydrogen and are predicted to be the first sources detected by space based gravitational wave detectors such as eLISA-NGO. I will present an overview of a survey of these systems to determine their optical outburst properties and X-ray/UV/Optical observations of one system, KL Dra over an outburst cycle.
37. Razdoburdin, Dmitry
38. Różańska, Agata
39. Różyczka, Michał
40. Rutkowski, Artur: "Title TBD" Show abstract
    TBD
41. Sarna, Marek
42. Sądowski, Aleksander: "Outflows and convective stability of accretion disks based on GRMHD simulations of ADAFs" Show abstract
    I will present results from two long-duration GRMHD simulations of an advection dominated accretion flow around a non-spinning black hole. The first simulation was designed to avoid significant accumulation of magnetic flux around the black hole, was run for a time of 200000 GM/c3 and achieved inflow equilibrium out to a radius 100GM/c2. The second simulation was designed to achieve substantial magnetic flux accumulation around the black hole in a magnetically arrested disc. This simulation was run for a time of only 100000 GM/c3 but managed to achieve inflow equilibrium within 200GM/c2. For the former, we did not see significant mass outflow. The mass outflow rate was larger for the latter, though even in this case, Mdot_out exceeded Mdot_BH only at radii well above 100GM/c2. I will also discuss the role of convection in both disks.
43. Schwarzenberg-Czerny, Aleksander
44. Shugarov, Sergey: "PR Her - a new cataclysmic variable of a WZ Sge-type" [poster] - S.Yu. Shugarov, N.A. Katysheva Show abstract
    We present multicolor CCD photometry during superoutburst of a new cataclysmic variable PR Herculis, bursted on November 22, 2011, and was classified as a new WZ Sge-type system. The analysis of our data revealed the presence of early and ordinary superhumps with the period close to 0.055 d. The common light curve of superoutburst was constructed and the duration of superoutburst was estimated. The evolution of superhumps profiles, its amplitude and the superhump period, connected with the changes in accretion disc around the white dwarf, is analysed. Two-colour diagrams together with the superoutburst evolutionary tracks of PR Her are presented.
45. Smak, Józef: "Dwarf Nova Superoutbursts" Show abstract
    TBD
46. Steeghs, Danny: "Maping the mass flow between the two stellar components in binary systems" Show abstract
    Time-resolved spectroscopy offers powerful diagnostics of the accretion flow dynamics in close binaries. Emission line tomography in particular has allowed us to map the complex accretion flow geometries in accreting binaries. I discuss some key insights revealed by Doppler tomography and eclipse mapping techniques, focusing in particular on the time evolution of accretion discs in dwarf novae.
47. Szuszkiewicz, Ewa: "Variability as a powerful diagnostic of AGN" Show abstract
    TBD
48. Tylenda, Romuald
49. Warner, Brian: "The nature of superhumps" Show abstract
    I will discuss the nature of superhumps - from their early discovery and interpretation, through to the remarkable results obtained in Kepler observations.
50. Wielgus, Maciej
51. Wynn, Graham: "Duplicating discs: simulations of accretion discs in binary stars" Show abstract
    TBD
52. Zdziarski, Andrzej
53. Zemko, Polina: "ER UMa - Dwarf Novae persistently switching from positive to negative superhumps" Show abstract
    Investigation of superhumps phenomenon in Dwarf Nova - ER UMa was held in 2011-2012. Light-curves for different timescales are presented. The evolution of the superhumps amplitudes, periods and profiles were studied. Two-color diagrams were also analyzed. Studying of superhumps period changes along the supercycles showed that the period is not stable at all, but varying abruptly from night to night. O - C diagram revealed the presence of both positive and negative superhumps. Variations of the superhumps amplitude along the supercycle allowed to make a supposition that the accretion disk tilt angle is stable.
    
    and "Accretion disk radii calculations for WZ Sge-type Dwarf Nova in Pegasus" [poster] Show abstract
    Photometric and spectral investigations of OT J213806.6+261957 in Pegasi were carried out. The Fourier analysis of the data taken in May-June 2010, revealed the presence of ordinary and late superhumps. The evolution of superhumps profiles was analyzed. Mass ratio, separation between the components and orbital period were determined too. From the obtained observational material and measured superhump period changes, the radius of accretion disk changes from the superoutburst to the minimum were calculated using simple dynamical treatment proposed by Osaki.
54. Zhuravlev, Viacheslav "Optimal transient growth in keplerian discs via variational technique" - V. Zhuravlev and D. Razdoburdin Show abstract
    Unbounded keplerian flows are known to be dynamically stable to adiabatic perturbations. The same can be concluded about axisymmetric tori with quasi-keplerian rotation, since the known sonic instability due to the coupling of sound modes ceases rapidly as one suppresses the torus thickness. Despite this boring picture we show that a prominent transient growth of optimal perturbations is possible both in quasi-keplerian tori and in infinite keplerian discs. These optimal perturbations are determined using an iterative scheme for cauchy problem for direct and adjoint hydrodynamical equations.
55. Ziółkowski, Janusz
56. Zola, Stanisław: "Dependence of the central engine in FRII-type radio quasars on their optical variability" [poster] - S. Zola, A. Kuzmicz, M. Jamrozy, M. Winiarski, D. Koziel-Wierzbowska, W. Ogloza, M. Drozdz, M. Siwak and D. Jableka Show abstract
    We present a progress report on monitoring of a sample of FRII-type radio-quasars in the optical band. Based on more than three years long, regular and homogeneous observations of the sample, we investigate correlations among the SMBH masses, the size of the radio lobes and the type of variations and amplitudes of light changes.
57. Życki, Piotr