Program of BHmag2013

The Sixth Workshop on Black Hole Magnetospheres, 2013 March 5-7, Taiwan

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  • March 2013
  • 4 (Mon) Pre-workshop Lectures (Kinwah Wu, plus alapha)
  • 5 (Tue ) 9:00-12:00 13:30-18:00 Workshop
  • 6 (Wed) 9:00-12:00 13:30-18:00 Workshop; 18:30- BH dinner
  • 7 (Thu ) 9:00-13:00 Workshop; 13:30- Excursion



 WOrkshop on Black Hole MAgnetospheres, 2013 March 5-7, National Tsing Hua University,  Taiwan
Name Affiliation Title Email

Algaba, Juan Carlos  ASIAA/VLBI Probing the magnetic structure of AGNs at 1pc with VLBI rotation measures
       Rotation measure (RM) observations have proven to be a powerful took in order to understand the magnetic fields at parsec/kilo-parsec scales of AGNs. Furthermore, they can also be a fantastic tool to investigate the core magnetic properties of these sources. Due to the apparent change of the location of AGN radio-cores with frequency (i.e, core shift), VLBI core rotation measure is expected to increase as we observe at higher frequencies. However, when we study polarimetric VLBA observations of a sample of quasars, we find that this dependence seems to be different than expected by assuming simple jet model with a toroidal magnetic field in equipartition. We discuss some of the possibilities for the origin of this discrepancy and possible correlations with the magnetic field at 1 pc from the central engine.
Asada, Keiichi ASIAA Greenland Telescope Project 
       We will introduce Greenland Telescope Project. ASIAA and SAO jointly acquired the ALMA NA proto-type telescope. Primal purpose of this project is to form submm VLBI with SMA in Hawaii, ALMA in Chile and another submm telescopes in order to image the shadow of the black holes. For this purpose, we have started site testing with 225 GHz tipping radiometer to monitor the opacity at Greenland. We also started some tests and retrofitting works of ALMA NA proto-type telescope. We will introduce another VLBI activities as well.   
Cheng, Chio- Zong NCKU  ---  
Fujisawa, Kotaro Univ. of Tokyo  Let's solve GS equation! 
       GS equation is the second order elliptic partial differential equation.  The structure of the stationary axisymmetric flow, magnetic field and magnetosphere are governed by GS equation.Therefore, we need to solve GS equation consistently
to obtain these structures. GS equation itself is simple and powerful equation. However, it is not easy to solve it consistently, because there are many problems such that the
presence of singular surface, boundary conditions and changing the type of differential equation from elliptic to hyperbolic. In this talk, we will consider and discuss these problems in order to solve GS equation consistently. As a first step, we analyze the Parker solution and the Weber-Davis solution to treat these problems consistently. 
Fukuyama, Takeshi Ritsumeikan Univ.  --
Hirotani, Kouichi ASIAA/TIARA High-energy emission from pulsar magnetospheres  
       In the HE/VHE regimes, the Fermi, VERITAS and MAGIC experiments have detected pulsed signals from the Crab pulsar up to 400 GeV. The light curves and the spectra obtained from the Crab and other rotation-powered pulsars, suggest that the gamma-ray pulsars have high-altitude emission zones, which avoid super-exponential cutoffs due to magnetic pair production and reproduce wide-separated double-peak light curves. I thus examine the outer-magnetospheric emission model both analytically and numerically, and demonstrate that their gamma-ray luminosity is naturally proportional to the square root of the spin-down luminosity, which is consistent with the Fermi observations.  
Inoue, Makoto ASIAA  ---  
Isoyama, Souithirou YITP Toward the adiabatic evolution of the extreme-mass-ratio inspirals in resonance
      Inspirals of stellar mass compact objects into massive Kerr black holes are an important source for future gravitational wave detectors such as Advanced LIGO, eLISA and DECIGO. Detection of these sources and extracting information from the signal relies on accurate theoretical models of the binary evolution. In the extreme mass ratio limit, past works have revealed that the leading order or adiabatic motion requires only knowledge of the orbit-averaged evolution of the constant motion; i.e., the energy, azimuthal angular momentum and the third non-trivial constant motion: Carter constant.  
  Although there is no conserved current composed of the perturbation field corresponding to the Carter constant, it has been shown that the averaged rate of the change of the Carter constant can be given by a simple formula, when there exists a simultaneous turning point of the radial and polar oscillations. However, an inspiralling orbit may cross a "resonance" point, where the frequencies of the radial and polar orbital oscillations are in a rational ratio. In this case, one cannot find a simultaneous turning point in general, hence, it seems to be quite difficult to evolve the binary even adiabatically. In this talk, we review the current status toward the adiabatic evolution of the binary system in extreme-mass ratio limit, particularly focusing on the resonant effect.
Kanai, Kenichiro Nagoya Univ. Numerical Simulation of Wave Scattering by Black Hole
Koide, Shinji Kumamoto Univ. Review of primary and recent GRMHD simulations
       GRMHD (general relativistic MHD) simulations had confirmed some predictions of theory with steady-state assumption and also revealed a number of drastic and dynamic phenomena of magnetized plasma around rotating black holes.  In this talk, I will show some basis of GRMHD simulations and their primary and recent results.   
Lee WooMin Tohoku Univ.  --
Masuda, Atuki Osaka City Univ. Propagation of wave with orbital angular momentum in Kerr space-time
Miyoshi, Makoto NAOJ A First Black Hole Imager, Caravan-submm
       I will talk about present status of Caravan-submm project that is a first black hole imagr in the earth. The system contains three 230GHz VLBI stations in Peru-Bolibia Andes, providing shorter 1000-2000 km beselines. Such a short baseline is important to enhance the qualities of images around massive black holes in SgrA*, M87, and so on.   
Mizuno, Yosuke IoA/NTHU  Current-Driven Kink Instability in a Magnetically Dominated Relativistic Jet
       Relativistic jets have been observed or postulated in various
astrophysical sources, including active galactic nuclei (AGNs), microquasars in the galaxy and gamma-ray bursts (GRBs). There are four major problems related to the relativistic jets: 1. formation mechanism, 2. acceleration mechanism, 3. collimation mechanism, and 4. long-term stability. The most promising mechanisms for producing and accelerating relativistic jets, and maintaining collimated structure of relativistic jets involve magnetohydrodynamical processes. We have investigated the temporal development of current-driven (CD) kink instability in magnetically dominated relativistic jets via 3D relativistic MHD simulations. In this investigation a static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depends moderately on the radial density profile and strongly on the magnetic pitch profile. We also present the influence of jet rotation on the temporal development of the CD kink instability.
Nakamura, Masanori ASIAA Exploring M87 with Sub-mm VLBI: How Can We Test Theories?
      The Greenland Telescope (GLT) project led by ASIAA-CfA is planning to conduct sub-mm VLBI observations towards M87, which is one of the most promising sources in order to image the BH shadow in coming decade. Besides, we will explorer fundamental issues in AGN physics; the origin of relativistic outflows and nature of innermost accretion flows in the vicinity of the SMBH. These are two key ingredients to build the imaging model for the BH shadow. Furthermore, sub-mm VLBI observations may give a clue to constrain the location of VHE TeV γ-ray flares in AGNs, which is one topics in Fermi era. I will discuss some of key science cases related to the GLT project.   
Nakao, Kenichi Osaka City Univ. On "Meissner" effect of extreme black hole
      It is known that no magnetic field line penetrates an event horizon of an extreme black hole, i.e., maximally rotating black hole or maximally charged black hole, if there is no electric current. This phenomenon is similar to the Meissner effect of the super- conductor. By contrast, it is still unknown whether this Meissner-like effect appears even if electric currents exist. In this talk, force-free magnetosphere around a  maximally charged black hole is discussed. We assume that the rotational speed of the magnetic field is very slow, and then investigate analytically the magnetosphere by perturbative analysis. We get a nonlocal equation from GS equation: nobody probably has ever seen such an equation. We discuss the solution given in the form of the Maclaurin expansion.
Nambu, Yasusada Nagoya Univ. Viewing black holes by waves
       Wave scattering problem by black holes have been investigated to understand diffraction effects of wave propagation in black hole spacetimes. This theme is expected to provide us deeper theoretical understanding of the physics of black holes. In this talk, I am planning to present  the method of image reconstruction from scattering waves by black holes and discuss the relation between the quasi-normal mode and structure of black hole images.  
Pu, Hung-Yi NTHU A New Look at the Black Hole Disk-Jet Coupling
       Relativistic jets can be launched form the black hole (BH) ergosphere by extracting the rotational energy of the black hole. When the BH magnetosphere is nearly vacuum, the extraction can be realized by the help of large-scale, hole-threading magnetic fields, as described by the Blandford-Znajek process. For accreting BH systems, on the other hand, the plasma near the horizon can further modify the Blandford-Znajek process by loading onto the field lines. Such modification is important when accretion flow near the event horizon has a quasi-spherical geometry. By investigating the extraction of the rotational energy from BH at different accretion rate (and therefore accretion disk type), we conclude that the relativistic jets can preferentially take place when the BH is surrounded by a combined disk (which consists of an outer thin disk and inner advection-dominated accretion flow) and a slim disk, but become less active or being quenched when surrounded by an advection-dominated accretion flow or a thin disk. Puzzling observed disk-jet features of black hole binaries and AGNs, such as why their radio emission suddenly drops when the dimensionless accretion rate , the ratio between the accretion rate and the Eddington accretion rate, exceeds a certain limit (~0.01), are also explained.  
Saida, Hiromi Daido Univ. Detecting black holes by waves
       We construct an observable which is used for direct detection/observation of black hole horizon. One observable suggested in this talk is found in waves coming from sources  which is falling into black hole. In principle, the strong gravitational redshift found in the wave gives us  the unique observable for direct detection of black hole horizon. However, it may be hard to detect this observable by present technology. Then, we discuss the second observable. This second one should be found in the strong gravitational lensing effect by black hole. To detect this second observable, we may need only one radio telescope of present technology.  
Sakai, Nobuyuki Yamaguchi Univ.  --
Takada, Masato Osaka City Univ. Brightness of rim of black hole shadow

   I will talk about the brightness of light sources surrounding Kerr black hole on the equatorial plane under these situations.

・Light sources are assumed to be optically thin and distributed spherically and homogeneously. 

・Wave lengths are short enough to make the geometrical optic arroximation be valid.

Under these situations, we can calculate the brightness by integrating spatial length along null geodesic passing through sources. From the result of this, we can determine spin parameter of black hole. 

Takahashi, Masaaki Aichi Univ. Edu.
GRMHD inflows and outflows in a BH magnetosphere
Takamori, Yousuke
Osaka City Univ.
Analysis of the Blandford-Znajek power for a rapidly rotating black hole

   The Blandford-Znajek (BZ) mechanism is well known as a mechanism to extract the rotational energy of a black hole with a magnetic field. The power depends on both the magnetic field configuration and the spin parameter of the black hole. The existence of plasma is important for the BZ mechanism, and therefore one should concern both plasma and electromagnetic field around a rotating black hole. Such system becomes highly nonlinear and, because of the difficulty of the nonlinear system, analytical research for the BZ mechanism has been devoted in the case of a slowly rotating black hole. In this talk, we suggest a perturbative method which is useful to obtain the BZ power
for a rapidly rotating black hole. In this method, we focus on the case that the magnetic field "corotates" with the black hole. As an example, we show the spin-dependence of the BZ power obtained by our method in the case that the magnetic field has a monopole configuration.
Wada, Tomohide NAOJ  Particle method for axisymmetric pulsar magnetosphere 
Wang, Joan National Tsing Hua Univ.  Can a neutron star recollapse? — A new perspective for the formation of SGRs/AXPs  
       Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are two groups of enigmatic objects, which have been extensively investigated in past few decades. Based on the ample information about their timing behaviors, spectra, and variability properties, it was proposed that SGRs/AXPs are isolated neutron stars (NSs) with extremely strong magnetic fields, the so-called magnetars. Nonetheless, some alternative models are probably equally convincing such as those proposing that they are accreting NSs with a fall-back disk or rotation powered magnetized and massive white dwarfs. The nature and nurture of SGRs/AXPs remain controversial. Based on the idea that a NS may recollapse after accreting enough material, I present several possible tracks by which the SGRs/AXPs can form. SGRs are a class of objects containing a neutron-drip core and denser crust with a stiffer equation of state, which is formed from re-explosion of normal NSs in binary systems. It is the accretion onto the denser crust that contributes to the observed hard emissions. AXPs are a group of NSs which reserve huge thermal energy in an insulating layer above the surface. This structure accretes material from a massive disk, manifesting themselves via release of deposited energy. The spin-period clustering is due to either the brake of a slowly rotating envelope or the frictional drag during the common envelope phase.  
Wu, Kinwah Univ. College London Gravito-magnetism and orbital dynamics of spinning neutron stars around massive black holes  
       Spinning gravitational objects give rise to gravito-magnetism analogous to classical electromagnetism. The gravito-magnetic interaction leads to complex dynamics in binary and multiple systems consisting of spinning compact objects. I will discuss the orbital dynamics of spinning single neutron stars and neutron-star binary systems revolving around massive black holes and present recent findings obtained by my collaborations. The implications of these works on broader astrophysics are discussed.  
Wu, Jason NTHU  --  
Yoshida, Shijun Tohoku Univ. New solutions of charged regular black holes and their stability
      Standard black holes have singularities inside the event horizons. The existence of spacetime singularities means that physics loses its predictive power there. Fortunately, the singularity theorems do not claim that the formation of the singularity is inevitable in all situations. Therefore, it might be interesting to consider black holes without singularities, regular black holes.
  In this talk, I will talk about new regular black hole solutions composed of a single de Sitter core whose surface boundary is a timelike charged massive thin shell. The geometry outside the shell is described by the Reissner-Nordstrom solution. The thin shell is assumed to have no pressure and to be inside the Cauchy horizon of the Reissner-Nordstrom solution. Thus, these solutions look like normal black holes if we look at them from the outside of the event horizon. Radial stability of the new regular black hole solutions is also studied.