2018 EHT Collaborate Meeting @ Nijmegen


Attendee List

2018.11.05 (1st day)

  • imaging of "Shadow" at the central SMBH
    • M87: diameter ~42 mas

Geoffrey Bower @ ASIAA: First publication of 2017 EHT (presentation file)

  • Simulation WG:
    • photon image of shadow ring
    • the role of forward/counter jets
    • see accretion flow?
  • toward and backward rings
  • Critical discussion of ring features: differences between Einstein rings, jet base, and photon orbit – how to distinguish?
  • Is the flux depression a shadow?
  • If this is a shadow, what does it imply for the mass of M87 and the systematics of dynamical measurements?
  • If this is a shadow, what does it imply for the nature of the central object? Is this a black hole? Does it have a horizon?

Akiyama & Johnson (Paper IV: imaging) (presentation file)

  • persistent asymmetric ring, southern part is brightened.
  • robust and reproducible
  • Types of images to test
    1. Thin rings, both with uniform brightness and with angular variation (e.g., crescents)
    2. Disks (with sharp edges; test for spurious rings and, e.g., Gibbs ripples)
    3. Images from GRMHD simulations (complex structure with ground truth photon ring with physical meaning)
    4. Images with varying types of extended structure, on scales that EHT baselines do not sample

Charles Gammie Theory and Simulation Working Group (presentation file)

  • Input

$b^{2}/\pi = P_{\rm gas}/10$
$F_{\nu} = 0.5$ Jy
$kT_{e}/m_{e}c^{2} = 10$
$D = 17$ Mpc
$R = 4GM/c^{2}$
thermal synchrotron

  • Output

$n_{e} = 4\times10^{4} \rm \, cm^{-3}$
B = 2.7 G

  • Plasma is collisionless
  • Synchrotron self-absorption cannot be neglected
  • Important parameters

$\Phi \sim B r_{g}^{2}$
$\dot{M} \sim \rho c r_{g}^{2}$

  • magnetic pressure balances ram pressure
    $\frac{B^{2}}{8\pi} \sim \rho c^{2}$ -> $\phi = \frac{\Phi} {(\dot{M} c r_{g}^{2})^{1/2}} \sim 1$
    simulations: $\phi_{\rm crit} \sim 50$
  • Radiative properties of plasma determined by electron DF collisionless: ions and electrons not in equilibrium how to set electron DF?
    1. 1st method
      • Alfvenic cascade: (Howes 10, Kawazura+18)
      • Reconnection: (Rowan+17)
      • example: (Ressler+16, Ryan+18, Chael+18)
    2. 2nd method
      • Assume DF = DF (local conditions)
      • thermal: (Moscibrodzka+18)
      • $\kappa$-DF: (Davelaar+18)
      • non-thermal: (Dexter+12)
  • Asymmetry of the ring can be constrained by the spin of the black hole
  • Jet model in MAD (Chael+18) and in SANE (Ryan+19)
    • MAD Jet is broader than SANE Jet
      -> the ring (forwarding jet and counter jet) is closer each other in MAD Jet.

Feryal Ozel: Shadow and Mass (Paper VI)

  • effects of scattering (Sgr A*; not dominant in M87)
  • Flux depression in the center -> if it arise from Shadow, then we can measure the BH mass.

2018.11.06 (2nd day)

Keiichi Asada & Heino Falcke: M87 parameters (presentation file)

  • Distance
    • Primary: Tip of red giant branch
    • Secondary: surface brightness fluctuation
    • $16.9 \pm 0.3$ Mpc (1 $\sigma$) (17.9 Mpc in previous measurement)
  • Mass (Walsh+13: by gas orbit, Gebhardt+11: by stellar orbit)
    • Primary:
      • timelyresolved stellar orbit
      • spatially resolved star/gas orbit
      • mega maser
    • Secondary:
      • reverberation mapping
      • single-epoch spectra
  • Jet viewing angle
    • Martens+16: $\Theta = 17.2^{\circ} \pm 3.3^{\circ}$
    • Wang & Zhou+09: $\Theta \sim 14^{\circ}$ and $16^{\circ}$
    • Perlman+11: $10^{\circ} < \Theta < 18^{\circ}$
    • Hada+16: $\Theta = 29^\circ - 45^\circ$
  • Proper motion of jet (Nakamura+18)
  • X-ray Luminosity (Di Matteo+03)

Kazuhiro Hada & Sera Markoff: M87 at radio/low frequencies (presentation file)

  • Jet collimation and acceleration scales well resolved by cm-VLBI
  • Core-shift: mm emission likely from BH vicinity
  • Active Multi-Wavelength(MWL) emission, flares through radio to TeV
  • Doeleman+12(data:09), Akiyama+15(Data:12), Hada+14
  • Goals:
    • detect the shadow of SMBH
    • image the jet launch structure
    • test disk-driven jet (BP) vs BH-driven jet (BZ)
    • image B-field structure near BH
    • connection to MWL data
  • EHT: limited FoV, less sensitive to extended emission -> Low-freq. is needed
    • The ring emission represents the main jet? Counter-jet? Accretion flows?
    • Jet detailed connect horizon scale to large scales
    • collimation transverse structure
    • Doppler factors
    • connection to GeV/TeV
    • global B-field
  • Large-scale morphology in 2017 (VLBI at 22/43 GHz)
    • beyond 5mas: jet well defined
    • within 2mas: jet more horizontal, the southern limb brighter
  • GMVA 86 GHz
    • jet near core: horizontal, southern limb brighter (consistent with VLBI 43 GHz)
    • hint of counter jet
  • EAVN 22/43 GHz
    • motions near the jet base
    • possible new ejection after the EHT period?
    • spectral index map (22/43 GHz): (Cui,KH+)
  • optically-thin jet spectral index $\alpha \sim -(0.7 - 1)$, possible flatter spectra in the southern limb

Sera Markoff: (higher frequency ) MWL WG (presentation file)

  • X-ray observation (Genzel+03, Yuan+03, Chandra XVP Science 2013)
  • X-ray Variability
  • X-ray view of M87 (Chandra: Sun+18)
  • Broadband SED modeling: Synchrotron (Prieto+16, Lucchini+18)
  • 0.8, 1.3, 3 & 7 mm + IR spectral index maps to understand thermal/nonthermal particle fraction
  • GMVA + EHT + GRAVITY + Chandra + NuSTAR -> massive legacy set for the flares

Masanori Nakamura (ASIAA): M87 Theory: Jet Physics (presentation file)

  • Limb-brightening feature, superluminal knots
  • origin of jet: opening angle, jet launching radius, jet stagnation surface, ..
  • Constructing a standard model for parabolic jets in AGN (similarity between RGs and Blazars)
  • global structure of AGN Jets
    • (Blandford & Konigl 79): flat spectrum core (self-absrobed) as an innermost jet in a conical shape (Marscher & Gear 95)
    • Marscher+08
  • Jet collimation break in M87 (Nakamura+2018)
  • HST-1 in M87
    • Re-collimation shock & a site of $\gamma$-ray emissions (Stawarz+06)
  • Parabolic jet is normal?
    • An extent of parabolic nozzle determines how fast AGN jets could be a transition from acceleration to decceleation at 10 pc in projections.
  • Reduction of the Bp line density at the outer jet -> Bunching effect -> more acceleration
    • Higher spin of BH leads to more collimation and acceleration
  • Spine-Sheath structure in M87 (Asada+16)
  • At MAD case, jet stagnation surface approaches to the event horizon compared with SANE

Jason Dextor (MPE): Predicted 230 GHz images of M87 (presentation file)

  • Crescent images in GRMHD (Dexter+12)
  • The lensed counter-jet can dominate the image (Dexter, McKinney, Agol 12)
    • Light bending hides forward jet and lenses counter-jet
  • Emergence of radio jet in better calculations (Moscibrodzka+16)
  • Counter jet (Ryan+18), Disk/Forward jet (Chael+18)
  • Polarization can determine the physical origin of the emission (Moscibrodzka+17, Jimenez-Rosales & Dexter 18)

breakout session: Simulation and Theory Working Group (Paper V)

  • How to score it (image domain or visibility domain)?
  • How to read GRRT image? (data structure & file format)
    • FITs -> example writing/reading code to github
  • Consider only 230 GHz or connection to multiwavelength information?

Discussion for Shadow and Mass Working Group (Paper VI)

  • Not Gaussian — Rice distribution

2018.11.07 (3rd day)

Monika Moscibrodzka: M87 Polarization near horizon (presentation file)

$T_{p}/T_e = \frac{1}{1+\beta^2} +100 \frac{\beta^2}{1+\beta^2}$

  • Polarization
    • constraints on plasma state, fields, black hole mass and spin (optical/Faraday depth)
    • synchrotron emission intrinsically has high linear polarization
  • 43 GHz: Walker+18; 86 GHz: Hada+16; 230 GHz: SMA 13, Kuo+14

Dan Marrone (Arizona): Time Domain Working Group: M87 and Sgr A*

S. Issaoun Sagittarius A* imaging (presentation file)

  • Strong double peak in X-ray by NuSTAR
  • Average GRMHD image and reconstructing without variability (Lu, Roelofs+16)
  • dynamical imagine
    • images at nearby times are not independent, all frames should be reconstructed simultaneously while enforcing continuity (via regularization)
  • Sgr A* is scattered and variable, and may flare
  • longer wavelength VLBI constrains scattering properties
  • MWL simultaneous observations informs of flaring activity

Guangyao Zhao (KASI) & Rusen Ru (SHAO) The multiwavelength Sgr A* in VLBI

  • Intrinsic source is not circular (Bower+14)
  • asymmetric structure in 1mm (Lu+18)
  • core-shift: Moscibrodzka+14, Bower+15
  • Nearly isotropic intrinsic structure
  • some indications of structural variability

Geoffrey C. Bower (ASIAA): Polarimetry of Sgr A* (presentation file)

  • Polarization fraction (Munoz+11)
  • Rotation Measure (RM) for Sgr A* (Bower+03, Marrone+06)
  • Polarized radiation propagates through dense magnetized accretion region
  • RM constrains accretion rate $\dot{M} \sim 10^{-8} \rm M_\odot yr^{-1}$
  • RM for Sgr A*: long-term stability but variable
  • EHT polarization of Sgr A*: Johnson+15
  • complex faraday effects in the accretion flow: Moscibrodzka+17

breakout session: Theory and Simulation (Paper V)

  • Parameterized model: Stagnation ring -> as a ring (Nakamura+17, Kawashima+in prep)
  • MAD can make larger rings!
  • Phenomenological Model Simplified Force-Free Jet (in THEMIS)
    • magnetic field and non-thermal particle density set by SED
    • magnetic stream function = $r^{p}(1-\cos(\theta))$, (p=2/3)
    • Model parameters: BH spin, jet opening angle, magnetic field normalization, terminal Lorentz factor, particle load height, equatorial jet inner edge.

11.08 (4th day)

Krichbaum: Non-EHT AGN

  • OJ287, 1055+018, 3C273, 3C279, Cen A, NRAO530 …
  • warbling jets

Kramer: Pulsars WG (presentation file)

  • raning capability of pulsar timing
  • $\delta t = 1 ms \rightarrow \delta r = 300 km \rightarrow 0.00025 mas$
  • orbital variation of pulsar orbit due to Lense-thirring gives 2-D projection (Liu+12)
  • scattering magneto-ionic medium
  • monitoring of GC magnetar (RM, scattering)

Path to 345 GHz

  • Opacity is 3x opacity at 230 GHz!

breakout session: Theory and Simulation

$c := \frac{M}{r} = \frac{M}{3M} \simeq 0.33$
$0 < c < 0.5$

  • w/o EH
    • w/o a surface (e.g. gravastar)
    • w/o a surface, regular (e.g. boson star)
    • w/o a surface, singular (naked singularity)
  • A shadow is robust (direct evidence)
  • evidence of EH is controversial (no direct evidence)
  • Shadow compatible with BH in GR
  • Distinguishing different BHs not possible at present
  • Scientifically very valuable to exclude alternative

Lia Medeiros Principal Component Analysis (PCA) as a Tool for Characterizing BH variability

  • Diagonalize to covariant and find eigenvalues and eigenvactor

Jason Dextor

  • SANE: different model of electron heating
  • MAD: computing electron heating is way difficult
  • "SANE" model is bigger, "MAD" often has more emission inside the photon orbit.
  • for M87, spin 0 SANE model is close to match the observation in a "rough cut"

11.09 (5th day)

Charles Gammie: Science Goals

  • repeated observations to ensure "shadow" is not a transient plasma effect
  • observations at 0.8mm to tease out the spatial distribution of the electron distribution and the efficiency of electron heating
  • Bower's observables:
    • Total flux, brightness temperature, constraints on rotation between epochs and secondary arcs/structures
    • Ring: diameter, width, sharpness, contrast, azimuthal symmetry contrast, azimuthal symmetry orientation, circularity, location
  • New Science Goal:
    • Can we make a robust measurement of black hole spin?
    • Can we present clear evidence ofor extraction of energy from a spinning black hole?

Dolemann: Technical development

  • simultaneous observation between 230 GHz and 345 GHz will provide more robust measurement of physical properties around black hole.

Satoki Matsushita (ASIAA): Status of Greenland Telescope (GLT)

breakout session

$\dot{M}$ (radiative transfer model, 0.5 Jy) -> fix
M -> fix
$R_{\rm high}$ -> vary (1,10,22,40, 80)
$R_{\rm low}$ -> fix
$\beta \,{\rm correction}$ -> fix
inclination -> fix

$\sigma_{\rm cutoff}$

  • electron distribution function (Dexter 12)
  • 21 mas shadow ring (photon ring?)