Abstracts by Lead Author

Kazunori Akiyama
Keiichi Asada
Lindy Blackburn
Katherine Bouman
Geoffrey Bower
Christiaan Brinkerink
Silke Britzen
Avery Broderick
Thomas Bronzwaer
Andrew A. Chael
Chi-kwan Chan
Ming-Tang Chen
Jordy Davelaar
Mariafelicia De Laurentis
Roger Deane
Jason Dexter
Sheperd Doeleman
Heino Falcke
Raquel Fraga-Encinas
Per Friberg
Christian Fromm
Peter Galison
Boris Georgiev
Roman Gold
Jose L. Gómez
Kazuhiro Hada
Mareki Honma
Shiro Ikeda
Makoto Inoue
Sara Issaoun
MIchael Janssen
Britton Jeter
Michael Johnson
Junhan Kim
MIchael Kramer
Thomas P. Krichbaum
Kazuki Kuramochi
Rusen Lu
Alex Lupsasca
Dan Marrone
Ivan Marti Vidal
Satoki Matsushita
Lynn Matthews
Lia Medeiros
Yosuke Mizuno
Monika Moscibrodzka
Cornelia Müller
Neil Nagar
Masanori Nakamura
Gopal Narayanan
Hector Raul Olivares Sanchez
Aleksandar Popstefanija
Oliver Porth
Hung-Yi Pu
Luciano Rezzolla
Freek Roelofs
Eduardo Ros
Benjamin Ransom Ryan
Hotaka Shiokawa
Leo C. Stein
Alexander Tchekhovskoy
Remo Tilanus
Huib Jan van Langevelde
Daniel van Rossum
Jonathan Weinthroub
Ziri Younsi




































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List of Lead Authors
EHT Globe  Credit: APEX, IRAM, G. Narayanan,
 J. McMahon, JCMT/JAC, S. Hostler, D. Harvey,
 ESO/C. Malin

 Click here for larger view.


Last Name First Name Affiliation
Akiyama Kazunori MIT Haystack Obs
The global structure of the archetypical quasar 3C 273
We report on multi-frequency observations of the archetypal quasar 3C 273 performed with the VLBA at 1.4/15/22/43 GHz, the VLA at 5/8/22 GHz, and MERLIN at 1.6 GHz.  The observations provide transverse resolution over a broad range from subparsec to kiloparsec scales, allowing us to profile the jet width as a function of core distance, as has previously been done for some radio galaxies (e.g. M87, 3C 84, and Cyg A).  For the first time in a quasar jet, we have discovered a parabolic profile, which transitions to a conical profile at a distance of ~10^5-10^6 Rs from the 7-mm core.  The similarity in these properties to the much lower-powered radio galaxy M87 suggests a universality of jet acceleration and collimation among AGNs with different accretion rates of the central super-massive black hole.  Future ultra-high-resolution VLBI observations with ALMA at 86 and 230 GHz will be able to effectively constrain the active collimation region and the launching point of the visible jet at the end the collimation profile in 3C 273 and other AGNs.

Akiyama Kazunori MIT Haystack Obs
Practical side of sparse modeling: review of the recent progress
The Event Horizon Telescope will have key advances in the next two years with the critical addition of ALMA, opening an exciting capability of imaging the black holes. I and Japanese EHT group have been working on developing sparse modeling techniques to obtain high-fidelity images with the EHT. In the two years after the last EHT 2014 meeting, we had many updates in our imaging software, accelerated by the maturity of the EHT imaging WG, such as the implementation of new regularizers, imaging with closure phases and full-polarization imaging. More practically, we also have worked on evaluating the performance of hybrid mapping with our techniques and also applications to actual data at lower frequencies. In this talk, I will present an overview of the recent progress of the sparse modeling team, particularly on the practical side.

Asada Keiichi ASIAA
Constrains on the accretion flow of M87
To extract the black hole properties from future EHT/GLT black hole shadow observations, proper understandings of the astrophysics on the accretion flow and/or jet base are essential. While understanding of the jet base is dramatically improved in last decade, constraint on the accretion flow is still very limited, especially for M87. Direct imaging of the accretion flow with high angular resolution observation by mm/submm VLBI and measurement of Faraday Rotation are only limited ways to probe those properties. We will reports on those aspects based on GMVA and SMA observation towards M 87.

Blackburn Lindy SAO

Bouman Katherine MIT
Discussion of the EHT Imaging Challenge

Bower Geoffrey ASIAA
The Galactic Center Pulsar
The discovery of the Galactic center pulsar SGR J1745-29 has provided an important new window into plasma processes in the Galactic center (GC) interstellar medium, the population of compact objects in the GC, and the prospects for probing general relativistic effects through timing of a Sgr A* pulsar companion. We discuss here radio observations of the pulsar and how they are providing fresh insights. In particular, we discuss how how understanding of the GC pulsar can impact analysis of EHT data.

Brinkerink Christiaan Radboud University, the Netherlands
Closure analysis of Sagittarius A* at 86 GHz from measurements with VLBA, LMT and GBT: results and discussion points
In observations of Sagittarius A* at 86 GHz, taken in May 2015 with the Very Long Baseline Array (VLBA), Large Millimeter Telescope (LMT) and Green Bank Telescope (GBT), we find evidence for an apparent East-West asymmetry that may either be due to scattering effects or may be intrinsic. An ongoing analysis of a more recent VLBA + GBT dataset from May 2016 will help to pin down the origin of this apparent asymmetry. Through closure amplitude model fitting of the 2015 data we also find an apparent source size that is in close agreement with the result from Ortiz et al (2016). However, in our analysis it has become apparent that there are systematics that so far have not been considered. These systematics potentially have a large impact on model fitting results. We illustrate this issue and invite the EHT community to have a discussion on a cautious but thorough treatment of these hidden uncertainties in closure analysis.

Britzen Silke MPIfR
A new view on the M87-jet origin
Due to it's proximity, jet prominence, and the large BH mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. We re-modeled and re-analyzed 31 VLBA observations at 15 GHz obtained within the MOJAVE programme. The data span a time range between 1995.6 and 2011.4. We performed a detailed investigation of the pc-scale jet kinematics on different time-scales and studied the jet ridge line behavior as function of time. Special care has been taken to analyze the region close to the 15 GHz core and the dynamics and distribution of newly emerging jet features in the jet. I will present our recent results and discuss the implications for the jet launching mechanism.

Broderick Avery Perimeter Institute / University of Waterloo
Probes of General Relativity with the EHT
The unprecedented access to the near-horizon region afforded by the EHT enables a number of probes of strong gravity. I will describe how some of these are performed in practice, from the least model dependent to the extreme limits that can be made by jointly modeling the accretion flow and spacetime.

Bronzwaer Thomas Radboud University
The RAPTOR Code: Time-dependent Radiative Transfer in Arbitrary Spacetimes
We present RAPTOR, a new, public code that is capable of numerically integrating the equations of motion of light rays and of solving the radiative transfer equation in arbitrary (analytical or numerical) dynamical spacetimes. We apply RAPTOR to the study of radiative transfer around black holes, focusing on reproducing the spectrum and appearance of Sgr A* and examining the difference between the unphysical "fast light" paradigm, in which light moves at infinite speed, and the more physically correct "slow light" paradigm, in which the light's motion is taken into account while producing images and light curves.

Chael Andrew A. Harvard-Smithsonian Center for Astrophysics
Evolving Non-Thermal Relativistic Electron Distributions in GRMHD Simulations of Sgr A*
The structure and dynamics of accretion flows around supermassive black holes are determined by the general relativistic form of the equations of magnetohydrodynamics (GRMHD). Recent advances in simulating accretion flows in numerical simulations include the incorporation of radiation pressure and fluxes and the simultaneous evolution of separate ion and electron temperatures in hot flows. All current GRMHD simulations assume that all particles are locally in thermodynamic equilibrium. However, processes like magnetic reconnection and shocks are likely to excite a fraction of electrons into nonthermal, power-law distributions which would not quickly thermalize at high energies or low accretion rates. Significant nonthermal electron populations can explain the low-frequency radio spectra of low luminosity AGN like Sagittarius A* (Sgr A*), the black hole in our Galactic Center. In this talk, I will describe initial efforts to incorporate the self-consistent evolution of a nonthermal electron population in the GRMHD code KORAL. The electron distribution is tracked across multiple bins in Lorentz factor space with evolution due to compression, radiation, and Coulomb coupling with the thermal electron and ion populations. Feedback on these populations are also taken into account. Simulations with the new code will be used for the interpretation of images produced by the Event Horizon Telescope.

Chan Chi-kwan Steward Observatory
GRay2: 8232Improving General Relativistic Ray Tracing
General relativistic ray tracing is an important tool to create mock images of accreting black holes such as Sgr A*.  When compared with EHT observations, these mock images can help us test general relativity and understand accretion processes and jet collimation.  In addition, mock images can also help us refine image reconstruction techniques for the EHT.  The standard algorithms in many existing ray tracing codes employ the Boyer-Lindquist coordinates, which have coordinate singularities along the poles.  These singularities cause numerical difficulties, which can slow down the calculations, lead to inaccurate geodesics, and can sometimes crash the codes.  We improve general relativity ray tracing in GRay2 by switching to the Cartesian form of Kerr-Schild coordinates.  By carefully rearranging terms in the geodesic equations, we show that numerical integration of geodesics in Kerr-Schild is not necessarily slower than in Boyer-Lindquist.  In fact, for special purpose hardware like the GPUs, integrating in Kerr-Schild can even out perform Boyer-Lindquist.  Using our new improved and more robust algorithm, we report here careful convergence tests and benchmarks and conclude that, for most applications, using Kerr-Schild coordinates is a better choice for geodesic integration.

Chen Ming-Tang ASIAA
The Status of The Greenland Telescope
The Greenland Telescope project is about deploying a 12-meter antenna to a high site in Greenland. We have two primary scientific goals: To image the shadow of supermassive black hole in M87, and to conduct astronomy observation in tera-hertz frequencies. Since the ALMA North America Prototype Antenna was awarded to the Smithsonian Astrophysical Observatory (SAO) in 2011, SAO and the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA) are working jointly to retrofit the antenna for the cold environment and to stage sites in Greenland for operations. I will show the status of the antenna retrofit and the work carried out at Thule Air Base. These activities are expected to last until the fall of 2017 when commissioning takes place. In parallel, design, fabrication and testing of the last components are taking place in Taiwan.

Cornelia Müller Radboud University
Zooming into the heart of Centaurus A
At a distance of only 3.8Mpc, Centaurus A is the closest radio galaxy. Its proximity allows us to study its relativistic jet at unprecedented linear resolution. VLBI observations in the framework of the TANAMI program provide the best-ever view of the innermost parsec of this extragalactic jet. The detailed study at sub-milliarcsecond scales provides valuable insight into jet kinematics and helps to constrain broadband emission models attempting to explain the gamma-ray emission of Cen A. At a declination of -43deg, this source has not been well accessible for mm-VLBI until now. The situation changed with the inclusion of ALMA, LMT and SPT in the EHT, offering now for the first time the opportunity to study the jet formation region at scales of less than 1 light-day. This talk will present the latest results of the cm-VLBI study and set the scene for the upcoming mm-VLBI observations.

Davelaar Jordy Radboud University Nijmegen
The effects of accelerated particles on the radiative properties of accreting black holes
To model emission of accreting black holes one often assumes that the source of the radiation is purely thermal. However, the observations of the SEDs of these sources typically show a power-law that can be explained by the presence of accelerated particles. These particles are expected to get ac- celerated in high magnetized regions inside the jet and/or disk. To be able to resolve the jet in GRMHD simulations properly we introduce a grid that is optimized for modeling jets. In this presentation, I will show our latest result from these GRMHD simulation combined with post processed radiative transport codes, and show how the radiative properties of accreting black hole models are affected if we assume that emission is produced by both thermal and accelerated particles.

De Laurentis Mariafelicia Goethe University
Astrophysical signatures in general black hole spacetimes: the spherically-symmetric case
A binary system composed of a supermassive black hole and a pulsar orbiting around it is studied. The motivation for this study arises from the fact that pulsar timing observations have proven to be a powerful tool in identifying physical features of the orbiting companion. In this study, taking into account a general spherically-symmetric metric, we present analytic calculations of the geodesic motion, the innermost stable circular orbit, and the possible deviations with respect to the standard Schwarzschild case of General Relativity. In particular, the advance at periastron is studied with the aim of identifying corrections to General Relativity. A discussion of the motion of a pulsar very close the supermassive central black hole in our Galaxy (Sgr A*) is reported.

Deane Roger Rhodes University
MeqSilhouette: a mm-VLBI interferometric simulator
The EHT’s objective to spatially resolve a supermassive black hole silhouette has a wide range of technical challenges to solve before it is successful. Realistic synthetic data generation will play an important role in many of these and bolster the scientific inference from future EHT campaigns, particularly for imaging. I will provide an overview of MeqSilhouette, which can implement physically derived signal corruptions, including the ISM, troposphere and antenna pointing errors. Time variability in all domains (source, system temperature, ISM, troposphere, pointing error, etc.) is implemented, enabling an exploration of their systematic effects on parameter estimation and feature extraction results. Current efforts are toward GPU-acceleration to enable a sufficient number of visibility dataset realisations to perform robust Bayesian parameter estimation in a reasonable period of time. The ultimate goal of MeqSilhouette is to strengthen the link between observational capabilities and theoretical predictions relevant to the EHT scientific objectives.

Dexter Jason MPE Garching
Event horizon scale polarization around Sgr A* and M87
GRMHD simulations of black hole accretion self-consistently evolve the magnetic fields that give rise to the observed, time-variable, polarized synchrotron radiation. The fields are usually toroidal and coherent on the small scales of the submm emission. I will discuss how plasma effects, and especially Faraday rotation from within the emission region, could scramble the polarization. EHT measurements constrain the strength of these effects and therefore the physical properties of the emitting gas. The low observed linear polarization fraction from M87 could be a result of strong Faraday rotation, and if so the accretion rate could be significantly higher than the inferred limit.

Doeleman Sheperd SAO/Harvard
Project Summary (Shep Doeleman, Director)
The Event Horizon Telescope project has made significant headway since the last meeting held two years ago at the Perimeter Institute. An organizational structure has been formed and a collaboration agreement nearly finalized with key posts now filled. Detailed planning for project activities from instrumentation to data collection and processing, to data analysis and science utilization has begun in earnest. Meanwhile, there are new science results that highlight the unique perspective and power of horizon-resolving observations, and two campaigns of instrument commissioning have positioned the EHT to make the highest resolution and sensitivity observations ever attempted in April 2017. This talk will summarize progress and the status of the project and introduce the rest of the meeting.

Falcke Heino Radboud University Nijmegen
The Africa Millimeter Telescope
The Event Horizon Telescope project currently consists of a number of telescopes around the globe to image the supermassive black holes in the Galactic Center and M87 at event horizon scales with very long baseline interferometry (VLBI) at wavelengths around one millimeter. A crucial factor to improve image quality and robustness of the image reconstruction is the number and distributions of telescopes. An obvious region still missing in the network is Africa. Hence, we propose to build mm-wave VLBI radio dish on the Gamsberg in Namibia. The Gamsberg is one of the highest mountains in south west Africa, close to the Namib, one of the driest deserts in the world. Also, the Galactic Center passes almost exactly overhead and there is mutual visibility on Sgr A* with the IRAM telescopes, the South Pole, ALMA and the LMT. The telescope would have a diameter of about 13 m and be optimized for high frequencies and VLBI.  At times when no EHT campaigns can take place, it can do 3mm survey work but also participate in cm-wave VLBI networks. The presentation describes background and the current status of the project.

Fraga-Encinas Raquel Radboud University
Probing spacetime around Sagittarius A using modeled VLBI closure phases
The emission region and black hole shadow of Sagittarius A* can be probed with millimeter Very Long Baseline Interferometry. Our goal with this work is to constrain the geometry of the emitting plasma around Sgr A* by using modeled mm-VLBI closure phase calculations at 1.3 mm. We have simulated images for different models of the emission of Sgr A*: a disk model, and a jet model. The disk and jet models are physically driven scenarios based on standard three-dimensional general relativistic magnetohydrodynamic simulations of hot accretion flows without and with a jet. We present our closure phase results for the triangle of stations formed by CARMA-Hawaii-SMT, compare them to currently available closure phase observational limits and discuss the implications on the geometry of the plasma.

Friberg Per East Asia Observatory
The JCMT 15 m telescope situated next to the SMA on Mauna Kea is participating in the EHT VLBI experiments. However, the JCMT is dependent on the SMA for generating frequency references and for down conversion and recording of the IF signal. In doing so the JCMT replaces a receiver on a SMA dish. This is not a feasible option any more when the SMA is operating in dual polarization mode - there is no longer any free capacity at the SMA. The paper describes the plans and design for the JCMT to become an independent VLBI station as well as plans for upgrading the 230 GHz receiver.

Fromm Christian Institute for Theoretical Physics
Synthetic imaging of relativistic jets
Future Very Long Baseline Interferometry (VLBI) observations will provide high resolution images of relativistic jets. To test different jet models and to compare them to VLBI observations we used relativistic magneto-hydrodynamic (RMHD) simulations and computed the non-thermal emission. We developed a fully dynamical emission code, taking the finite speed of light into account (slow light), and computed synthetic radio maps, light curves and spectra. In the post processing we included the properties of observing array and the image reconstruction algorithm which allowed us a more direct comparison to the observations. In the talk we present the first results of our simulations for different jet models and show the difference between the slow light and the fast light approach.

Galison Peter Harvard University
History of Black Holes

Georgiev Boris University of Waterloo
Radiatively Inefficient Accretion Flows in Modified Gravity Spacetimes
The EHT will probe the near-horizon region of accreting black holes, enabling novel probes of modified gravity.  Determining the practical constraints that can be placed on these gravitational theories requires an understanding of the impact of the modified geometry on both the propagation of photons and the dynamics and structure of the accretion flow.  We have begun the process of computing radiatively inefficient accretion flow (RIAFs) in modified spacetimes.  We have replicated the results of Yuan et al. 2000, where a Pacynzki-Witta potential was used to simulate some aspects of GR and the primary emission mechanism was assumed to be synchrotron.  We are in the process of replicating this formalism in a covariant form for stationary, axisymmetric spacetimes that will enable the computation of RIAFs in non-GR spacetimes.

Gold Roman Perimeter Institute for Theoretical Physics
Towards a community-wide Validation of Theoretical Predictions for the EHT
The scientific impact of EHT products relies in large parts on understanding and characterizing systematics and uncertainties in theoretical predictions. Full utilization of the capabilities of the EHT therefore requires rigorous and careful validation of theoretical models on several fronts. In this presentation I will propose what characteristics possible tests should have and suggest several concrete tests to begin this essential validation process. One of the goals of this presentation is to stimulate a discussion, to invite further suggestions and to define a common path forward.

Gómez Jose L. Instituto Astrofisica Andalucia - CSIC
EHT+ALMA imaging of the candidate binary SMBH in OJ287
The blazar OJ287 is one the best candidate for hosting a compact supermassive binary black hole (SMBBH) system and an excellent candidate to study jet formation in magnetically dominated AGN. EHT+ALMA observations have been approved for spring 2017 to image the jet in OJ287 in combination with quasi-simultaneous 3 mm GMVA+ALMA and 1.3 cm space VLBI RadioAstron observations at similar angular resolutions, approaching linear scales of only 26 Schwarzschild radii. This would allow determination of the spectral energy distribution in the jet and the three dimensional structure of the magnetic field to test the SMBBH scenario and magnetically driven jet formation models. Confirming the SMBBH model will establish OJ287 as an excellent candidate for studying strong-field relativistic effects before the launch of space-based gravitational wave detectors and the operation of pulsar timing arrays.

Hada Kazuhiro NAOJ
An improved view of the M87 jet revealed at low frequencies and plans of multi-frequency monitoring toward EHT-2017 session
The EHT with ALMA observations of M87 scheduled in next April will offer the first-ever opportunity to image the shadow of this black hole and the site of jet launching. This will allow us to solve some primary questions about jet formation physics. To maximize the science output based on the EHT data, complementary VLBI observations at the lower frequencies (and also other facilities such as at gamma-ray) are very useful. I will present some of our current VLBI studies of M87 that are made at low frequencies (<=86GHz) but that are closely related with the EHT science. I will also overview the current plans of our complementary monitoring observations with other instruments (KaVA/EAVN, VLBA, EVN (and TeV)) that will be conducted in concert with the EHT-2017 session.

Honma Mareki NAOJ
BH imaging and beyond: self-calibration and feature extraction
In this talk, I will briefly introduce our on-going works related with black hole imaging to kick off the discussions on the future tasks toward EHT observations in 2017. First I would like to present simulation results of imaging with self-calibrations, and discuss its implication for the observations of the black hole shadow. I will also comment on possibilities of feature extraction with simple parameterization approach, which may be useful to derive physical parameters of the black hole and accretion disk.

Ikeda Shiro Institute of Statistical Mathematics
Sparse modeling methods for interferometry imaging
The imaging of VLBI, including EHT is an ill-posed problem. Many methods have been proposed to solve the problem, and Japanese EHT group including K. Akiyama (MIT) has proposed a collection of methods based on sparse modeling. We are finalizing the software development and will be ready for the EHT imaging soon. Since the problem is ill-posed, there is no single method which works perfectly for every type of images. This is why we have proposed multiple methods, including sparse imaging, TV-regularized imaging, and squared TV-regularization. I will explain them and how they work for imaging. I will also present how to choose the tunable parameters automatically, and possible extension for movie reconstruction.

Inoue Makoto ASIAA
Observation of Binary SMBHs with submm VLBI
Thanks to the superb angular resolution of submm VLBI, we are now having a possibility to observe binary system of SMBHs. In fact, the angular size of a binary model of OJ287 would be detectable with submm VLBI, if the two SMBHs have enough intensity in submm regime. This type of observation could create new synergy with pulser timing observations of gravity wave detection. One possible scenario of SMBH evolution is a merging process of smaller SMBHs to larger ones, and through these processes, many binary SMBH systems should exist. Indeed, several binary candidates are recently observed. Here in this presentation, basic ideas of the observation will be discussed.

Issaoun Sara Radboud University
Absolute calibration of the Sub-Millimeter Telescope in preparation for the EHT + ALMA run in Spring 2017
The Sub-Millimeter Telescope (SMT) is an integral part of the EHT and will participate in the upcoming Spring 2017 run. However, it is used almost exclusively for spectroscopy and does not possess a complete calibration procedure suitable for continuum observations. Working jointly with staff at the University of Arizona, single-dish data of various sources taken during the EHT March 2015 and April 2016 runs were used: to determine a previously unknown elevation-dependent gain correction for the telescope; to establish a complete single-dish continuum calibration procedure at 1.3 mm within the SMT's in-house program LinuxPops; to perform single-dish intra-day variability studies of AGN; and to begin a 1.3 mm flux density catalog for future AGN monitoring with a 10% relative error margin. Close communication with software developer Thomas Folkers enabled an analysis of the calibration and data collection processes, their issues and their limitations. The findings include: a better constrained gain curve peaking at 50ο , improving on the previous gain curve that exhibited an uncharacteristic 20% drop in flux density from low to high elevation; a longer integration time at low elevation of 10 seconds; a 20ο elevation limit imposed by the tree line and neighboring observatories; improved scaling of the flux density outputs due to a reduction of the relative uncertainty from 40% to10%, in agreement with previous gain corrections by Dr. Vincent Fish in 2013; and an optimal understanding of the calibration method within LinuxPops, transferable to other stations within the EHT. These results thus lead to a complete and fully automated absolute amplitude calibration procedure, an important aspect of the EHT data reduction process.

Janssen Michael Radboud University Nijmegen
The Development of a Data Reduction Pipeline for the EHT
Currently, HOPS and AIPS are the primary choices for the calibration of mm-VLBI data. However, the upcoming CASA release in 02/2017 will also have the full potential to handle VLBI observations. With the ability to associate station-based SNRs with fringe detections, full support for the EHT data format, a readily scriptable python interface and the possibility to easily incorporate a flagging algorithm for mm-VLBI data, CASA will provide an ideal basis for the development of an automated EHT data calibration tool. For a meaningful comparison of the observational data with simulations, the MeqTrees software package offers a broad set of useful tools. Realistic synthetic data can be generated (in batch mode) by incorporating various effects from a mimicked observation with a given uv coverage. These influences include atmospheric effects, interstellar scattering and thermal noise. These features make CASA and MeqTrees promising options for building blocks within a complete EHT data processing pipeline.

Jeter Britton University of Waterloo
Distinguishing Jet Launching Mechanisms in M87 with Dynamical EHT Observations
VLBI movies of M87’s jet show clear signs of spatial structure and short-timescale variability.  The Event Horizon Telescope will provide exclusive access to jet-launching physics at the horizon scale, and so it is important to understand the impact of variable emission near the horizon in both the image and visibility domains.  We model this variability by constructing an electron over-density near the black hole horizon, and allow this over-density to shear and deform as it moves in the velocity field around the black hole.  Both image and visibility data, e.g. visibility amplitudes and closure phases, depend strongly on the initial launch position of the electron over-density, and leave clear signals that separate jet-driven and disk-driven jet launching mechanisms.

Johnson Michael CfA/SAO
Stochastic Optics: A Scattering Mitigation Framework for VLBI Imaging
Just as turbulence in the Earth's atmosphere can severely limit the angular resolution of optical telescopes, turbulence in the ionized interstellar medium fundamentally limits the resolution of radio telescopes. This interstellar scattering dominates the observed image of Sgr A* at centimeter wavelengths, providing a major impetus to develop the EHT. Yet, even at 230 GHz, scattering can strongly affect observations of Sgr A*. I will discuss the role of scattering in EHT observations and a new scattering mitigation framework for EHT modeling and imaging.

Kim Junhan University of Arizona
Bayesian techniques for comparing time-dependent GRMHD simulations to variable Event Horizon Telescope observations
Early observations of the Event Horizon Telescope (EHT) have revealed variable horizon-scale emission in the Galactic Center black hole, Sagittarius A* (Sgr A*). Comparing such observations to time-dependent general relativistic magnetohydrodynamic (GRMHD) simulations requires statistical tools that explicitly consider the variability in both the data and the models. We develop here a Bayesian method to compare time-resolved simulation images to variable VLBI data, in order to infer model parameters and perform model comparisons. We use mock EHT data based on GRMHD simulations to explore the robustness of this Bayesian method and contrast it to approaches that do not consider the effects of variability. We find that time-independent models lead to offset values of the inferred parameters with artificially reduced uncertainties. Moreover, neglecting the variability in the data and the models often leads to erroneous model selections. We finally apply our method to the early EHT data on Sgr A*.

Kramer Michael
Combing methods: Probing the spacetime of Sgr A in an optimal way
In order to test the description of black holes in different theories of gravity, we need to determine the corresponding spacetime properties. This can be achieved with various methods, each of them usually offering different insight. For instance, images of the black hole shadow allow us to probe the near-field, but on its own it may not be sufficient to test deviations from the Kerr metric. Timing observations of an orbiting pulsar would, in contrast, provide far-field information, which has to match up with that provided in the near-field. We demonstrate that a combination of different methods is thereby an optimal way to extract the full information from black hole observations, providing the best possible way to uniquely test of theories of gravity under extreme conditions. We will also comment on practical aspects of EHT data analysis strategies.

Krichbaum Thomas P. Max-Planck-Institut fuer Radioastronomie
The micro-arcsecond scale fine structure of AGN jets
Global VLBI imaging observations at millimeter wavelength trace AGN jets to the region where they are launched and accelerated. This allows the study of the physical conditions in the vicinity of super-massive black holes on scales ranging from a few to several 1000 gravitational radii. For the nearest AGN like M87, measurements close to the Event Horizon scale are already reached. The multi-frequency study of the brightness temperature profiles of the inner jets helps to discriminate between the variety of jet models. This is applied to existing 1mm-VLBI data. Global 3 millimeter VLBI now provides maps of good enough fidelity to facilitate the accurate measurement of jet ridge-lines and profiles with an angular resolution of up to 40 micro-arcseconds. The 1mm VLBI imaging with the EHT reveals even smaller regions of compact emission. The future addition of ALMA to the EHT and to the GMVA will further enhance the imaging capabilities and help to solve remaining ambiguities in the registration of the observed ultra-compact structural components. The good complementarity of both VLB-interferometers is presented and discussed based on new data for a number of well known AGN and extrapolated to the future.

Kuramochi Kazuki The University of Tokyo/NAOJ
Hybrid Mapping of the Black Hole Shadow with the Event Horizon Telescope
The supermassive black holes in Sgr A* and M87 provide an excellent opportunity to image the black hole shadow with the Event Horizon Telescope (EHT), a global millimeter VLBI array. VLBI observations, particularly at short-mm wavelengths, have a difficulty in accurate measurements of visibility phases due to short coherence timescales and a lack of good phase calibrators. Traditionally, the hybrid mapping, an iterative technique combining imaging and self-calibration processes, has been used to calibrate visibility phases in VLBI observations. We propose the optimal method for the hybrid mapping of the black hole shadow with the EHT. We find that a widely-used point source model do not lead to reconstruct correct images and therefore is not appropriate as the initial model for black-hole shadow images. This can be resolved by adopting images reconstructed from closure phases as an initial model. In addition, self-calibration is also beneficial to closure imaging itself, since this enables to estimate image noise levels from residual maps. In this poster, we present simulated observations of Sgr A* with the EHT 2017 array, and example images of the hybrid mapping with sparse modeling techniques.

Lu Rusen MPIfR
Anatomy of the event-horizon-scale structure of SAGITTARIUS A with a resolution of 3 Schwarzschild
We report results from EHT observations of Sgr A* at 230 GHz in 2013. The observations were made with stations at four sites, including CARMA, SMT, Hawaii, and APEX. The addition of the APEX telescope has greatly improved the baseline coverage of the array, providing a spatial resolution of ~3 Schwarzschild radii on Sgr A*. With the improved array performance, the horizon scale structure of Sgr A* has been spatially resolved and is more complex than previously modeled. We show the possible small scale brightness distribution of the source in terms of multiple-Gaussian and crescent-like models and discuss our results in the context of disk-dominated and jet-dominated accretion flow models.

Lupsasca Alex Harvard University
Optical appearance of a hot spot orbiting near the ISCO of a near-extremal black hole
General relativity predicts that near-extremal black holes develop an emergent conformal symmetry in their near-horizon region. Near extremality, the ISCO radius lies deep in the black hole's throat, where physics is governed by this conformal symmetry. This makes it possible to analytically compute the optical appearance of a star, or hot spot, orbiting near the ISCO of a near-extremal black hole. We find that the number of observed images appearing simultaneously diverges as the black hole approaches extremality for a hot spot on the ISCO. All these images appear on the vertical edge of the shadow. This distinctive result could provide a simple test of extremality, and its experimental detection would constitute the first observation of conformal symmetry in the sky.

Marrone Dan University of Arizona
One of: - SPT status- Statistics and the Analysis of EHT Data

Marti Vidal Ivan Onsala Space Observatory

Matsushita Satoki ASIAA
Greenland Telescope GLT Project for M87 Black Hole Shadow Imaging
M87 is a promising candidate to reveal the shadow image of its Supermassive Black Hole (SMBH).  Greenland Telescope (GLT) project is aiming to image the SMBH shadow using submillimeter VLBI technique together with other submillimeter telescopes like the Phased ALMA in Chile, and JCMT/SMA in Hawaii.  The big triangle formed by GLT-ALMA-JCMT/SMA provides 20 micro arcsecond resolutions at 350 GHz towards M87, whose shadow size are expected to be about 40 micro arcsecond.  LMT in Mexico is located almost at the center of the big triangle, and other Event Horizon Telescope (EHT) antennas would provide the high quality image of the shadow.  GLT project is led by ASIAA, Taiwan, collaborating with SAO, MIT Haystack Observatory, NRAO, NAOJ, and Osaka Prefecture University.  Main components of the GLT antenna are already shipped to Thule, Greenland, and currently we are reassembling.  We are planning to make a few initial VLBI observations in 2017/2018.  We will also arrange the infrastructures of the final destination, the summit of Greenland.  In this presentation, we will report the current status of the telescope.

Matthews Lynn MIT Haystack Obs
Phased ALMA

Medeiros Lia University of Arizona
Variability in GRMHD simulations of Sgr A*: Implications for EHT amplitude and closure phase observations
Traditional synthesis imaging of sources with interferometric observations rests on the assumption of a stationary image. We explore the limitations of this assumption for the EHT using high-cadence GRMHD simulations of Sgr A*. We find that the location and depth of salient features of visibility amplitude maps in the u-v plane are highly variable, especially in disk-dominated models. We also find that, in general, closure phases along small baseline triangles show little variability, except in the cases when one of the triangle vertices crosses a small region of low visibility amplitude. The closure phase variability increases with the size of the baseline triangle, as larger baselines probe the small-scale structures of the images, which are highly variable. On average, jet-dominated MAD models show less variability in the predicted visibility amplitudes and closure phases than disk-dominated SANE models, even in the large baseline triangles, because the images from the latter are more sensitive to the turbulence in the accretion flow. Our results suggest that image reconstruction techniques need to explicitly take into account the amplitude and closure phase variability, especially if the quality and quantity of data allow for a detailed characterization of the nature of variability. This also implies that, if image reconstruction techniques that rely on the assumption of a static image are utilized, regions of the u-v space that show a high level of variability will need to be identified and excised.

Mizuno Yosuke Goethe University Frankfurt
GRMHD simulations in alternative theories of gravity
Future mm and sub-mm very long baseline interferometry will provide the first images of the shadow cast by the candidate supermassive black hole in our galactic center, Sgr A*. If the observations are sufficiently accurate, they will not only provide convincing evidence for the existence of an event horizon, but they could also indicate if deviations exist from the predictions of general relativity. Rezzolla & Zhidenko (2014) have proposed a new parametric framework to describe the most generic spherically symmetric black hole geometry through a finite number of adjustable quantities. Here, as a first test, using this new parametric framework we have performed 2D general-relativistic MHD simulations of magnetized torus of a non-rotating dilaton black hole using the newly developed BHAC code. Initially we consider a magnetized torus with constant angular momentum with a weak single poloidal magnetic field loop inside the torus. The simulations show a behaviour that is qualitatively very similar to those for a Schwarzschild black hole, but also some quantitative differences in terms of the mass-accretion rates and of the appearance of the shadow.

Moscibrodzka Monika Radboud University
Faraday rotation in GRMHD simulations of the jet launching zone of M87
Non-VLBI measurements of Faraday rotation (RM) around millimeter wavelengths are used to constrain mass accretion rates onto supermassive black holes in at least two systems: in the center of the Milky Way and in the center of the M87 galaxy. We constructed disc plus jet GRMHD models for these sources that qualitatively well describe their SEDs and radio/mm images. By using general relativistic polarized radiative transfer, we now model RM in disc plus jet models by tracing the position angle of the linear polarization plane around millimeter wavelengths as a function of mass accretion rate onto the black hole. Our calculations, based on the example of M87, indicate that model RM is independent of the assumed accretion rate. The result is due to the fact that disc plus jets models are Faraday optically thick for millimeter waves. RM based on fully consisitent radiative transfer calculations are smaller compared to RM based on integral that applies to Faraday thin sources only that is often used in the literature to model RM near black hole. We find that RM based on models with accretion rates larger than 9 times 10^-4 Msun/yr are consistent with observations of M87 core.

Müller Cornelia Radboud University
Zooming into the heart of Centaurus A
At a distance of only 3.8Mpc, Centaurus A is the closest radio galaxy. Its proximity allows us to study its relativistic jet at unprecedented linear resolution. VLBI observations in the framework of the TANAMI program provide the best-ever view of the innermost parsec of this extragalactic jet. The detailed study at sub-milliarcsecond scales provides valuable insight into jet kinematics and helps to constrain broadband emission models attempting to explain the gamma-ray emission of Cen A. At a declination of -43deg, this source has not been well accessible for mm-VLBI until now. The situation changed with the inclusion of ALMA, LMT and SPT in the EHT, offering now for the first time the opportunity to study the jet formation region at scales of less than 1 light-day. This talk will present the latest results of the cm-VLBI study and set the scene for the upcoming mm-VLBI observations.

Nagar Neil Universidad de Concepcion
The jet launching region (and black hole shadow?) in Nearby AGNs beyond SgrA* and M87
We are charactizing a sample of ~25 nearby AGNs with the goal leveraging the near future EHT results on SgrA* and M87 to better understand jet launching over a larger parameter space of jet power and morphology. Additionally, there is a very small but non-zero probability of imaging a black hole shadow (due to a larger than presumed black hole mass and/or an accretion disk counterrotating wrt black hole spin) in an AGN other than SgrA* and M87. We are pursuing two main avenues leading up to a future EHT (or VLBI with the Beamformed ALMA) program targeting the best candidates in the sample: (a) direct measurement of black hole masses in nearby AGNs with ALMA (ongoing: molecular gas kinematics) and VLT/MUSE-AO (future; stellar and ionized gas kinematics). We will present our approved pilot program to measure BH masses in 8 AGNs with ALMA (three galaxies have been observed over 29-31 October, and data may be delivered in time for the EHT meeting); and (b) a full characterization of the sub-mm fluxes (ALMA) and pc-scale jet morphologies of the sample (eg., VLBA and GMVA). While this is a long term project, likely requiring phase referenced observations with the EHT and/or Beamformed ALMA, our initial (pre-EHT) results will already allow significant synergies with EHT results on SgrA* and M87. Additionally, we will briefly discuss the science exploitation of the ALMA-only interferometry datasets obtained during approved and future EHT observations using the Beamformed ALMA.

Nakamura Masanori ASIAA
AGN Jets with the EHT: Exploring Fundamental Physics from Origin to Galactic Scale
We suggest that the EHT will provide us a clue for the origin of the M87 jet as well as new paradigm for AGN jets, although we have been struggling to understand some basic properties of relativistic jets in AGN during the century. In this presentation, I will summary our current understanding of the M87 jet in terms of observational and theoretical aspects; i) possible scenario for the jet initiation from the rotating black hole and ii) the jet collimation break (JCB: a transition form parabolic to conical geometry) at the sphere of gravitational influence. With the sub-mm VLBI observations, we will, for the first time, perform a quantitative test i) regarding the MHD jet paradigm for M87. Examining ii) for blazars will support how the JCB in AGN jets is correlated with the black hole-galaxy co-evolution. Thus, we conclude that the EHT project will bring a brand new world in AGN jets.

Narayanan Gopal University of Massachusetts, Amhers
EHT Receivers for the Large Millimeter Telescope

Olivares Sanchez Hector Raul ITP, Goethe-University Frankfurt
Adaptive Mesh Refinement and Constrained Transport in the code BHAC
Previously, we showed that the method to enforce divB=0 in a GRMHD simulation can lead to important differences in the results, as the presence or absence of a jet in an accretion process onto a black hole. Flux-interpolated Constrained Transport (FCT) can enforce divB=0 to machine precision, and was observed to preserve better stationary solutions and to be less diffusive compared to the GLM method. Nevertheless, to make it compatible with AMR, special divergence-preserving interpolation operators for the magnetic field at cell faces are needed. Starting from a minimal set of requirements, we derive a general form of these operators, which for a choice of parameters results in those existent in the literature. We found that, in three dimensions, all linear operators introduce field components not present in the original magnetic field, and we propose a new nonlinear interpolation to minimise this effect. Details on the implementation of an FCT scheme on the the finite-volume AMR GRMHD code BHAC, as well as a comparison of the results obtained using the linear and nonlinear interpolation in generic tests, are provided.

Popstefanija Aleksandar University of Massachusetts, Amhers
The LMT Interim 1-mm EHT Receiver

Porth Oliver ITP Frankfurt
Conditions for jet formation in GRMHD simulations of Black Hole accretion
Upcoming mm-VLBI observations will probe the SMBH in our galactic center and the giant BH in M87 on the horizon scale.  While both objects accrete in a similar, highly sub-Eddington regime, only M87 shows clear evidence for a persistent relativistic jet. In anticipation of direct observations of the jet (non-) formation site,  I will discuss new simulations with the GRMHD code BHAC on the formation of relativistic jets.  The analysis focusses on presence or absence of a jet, intrinsic variability and the accretion/ejection efficiency.  We find a new regime of sporadic or “fluctuating"" jet emission when the accretion flow is initialised with small scale fields.  In this case, the black hole is not saturated with magnetic flux and a jet is emitted only when the ergosphere is sufficiently magnetised.  This is accompanied with formation of large-scale plasmoids in the black hole magnetosphere and could give rise to jet-like emission observed in the flaring state of Sgr A*.

Pu Hung-Yi ASIAA
Non-thermal Emission Features of Black Hole GRMHD Jet on Horizon-scale
The separation surface, which separates inflow and outflow along black hole-threading field lines, proves a unique feature of GRMHD origin of a black hole jet. Assuming non-thermal electrons can be injected from the separation surface in a stationary fashion, we compute the spatial variation of the energy distribution of the electrons, as they are accelerated outward. Taking synchrotron cooling and adiabatic cooling into account, we discuss interesting non-thermal synchrotron emission features of a GRMHD jet. The typical location of the separation surface is about several tens gravitational radius. It is expected that future EHT/GLT observations of M87 on horizon scale can further test the predicted features.

Rezzolla Luciano Institute for Theoretical Physics
Theoretical work on modelling BH images in Frankfurt
I will report on the efforts made in Frankfurt in developing BHAC (Black Hole Accretion Code): a new and flexible computational infrastructure to study generic accretion flows onto black holes. I will also discuss a new parametric framework to describe the spacetime of axisymmetric black holes in generic metric theories of gravity.

Roelofs Freek Radboud University Nijmegen
Studying Rapid Variability of Sgr A with Closure Phases
General relativistic magnetohydrodynamic simulations exhibit millimeter emission originating from accretion disks and jets of supermassive black holes that is variable on timescales shorter or longer than a gravitational timescale $t_G=GM/c^3$. For Sgr A*, $t_G$ is much shorter than the typical duration of a VLBI experiment, which enables us to study this variability within a single observation. Closure phases, the sum of interferometric visibility phases on a triangle of baselines, are robust against station-based errors, which makes them particularly useful for studying this variability. Possible sources of closure phase variability are orbital dynamics, turbulence, interstellar scattering, baseline evolution due to Earth rotation, and thermal noise. We present a metric that is able to distinguish variability due to Earth rotation and thermal noise from intrinsic variability of Sgr A*. This metric is validated using synthetic observations of GRMHD simulations of Sgr A*. When applied to existing EHT data of Sgr A*, the metric shows that the data are most consistent with source models containing intrinsic variability from source dynamics, interstellar scattering, or a combination of those. The effects of black hole inclination, orientation, spin, and morphology (disk or jet) on the observed variability are also discussed. Power spectra and structure functions of the closure phase time series allow us to probe turbulent time scales, though distinguishing between models with different spins and morphologies based on the time scales will be challenging.

Ros Eduardo MPIfR
Pinpointing the supermassive black hole in NGC 1052
NGC 1052 is located at a distance of 19 Mpc, similar to M 87 and is a prime target to examine the formation of jets powered by supermassive black holes at scales of several hundred of gravitational radii. In contrast to the one-sided morphology of the latter, NGC 1052 shows a twin jet with both jet and counterjet bases being visible and almost unaffected by differential Doppler boosting. Recent 3-mm results have shown that both jets are detectable and extend from a bright and compact central feature, which marks the location of the black hole, with estimated magnetic fields between 200 G and 83000 G. VLBI observations with EHT+ALMA at Band 6 in Cycle 4 have been approved by the network (project 2016.1.01290.V). In parallel, RadioAstron observations performed on November 5/6, 2016 will address the structure of the source at 13 mm wavelength with the space antenna Spekt-R and a ground array of over 30 telescopes in both hemispheres. This provides matching resolution to 1.3 mm if fringes are obtained at baseline distances of 10 Earth diameters. Successful EHT and RadioAstron observations over the next months will provide unprecedented angular resolution and sensitivity that are vital to directly investigate the region where both jets initially form, and to resolve transversally both jets to tailor the involved jet physics. I will provide an overview about the present knowledge of the source and the expected improvements after planned observations.

Ryan Benjamin Ransom University of Illinois
Relativistic Radiation MHD Models of M87
The supermassive black hole at the center of M87 is likely accreting at a rate that, while significantly sub-Eddington, is high enough that radiative cooling is important to the thermodynamics of the accretion flow. The flow is likely to be Coulomb collisionless, and electron heating thus depends on kinetic turbulent dissipation. In addition, the low optical depth and order unity Compton y parameter motivate frequency-dependent full transport. We introduce a numerical scheme, ebhlight, that solves the time-dependent equations of general relativistic radiation magnetohydrodynamics with Monte Carlo transport and a prescription for collisionless electron heating. We use this scheme to model the observational signature of M87.

Shiokawa Hotaka SAO
Time Domain Filtering of Resolved Images of Sgr A
The Event Horizon Telescope (EHT) will soon provide spatially resolved images of Sgr A*, the source associated with the Galactic Center black hole.  Because Sgr A* varies on timescales short compared to an EHT observing campaign, it is interesting to ask whether variability contains information about the structure and dynamics of the accretion flow.  I will show results from time-domain filtering on mock image data generated from general relativistic magnetohydrodynamics models. We show that the image variability is tightly correlated to the radial origin of the light-rays because disk emissivity fluctuates on a timescale that scales with the local orbital period.  Time-domain filtered images therefore reflect the model dependent emission radius distribution that is not accessible from time-averaged images.  We show that in principle filtered data have the power to distinguish between models with different black hole spins, different viewing angles of the disk, and different disk orientations in the sky.

Stein Leo C. California Institute of Technology
Present and future tests of general relativity
We're now a century after the conception of general relativity. With technology's steady advance, observations are finally beginning to access the most extreme environments predicted by GR: the event horizons of black holes, both stellar mass and supermassive. As empiricists, we have the obligation to test GR in this new regime. I will review some present approaches to black-hole based tests of general relativity, comment on their shortcomings, and motivate future studies which will inform the next generation of GR tests.

Tchekhovskoy Alexander UC Berkeley
Electron Thermodynamics and The Disk-Jet Symbiosis in Sagittarius A*
The Event Horizon Telescope will soon produce the first images of the accretion flow at the event horizon scales of the supermassive black hole at the Galactic Center, Sagittarius A* (SgrA*). In order to fully interpret these revolutionary observations, first-principles models of SgrA*'s accretion flow are highly desirable. However, they are challenging to construct. This is because at the extremely low luminosity of SgrA* the plasma becomes collisionless: Coloumb collisions between the protons and electrons in the accretion flow become so rare that the electron temperature, which determines the emanating radiation, decouples from the proton temperature, which is given by the simulations. A standard approach to modeling such systems is to assume that the electron temperature is a fraction of the proton temperature. In this talk, I will show how to compute the electron temperature from first principles, by constructing a sub-grid model that accounts for the collisionless plasma effects responsible for the heating of the electrons in the accretion flow. I will show how this model naturally leads to disk-jet symbiosis, with the lower frequency emission coming from the outflow and higher frequency from the inflow. I will also present the predicted spectra, images, and time-variability, and compare to existing observations.

Tilanus Remo Radboud Uni. Leiden Observatory
The EHT: Project Update and Technical Rollout

van Langevelde Huib Jan JIVE
Living on the fringe: making CASA ready for VLBI
Over the past decade CASA has become the package of choice for calibration of current and next generation radio telescopes. At the moment, JIVE and NRAO are making rapid progress in preparing CASA for data processing of very long baseline interferometry. This involves porting the task FRING from AIPS to the new CASA fringecal task, and upgrading several CASA tasks to ingest data and metadata in VLBI format. Implementing this functionality in CASA will be a major step forward in calibration for a wide range of local instruments such as ALMA and LOFAR, and crucial for the development of sustainable calibration pipelines for global radio telescope networks such as EVN and EHT. It is a key ingredient for giving the community access to VLBI data, as ALMA and VLA users have mastered CASA. This talk will give an overview of the ongoing work, describe our efforts to verify and validate the software with simulations and actual data, and present our future plans.

van Langevelde Huib J. JIVE
Living on the fringe: making CASA ready for VLBI
Over the past decade CASA has become the package of choice for calibration of current and next generation radio telescopes. At the moment, JIVE and NRAO are making rapid progress in preparing CASA for data processing of very long baseline interferometry. This involves porting the task FRING from AIPS to the new CASA fringecal task, and upgrading several CASA tasks to ingest data and metadata in VLBI format. Implementing this functionality in CASA will be a major step forward in calibration for a wide range of local instruments such as ALMA and LOFAR, and crucial for the development of sustainable calibration pipelines for global radio telescope networks such as EVN and EHT. It is a key ingredient for giving the community access to VLBI data, as ALMA and VLA users have mastered CASA. This talk will give an overview of the ongoing work, describe our efforts to verify and validate the software with simulations and actual data, and present our future plans.

van Rossum Daniel Radboud University
The VLBI Monitor: A Web Server for Monitoring EHT VLBI Campains
Monitoring and Control is one of the core tasks laid out by the EHTC.  The VLBI Monitor software is developed at the Radboud Radio Lab for the specific tasks of 1. the real-time monitoring of participating observatories, and 2. the central storage of metadata and status information during and in between of observations.  The information gathered, presented, and made easily accessible by the VLBI Monitor provides a basis for the extension to ""control"" functionality in the future.  In this presentation we describe the design of the VLBI Monitor and demonstrate the features of the current web interface.  This information can serve as a basis upon which user feedback and feature requests can be made to guide future development.

Weinthroub Jonathan CfA/SAO
SWARM: A 32 GHz bandwidth correlator and phased array for the submillimeter array
The SMA Wideband Astronomical ROACH2 Machine (SWARM) is a high spectral resolution  correlator and phased array with 140 kHz bin width across its full band.  A quadrant of SWARM either processes 2 GHz of usable bandwidth per polarization in full Stokes polarization mode or 4 GHz of IF from a single receiver. Three quadrants of SWARM have been available for SMA science since September 2016. By December 2016 we expect four SWARM quadrants to be in operation, quadrupling the SMA’s instantaneous bandwidth to 32 GHz in two polarizations. SWARM is natively VLBI enabled, and SMA used it to record phased SMA dual polarization data at a rate of 32 Gbps during the April 2016 EHT campaign.  SWARM improves the SMA’s continuum sensitivity twofold, or alternatively, enables observations of a given sensitivity in one-quarter the time. This presentation will outline the design of SWARM and give examples of the science it enables.  I will also touch on a funded ALMA development study which examines a possible next generation EHT-enabled digital back end for ALMA with some aspects of the study informed by our experience with SWARM.

Younsi Ziri Goethe University, Frankfurt
Ray-tracing radiative transfer: modelling the emission from black holes in GR and other theories of gravity
In the coming years, VLBI observations will be able to resolve nearby SMBH candidates, most notably Sgr A* and M87, on event horizon scales. Promisingly, recent observations of Sgr A* have revealed structure on event horizon scales. I will discuss how we can combine time-dependent general-relativistic radiative transfer calculations with the GRMHD code BHAC to model the images, spectra and lightcurves from Sgr A*, addressing questions concerning variability therein. Additionally, whilst we expect Sgr A* to be a Kerr BH, several other BH solutions exist, both in GR and in alternative theories of gravity which cannot presently be ruled out. I will also discuss and present results from radiative transfer calculations of GRMHD simulations in other theories of gravity, with the aim of helping interpret upcoming observations of Sgr A*, testing the Kerr BH hypothesis and potentially excluding (or at least constraining) other BH solutions and theories of gravity.

Questions/Comments: EHT2016@cfa.harvard.edu