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\clearpage

\title{The Event Horizon Telescope: New Results and Future Plans}
\begin{document}


\maketitle
\scalefont{1.5}

\section*{EHT Collaboration}
Shep Doeleman,   Chris Beaudoin,  Michael Titus, Alan Rogers, Daniel Smyth, Jason SooHoo   \& Vincent Fish (Haystack), 
Dick Plambeck, David MacMahon, Matt Dexter,  Melvyn Wright \& Geoff Bower (Berkeley),   
 Rurik Primiani,  Jonathan Weintraub, Ray Blundell, Ken Young, Mark Gurwell, Lincoln Greenhill \& Jim Moran (CFA),
David Woody, James Lamb, David Hawkins, (CARMA),  Dan Marone (Chicago),
Per Friberg \& Remo Tilanus (JCMT),
Richard Chamberlin (CSO),
Bob Freund, Peter Strittmatter \& Lucy Ziurys (ARO - AZ)
Tomoaki Oyama \& Mariki Honma (NRO - Japan)
Mark Wagner, Vinayak Nagpal, Henry Chen \& Dan Werthimer (CASPER) ,


\clearpage

\section*{SUMMARY}
\begin{itemize}
\item EHT is a  network of  $\lambda$ (sub)mm  antennas to make a Global VLBI array. 
\item At  $\lambda$ 1.3mm and 0.8mm,  angular resolution $\sim$ 20 micro $\mu as$
\item SgrA* and M87 have the  largest apparent BH  Event Horizons.
\subitem  General Relativity in the strong-field regime.
\subitem  Accretion and outflow at the edge of a BH.
\item SgrA*  $\sim 4~10^6  M_0 $  BH at Galactic Center. 
\subitem We resolve structures on scale  of  Event Horizon.  
\item  M87  giant elliptical galaxy with $\sim 8~10^9  M_0 $  BH in nucleus.
\subitem  We detect structure at the base  of  relativistic jet.
\item  EHT  Roadmap  2010 - 2015;  critical contribution of CARMA.  

\clearpage

\section*{SgrA* Evidence for a Black Hole}
\slshape
\item  Evidence suggests SgrA* is a $4~10^6$ solar mass black hole at the galactic center:
\item  Mass estimates from orbitting stars (Gillessen et.al 2008, Ghez. et el. 2008),
\item Proper motion limits on SgrA* itself (Backer \& Sramek 1999, Reid \& Brunthaler 2004).
\item Size limits on SgrA* from VLBI (Bower et al.  2004, Shen et al. 2005, Doeleman et al. 2008). 
\item The observations imply a mass density for SgrA*  $ > ~9~10^{22} M_0$  per cubic parsec. 
\item Close observational correlation between the mass of our galaxy and it's
velocity dispersion suggest strong connection between formation of the black hole and the galaxy itself.
\item The best evidence thus far is from studying the proper motion of stars near SgrA*. 
\item  EHT will increase our understanding and add to the mounting evidence for a Massive Black Hole at the
Galactic center.
\clearpage

\begin{figure*}[t]
\begin{center}
\vskip -0.2in
\includegraphics[scale=0.6]{star-orbits2.jpg}
\caption{\small
   \setlength{\baselineskip}{0.85\baselineskip}
   Star orbits
   \label{fig:star-orbits2}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage

\section*{The Event Horizon Telescope}
\item The EHT is a  network of (sub)mm
wavelength antennas that are linked together to function as a Global VLBI array.
\item At  $\lambda  1.3 mm $, the angular resolution of the
EHT $\sim$ 20 micro arcseconds.
\item Need $\lambda mm$  observations to minimize dispersion by the Inter-Stellar Medium which goes as $\lambda^2$.
\item For SgrA*, the $4~10^6 M_0 $ black
hole at the Galactic Center, the EHT  has resolved structures on  scale of the Event Horizon.  
\item Similar scale structures have also been detected at the base of the relativistic jet in M87, a giant
elliptical galaxy harboring a $\sim 10^9 M_0$ black hole.
\item Currently IBOB and BEE2 boards and CASPER firmware are used to phase up and process the signals from the antennas, then pass the data to the Mark VB data recorder.
\item Closure phase ($ O = \phi_1 + \phi_2 - \phi_3$) is used for calibration as phase errors are subtracted out.
\item  2007-2010  SgrA* observations with ARO/SMT, CARMA, and JCMT  estimated Schwarzschild radius ~$0.37 AU$.
\clearpage

\begin{figure*}[t]
\begin{center}
\vskip -0.2in
\includegraphics[scale=0.76]{vlbi-overview.jpg}
\caption{\small
   \setlength{\baselineskip}{0.85\baselineskip}
   VLBI overview
   \label{fig:vlbi-overview}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage

\begin{figure*}[t]
\begin{center}
\vskip -0.2in
\includegraphics[scale=0.3]{carma-moon.jpg}
\caption{\small
   \setlength{\baselineskip}{0.85\baselineskip}
   CARMA MOON 
   \label{fig:carma-moon}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage

\begin{figure*}[t]
\begin{center}
\vskip -0.2in
\includegraphics[scale=0.5]{croppedsmapan.jpg}
\caption{\small
   \setlength{\baselineskip}{0.85\baselineskip}
   JCMT and SMA telescopes on Mauna Kea
   \label{fig:sma}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage

\begin{figure*}[t]
\begin{center}
\vskip -0.2in
\includegraphics[scale=0.6]{maserphoto.jpg}
\caption{\small
   \setlength{\baselineskip}{0.85\baselineskip}
   VLBI maser 
   \label{fig:maser}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage


\section*{CASPER Libraries and Hardware}
\slshape
\item CASPER (Collaboration for Astronomical Signal Processing and Engineering Research.)
\item FPGA based hardware is now used in phasing up the antennas with 1 GHz Bandwidth
\item The system design uses modular DSP
boards with a flexible interconnect architecture which allows 
reconfiguration of the computing resources for multiple applications.
\item The programming model uses a system generation library with
hardware abstractions which allow the application programmer to focus
on the application rather than the details of the hardware.
\item The system design and programming model together allow the application
software to survive by using a technology independent design flow.
.
\item Scalable CASPER technology allows for the phased arrays  that improve sensitivty .
\item Next generation architecture of the broadband phased array processor upgrade
based on the ROACH Virtex-5, is targeted for deployment in 2012.
\item This will allow double the bandwidth and increased sensitivity.

\vspace{1pc}
\slshape
\includegraphics[scale=0.3]{sma-hw-diagram.pdf}
\clearpage

\begin{figure*}[t]
\begin{center}
\vskip -1.0in
\includegraphics[scale=0.9]{CARMA_network_layout.pdf}
\caption{\small
   \setlength{\baselineskip}{0.85\baselineskip}
   CARMA Mark5B, DBE, and Network Setup 
   used for the uVLBI experiment held March 26th 2009 through April 8th 2009 at CARMA.
   \label{fig:CARMA_network_layout.pdf}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage


\begin{figure*}[t]
\begin{center}
\vskip -0.2in
\includegraphics[scale=1.28]{SgrA-BH-sim.pdf}
\caption{\small
   \setlength{\baselineskip}{0.85\baselineskip}
   SgrA Results and Black Hole models:  Solid black line is apparent diameter with lensing by a black hole.
Dashed line with no lensing. The intrinsic size of SgrA* observed with  $\lambda 1.3mm $ VLBI  (red line) is smaller than the minimum apparent size of the black hole event
 horizon suggesting that the submm emission of SgrA* must be offset from the black hole position.
 This can be understood in the context of General relativistic MHD accretion disk simulations
(right), which exhibit compact regions of emissions due to Doppler enhancement of the approaching side of an accretion disk.
   \label{fig:SgrA-BH-sim}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage

\begin{figure*}[t]
\begin{center}
\includegraphics[scale=1.0]{Sgra-BlackHole.pdf}
\caption{\small
   \setlength{\baselineskip}{0.7\baselineskip} 
 \label{fig:SgrA Black Hole}
}
\end{center}
\vskip -0.2in
\end{figure*}

\section*{What did we see?}
\slshape

\item A symmetric emitting surface surrounding a black hole is gravitationally lensed to appear larger than its true diameter. 
%\item  The solid black line shows the apparent diameter with lensing by a black hole.
%\item  The dashed line with no lensing.
\item The intrinsic size of SgrA* observed with $\lambda 1.3mm$ VLBI  is smaller than the minimum apparent
size of the black hole event horizon suggesting that the submm emission of SgrA* must be offset from the
black hole position.  
\item This can be understood in the context of General relativistic MHD accretion disk simulations, which exhibit compact regions of emissions due to Doppler enhancement of the approaching side of an accretion disk.
\clearpage

\section*{What should we see?}
\slshape
\item VLBI simulations of SgrA* have given us a good idea of what to expect from imaging.
\item  Left:  models that have been scatter broadened by the Inter Stellar Medium.
\item Middle: images reconstructed using a 7-station $\lambda=0.8mm$ wavelength
array that could reasonably scheduled within the next 3-5 years.
\item Right:  images reconstructed using 13-station array that could be assembled  this decade.

\vspace{1pc}

\slshape
\includegraphics[scale=0.5]{vlbi-sim.jpg}

\clearpage


\section*{Improving Sensitivity}

\item Enhancing EHT sensitivity: dual polarization, phased arrays, wideband VLBI backends,
and high-speed VLBI recorders.
\item Time-variable changes can be resolved and monitored on 10-second time scales.  
\item Simulations model flares in
SgrA* as orbiting hot-spots in the accretion flow, EHT can potentially
time these orbits and provide new estimates of the black hole spin.
\item Planned upgrade to SMA and CARMA this year will allow us to form beams at these locations, improving the image
and sensitivity from the 2007-2009  observations.
\item ALMA will be phased up and contributing to the EHT within a few years.
\clearpage

\begin{figure*}[t]
\begin{center}
\vskip -0.2in
\includegraphics[scale=0.16]{EArray424KB.jpg}
\caption{\small
   \setlength{\baselineskip}{0.85\baselineskip}
   E-configuration
   \label{fig:E-configuration}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage

\begin{figure*}[t]
\begin{center}
\includegraphics[scale=3.1]{Closure-Phase-D230-apex.jpg}
\caption{\small
   \setlength{\baselineskip}{0.8\baselineskip}
   Closure Phase with APEX
 \label{fig:SgrA Closure Phase}
}
\end{center}
\vskip -0.2in
\end{figure*}

\begin{figure*}[t]
\begin{center}
\includegraphics[scale=3.1]{Closure-Phase-D230-alma10.jpg}
\caption{\small
   \setlength{\baselineskip}{0.8\baselineskip}
   Closure Phase with ALMA10
 \label{fig:SgrA Closure Phase}
}
\end{center}
\vskip -0.2in
\end{figure*}


\begin{figure*}[t]
\begin{center}
\includegraphics[scale=3.1]{Closure-Phase-D230-alma50.jpg}
\caption{\small
   \setlength{\baselineskip}{0.8\baselineskip}
   Closure Phase with ALMA50
 \label{fig:SgrA Closure Phase}
}
\end{center}
\vskip -0.2in
\end{figure*}
\clearpage

\section*{STATION CALIBRATION}

\item    Correlated flux on VLBI target source = 
\subitem correlation coeficient
                x sqrt(Ta/Tsys(i) Ta/Tsys(j))
                x phasing efficiency

\item  $ T_a$  on target source: SgrA* in complex FoV.
\subitem  phasing efficiency: atmospheric phase;  pointing errors; wind.

\item    Real time calibration of array stations using station correlator.
\subitem  Need good station uvcoverage to isolate and calibrate target source.
\subitem  Use extended array configurations to
spatially filter out large scale structure if atmospheric phase correction is good enough.

 \item     High instantaneous bandwidth. (Maximum atmospheric correlation time $\sim 10 s$)
\clearpage

\section*{ROADMAP FOR MMVLBI}
%\begin{itemize}
\item 2008-2010:   500 MHz band on 1-2 antennas at CARMA. 
\subitem  Analog input into ADC for each antenna in VLBI station.
\subitem  Custom formatting into VLBI recorder.

\item  2011-2012  Two 500 MHz bands.
\subitem  digital beamforming at single phase center.
\subitem use CARMA correlator for  beamformer  calibration.
\subitem  Custom formatting into VLBI recorder.
\subitem      (e.g. CARMA  4-8 antennas x 2 pols x 4 500 MHz bands)
  
\item 2015+ High speed digitized data for each antenna in VLBI station.
\subitem frequency domain delay and fringe rate correction.
\subitem  digital beamforming at multiple phase centers. 
\subitem use station correlators for  beamformer  calibration.
\subitem  industry standard data to disk. (e.g. 10GbE)
\subitem       (e.g. CARMA  15 antennas x 2 pols x 8 GHz) 
      
\clearpage

\section*{ MMVLBI  with ALMA}

\item 2010-2012   Limited station commitment to VLBI .
\subitem Typical 1 week/year.
 \subitem No ALMA participation.

\item 2015+      Major station committment to VLBI with ALMA
\subitem VLBI as a science motivation for maintaining university facilities.
\subitem  2 sessions (e.g. Spring and Fall) 
\subitem  1-2 week gap to reduce data and mitigate bad weather.
\item  Heterogeneous VLBI stations

\subitem  Long Term Plan to align station capabilities.
\item  Frequency, Pols x Bandwidth. 
\subitem  CARMA 230 GHz x 2 pols. Analog data from antennas.
\subitem  SMA   230 GHz x 1 pol;  345 GHz x 2 pols. Analog data from antennas.
\subitem  ALMA  230 GHz and 345 GHz dual polarization.  2 Ghz digital data from antennas.
\clearpage
     
 \section*{CONCLUSION}
\item  VLBI using CARMA,  JCMT and  ARO/SMT on Mt. Graham in Arizona  at 1.3mm.
\subitem  We resolve structures on scale  of  Event Horizon.
\subitem  SgrA* emission varies over a  few hours on scales of several Schwarzschild radii.  
\item Simulations model flares in SgrA* as orbiting Ôhot-spotsÕ in the accretion flow.
\item  EHT adds  DSP  to  existing (sub)mm facilities for  VLBI  
\item  Phased arrays, wideband backends,  and high-speed recorders can  monitor 10-s  time scales.
\item  EHT can  time these orbits and provide estimates of black hole spin.  
\item M87:  Size constrains  jet formation and 
production of TeV photons observed with Fermi Gamma-ray satellite.  
\item  EHT  bring us as close to the edge of BH  as we are likely to come for decades.
\end{itemize}
\end{document}  
