(sub)mm-VLBI: Creating an Event Horizon Telescope Shep Doeleman MIT Haystack Observatory

The Event Horizon Telescope An international collaborative project assemble a global submm-VLBI array for observing and resolving Event Horizons. Key observations have removed scientific uncertainty (i.e. will we see anything?). Technical Elements: low risk extensions of ongoing efforts and leverage investments from ALMA and other development projects. Collaboration: necessarily a international project but with well defined boundaries. Strong element of training at intersection of submm science and interferometry.

Technical Elements of EHT Adding Telescopes: uv coverage, flare coverage, closure quantities for real-time modeling. ALMA quality, dual pol rx and LO for all sites. Testing hardware for in-situ verification. Central correlation facility. VLBI backends/recorders at rates up to 64Gb/s Phased Array processors (ALMA, PdeBure, CARMA, Hawaii) Low noise freq. references. Logistics/Observations/Project Management

Event Horizon Telescope Phase 1: 7 TelescopesPhase 2: 10 Telescopes Phase 3: 13 Telescopes

Progression to an Image GR Model7 Stations 13 Stations

Hawaii Phased Array Success (CSO+JCMT+SMA)-CARMA

Phasing ALMA for VLBI

230GHz Rx with ALMA Mixers Proposal submitted to NSF ATI program for 230GHz Rx development using ALMA band 6 mixer/preamps. To be installed at JCMT (Fall 2011): Tsys improves by x2.5 BW improves by x4 Dual pol UMass to build dewar, Haystack VLBI testing, JCMT assistance with install and commissioning.

Other Development Burst Mode: – Not possible using Mark5c architecture. – Now examining COTS solution. Sapphire Oscillator: – Will work on slaving excellent crystal to CSO and to GPS (on long time scales). – Hopefully will have CSO at Haystack by Spring Modified Masers: – Discussions with Symmetricom on installing excellent crystal (oscilloquartz 8607) in their maser. – Difficulty: increasing hydrogen flux to boost stability.

EHT Phases: Phase I: 7 station 8Gb/s array ALMA phasing, preliminary Rx/LO work, new frequency standards, new site studies, operations Phase II: 10 station 32Gb/s dual-pol array Activate SEST, equip S.Pole, new frequency standards, install new 0.8/1.3mm dual-pol Rx, increase bandwidth of VLBI backends/recorders, relocate ATF dishes, operations Phase III: 12 station array up to 64Gb/s install ATF dishes, array operations for 5 years

EHT: A Phased Approach No ‘first-light’: we are ‘lit’ from the very beginning, so no waiting/uncertainty. Each year, new capability will expand science results. Impact of technical work on science can be assessed each year: transparency of progress. Allows project to flexibly adapt to new science results: crystal ball very clear for Phase I (and will be for Phase II with results from Phase I). Leverages existing facilities - no need for initial build up.

Status of Collaboration and WB Haystack: Recorder and Digital Backend Frequency Standards ALMA Phasing Organization of observations Harvard-CfA: Phased Array development SMA support ALMA Phasing U. Arizona/ARO: SMTO support Test observations CARMA: Phased Array work Site support ASIAA: H-maser cost-share JCMT/CSO: Telescope support. NAOJ: ASTE support MPIfR-Bonn Plateau de Bure/IRAM 30m APEX support IRAM: IRAM site support Plateau de Bure phasing NRAO: ALMA Phasing RDBE + Mark5c UC Berkeley: Digital Backend

Summary 1.3mm VLBI confirms Event Horizon scale structure SgrA* Imaging the Event Horizon and observing BH orbits are within reach in ~10 years. Science/Technical advances: rapid change. SgrA* detection, tech. validation, team, sites. Assembling strong international collaboration. Competitive with (and complementary to) much larger space-based mission (e.g., IXO). All the ingredients for the EHT exist.