Haystack VLBI Requirements/Plans Astronomy

1. Haystack VLBI Requirements/PlansAstronomy Sheperd Doeleman Haystack Observatory

2. Haystack Astro Context: • Haystack Requirements/Plans driven by ongoing programs: • UVLBI, Digital Backend (DBE), Burst System, eVLBI • Observational efforts: cm/mm science • Technical efforts: • Develop wideband, low cost, digital VLBI inst. that optimizes science for astronomical community. • Develop wideband, IF systems that flexibly link telescopes to new VLBI backends. • Collaborate on deployment of new systems. • Collaborate on using new mml sites for VLBI. • Explore and characterize VLBI frequency standards. • Point of View: Important role for University based group to contribute to VLBI infrastructure – impact of Senior Review.

3. UVLBI Science Directions • Projects • >=230GHz VLBI: SgrA* (<50uas, few Rsch), M87. • ULIGS – faint RSN, embedded AGN. • GRB’s – expansion vs. time • Stellar VLBI (pulsars). • Gravitational Lenses – missing images. • Commissioning obs vital part of development, also NSF obligations. • Some proposals encounter triple jeopardy (NSF, NRAO, EVN). • User Instrumentation Program (UIP): allows both collaborative obs. and instrument development.

4. H1413+117 B2114+022 Central Gravitational Lens Images • Lens theory predicts ‘odd’ number of images, but almost all systems have 2 or 4: a mystery. • ‘Missing’ images are faint and close to lensing galaxy: can’t see them in the optical. • Only one central image has been detected so far, but UVLBI sensitivities should be sufficient to detect ~50%. • Statistical studies of central regions of galaxies possible.

5. Ultra Luminous Infrared Galaxies • ULIGs result from gas-rich galactic mergers triggering nuclear star formation and eventually an embedded AGN. • High sensitivity maps of Arp220 show Radio Supernovae exploding in both nuclei (~30). • UVLBI will increase sensitivity by x4 at L-band to follow RSN light curves: gives star formation rates. Diamond et al • 4Gb/s UVLBI at L • and C band will allow • many other ULIGs to • be studied and sensitive • searches for obscured • nuclei carried out.

6. Measuring Faint GRB Afterglows • Tests of GRB models rely on afterglow intensity and size as functions of time (fireball model). • Nearby GRBs: direct VLBI imaging – one case: GRB 030329 (z=0.1685). • Expansion rate measured: constrains explosion energy and wind density profile. • GRB030329 size meaured at t+2.2 years (Pihlstrom et al 2007): expansion non-relativistic at t >1 yr. • Re-brightening expected as counter-jet appears. Pihlstrom et al 2007

7. Stellar UVLBI • Stars exhibit radio activity all over HR diagram - at various stages of stellar evolution. • Non-thermal radio emission, due to magnetic activity – VLBI scales. • Magnetic fields are critical in Pre Main Sequence stellar evolution with energetic particles emitting both Xrays and gyromagnetic radio. • Excellent path to collaboration with other wavebands. • Brown Dwarfs: mysterious mechanisms. • Pulsars: VLBI very useful for proper motion studies of potentially broad pulsar population.

8. Getting to the Event Horizon: The Galactic Center • SgrA* likely marks the position of a super massive (3.7x106 Msol) black hole in the Galaxy: • small proper motion of SgrA* • extreme motions and orbits of surrounding stars: Ghez et al 2005 • VLBA: intrinsic sizes are • ~24 Rsch (7mm) • ~12 Rsch (3mm). • r~6.5x1021 Msol/pc3 • To test for strong GR • effects, increase r by • orders of magnitude and • test for asymmetry • requires high freq. VLBI.

9. Viewing the Shadow with VLBI Falcke et al free fall rotating orbiting non- rotating 0.6mm VLBI GR Code 1.3mm VLBI Dependent on optically thin emission. GR effects important and visible as VLBI approaches 230, 345 GHz

10. Observations • Observed: • GRB030329: Global VLBI call for proposals. Observed in June 2005. • ULIGS: Global call for proposals. Observed in Oct 2005. • 230GHz VLBI (SgrA*): Proposed to CSO/SMTO. Observed in April 2006. • 230GHz VLBI (SgrA*): Proposed to JCMT-SMTO-CARMA/SMA. Observed in April 2007. • Planned: • Gravitational Lenses (4Gb/s with DBEs) • successful 4Gb/s AR-GBT proposal (20 hours, 8 srcs) + VLBA at lower bitrate. • AR/GBT obs will approach 1-2uJy noise (in ~2hrs).

11. Haystack Technical Plans • Push Bandwidth: • VLBI polarimetry (x2) • Rx front ends ~8GHz (64Gb/s if dual pol). • Correlator capability: software, WIDAR. • Pursue DBE work: • DBBC capability (spectral line) • Move to 16Gb/s requires 10GbE interface and protocol. • Burst Recorder System: • 16Gb/s for ~30 sec or pulsar recorder gating. • Fast switching for phase referencing: astrometry, spacecraft navigation. • High frequency work: short coherence times. • Exploration of new frequency standards for mm VLBI. • Performance of H-masers at high Hydrogen flux.

12. Exploring Future Observations • VLBA at 4Gb/s with prototype DBEs • SgrA* imaging at 86GHz • Parallax: 4% in 18 months (10% now) • 230, 345GHz VLBI of SgrA*/Calibrators • ALMA prototype antennas • Use of ALMA prototype receivers. • Value in near-term application of new instrumentation to potentially high pay-off science. • UIP can be an important piece.

13. Summary • VLBI technical projects at Haystack aimed at advancing VLBI infrastructure and science. • Best done collaboratively (NASA). • Necessary for optimizing impact of VLBI science on future committees and funding sources. • Items to discuss: UIP, ALMA dish participation, ALMA receivers, collaborative DBE obs. with VLBA.