Haystack VLBI Requirements/Plans Astronomy Sheperd Doeleman Haystack Observatory

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 mm 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.

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.

Central Gravitational Lens Images Lens theory predicts ‘odd’ number of images, but almost all systems have 2 or 4: a mystery. H B ‘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.

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. 4Gb/s UVLBI at L and C band will allow many other ULIGs to be studied and sensitive searches for obscured nuclei carried out. Diamond et al

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 (z=0.1685). Expansion rate measured: constrains explosion energy and wind density profile. GRB 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

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.

Getting to the Event Horizon: The Galactic Center SgrA* likely marks the position of a super massive (3.7x10 6 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).  ~6.5x10 21 Msol/pc 3 To test for strong GR effects, increase  by orders of magnitude and test for asymmetry requires high freq. VLBI.

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

Observations Observed: GRB030329: Global VLBI call for proposals. Observed in June ULIGS: Global call for proposals. Observed in Oct GHz VLBI (SgrA*): Proposed to CSO/SMTO. Observed in April GHz VLBI (SgrA*): Proposed to JCMT-SMTO- CARMA/SMA. Observed in April 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).

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.

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.

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.