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 mmλ 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
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>=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.
B2114+022
H1413+117
• ‘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.
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.
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 nonrelativistic 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 (3.7x106 Msol) black hole in the Galaxy:
– small proper motion of SgrA*
– extreme motions and orbits of surrounding stars:
• VLBA: intrinsic sizes are
~24 Rsch (7mm)
~12 Rsch (3mm).
• ρ~6.5x1021 Msol/pc3
• To test for strong GR
effects, increase ρ by
orders of magnitude and
test for asymmetry
requires high freq. VLBI.
Ghez et al 2005
Viewing the Shadow with VLBI
Falcke et al
free fall
rotating
orbiting
nonrotating
GR Code
0.6mm VLBI
1.3mm VLBI
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 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-SMTOCARMA/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).
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.