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High Sensitivity VLBI

High Sensitivity VLBI. Sheperd Doeleman MIT Haystack Observatory. BW and Continuum Sensitivity. Bandwidth much cheaper than steel. New technical developments – Disk based VLBI systems Digital wideband backends VLBA now: 256Mb/s sustainable.

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High Sensitivity VLBI

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  1. High Sensitivity VLBI Sheperd Doeleman MIT Haystack Observatory

  2. BW and Continuum Sensitivity • Bandwidth much cheaper than steel. • New technical developments – • Disk based VLBI systems • Digital wideband backends • VLBA now: 256Mb/s sustainable • EVLA WIDAR Correlator and software correlators can process 8GHz stations.

  3. cm UVLBI Array • Arecibo, Jodrell Bank (Lovell), Effelsberg, Westerbork, GBT • Rms map sensitivities: (2 hours with Arecibo)

  4. Motivation for wideband DBE • VLBI data rates up by only x4 since 1980’s: • Moore’s Law ~10,000 • SNR~(BW)0.5 * (Diam)2 • Modern FPGAs give increased performance at small fractions of Mark4/VLBA cost (sample IF, filter digitally). • For continuum obs. widebanding now cost effective vs. larger dishes: 512Mb/s to 4Gb/s same as 42m VLBA dishes. • DBE systems are portable. • Wideband obs. important for key science: • SgrA*, GRB afterglows, ULIGs, Gravitational Lenses, Pulsar Astrometry, Astronomical Masers • Industry driven growth path: DSP, storage media, high speed data protocols (10GbE).

  5. DBE prototype H Maser Current modes: 15 channels, each 32MHz, 2-bit = 1920Mb/s 15 channels, each 16MHz, 2-bit = 960Mb/s

  6. Prototype DBE Hardware developed by Berkeley Space Sciences Lab (CASPER) iBOB board and iADC sampler. Haystack/CASPER collaboration on Firmware. Sampler boards iBOB COST: $7.5K (includes purchase of Virtex2Pro FPGA) for 4Gb/s.

  7. 16MHz vs 32MHz Channels8 vs 4 filter taps 16MHz Channel 4 taps 32MHz Channel 8 taps

  8. Disk Based Recorders Final piece of the system Next stop 16Gb/s Mark5B: 2Gb/s using VSI interface. Mark5C: 4Gb/s using 10GbE Next Gen: 8-16Gb/s using 10GbE (Commercial Off The Shelf – COTS)

  9. 230GHz VLBI2x 2Gb/s = 4Gb/s Tcoh~60sec SMTO-JCMT: 1749+096 - 60uas fringe spacing.

  10. 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. • Radio follow up of identified PMS stars from Spitzer surveys. • Use UVLBI to differentiate between stellar flares, magnetospheres, star-disk interfaces. • Brown Dwarfs: mysterious mechanisms.

  11. xray/radio correlation Dwarf LP944-20 Violates this relation by 4 orders of magnitude.

  12. 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.

  13. Winn et al 2004 J1632-0033 Free-free absorption in lensing galaxy, 200pc from core. Central Image

  14. Density and BH mass • Detection or limits on central • image flux density constrains • core size and steepness of • density profile. • SMBH at center of lensing • galaxy can create a 4th image • (central) that can be used to • directly estimate mass of • BH. • - 30% flux density of • first central image. • - ~20mas separation Boyce et al 2006

  15. Planned Observations • Nov 2007 – 8 asymmetric double lens systems. • Arecibo – GBT at 4Gb/s (s<2mJy/beam) • factor of x10 improvement in limits. • VLBA at lower bit rate to model bright images and subtract from AR-GBT data. • Goal: probe cores of z~0.3-1 galaxies on same scales as HST does for local galaxies. • High resolution and high sensitivity required. • SKA ideal instrument • AR-anchored VLBI arrays available now (>0.1SKA)

  16. Pulsar Astrometry • New VLBI instrumentation allows record-time gating of pulsar data: wide bandwidths but conserving of media. • Astrometry complements pulsar timing: • VLBI observes all pulsar types (not just MSP). • Supernovae core collapse (pulsar proper motions) • NS-supernovae associations. • Timing vs. VLBI: ties together extragalactic and solar system ref. frames.

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