mmVLBI in the Future:technical/experimental

Shep Doeleman

Haystack Observatory

In Defense of Theory

Do I contradict myself? Very well then I contradict myself, (I am large, I contain multitudes.) --Walt Whitman, "Song of Myself"

High Frequency VLBI Challenges

• Sensitivity: limited by atmospheric coherence, telescope apertures, bandwidth, weather (opacity and coherence).– Past observations limited to brightest

sources.• Baseline coverage: limited by relatively small

number of high demand sub/mm telescopes.• LO quality: phase noise in electronics

increases – loss of fringe amplitude.– First VLBI at new mm sites requires effort.

Challenges cont’d• Scheduling: mm/submm telescopes difficult to

schedule.• Array phasing: all antennas must be phased

prior to summing (you only get one chance).• Hydrogen masers: if atmosphere is good, maser

should not limit coherence time.• Amplitude calibration is difficult: array

phasing, pointing, atmosphere, gain curves.• BBCs have limited Bandwidth• Major improvements can be expected in some

of these areas.

Sensitivity: a solution.

• Old conventional wisdom: collecting area.

• New technical developments – new wisdom– 1983 VLBI BW: 224Mb/s, – 2004 VLBA BW: 512Mb/s.– New disk based VLBI recording systems will

allow multi Gb/s data rates

Mark 5A VLBI Data System

Mk5 cost ~ $15K700 GB disks expected ~2005 – 24 hours @ 1 Gbps unattended(comparable to ~19 VLBA tapes)

Sensitivity: a solution.

• Old conventional wisdom: collecting area.• New technical developments – new wisdom

– 1983 VLBI BW: 224Mb/s, – 2004 VLBA BW: 512Mb/s.– New disk based VLBI recording systems will

allow multi Gb/s data rates.– Leverages COTS technology and industry

demand for affordable, high capacity, high speed hard disks.

– Units can be used in parallel for N Gb/s.

Tape vs. Disc Price Comparison

mmVLBI at Haystack

• 2001-present: focus on 1-2mm VLBI

• 2002: Carried out successful 129, 147GHZ VLBI on Pico Veleta, KittPeak12m, SMTO triangle: – High resolution: Pico-SMTO fringes – 49as– SiO Masers– Collaborators: MPIfR, IRAM, Onsala,

Metsahovi, Arizona Radio Observatory

mmVLBI In the News

v=1 J=3-2 SiO Masers in VY CMa

30 AU

• First 129GHz VLBI image using all phase and amp information.

•Relative astrometry small fraction of beam.

mmVLBI at Haystack• 2001-present: focus on 1-2mm VLBI• 2002: Carried out successful 129, 147GHZ VLBI

on Pico Veleta, KittPeak12m, SMTO triangle: – High resolution: Pico-SMTO fringes – 49as

– SiO Masers

• 2003: Carried out 129, 230GHz VLBI using Pico, KittPeak, SMTO, Plateau de Bure– Detected Pico-SMTO 1.3mm fringes – 34as on 3C279

– World Record: equivalent to 5 RSCH of SgrA* MBH

– Used new generation of VLBI recorders.

• Very promising, but future depends on funding.

Evolution of 3mm Capability

Antenna SEFD

(Jy)

VLBA 5170

PicoVeleta 1700

P. de Bure 1700

Onsala 4000

Effelsberg 2000

Present: 256Mb/s

Antenna SEFD

(Jy)

GBT 500

Apex (Chile) 5000

CARMA 1700

LMT 350

Nobeyama 3000

3-5 years: 1Gb/s

Antenna SEFD

(Jy)

ALMA 60

5-10yrs: 10Gb/s

VLBA-VLBA = 0.8JyPicoV-PdeB = 0.25JyPicoV-PdeB = 0.13Jy*PicoV-VLBA = 0.5Jy

VLBA-VLBA = 0.4JyGBT-LMT = 0.032JyGBT-LMT = 0.016Jy*LMT-VLBA = 0.1Jy

VLBA-VLBA = 0.13JyALMA-LMT = 0.004JyALMA-VLBA = 0.014Jy

Resolution (8000km)=90asTcoh = 20 seconds

Higher recording rates.

Evolution of 1mm Capability

Antenna SEFD

(Jy)

KittPeak 22000

PicoVeleta 2500

P. de Bure 2500

SMT 15000

Present: 0.5Gb/s

Antenna SEFD

(Jy)

JCMT 7800

APEX-Chile 5500

CARMA 2500

LMT 500

SMA 2500

CSO 15000

3-5 years: 4Gb/s

Antenna SEFD

(Jy)

ALMA 100

5-10yrs: 10Gb/s

PicoV-PdeB = 0.4JyPicoV-KittPeak = 1.15Jy LMT-CARMA = 0.06Jy

LMT-SMT= 0.15Jy

ALMA-LMT = 0.008JyALMA-SMT = 0.042Jy

Resolution (8000km)=34asTcoh = 10 seconds

UltraVLBI Proposal• Submitted to ATI program at NSF• Outfit largest cm antennas (Effelsberg, Arecibo,

GBT, WSRT, Jodrell bank) with 4Gb/s recording systems: <1Jy/beam rms.

• Outfit best mm sites with 4Gb/s systems: JCMT, SMTO (CARMA, LMT, SMA, ALMA, APEX)

• Target science requiring sensitivity: SNR in Galactic mergers, GRBs, Grav. Lenses, Stellar VLBI, SgrA*!!

• Waiting to hear …

230GHz VLBI Observations

Proposed VLBIon JCMT-HHTbaseline.

Just a detection willprovide a firm uppersize limit.

Next Generation VLBI System• Multiple Digital BBC units (500MHz each).

– Cost: 20K each.

• Multiple MK5b units (1Gb/s each).– Cost: 16K each.

• H-maser with y(10sec)<=3e-14.– Cost: 175K.

• Rack with power supplies, backplane, GPS clock, – Cost: 20K

• Total: $270K/new station, much less if maser is already available.

Summary• Over next decade: BW x40, Element area x25, means

capable 230GHz imaging arrays.• Phase stability of mm/submm arrays is very important:

CARMA, ALMA, PdeBure.• Creating low phase noise LO systems for submm

VLBI is necessary.• VLBI arrays up to 345 and 450GHz are possible.• ‘Widebanding’ IFs and receivers will be a

requirement.• Scheduling: need turn-key operation from single dish

to VLBI.• Current proposed work: 4Gb/s VLBI on SgrA* in 3

years.

END