21st Century VLBI

Mike Garrett (JIVE)

Astro-lunch, 16 April 2003.

www.evlbi.org www.jive.nl

Current Developments in Continuum VLBI • Replacement of Tape by Disks:

– More reliability – Higher Data rates can be employed (> 1 Gbps)– Naturally leads to…

• Real-time VLBI: – Psuedo real-time “ftp-VLBI”– Real-time fibre-optic e-VLBI (meeting tomorrow!)– Data rates of tens of Gbps per antenna

• Replacement of analogue back-end electronics with digital systems

• Broadband receivers 1-4 GHz; 4-8 GHz etc. – Wide-band MFS Imaging

Will lead to better sensitivity (a few microJy/beam)

Not just deeper but wider…!

• Typical VLBI field-of-view few pixels on this screen!

6 arcmin [FWHP] Effelsberg beam

VLBI FoV x 100

• Compute resources required to maintain a given FoV scale as

Baseline2…

• Implications for EVN Correlator data output-rate: PC Int Project at JIVE

Offline data processing

(Local PC Cluster/GRID Access)

Some lessons learned from the HDF-N…

• EVN did not reach the thermal-noise level (Gross Calibration errors)

• Within 1 arcmin FoV the HDF-N delivered ~ 1 mJy in (summed) flux-density…

> 100 mJy of summed flux over 10 arcmin FoV !

Promise of VLBI as a phase-stable VLBI instrument at cm wavelenghts…

VLBA+GBT DWFS of Bootes Field- Garrett, Wrobel & Morganti

• In-beam phase referencing employed

• 3 x 5.5 (8) hours @ 256 Mbps

• VLBA correlator running flat out:– 0.5 second integrations,– 1024 x 62.5 kHz channels

2 x 60 Gbytes of data

• Calibration performed on averaged data.

• Full sensitivity limited to a region 3 arcmin across (due to smearing).

• Image processing is very slooooow!– Co-addition of Dirty

Images/Beams from each 8 hr run

• Work in progress… astro-ph-xxx (Jan 2003).

2 sub-mJy sources detected in inner 3’

Imaging out the VLBA P-beam

• Can we detect sources well beyond the GBT primary beam (FWHM) ?

• Data tapered successively as a function of distance from field-centre

• Sources in the field brighter than a few mJy were targeted…

Garrett, Wrobel & Morganti

VLBA + GBT24 hr @ 256Mb/s

9 microJyRms noise

Full-beam Calibration

• At frequencies 1-5 GHz, phase-stable VLBI observations can be made in ANY area of the sky !

• Standard self-calibration techniques can use the Summed Response of all detectable sources in the beam.

• Requires good input model conventional phase-referencing or in-beam referencing required initially.

• Compute requirements are considerable – requires PC cluster, parallel code/data streams and possibly access to GRID resources.

Future Challenges• In the next few years VLBI will be transformed into a true survey instrument!

– Huge areas of sky can be imaged-out at with milliarcsec resolution and full sensitivity,

- Dozens of radio sources will be detected simultaneously in a single observation,

- Deep VLBI Surveys will be conducted of high quality fields (e.g. FLSv Strip)

– VLBI will emerge as a very efficient AGN detector (Starburst-AGN descriminator)

- What fraction of faint, obscured SCUBA and microJy source populations harbour AGN ? Will faint AGN also be (on average) more distant ?

- Milliarcsecond astrometry for every source detected, spatial comparison between VLBI structures and other high-resolution instruments of the day e.g. VLTI

- Large surveys will be conducted e.g. extending the search for gravitational lenses to image separations < 0.3”

- Surveys will be able to “piggy-back” on any observation (AVO)