21 st Century VLBI

1. www.jive.nl www.evlbi.org 21st Century VLBI Mike Garrett (JIVE) Astro-lunch, 16 April 2003.

2. 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)

3. Not just deeper but wider…! • Typical VLBI field-of-view few pixels on this screen!  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) 6 arcmin [FWHP] Effelsberg beam

4. 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…

5. 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).

6. 2 sub-mJy sources detected in inner 3’

7. 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… Imaging out the VLBA P-beam

9. VLBA + GBT24 hr @ 256Mb/s 9 microJy Rms noise Garrett, Wrobel & Morganti

10. 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.

11. 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)