A New Strategy for Routine VLBI Imaging of Faint sub-mJy and
MicroJY Radio Sources
VLBI arrays are sensitive instuments able to produce mas resolution
images with rms noise levels that are comparable to connected arrays.
Neverthless, the choice of VLBI target sources is limited since
the arrays are not phase-stable and rely on phase self-calibration
technqiues to correct the data. This reliance of self-calibration
often limits VLBI to the investigations of relatively bright sources
> several mJy. Even with phase-rferencing the imaging of sub-mJy
sources is rare and the results indifferent (esp. w.r.t. image
fidelity). I have proposed a new strategy for the routine
detection and imaging of sub-mJy and microJy radio sources with VLBI.
This relies on three main techniques:
- The strategy relies on a combination of in-beam
phase-referencing,
- Wide-field VLBI imaging ,
- simultaneous correlation of multiple field centres,
- the steeply rising radio source counts
observed at cm wavelengths,
- Reverse the traditional of selecting the target
before the calibrator!
Some proof-of-concept investigations have begun....
The image above shows the clear VLBI detection of a known VLA FIRST
source in a sub-field that is part of a patch of the primary beam that
is located 1 arcminute from the phase-centre and target source. Details
of the processing requirements for this (and longer runs) is beyond the
scope of this paper but they are not unreasonable (it takes several
hours but less than a day to map out one 4 x 4 arcmin patch from 6
hours of data on a standard Sun Ultra 1).
More details .. Read the Paper! .
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