Authors: Justin C. Kasper, Miguel Morales, Alan J. Lazarus; Divya Oberoi,
Joe Salah, Colin Lonsdale
Affiliation: Center for Space Research, Massachusetts Institute of Technology;
Haystack Observatory, Massachusetts Institute of Technology
We present the results of an ongoing study of the potential for conducting
LWS science and supporting LWS missions with next generation low-frequency digital
aperature synthesis radio interferometers. These new designs for ground-based
radio observations build on the rapid advancement in computing power and network
bandwidth to enhance observational capabilities. The signals from each antenna
may be digitized and sent to a central processing facility for simultaneous
aperature synthesis in multiple directions limited solely by the available computing
power. Tracking of sources from many locations coupled with sophisticated real-time
models of the ionosphere permit the extension of measurements to previously
unexplored low-frequencies. It is possible that these telescopes could be used
to remotely measure magnetic field and density structures from the lower corona
out to 1 AU.
Our study has focused on the baseline design for the Low Frequency Array (LOFAR),
a potential future radio array which would operate in the frequency range of
about 40 to 240 Mhz. In the current design LOFAR is a centrally-condensed array
with 25\% of the collectors within a 2 km diameter, 50\% within 12 km, 70\%
within 75 km, and the remainder extending to 400 km. We have identified promising
capabilities in the Wide-Field Correlator (WFC) design for LOFAR that would
permit new observations of the state of the inner heliosphere. An All-Sky Monitor
(ASM) making use of the WFC could produce images of the heliosphere at a cadence
of half a second with sub arc-minute resolution. These images could then be
used to reconstruct the Faraday Rotation (FR) due to the magnetic field of the
inner heliosphere. The output from the WFC could also be used to simultaneously
monitor several hundred sources for interplanetary scintillations (IPS).
The new observations possible are outlined in a series of case studies. It is
shown that there are a sufficient number of linearly polarized extra-galactic
sources for the telescope to monitor the FR of about 1,000 sources within $30^\circ$
of the Sun. Simulations of transient Coronal Mass Ejections suggests that flux
ropes could be detected in up to 10,000 sources in the case of Earthward directed
events, and that these observations could be used to determine the magnetic
topology of the CME ejecta. IPS at lower frequencies could detect the formation
of interaction regions and the evolution of interplanetary shocks.