Solar System Physics Group Heliospheric physics with LOFAR Andy Breen, Richard Fallows Solar System Physics Group Aberystwyth University Mario Bisi Center for Astrophysics and Space Sciences University of California, San Diego

Solar System Physics Group Solar Flare Radio Burst EISCAT/MERLIN observation of on : Sudden intense variation in signal power received simultaneously at all EISCAT and MERLIN sites. Seen before at EISCAT, but this is first confirmation from an independent radio system.

Solar System Physics Group Solar wind: supersonic outflow of plasma from Sun into space Carries solar magnetic field with it Carries solar disturbances out to planets Carves out cavity in interstellar medium – heliosphere Similar winds found around all Sun- like stars (& dwarf stars)‏ Heliospheres and stellarspheres

Solar System Physics Group Examples of heliospheric structures Macrostructure Background structure basically bimodal (most clearly at solar minimum) fast flow above open field regions, slow flow above streamers origin of slow wind not well-understood Stream interaction regions Coronal mass ejections “Mesostructure” Smaller scale features than macrostructure Very obvious in STEREO HI images CME internal structure Smaller transients (“Rouillard blobs”)‏ Other uncatagorised “stuff” - but lots of it Microstructure IPS scale irregularities (10s-100s km)‏ Turbulence

Solar System Physics Group Examples of macro- and mesoscale structures in the solar wind, April 2007 (STEREO HI-1A)‏ How do these structures interact with each other and with the background wind? How is the structure of the background wind influenced by interaction with these structures? Interaction between structures and solar system objects (e.g. comets, planetary environments..)

Solar System Physics Group White-light imaging and radio observations or, why do we need radio observations now we've got STEREO? Temporal resolution STEREO HI cameras return images every 40 minutes (inner field, HI-1) or 2 hours (outer field, HI-2). Radio scintillation (IPS) measurements can give density-proxy and bulk velocity estimates on < 10 minute cadences Different sensitivity to electron density: White light imagers observe photospheric light Thomson-scattered by solar wind electrons – linear sensitivity to N e IPS observes interference pattern cast by refraction (by solar wind turbulence) of signals from deep-sky sources - ~ N e 2 sensitivity Multi-site IPS measurements can detect other solar wind properties e.g. magnetic field rotation in CMEs/transients....

Solar System Physics Group Long-Baseline IPS Cross-correlation used to determine solar wind velocity. Longer antenna baselines allow different solar wind streams in line of sight to be determined accurately. EISCAT IPS observation of CME on 14 th May 2005; auto-correlation is top, remaining are cross-correlations. Cross-correlation functions also show two adjacent fast streams. Baselines projected onto sky plane: Bpar in radial direction, Bperp in meridional direction.

Solar System Physics Group Some current IPS facilities – what they can do Some current IPS facilities – what they can do Ootacamund: single antenna, 560m x 30m, observes ~ >1000 sources/day at distances of R Sun Can produce near-real time images of N e proxy, bulk flow speed Used as input to 3D tomographic reconstruction, yields 3D N e proxy and velocity distributions with ~10° angular resolution Ootacamund radio telescope (P.K. Manoharan) Nagoya (STELab): 106m x 41m antenna, 100m x 20 m antenna, 74m x 27 m antenna, observes ~ 50 sources/day, inc. ~ site observations at distances of R Sun Can produce daily maps of N e proxy, velocity Good monthly maps of N e proxy, velocity Used as input to 3D tomography, ~20° angular resolution Fuji radio telescope (M. Tokumaru) EISCAT: 3 32m dishes, makes ~5 2-site observations /day at distances of ~ R Sun Accurate measurements of velocity Can detect other solar wind parameters e.g. field rotation Even small number of long-baseline measurements greatly improve accuracy of tomographic reconstructions

Solar System Physics Group 3D velocity reconstruction from EISCAT IPS data (B.V. Jackson and M.M. Bisi) To study: Internal structure of CMEs CME/solar wind interaction CME/SIR interaction Evolution of mesoscale structure Interaction of mesoscale structure with CMEs and SIRs Interaction of solar wind structures with comets and planetary environments Cometary and planetary tails Need at least as good spatial resolution (sources/day..) as Ootacamund, many more long- baseline 2-site observations/day than STELab or EISCAT

Solar System Physics Group Combining Both IPS Methods: CME, 13/14 May 2005 Tomography image of CME used to constrain EISCAT IPS line of sight. More accurate speed of CME in interplanetary space; adjacent fast stream (or associated magnetic field) appears diverted ~15 º from radial: – Better determination of evolution of CMEs through interplanetary space. EISCAT IPS line of sight through tomography image of CME. CME gave Earth glancing blow; registered in ACE spacecraft data. Paper submitted to ApJ Letters by Breen et al.

Solar System Physics Group LOFAR LOFAR should provide all these things! Ample collecting area Plenty of combinations of 2-site observations Should be able to match Ootacamund’s number of source-observations/day, exceed site observations/day (currently being verified!) ~5°angular resolution in tomographic reconstructions looks achievable with LOFAR data MWA will match (and probably exceed) number of source- observations/day, but won’t offer 2-site measurements Won’t be able to study physical parameters (turbulence, flow direction) that LOFAR will be able to detect

Solar System Physics Group What’s needed IPS requires: Rapid sampling rate (>50 Hz, ideally >100 Hz) Wide receiver pass-band (> 10 MHz) Only total received power measurements are required Want to observe as many sources/day as possible, on as many days as possible Want to make many 2-site measurements  Experiment should run on “remote” (non-core) sites, ideally in background mode Need to safeguard non-core observing time for solar and heliospheric experiments IPS experiment for LOFAR needs building Initial input – data stream produced by generic solar/heliosphere mode running at each remote station? Need format for this data stream, sample data – and to start taking real data as soon as possible

Solar System Physics Group Acknowledgements EISCAT scientific association (EISCAT data) B.V. Jackson, P. Hick and M.M. Bisi (CASS, UCSD), for tomographic reconstructions P. Manoharan and M. Tokumaru for Ootacamund and Nagoya STELab information