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Solar observation modes: Commissioning and operational

Solar observation modes: Commissioning and operational. C. Vocks and G. Mann. Spectrometer and imaging modes Commissioning proposals Operational phase Summary and outlook. 3 rd Solar KSP Workshop, 05.-06. July 2010. Use of a single LOFAR station. Station beam (70 m Ø):.

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Solar observation modes: Commissioning and operational

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  1. Solar observation modes: Commissioning and operational C. Vocks and G. Mann Spectrometer and imaging modes Commissioning proposals Operational phase Summary and outlook 3rd Solar KSP Workshop, 05.-06. July 2010

  2. Use of a single LOFAR station Station beam (70 m Ø): • Low band: > 3 deg • High band: > 1 deg The Sun is essentially a point source! Consequences: • No imaging • Spectral intensities as function of time Single station as spectrometer!

  3. Use of several LOFAR stations Frequency coverage: 6 stations needed for full coverage Sample frequencies: • 160 MHz for station V • 200 MHz otherwise 48 MHz station bandwidth: • 1 station less for each low and high band?

  4. Basic spectrometer mode Station data processing: • Station takes samples with 200 (160) MHz rate • 1024 data points are collected, Fourier-transformed Result: • Sub-bands of 195 (156) kHz width • Values for complex amplitudes every 6.4 (5.1) µs Temporal resolution of 0.01 s: • Average over complex amplitudes squared • Can be handled by a PC on the station level Resulting data rate: • Total # of sub-bands in the LOFAR frequency range: 912 • bb = 912 * 100/s * 4B = 365 kB/s = 1.3 GB/h

  5. Better spectral resolution Higher frequency resolution: • Fourier-transform series of sub-band samples For 100 kHz frequency resolution: • DFT with 2 samples sufficient • Average again over 0.01 s • Computational effort: About doubled Resulting data rate: • be = 730 kB/s = 2.6 GB/h

  6. Solar corona: • Scattering of radio waves • Resolution 40-60'' Solar imaging LOFAR will provide radio images of the middle and upper solar corona. Baselines: • More than 20 km not needed • Central core + 1st ring

  7. Commissioning proposals Spectrometer mode: • Spectrum of the quiet Sun • Dynamic radio spectra Imaging mode: • Center-to-limb variation • Solar imaging

  8. Spectrum of the quiet Sun Objectives: • Test use of single stations as spectrometers • Quiet Sun: Thermal radiation • I(f) = 2000 Jy * (f / 40 MHz)2 Observations: • Multiple stations cover full frequency range • Spectral resolution 100 kHz • RFI mitigation • Calibration tests

  9. Dynamic radio spectra Objectives: • Test spectrometer observing mode • Identification of solar radio bursts  Triggering Observations: • Multiple stations cover full frequency range • Spectral resolution 100 kHz • RFI mitigation • Calibration tests

  10. Center-to-limb variation Objectives: • Thermal structure of the corona • Intensity variation across the solar disk • Preparation for solar imaging Observations: • Scan across the solar disk • Tied-array mode • Multiple frequencies • Multiple beams

  11. Solar imaging Objectives: • Based on standard imaging • Solar imaging: Sun outshines calibration sources • Sun is bright, extended source Observations: • First observations with strong calibrators, quiet Sun • Snapshot imaging • Calibration and image synthesis • Location of radio sources on the disk

  12. Operational phase Imaging modes: • Limited resolution • Core and nearest remote stations • Image cadence depends on solar activity Spectrometer mode: • Runs continuously with remote and int’l stations not needed for imaging • Covers full LOFAR frequency range • Resolution: 100 kHz, 10 ms

  13. Scientific objectives: • Active region development • Sources of radio bursts Solar monitoring LOFAR monitoring: • Image cadence 1 min • Selected frequencies • Depend on available band • Combination with: • Optical images • Dynamic radio spectra

  14. Response to bursts: • Alert other groups/instruments • Predefined series of follow-up observations, e.g. evolution of the radio source both in space and frequency Burst mode Detection of radio bursts (“burst bell”): • Record intensity on selected frequencies • Calculate average and variance (s) • If the intensity increases by more than 5.5 s Burst detected!

  15. Future work: • Right now: First solar observations • Space weather, scintillation • Simultaneous solar imaging in low and high band Summary and future work Summary: • Single LOFAR stations: Used as spectrometer • Solar imaging: Core + nearest remote stations • Commissioning proposals on spectrometer and imaging • Operational phase: Spectrometer always on • Image cadence dependent on solar activity

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