Solar observation modes: Commissioning and operational C. Vocks and G. Mann 1. Spectrometer and imaging modes 2. Commissioning proposals 3. Operational phase 4. Summary and outlook 3 rd Solar KSP Workshop, July 2010

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 rd Solar KSP Workshop, July 2010 Use of several LOFAR stations Frequency coverage: Sample frequencies: 160 MHz for station V 200 MHz otherwise 6 stations needed for full coverage 48 MHz station bandwidth: 1 station less for each low and high band?

3 rd Solar KSP Workshop, July 2010 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 b b = 912 * 100/s * 4B = 365 kB/s = 1.3 GB/h

3 rd Solar KSP Workshop, July 2010 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: b e = 730 kB/s = 2.6 GB/h

3 rd Solar KSP Workshop, July 2010 Solar imaging Solar corona:  Scattering of radio waves  Resolution 40-60'' LOFAR will provide radio images of the middle and upper solar corona. Baselines :  More than 20 km not needed  Central core + 1 st ring

3 rd Solar KSP Workshop, July 2010 Commissioning proposals Spectrometer mode: Imaging mode: Spectrum of the quiet Sun Dynamic radio spectra Center-to-limb variation Solar imaging

3 rd Solar KSP Workshop, July 2010 Spectrum of the quiet Sun Objectives: Quiet Sun: Thermal radiation I(f) = 2000 Jy * (f / 40 MHz) 2 Test use of single stations as spectrometers Observations: Multiple stations cover full frequency range Calibration tests Spectral resolution 100 kHz RFI mitigation

3 rd Solar KSP Workshop, July 2010 Dynamic radio spectra Objectives: Test spectrometer observing mode Identification of solar radio bursts  Triggering Observations: Multiple stations cover full frequency range Calibration tests Spectral resolution 100 kHz RFI mitigation

3 rd Solar KSP Workshop, July 2010 Center-to-limb variation Objectives: Intensity variation across the solar disk Preparation for solar imaging Observations: Scan across the solar disk Tied-array mode Multiple frequencies Multiple beams Thermal structure of the corona

3 rd Solar KSP Workshop, July 2010 Solar imaging Objectives: Solar imaging: Sun outshines calibration sources Based on standard imaging Sun is bright, extended source Observations: First observations with strong calibrators, quiet Sun Location of radio sources on the disk Snapshot imaging Calibration and image synthesis

3 rd Solar KSP Workshop, July 2010 Operational phase Spectrometer mode: Runs continuously with remote and int’l stations not needed for imaging Covers full LOFAR frequency range Resolution: 100 kHz, 10 ms Imaging modes: Limited resolution Core and nearest remote stations Image cadence depends on solar activity

3 rd Solar KSP Workshop, July 2010 LOFAR monitoring: Image cadence 1 min Selected frequencies Depend on available band Combination with:  Optical images  Dynamic radio spectra Scientific objectives: Active region development Sources of radio bursts Solar monitoring

3 rd Solar KSP Workshop, July 2010 Detection of radio bursts (“burst bell”): Record intensity on selected frequencies Calculate average and variance (  ) If the intensity increases by more than 5.5  Burst detected! Response to bursts: Predefined series of follow-up observations, e.g. evolution of the radio source both in space and frequency Alert other groups/instruments Burst mode

3 rd Solar KSP Workshop, July 2010 Summary and future work Summary: Single LOFAR stations: Used as spectrometer Solar imaging: Core + nearest remote stations Commissioning proposals on spectrometer and imaging Future work: Right now: First solar observations Space weather, scintillation Simultaneous solar imaging in low and high band Operational phase: Spectrometer always on Image cadence dependent on solar activity