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

3rd Solar KSP Workshop, 05.-06. July 2010

3rd Solar KSP Workshop, 05.-06. July 2010

Use of a single LOFAR station

Station beam (70 m Ø):

• Low band: > 3 deg

• High band: > 1 deg

The Sun is essentiallya point source!

Consequences:

• No imaging

• Spectral intensities as function of time Single station as spectrometer!

3rd Solar KSP Workshop, 05.-06. 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?

3rd Solar KSP Workshop, 05.-06. 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

• bb = 912 * 100/s * 4B = 365 kB/s = 1.3 GB/h

3rd Solar KSP Workshop, 05.-06. 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:

• be = 730 kB/s = 2.6 GB/h

3rd Solar KSP Workshop, 05.-06. July 2010

Solar imaging

Solar corona:Scattering of radio wavesResolution 40-60''

LOFAR will provide radioimages of the middle

and upper solar corona.

Baselines:

More than 20 km not neededCentral core + 1st ring

3rd Solar KSP Workshop, 05.-06. July 2010

Commissioning proposals

Spectrometer mode:

Imaging mode:

• Spectrum of the quiet Sun

• Dynamic radio spectra

• Center-to-limb variation

• Solar imaging

3rd Solar KSP Workshop, 05.-06. 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

3rd Solar KSP Workshop, 05.-06. 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

3rd Solar KSP Workshop, 05.-06. 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

3rd Solar KSP Workshop, 05.-06. 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

3rd Solar KSP Workshop, 05.-06. July 2010

Operational phase

Spectrometer mode:

• Runs continuously with remote andint’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

3rd Solar KSP Workshop, 05.-06. 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

3rd Solar KSP Workshop, 05.-06. 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 inspace and frequency

• Alert other groups/instruments

Burst mode

3rd Solar KSP Workshop, 05.-06. 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