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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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slide1

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

use of a single lofar station
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!

use of several lofar stations
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?
basic spectrometer mode
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
better spectral resolution
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
solar imaging

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
commissioning proposals
Commissioning proposals

Spectrometer mode:

  • Spectrum of the quiet Sun
  • Dynamic radio spectra

Imaging mode:

  • Center-to-limb variation
  • Solar imaging
spectrum of the quiet sun
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
dynamic radio spectra
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
center to limb variation
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
solar imaging1
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
operational phase
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
solar monitoring

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
burst mode

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!

summary and future work

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