solar observations with single lofar stations c. vocks 1. introduction: solar radio radiation 2....
DESCRIPTION
Solar KSP Workshop II, Heliospheric density model Parker's wind equation (1958) A special solution agrees well with density measurements up to 5 AU (Mann et al., 1999)TRANSCRIPT
Solar observations withsingle LOFAR stations
C. Vocks
1. Introduction: Solar Radio radiation
2. Observations with single LOFAR stations
3. Spectrometer mode
4. Summary
Astrophysical Institute Potsdam
Solar KSP Workshop II, 25.06.2009
Solar KSP Workshop II, 25.06.2009
Solar radio radiation
The Sun is a strong radio source:• Thermal: 106 K corona• Nonthermal: Flares, CMEs
Itensities:• Thermal: some 104 Jy• Nonthermal: up to 107 Jy
• Plasma emission
Radio wave emission:
The frequency f depends onlyon the density N
Solar KSP Workshop II, 25.06.2009
Heliospheric density model
weightmolecularmean6.0~v2/GMr
)m~/Tk(v
3rr4
rrln4
v)r(vln
v)r(v
2cSc
2/1pBc
c
c2c
2
2c
2
Parker's wind equation (1958)
A special solution agrees well withdensity measurements up to 5 AU(Mann et al., 1999)
Solar KSP Workshop II, 25.06.2009
Dynamic radio spectra
Observations of solar radio bursts:
dynamic radio spectrogram height-time diagram
Frequency drift rate (phase) velocity of the source
Solar KSP Workshop II, 25.06.2009
LOFAR frequencies in the corona
2.5210
2.0120
1.8030
1.6840
1.4870
1.37100
1.24170
1.17240
r/RSf/MHz
LOFAR Frequencies:
Middle and uppercorona
Solar KSP Workshop II, 25.06.2009
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 asfunction of time Single station as spectrometer!
Solar KSP Workshop II, 25.06.2009
Use of spectrometer data
Dynamic radio spectra:• Frequency drift rates• Heliosph. density model• Source phase speed
Insights into thephysical processesof the radio source
Resolution needed:
• Frequency: 100 kHz• Time: 10 ms
Solar KSP Workshop II, 25.06.2009
LOFAR station as spectrometer
Itensity of solar radio bursts:
• High enough for single station observations, by far!
• 107 Jy
Frequency range:• Low band: 30 – 80 MHz• High band: 120 – 240 MHz
Some constraints:• Only 32 MHz (48 MHz?) bandwidth• Either low or high band• Either 160 MHz or 200 MHz sample frequency• 160 MHz sample frequency must be used between190 and 210 MHz
Solar KSP Workshop II, 25.06.2009
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?
Solar KSP Workshop II, 25.06.2009
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• Station electronics capable of this?
Resulting data rate:• Total number of sub-bands in the LOFAR frequency range: 912• bb = 912 * 100/s * 4B = 365 kB/s = 1.3 GB/h
Solar KSP Workshop II, 25.06.2009
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• Station electronics capable of this?
Resulting data rate:
• be = 730 kB/s = 2.6 GB/h
Solar KSP Workshop II, 25.06.2009
Data handling
During commissioning phase:• Station not connected to network?• Write data to local disk
Operational phase:• Send data to Solar Science Data Center• Via Jülich or Groningen?
• How will the stations be controlled? (GLOW issue)
• Data reduction on the station level?
• Controlled by ASTRON, treated as sub-array?
Solar KSP Workshop II, 25.06.2009
Summary and outlook
Solar radio radiation:
Single station spectrometer mode:
• Plasma emission• LOFAR frequencies: Middle and upper corona• The Sun is a point source for single stations• Dynamic radio spectra
• Record spectral intensities as function of time, dt = 0.01 s• 4-6 stations needed for full coverage of LOFAR frequencies• Basic spectrometer mode with sub-band resolution• Simple DFT for better frequency resolution• Data handling issues