Solar observations with single 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,

Solar radio radiation The Sun is a strong radio source: Thermal: 10 6 K corona Nonthermal: Flares, CMEs Itensities: Thermal: some 10 4 Jy Nonthermal: up to 10 7 Jy Plasma emission Radio wave emission: The frequency f depends only on the density N

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)

Solar KSP Workshop II, 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, LOFAR frequencies in the corona r/R S f/MHz LOFAR Frequencies: Middle and upper corona

Solar KSP Workshop II, Solar physics with LOFAR The Sun is an active star. LOFAR will be able to monitor the solar activity. Scientific topics:  Plasma processes related to highly energetic electrons  Initiation of CMEs  Shock formation and development  Energetic particles generation observations to space missions, e.g. RHESSI, STEREO, Hinode, SDO.  Complementary ground-based

Solar KSP Workshop II, 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!

Solar KSP Workshop II, Use of spectrometer data Dynamic radio spectra: Frequency drift rates Heliosph. density model Source phase speed Insights into the physical processes of the radio source Resolution needed: Frequency: 100 kHz Time: 10 ms

Solar KSP Workshop II, LOFAR station as spectrometer Itensity of solar radio bursts: High enough for single station observations, by far! 10 7 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 between 190 and 210 MHz

Solar KSP Workshop II, 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, 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 b b = 912 * 100/s * 4B = 365 kB/s = 1.3 GB/h

Solar KSP Workshop II, 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: b e = 730 kB/s = 2.6 GB/h

Solar KSP Workshop II, 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, 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