Low Frequency Array (LOFAR): The French LOFAR Super Station Helmut O. Rucker Commission for Astronomy Austrian Academy of Sciences AW, Vienna, Dec 14 15, 2015 Radio telescope (1,06 GHz/3,5 GHz) Radio heliograph (150 MHz 450 MHz) LOFAR FR606 Zarka et al., 2013 LSS = LOFAR Super Station = NenuFAR : New extension in Nancay upgrading LOFAR 19 antennas mini array = LF tile Inverted-V dipole (linearly polarized crossed dipole) Girard et al., mini-arrays (green) testing the antenna preamplifier: key element for antenna gain susceptibility to RFI Girard et al., 2014 NenuFAR-1 (pink) as phase 1 deployment (done) with properties: 285 antennas 10 80 MHz frequ. range dedicated receiver enables spectral resolution of delta f = 3 kHz, delta t = 5 microseconds waveform snapshots 5 ns Polarization: 2 linear polarizations measured by each antenna 4 Stokes p. Girard et al., 2014 Total NenuFAR instrument consisting of 96 mini-arrays (96 x 19 = 1824 antennas) Antenna distribution optimized for Gaussian coverage of the (u,v) plane Consideration of constraints (forbidden areas as FR606 and other antennas on site) NenuFARs Technical Characteristics (NenuFAR standalone) Giant phased array and interferometer compatible with LOFAR 96 mini-arrays with 19 antennas each = 1824 antennas Collective area: m^2 (at 30 MHz) Frequency range: MHz Sensitivity: < 10 mJy [1 Jy = 10^(-26) W/Hz m^2] Angular resolution: 1,5 Polarization: 4 Stokes Dedicated and independent receiver (TBD) enables use beyond the 10% fraction of time guaranteed by Internat. LOFAR Telescope board (i.e. increase of duty cycle, but pointing constraints within the 10 - 50 analog LF tile beam). NenuFAR in connection with LOFAR (Zarka et al., 2013) LOFAR core Exloo, The Netherlands (2010) Scientific objectives of NenuFAR-1 (Zarka et al., 2013) Pulsars and Rotating Radio Transients (RRATs) Galactic interstellar medium (ISM) Radio sources monitoring and spectra Epoch of Reionization (EoR) Exoplanets Binary, eruptive stars Solar system physics Transient Luminous Events (LTEs) in terrestrial and planetary atmospheres Scientific objectives of NenuFAR-1 (Zarka et al., 2013) Pulsars and Rotating Radio Transients (RRATs) Galactic interstellar medium (ISM) Radio sources monitoring and spectra Epoch of Reionization (EoR) Exoplanets Binary, eruptive stars Solar system physics Transient Luminous Events (LTEs) in terrestrial and planetary atmospheres Scientific objectives of NenuFAR-1 (Zarka et al., 2013) Pulsars and Rotating Radio Transients (RRATs) NenuFAR-1 enables efficient detection of pulsars, study of their environment, study of the nature of RRATs (similar to pulsars, but irregular pulsing behaviour) to increase number of LF targets (only ~ 40 out of 2000 pulsars [Zakharenko et al., 2013] are known as emitters below 30 MHz) study of distant magnetosphere of pulsars, emission mechanism, acceleration processes via pulse profile variations versus observing frequency [Stappers et al., 2011] Observations of pulsar B The left sub-panels show an average pulsar profile (upper) and its frequency dependence (lower). Upper right panel: the normalized dynamic spectrum with individual pulses (after interference mitigation). Lower right panel: intensity of average pulse profile versus deviation in dispersion measure from the correct value Konovalenko et al., 2015 UTR-2 (Kharkov, Ukraine) 15 UTR-2 (Kharkov, Ukraine) Konovalenko et al., 2015 Scientific objectives of NenuFAR-1 (Zarka et al., 2013) Pulsars and Rotating Radio Transients (RRATs) Galactic interstellar medium (ISM) Radio sources monitoring and spectra Epoch of Reionization (EoR) Exoplanets Binary, eruptive stars Solar system physics Transient Luminous Events (LTEs) in terrestrial and planetary atmospheres Rucker, ESA-SP, 518, 421, 2002 Radio flux density reaching Earth Range of NenuFAR-1 Search for exoplanets LF radio emissions can be produced by star-planet plasma interaction (quantitative frequency ranges and intensities however uncertain) Exoplanets Dedection of exoplanets would permit to determine exoplanet rotation magnetic field magnitude and tilt orbit inclination identification of type of star-planet plasma interaction Radio emission of full auroral oval of exoplanetary magnetosphere: Model dynamic spectra (Hess and Zarka, 2011) x-axis: 2 years = 5 exoplan. rotations y-axis: 0 40 MHz inclination = 0 magn. tilt = 0 inclination = 15 magn. tilt = 0 inclination = 0 magn. tilt = 15 inclination = 15 magn. tilt = 15 Polarization: Black from Northern hemisph. White from Southern hemisph. Scientific objectives of NenuFAR-1 (Zarka et al., 2013) Pulsars and Rotating Radio Transients (RRATs) Galactic interstellar medium (ISM) Radio sources monitoring and spectra Epoch of Reionization (EoR) Exoplanets Binary, eruptive stars Solar system physics Transient Luminous Events (LTEs) in terrestrial and planetary atmospheres Ground-based detection and studies of the Saturn electrostatic discharges with the UTR-2 Zakharenko et al., 2012 UTR-2 observations: long term SED activity with variations, time resolutions are 20 millisec and 15 nanosec (!) ( J-storm, ) Konovalenko et al., 2015 Time delay (dispersion) of the signals at different frequencies is t (f 1 )- t (f 2 ) = 4.5 x 10 6 DM (f f 2 -2 ), with t in ms, f in MHz and DM = N e l, dispersion measure given in pc cm -3. N e =1 cm -3, l = 9 AU DM 5 x pc cm -3. t 1 t 2 1.5 ms between f 1 = 10 MHz and f 2 = 20 MHz Konovalenko et al., Icarus, 2013 Zakharenko et al., P&SS, 2013; Zarka et al., Sp.Sci.Rev., 2007; LF instruments (existing, in development, planned) name antennas eff. area [m] freq. range [MHz] ang. res. polarization NDA 144 circ. dip 4 Stokes UTR dipoles 1 lin. polar. VLA 27 dish. X 25 m ~ 4 Stokes LWA 256 X dipoles ~ 88 6 4 Stokes NenuFAR X dip. ~ 80 5 4 Stokes NenuFAR X dip 4 Stokes standalone LOFAR-LBA X dip 80 2 4 Stokes NenuFAR X dip 80 2 4 Stokes LOFAR-LBA SKA > dishes ~ 10^ > 10 GHz < 0.1 4 Stokes + apert. array (adapted after Zarka et al., 2013) 25 Problems of low-frequency radio astronomy Possible solution High temperature of the Galactic background High effective are (10 4 10 6 m 2 ) Multi-telescope observations Ground-based interferences (natural, artificial, narrow-band, broad- band) High dynamic range of the front-end High dynamic range and resolutions back-end Broad-band antenna High directivity, low side lobes of antenna Special processing (clean) Space-borne instruments Multi-telescope observations Ionosphere influence (refraction, scintillations, absorption) Large field of view (multi-beams) Adaptive antenna Special processing (clean) Space-borne instruments Multi-telescope observations Low angular resolution in single-dish mode (low D/ ratio) VLBI (ground-ground; ground-space) Multi-telescope observations Multi-telescope synergy in the low-frequency radio astronomy (Konovalenko et al., 2015)