Low Frequency Array (LOFAR): The French LOFAR Super Station Helmut O. Rucker Commission for Astronomy Austrian Academy of Sciences ÖAW, 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)

NenuFAR‘s 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 [m²] 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)