1 / 28

Nançay current capabilities and some results in connection with SIRA

This article discusses the current capabilities of the Nançay Radio Observatory in solar radio interferometry, decameter radio astronomy, and data processing of space-borne radio astronomy experiments. The observatory's instruments can be used to test open issues and extend SIRA measurements. It also explores the detection of weak emissions, solar fine structures, polarisation of solar bursts, ionosphere cut-offs, and coronal and IP radio signatures.

nellab
Download Presentation

Nançay current capabilities and some results in connection with SIRA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Nançay current capabilities and some results in connection with SIRA Alain Lecacheux Observatoire de Paris- LESIA SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  2. Existing capabilities in Nançay/LESIA • long experience in solar radio interferometry (NRH at meter ). • long experience in decameter radio astronomy (broadband DAM array in 10-100 MHz range). • long experience in building (LESIA) and in data processing of space borne radio astronomy experiments. • Development (since 1995) of wide band, high dynamic range receivers for LF radioastronomy and of associated RFI mitigation techniques. • Nançay instruments may be used to test several open issues • Nançay can extend SIRA measurements (from f > 10 MHz) at geographic longitude ~ 0° SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  3. Nançay Radioheliograph: 5m antennas (North-South array) SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  4. Nançay Radioheliograph (NRH) • General characteristics • frequency range: 150 - 450 MHz • 576 baselines from 50 to 3200m (25 to 4,800 l) • spatial resolution: ~4 to 0.3 arcmin (depending on frequency, declination, snapshot/synthesis) • field of view: from 3 to 0.5 degrees • Stokes I and V • time resolution: 5 ms  number of frequencies • further integration gives standard mode: 8 images/sec in 5 almost simultaneous frequencies • Solar-dedicated instrument SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  5. Nançay Radioheliograph array configuration 1600 m 1600 m H16 H8 H7 H2 H1 NS1 Ext0 Ext1 Ext2 NS2 • « Anti Aliasing » antennae • Log Periodic • 150-450 Mhz • 2 polarizations A0 A1 A2 A3 NS8 • « Est-West » antennae • 150-450 Mhz • 1 polarization 1248 m NS12 North • « Est-West Extension » antenna (Ext0) • « North-South Extension » antenna (NS24) • 7 m diameter • 150-450 Mhz • 2 polarizations South • « Est-West Extensions » antennae (Ext1, 2) • 10 m diameter • 150-450 Mhz • 2 polarizations NS23 • « North-South » antennae • 5 m diameter • 150-450 Mhz • 2 polarizations 1200 m NS24 SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  6. Detection of weak emissions (Bastian et al.,2001) CME-Driven shock Plasma front (Maia et al., 2001 CME Radio imaging SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  7. Nancay Decameter Array SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  8. The Nançay Decameter Array • Filled aperture, phased array: • elementary antenna: log-periodic helix spiral (as CLRO) • two sub arrays (72 elements each) in circular polarisations • Main characteristics: • full bandwidth: 10-120 MHz (practical 10-80 MHz) • instantaneous bandwidth: one octave (selectable) • maximum effective aperture (at 25 MHz): 2  4000 m2 • declination coverage : -20°    50° • tracking time:  4 hr from meridian transit time) • four Stokes parameters • set of high resolution, wideband spectrum analysers • Not a solar-dedicated instrument, but provides daily, spectral coverage of the solar activity in the 20-70 MHz range. SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  9. Solar fine structures at the sub-second level SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  10. SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  11. Polarisation of solar bursts Type IIIb SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  12. Ionosphere cut off SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  13. Coronal and IP Radio signatures • Wide spectral coverage • Radio source (dm-m) • 5 /11events: complex evolution (spectral, spatial and temporal) • EPAM/ACE 38-315keV (Haggerty and Roelof, 2001) WIND DAM 09:28 NRH 18 February 2000 Pick et al., 2003 SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  14. SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  15. Several questions: • Ground-based, solar radio spectro-imagers are needed to « continue » SIRA at lower (higher) solar altitudes (frequencies). is LOFAR enough ? • is the SIRA top frequency (15 MHz) adequate ? • can we get, from the ground (and below ~ 50 MHz), radio data with sufficient quality in spite of the ionosphere presence ? SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  16. Ionospheric scintillations SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  17. Dynamic spectrum of ionospheric scintillations on Cas A SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  18. Dynamic imaging the Crab Nebula at 20 MHz • UTR-2 (Konovalenko, 1999) • T shaped, phased array operating in 8-40 MHz • multi-beam capability (5 in NS direction) • Fast scanning operation: • NS and EW beams are correlated by using high dynamic range correlator (DSP receiver)  5 pixels in  • the process is repeated for 8 positions in RA • produces 8x5 « images » (0.5° angular spacing), at sub-second speed. • frequency band and resolution are provided by the DSP receiver. EW x NS NS arm EW arm SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  19. IPS scintillations on Crab Nebula (UTR-2 + DSP receiver) 10 sec. time resolution SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  20. IPS scintillations on Crab Nebula (UTR-2 + DSP receiver) 20 millisec. time resolution SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  21. Solar Corona propagation (f  1MHz) • Effects detected on Type III bursts, well summarized by Dulk (1999, AGU monogr. on LF radioastronomy), and based on works, namely by Fainberg et al (1972), Lin et al. (1981), Steinberg et al. (1984,1985), Dulk et al. (1985), Lecacheux et al. (1989), Bastian (1995a, 1995b), Hoang et al. (1997,1998): • apparent source radial distances much larger than plasma altitudes • F and H sources abnormally coincident, at a given frequency. • apparent source sizes impossibly large. • anomalous time delay up to 500 sec. (1 AU !) when observations of several S/C are compared. • F and H radiation reception depends on S/C position wrt the e- beam; F and H radiation are differently beamed. • sources, located behind the Sun, are only weakly attenuated. SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  22. Re-visiting Voyager-ISEE 3 comparison • Analysis of 216 type III bursts over 18 frequencies (47-1000 kHz) • Voyager at distance > 4AU • Voyager provided intensity time profiles. • ISEE-3, in addition, measured direction of arrival and source size. SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  23. Voyager-ISEE : solar type III’s time delay excess vs. intensity ratio (unpublished) SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  24. (unpublished) SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  25. SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  26. SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  27. SIRA Jupiter DAM radiation might be a concern for SIRA sensitive astronomy observations • Jupiter < 15 MHz, at 4 AU : • permanent radio source in antenna primary beams • average intensity ~ 104 Jy • highly variable at various time scales (hour to msec.) (after Zarka,1997) SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

  28. Summary and suggestions • SIRA solar science return would be greatly enhanced by an array of dedicated, “simplified” radio spectro-imagers, in addition to LOFAR and FASR instruments. They would cover the band 15-100 MHz and be located at various longitudes. • Image quality, obtainable from the ground, should be assessed (f < 30 MHz) and the SIRA upper frequency redefined accordingly. • While SIRA is primarily an imager, spectroscopy is important from scientific and operational aspects (data selection, RFI mitigation, etc…). • “Inverting” LF radio images of the Sun is maybe a challenge, because of coronal plasma scattering properties. Should be tested both from theoretical and (ground based) observing points of view. • IPS regime (astronomy studies) at f < 30 MHz can be studied, on selected radiosources, with existing instruments. • Jovian radiation continuous presence, might be a difficulty for sensitive sky mapping. SIRA Science Workshop, Greenbelt, 2003 May 13-14 - A.Lecacheux

More Related