Long Wavelength Array

1. Long Wavelength Array Joseph Lazio Naval Research Laboratory

2. High Angular Resolution, Long-Wavelength Radio Astronomy • An Historical Overview Why now? • The Long Wavelength Array • Science • Technology

3. Early Days: Telescopes • Jansky first detected celestial radio emission at 20 MHz. • Long wavelength astronomy stimulated much of modern astronomy. Non-thermal emission, Pulsars, Quasars, … • Large telescopes built. Jansky Clark Lake TPT UTR-2

4. Early Days: Science • Ultra-high Energy Cosmic Rays: 45 MHz (~ 1965) • Pulsars: 80 MHz (1967) • VLBI: (1967) What happened? Jansky Clark Lake TPT UTR-2

5. > 5 km <5 km Correlation Preserved Correlation Destroyed Ionospheric Phase Effects Ionosphere • If antennas are close together, Df << 1 radian • Imaging possible • If antennas are far apart, Df > 1 radian • Imaging possible only if phase effects can be corrected Df = rel DNe

6. Ionosphere Refraction • Both global and differential refraction seen. • Time scales of 1 min. or less • Equivalent length scales in the ionosphere of 10 km or less

7. Confusion q = l/D • ~ 1´ rms ~ 3 mJy/beam • ~ 10´ rms ~ 30 mJy/beam

8. > 5 km <5 km NRL-NRAO 74 MHz Very Large Array • Early 1980s: development of self-calibration • Data driven • Solve for N antenna phases using N(N-1)/2 observed interferometric phase differences • Early 1990s: 8-antenna prototype • 1998: All 27 antennas outfitted

9. NRL-NRAO 74 MHz Very Large Array 74-MHz VLA is the world’s most powerful long-wavelength interferometer.

10. First Sub-arcminute Imaging74 MHz VLA (a) (b) Cas A (Kassim et al. 1995) Crab (Beitenholz et al. 1996) (d) (e) Hydra A (Lane et al. 2004) M87 (Kassim et al. 1995)

11. VLA Approaching Arcsecond ImagingVLA+PT Cygnus A: A Long-Wavelength Resolution of the Hot Spots (Lazio et al.) Highest angular resolution imaging at wavelengths longward of 3 m ( < 100 MHz) ~ 10" angular resolution PT antenna, 70 km distant 

12. VLA Low-frequency Sky Survey Summary • Image 3π sr north of d = 30° 95% complete • Frequency = 74 MHz (l4 m) • Resolution = 80" (FWHM) VLA B configuration • Noise level ≈ 0.1 Jy beam-1 • Point-source detection limit  0.7 Jy • Nearly 70,000 source catalog Methodology Survey region covered by 523 individual pointings TOS: 75 minutes per pointing Each pointing is separated into five, 15-min. observations spread out over several hours Data reduced by completely automated pipeline Once reduced and verified, all data posted to the Web

13. Self-Calibration Field-Based Calibration Correcting the Ionosphere Field-Based Calibration Take snapshot images of bright sources in the field and compare to NVSS positions. Fit to a 2nd order Zernike polynomial phase delay screen for each time interval. Apply time variable phase delay screens Field-Based Calibration developed by J. Condon & W. Cotton

14. 2.5° VLSS Image Gallery Imaging Parameters: RMS noise level: ~0.1 Jy/beam Resolution: 80 '' Gallery of unusually large objects 5'

15. Long Wavelength Array Long Wavelength Array Long Wavelength Array A New Window on the Universe Angular resolution Sensitivity Current Capabilities LWA

16. LWA Science Case • Acceleration of Relativistic Particles • Supernova remnants (SNRs) in normal galaxies (E < 1015 eV) • Radio galaxies & clusters at energies (E < 1019 eV) • Ultra-high energyc cosmic rays (E ~ 1021 eV?) • Cosmic Evolution & the High-z Universe • Evolution of Dark Matter & Energy by differentiating relaxed and merging clusters • Study of the 1st black holes • H I during the Dark Ages? • Plasma Astrophysics & Space Science • Ionospheric waves & turbulence • Acceleration, Turbulence, & Propagation in the interstellar medium (ISM) of Milky Way & normal galaxies • Solar, Planetary, & Space Weather Science • Radio Transient Sky

17. PSR B0809+74 Pulsars at Long Wavelengths • 4C 21.53W recognized as steep spectrum source. • Later identified as PSR B1937+21. • A high dynamic range, long-wavelength instrument may find interesting pulsars. • PSR B0809+74 is steepest spectrum source in pilot VLSS observations. • Viz. PSR J0737-3039 (S1400 ≈ 5 mJy).

18. 400 km Long Wavelength Array • 20–80 MHz • Dipole-based array stations • 50 stations across New Mexico • 400-km baselines  arcsecond resolution

19. Long Wavelength Demonstrator Array • 60–80 MHz • 16-element dipole station + 1 outlier • At VLA site in NM

20. Long Wavelength Demonstrator Array • Dual-polarization dipole + active balun • Cable to (shielded!) electronics hut • Receiver (reconfigurable FPGA) selects frequency, digitizes, time-delays, filters to 1.6 MHz bandwidth • Beamforming or all-sky imaging

21. LWDA First Light Movie Cas A Cyg A Galactic plane

22. LWDA First Light Movie

23. LWDA First Light Movie Cas A Cyg A = 17 kJy @ 74 MHz cf. STARE program found no transients above 27 kJy at 610 MHz Cyg A Galactic plane

24. RFI Environment

25. RFI Environment HF COMM TV audio and video carriers FM radio Frequency (MHz)

26. LWA Progress • Several candidate antennas being field tested • Site testing around New Mexico • Program office at the U. New Mexico • Southwest Consortium • UNM, NRL, ARL:UT, LANL • U.Iowa • Multi-year funding through Office of Naval Research • Target is first, full LWA station, LWA-1, in 12–18 mon. • LWA Science and Operations Center in New Mexico in ~ 3 yr

27. LWAPhased Development

28. SUMMARY • LWA will open a new, high-resolution window below 100 MHz  one of the most poorly explored regions of the spectrum • Key science drivers: • Particle Acceleration • Cosmic Evolution & the High-z Universe • Plasma Astrophysics & Space Weather • Radio Transient Sky • Long Wavelength Demonstrator Array (LWDA) already demonstrating potential for transient surveys. • Rapid progress being made toward Long Wavelength Array deployment