Long Wavelength Array Joseph Lazio Naval Research Laboratory

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

Early Days: Telescopes Jansky Clark Lake TPT UTR-2 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.

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

Ionospheric Phase Effects If antennas are close together,  << 1 radian  Imaging possible If antennas are far apart,  > 1 radian  Imaging possible only if phase effects can be corrected Correlation Preserved Correlation Destroyed > 5 km <5 km Ionosphere  = r e  N e

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

Confusion  ~ 1´ rms ~ 3 mJy/beam  ~ 10´ rms ~ 30 mJy/beam  = /D

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 > 5 km <5 km

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

First Sub-arcminute Imaging 74 MHz VLA (d)(e) (b) (a) Crab (Beitenholz et al. 1996) Cas A (Kassim et al. 1995) M87 (Kassim et al. 1995) Hydra A (Lane et al. 2004)

Approaching Arcsecond Imaging VLA+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) VLA PT antenna, 70 km distant  ~ 10" angular resolution

VLA Low-frequency Sky Survey Summary Image 3π sr north of  =  30° 95% complete Frequency = 74 MHz ( 4 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

Correcting the Ionosphere Self-CalibrationField-Based Calibration Take snapshot images of bright sources in the field and compare to NVSS positions. Fit to a 2 nd 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

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

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

LWA Science Case 1. Acceleration of Relativistic Particles Supernova remnants (SNRs) in normal galaxies (E < eV) Radio galaxies & clusters at energies (E < eV) Ultra-high energyc cosmic rays (E ~ eV?) 2. Cosmic Evolution & the High-z Universe Evolution of Dark Matter & Energy by differentiating relaxed and merging clusters Study of the 1 st black holes H I during the Dark Ages? 3. 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 4. Radio Transient Sky

Pulsars at Long Wavelengths 4C 21.53W recognized as steep spectrum source. Later identified as PSR B A high dynamic range, long- wavelength instrument may find interesting pulsars. –PSR B is steepest spectrum source in pilot VLSS observations. –Viz. PSR J (S 1400 ≈ 5 mJy). PSR B

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

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

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

LWDA First Light Movie Cas A Cyg A Galactic plane

LWDA First Light Movie

Cas A Cyg A Galactic plane Cyg A = MHz cf. STARE program found no transients above 27 kJy at 610 MHz

RFI Environment

Frequency (MHz) FM radio TV audio and video carriers HF COMM

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

LWA Phased Development TimePhaseDescription 1998-present0 Existing 74 MHz VLA 2005–presentI Long Wavelength Development Array (funded by NRL/ONR) 2007–2010II 9-station Long Wavelength Intermediate Array 2010–2012III LWA Core 2012–2014IV High-Resolution LWA 2009–V LW Operations & Science Center

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