Long wavelength array
Download
1 / 28

Long Wavelength Array - PowerPoint PPT Presentation


  • 100 Views
  • Uploaded on

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 first detected celestial radio emission at 20 MHz.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Long Wavelength Array' - daphne


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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Long wavelength array

Long Wavelength Array

Joseph Lazio

Naval Research Laboratory


High angular resolution long wavelength radio astronomy
High Angular Resolution, Long-Wavelength Radio Astronomy

  • An Historical Overview

    Why now?

  • The Long Wavelength Array

    • Science

    • Technology


Early days telescopes
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


Early days science
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


Ionospheric phase effects

> 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


Ionosphere refraction
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
Confusion

q = l/D

  • ~ 1´

    rms ~ 3 mJy/beam

  • ~ 10´

    rms ~ 30 mJy/beam


Nrl nrao 74 mhz very large array

> 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


Nrl nrao 74 mhz very large array1
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
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)


Approaching arcsecond imaging vla pt

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 


Vla low frequency sky survey
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


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


2.5°

VLSS Image Gallery

Imaging Parameters:

RMS noise level: ~0.1 Jy/beam

Resolution: 80 ''

Gallery of

unusually large objects

5'


Long Wavelength Array

Long Wavelength Array

Long Wavelength Array

A New Window on the Universe

Angular resolution

Sensitivity

Current Capabilities

LWA


Lwa science case
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


Pulsars at long wavelengths

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).


Long wavelength array1

400 km

Long Wavelength Array

  • 20–80 MHz

  • Dipole-based array stations

  • 50 stations across New Mexico

  • 400-km baselines  arcsecond resolution


Long wavelength demonstrator array
Long Wavelength Demonstrator Array

  • 60–80 MHz

  • 16-element dipole station + 1 outlier

  • At VLA site in NM


Long wavelength demonstrator array1
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
LWDA First Light Movie

Cas A

Cyg A

Galactic plane



Lwda first light movie2
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



Rfi environment1
RFI Environment

HF COMM

TV audio and video carriers

FM radio

Frequency (MHz)


Lwa progress
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
LWAPhased Development


Summary
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


ad