Exploring the Transient Universe with the Long Wavelength Array (LWA: lwa.nrl.navy.mil )
Long Wavelength Array
description
Transcript of Long Wavelength Array
![Page 1: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/1.jpg)
Long Wavelength Array
Joseph LazioNaval Research Laboratory
![Page 2: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/2.jpg)
High Angular Resolution, Long-Wavelength Radio
Astronomy
• An Historical OverviewWhy now?
• The Long Wavelength Array– Science – Technology
![Page 3: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/3.jpg)
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.
![Page 4: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/4.jpg)
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?
![Page 5: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/5.jpg)
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
CorrelationPreserved
CorrelationDestroyed
> 5 km<5 km
Ionosphere
= reNe
![Page 6: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/6.jpg)
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
![Page 7: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/7.jpg)
Confusion
~ 1´rms ~ 3 mJy/beam
~ 10´rms ~ 30 mJy/beam
= /D
![Page 8: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/8.jpg)
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
![Page 9: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/9.jpg)
NRL-NRAO 74 MHz Very Large Array
74-MHz VLA is the world’s most powerful long-wavelength
interferometer.
![Page 10: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/10.jpg)
First Sub-arcminute Imaging74 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)
![Page 11: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/11.jpg)
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)
VLA
PT antenna, 70 km
distant
~ 10" angular resolution
![Page 12: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/12.jpg)
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
![Page 13: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/13.jpg)
Correcting the Ionosphere
Self-Calibration Field-Based Calibration
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 Calibrationdeveloped by J. Condon & W. Cotton
![Page 14: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/14.jpg)
2.5°
VLSS Image Gallery
Imaging Parameters: RMS noise level: ~0.1 Jy/beam Resolution: 80 ''
5'
Gallery ofunusually large objects
![Page 15: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/15.jpg)
Long Wavelength ArrayA New Window on the
Universe
Long Wavelength Array Long Wavelength Array
Current Capabilities
LWA
Angular resolution Sensitivity
![Page 16: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/16.jpg)
LWA Science Case1. 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?)
2. 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?
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
![Page 17: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/17.jpg)
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).
PSR B0809+74
![Page 18: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/18.jpg)
Long Wavelength Array
• 20–80 MHz• Dipole-based array stations• 50 stations across New Mexico• 400-km baselines arcsecond resolution
400 km
![Page 19: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/19.jpg)
Long Wavelength Demonstrator Array
• 60–80 MHz• 16-element dipole station + 1 outlier• At VLA site in NM
![Page 20: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/20.jpg)
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
![Page 21: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/21.jpg)
LWDA First Light Movie
Cas A
Cyg A
Galactic plane
![Page 22: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/22.jpg)
LWDA First Light Movie
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
![Page 23: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/23.jpg)
LWDA First Light Movie
Cas A
Cyg A
Galactic plane
Cyg A = 17 kJy @ 74 MHz
cf. STARE program found no transients above 27 kJy at 610 MHz
![Page 24: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/24.jpg)
RFI Environment
![Page 25: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/25.jpg)
RFI Environment
Frequency (MHz)
FM radioTV audio and video carriers
HF COMM
![Page 26: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/26.jpg)
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
![Page 27: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/27.jpg)
LWAPhased Development
Time Phase Description
1998-present 0 Existing 74 MHz VLA
2005–present ILong Wavelength Development Array
(funded by NRL/ONR)
2007–2010 II9-station Long Wavelength Intermediate
Array
2010–2012 III LWA Core
2012–2014 IV High-Resolution LWA
2009– V LW Operations & Science Center
![Page 28: Long Wavelength Array](https://reader036.fdocuments.net/reader036/viewer/2022062423/56814bcb550346895db8a304/html5/thumbnails/28.jpg)
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