LWA: The Long Wavelength Array

LWA Web sites:   http://lwa.nrl.navy.mil/, http://lwa.unm.edu, and links therein.

I. General project/facility description

1. Overview of the facility/project
   The Long Wavelength Array (LWA) will be a major new instrument for low frequency (10-88 MHz) radio science, serving the radio astronomy, space physics, and ionospheric science communities. The instrument will be developed with the combined expertise and involvement of the participating universities, the Naval Research Laboratory (NRL) of the Department of Defense, the Los Alamos National Laboratory (LANL) of the Department of Energy (DoE), and the National Radio Astronomy Observatory (NRAO). A major focus will be to engage individual astronomers and the US university radio astronomy community in development and use of this instrument.

2. Managing institution and organization
   The South West Consortium (SWC) consists of four institutions: the University of New Mexico (UNM); the University of Texas at Austin through its Applied Research Laboratories (ARL-UT); the Los Alamos National Laboratory (LANL) operated by the University of California for the DoE; and the Naval Research Laboratory (NRL) of the DoD (Basic research at the Naval Research Laboratory is supported by the Office of Naval Research.). In addition, the SWC has significant collaborations with non-member entities including the NRAO as well as individuals who are participating in the LWA development. UNM is providing fiscal and program oversight for the LWA through individual institutions that also participate independently in the R&D of this project.

3. Funding source(s)
   Current activities are funded by individual members of the SWC including key personnel, workshops and related support. Phase I of the LWA is a demonstration array of two stations and is primarily funded through program funds of NRL. LANL supports LWA activities through internal funding, including the Laboratory Directed Research and Development program. Significant contributions for funding of future stages are expected from more than one federal agency, including DoE, DoD, and the National Science Foundation (NSF).

4. Construction history and cost
   

   Time	Phase	Description	Acronym	Est Cost
   1991-1998	0	Existing 74 MHz VLA	VLA74	completed
   2004-2006	I	Long Wavelength Development Array (2 Stations + 74 MHz VLA)	LWDA	funded
   2006-2009	II	Long Wavelength Intermediate Array (7 new stations + infrastructure)	LWIA	$18.5M
   2008-2010	III	LWA Core	LWAC	~$20M
   2010-2012	IV	High Resolution LWA	LWA	~$20M
   2010-	V	LW Operations and Science Center	LWOSC	0.25M

   
   
5. Operational history and cost
   

   Time	Phase	Description	Acronym	Est Cost
   1998	0	Existing 74 MHz VLA	VLA74	funded
   2005-2006	I	Long Wavelength Development Array (2 Stations + 74 MHz VLA)	LWDA	funded
   2006-2009	II	Long Wavelength Intermediate Array	LWIA	$1.5M
   2008-2010	III	LWA Core	LWAC	$1.0M
   2010-2012	IV	High Resolution LWA	LWA	$1.0M
   2010-	V	LW Operations and Science Center	LWOSC	0.5M/yr

   
   

II. Technical details

1. Specifics of telescope/instrument
   

   Frequency Range	10- 88 MHz
   	(20 - 80 MHz optimized)
   Effective Collecting Area	106 (15 MHz/ν2)m2
   Number of Dipole Elements	~ 13,000
   Number of Dipole Stations	~52
   Baseline Range	0.2 - 400 km
   Point-Source Sensitivity	2.2 mJy @ 15 MHz
   (2 polarization, 1 hour, 4 MHz BW)	1.1 mJy @ 30 MHz
   	0.7 mJy @ 75 MHz
   Angular Resolution	10″ @ 15 MHz
   	5″ @ 30 MHz
   	2″ @ 75 MHz
   Mapping Capability	Full field of view
   Number of Independent FOV (beams)	8
   Maximum Observable Bandwidth	32 MHz
   Spectral Resolution	≤ 1 KHz
   Image Dynamic Range	≥ 104
   Digitized Bandwidth	Full RF

   
   See also http://lwa.nrl.navy.mil/LWA/LWA.specs.html)

2. New capabilities anticipated/planned in next 5-10 years
   

   The LWA is being developed as a staged project in 5 phases. Phase 0 is the currently operational NRL-NRAO developed 74 MHz system on the VLA. The project has been funded through Phase I, which is currently under construction.Please see http://lwa.nrl.navy.mil/LWA/steps/.

   Many of the greatest discoveries in astrophysics have coupled key technical innovations with the opening of new windows on the EM spectrum. The technical breakthrough in long wavelength astronomy has already occurred in the demonstration of ionospheric calibration with 74 MHz VLA. The LWA also introduces new observing paradigms such as multi-beaming and wide-field sky monitoring. The wavelength range below 100 MHz remains the last poorly explored spectral regime.
   When completed, the LWA will provide improvements of 2-3 orders of magnitude in imaging power (resolution and sensitivity) over past and present instruments.

   UNM is a member of a major initiative between US universities and private companies to provide a national scale network beyond Internet 2 called National LambdaRail ( http://www.nlr.net/index.html). The LambdaRail would be used by the LWA to serve LWA data to distributed computing facilities or to other research facilities.

III. User profile

1. % of "open skies" time
   100%
2. Institutional affiliations of users
   US universities, US national laboratories, and international users.

3. Student access, involvement, usage
   Students will be an integral part of the LWA instrument planning and development process. Undergraduate and graduate students are currently being supported at NRL and ARL-UT for LWA science and technology development; LWA Phase 0 observations have and continue to support the PhD thesis work of many graduate students. Students will also be involved in science activities at all stages of the instrument as part of our commitments to revitalize radio astronomy at the university level, to develop the next generation of technically-aware and scientifically-astute radio astronomers, and to craft new, powerful techniques for the use of modern instrumentation.

IV. Science Overview

1. Current forefront scientific programs
   On-going science programs with LWA Phase 0 - includes VLA 74 and 330 MHz.
   • Supernova Remnants and interactions in the ISM
   • Wide field imaging of the Galactic Center region
   • Magnetic fields in radio galaxies and galaxy clusters
   • Identification of ultra-steep spectrum sources as candidate galaxy clusters and high redshift radio galaxies
   • Searches for transient radio sources in and around the Galactic Center.
   • Major astronomical surveys:
     • VLA Low-frequency Sky Survey (VLSS: 74 MHz)
     • Targeted extragalactic (e.g. 74 MHz survey of XMM-LSS deep field)
     • Galactic (eg. 74 and 330 MHz Galactic plane survey)
   • 3-D investigation of electron content in mid-latitudes
   • Ionospheric diffraction tomography
   • Studies of traveling ionospheric disturbances (TID's)
   • High temporal resolution studies of small-scale structures
   • Assimilation of ionosphere data into global models, e.g. GAIM (Global Assimilation of Ionospheric Models)
   Technical studies
   • Broad-band active antennas & baluns
   • High dynamic range digital receivers for diverse environments
   • Ionospheric calibration for radio astronomy observations
   • Pre- and post-correlation RFI mitigation
   • Site-evaluation of southwest US for LWA, FASR, EVLA, & SKA.
   • Development of new observing modalities
     • RAPTOR,GENIE (Genetic Imagery Exploitation), GASE(GRB All-sky Spectrometer Experiment) for transient detection
     • Techniques for data mining and knowledge discovery and dissemination
   • Development of complementary computing technologies
     • Massive parallel processing techniques for image recovery
     • FPGA (fieldprogrammable gate arrays) for dedicated computing operations
   • Development of 3-D mapping technologies for backscatter studies of lightning
   
   
2. Major discoveries (through 1999)
   With Phase I under construction, the LWA is currently operational under Phase 0, which is comprised of the 74 MHz system at the VLA. While this modest narrow-band system is very limited in resolution and sensitivity compared to the broad-band LWA, it nonetheless represents a major step forward over previous capabilities below 100 MHz. Results from Phase 0 are validating many aspects of the broad-based LWA science case, and have resulted in unique astronomical achievements, a few of which are listed below. (Includes results from both the 74 and 330 MHz VLA systems, the latter providing the platform on which software solutions to many generic data reduction challenges - e.g. RFI excision and wide-field imaging - have been pioneered.) An extensive bibliography of scientific results from both the 330 MHz and 74 MHz low frequency VLA systems can be found at: http://lwa.nrl.navy.mil/LWA/publications.html. The far more powerful LWA instrument will go much further to open this poorly explored spectral region, bringing the strong potential for unique discovery science.
   • First sub-arcminute resolution imaging below 100 MHz with a connected element interferometer
   • First non-parallel Galactic Nonthermal Filament
   • First radio detection of unshocked ejecta in Galactic SNR
   
   
3. Science highlights of last 5 years
   
   • First wide-field imaging of the Galactic center
   • First spatially resolved ISM absorption towards Galactic nonthermal source
   • Lowest frequency radio detection of Sgr A*
   • First spatially resolved observations of ionized interface between SNR/MC interaction
   • New, unique Galactic center transient
   • First spatially resolved connection between X-ray deficits and buoyant radio lobes
   • The VLA Low Frequency Sky Survey (VLSS), available on-line (at http://lwa.nrl.navy.mil/VLSS/> ) and used by astronomers around the world. The VLSS is currently about half-finished, and is expected to be substantially completed in the next year. The VLSS will also serve as the critical initial calibration grid for both the upper and lower portions of the LWA and LOFAR frequency bands, respectively.
   
   
4. Main future science questions to be addressed
   
   • Detection and study of the first supermassive black holes
   • Search for localized HI absorption during the Epoch of Reionization
   • Identification of merging galaxy clusters and large scale structure filaments through their diffuse synchrotron emission
   • Cluster emission used to study Dark Matter dominated merging systems
   • Identification of relaxed or non-merging systems sample for study of Dark Energy
   • Study of SNRs in normal galaxies at energies up to 10¹⁵ eV: Cosmic ray tomography to study the distribution, spectrum, and origin of Galactic cosmic rays; Spectral SNR studies to probe shock acceleration theory, SNR evolution, and interactions with the surrounding environment
   • Study of radio galaxies and clusters at energies up to 10¹⁹ eV: self-absorption processes, the low-γelectron population, Intra-cluster magnetic fields, and merger shocks; Radio galaxy lifecycles and radio jet composition
   • Ultra high energy cosmic rays at energies up to 10²¹ ev and beyond: Cosmic Ray air-showers; ultimate source unknown.
   • Ionospheric turbulence and structures, including TID's
   • Both active and quiet sun studies, measurements of Coronal Mass Ejections (CMEs), interplanetary shocks and scintillations
   • The interstellar medium (ISM) and beyond: Propagation, scattering, and absorption in the ISM of the MW and normal galaxies; Scattering from the intergalactic medium; Census of Galactic SNRs with distances
   • Discovery science made possible by opening this new spectral window. Some potential new horizons: extra-solar transients and coherent emission sources such as Jupiter-like planets.

   A text description of these goals can be found at http://lwa.nrl.navy.mil/LWA/LWA_science_summary.html

5. Synergies with other major forefront facilities
   
   • Radio
     • GMRT, VLA, WSRT, VLBA, and others: bridging observations (WSRT: 150, 330, 610, ≥ 700 MHz; GMRT: 160, 235,330, 610, 1400 MHz; VLA: 74, 330, ≥ 1400 MHz, VLBA: 330, 610, ≥ 1400 MHz,) that will connect LWA observations to cm- and mm-wavelength radio astronomy.
     • FASR & EVLA: LWA-based ionospheric specification for calibrating proximate instruments, including FASR and the EVLA. Combined LWA and FASR space weather observations.
     • LOFAR/other (future): LWA to provide foreground source maps needed to search for global Epoch of Reionization signature.
     • MWA: space weather and transient observations (≥ 80 MHz) that will link to lower frequency (≤ 80 MHz) LWA observations.
     • Arecibo, HAARP: potential for solar radar (for geomagnetic storm prediction, space weather studies) with the Arecibo or HAARP transmitter, and the LWA as a receiver.
   • X-ray and γ-ray:
     • Chandra, XMM-Newton, Astro-E2, and other planned X-ray instruments: thermal (hot gas) and nonthermal (inverse-Compton, shock-acceleration related) X-ray observations will link studies of supernova remnants, radio galaxies, and clusters to LWA observations of the low-γ electron population encompassing most of the energy density in relativistic particles.
     • GLAST and future planned high energy astrophysics missions will extend such studies to higher energies in supernova remnants, cosmic rays, AGN, and clusters.
     • SWIFT: Phase I of the LWA (aka the Long Wavelength Development Array) will conduct rapid follow-ups of SWIFT Gamma-ray Burst Mission triggered GRBs to search for prompt, coherent radio emission.
   • Solar, Space Science Satellites:
     • SOHO, STEREO, TWINS, IMAGE, National Solar Observatory (and other planned solar/space weather instruments): complementary observations of Sun-Earthconnection phenomenology (e.g. Coronal Mass Ejections)
   • Optical:
     • All powerful ground or space based optical and IR telescopes will complement LWA observations, e.g. IR-photometry, optical and IR-spectroscopy for follow-ups of LWA-obtained high redshift radio galaxy candidates
     • RAPTOR: for transient searches.
   
   
6. Unique contributions
   
   • High sensitivity, high resolution imaging of radio sources below 100 MHz.
   • Revitalization of university based radio astronomy programs through direct university involvement in design, development and scientific implementation of the LWA over the next decade.
   • Development of new observing modalities; multi-beaming, wide-field transient monitoring.
   • Milli-TEC-unit precision spatial resolution and high temporal resolution imaging and modeling of ionospheric turbulence, e.g. Traveling Ionospheric Disturbances (TIDs)
   • Data assimilation into and improvement of global ionospheric models (e.g. GAIM: Global Assimilation of Ionospheric Measurements)
   • Solving the challenge of imaging through the ionosphere with high resolution and fidelity at low frequencies.
   • High performance computing solutions to radio astronomy RFI mitigation, calibration, imaging challenges, data mining and exploitation.
   • Space Weather observations
     • Passive: synchrotron emission and scintillation studies of Coronal Mass Ejections (CMEs), other HF/VHF observations of space weather related phenomena, e.g. solar flares and bursts.
     • Active: Solar radar imaging of the corona and space-weather phenomena (required transmitter, e.g. at Arecibo or HAARP) e.g. for geomagnetic storm prediction

V. Education/Outreach activities

1. Visitor facility
   A key visitor and educational center associated with the LWA will be the existing LodeStar Astronomy Center (LAC), which is a UNM project located at, and operating in partnership with, the New Mexico Museum of Natural History (a State of New Mexico project) in Albuquerque. The LAC serves about 350,000 people per year, many from underserved populations in New Mexico and the Southwest, with informal educational programs at the facility, which includes a fully digital planetarium. It reaches an additional 25,000 people each year through its state-wide outreach program based on portable planetariums, star parties, teacher workshops, and hands-on activities. We propose to tie the Long Wavelength Array education and public outreach efforts into the LAC, which currently lacks a radio astronomy component. This would include new exhibit development at the LAC, and incorporation of radio astronomy content into the informal educational programs.
   Near the telescope core, the SWC will cooperate in the activities at the VLA visitor center near the VLA site in central NM. We also expect to engage in joint visitor and educational activities with FASR and any other projects doing science on the Plains of San Augustin.

2. Student programs
   Two university led efforts will emerge which provide a strong educational focus to the LWA activities. First there will be the LWA Science Center affiliated with the Physics and Astronomy Department at the University of New Mexico which will attract scientists and students, and will house the imaging center and the computing facility associated with LWA. There will be an aggressive program of research activities for undergraduates (such as REU type programs), graduate student participation, postdoctoral funding and facilities and visiting scientist facilities. A second important center will be located at the University of Texas, Austin and will focus on ionospheric studies. As part of the Advanced Research Laboratories at UT (ARL-UT), the Ionospheric Center will host both undergraduate and graduate students as well as post-docs and other visitors interested in ionospheric studies. These two university based science centers will focus on directly engaging students interested in radio astronomy in LWA activities.
   The SWC team institutions will host a variety of scientific activities, which in addition to astronomy programs include: physics, computing, imaging, and engineering activities. LANL and NRL have a long tradition of supporting students and postdocs in their activities and will make LWA a key focus for this type of outreach activity. The founding universities involved in the LWA have degree programs in astrophysics, physics, mathematics and statistics, computer science, and electrical and computer engineering. In addition, the SWC is actively courting participation by other interested higher-education institutions with similar academic and research interests. Thus the training of many students across these various departments will help strengthen the US university base in radio astronomy and instrumentation.
   Of particular interest for the development of the next generation of engineers, physicists, astronomers, and computer scientists, is the ability of the southwestern universities to engage minority (largely Hispanic and Native American) students in exciting scientific projects and discoveries. UNM and UT-Austin are federally-recognized Minority Serving Institutions. NRL and LANL are committed to supporting diversity in their institutions and to serving the aspirations of their communities.

3. Other
   In September 2004 an SWC-organized international conference with over 80 attendees was held in Santa Fe, New Mexico. The meeting honored Professor Emeritus William C. Erickson, a pioneer in low frequency radio astronomy. It brought together a diverse group of scientists whose interests included astrophysics, space physics, solar and planetary science, space weather, and ionospheric physics. The successful meeting helped validate the underlying low frequency science case and demonstrated community-wide support for development of the project. More information about the meeting, including PDF files of many of the presentations, can be found at the link below. The proceedings will be published by PASP and are currently under preparation (http://lwa.nrl.navy.mil/WCE/).

VI. Documentation/website URLs

1. URL of facility website
   
   • http://lwa.nrl.navy.mil/
   • http://lwa.unm.edu
   • http://sgl.arlut.utexas.edu/research/lwa.html
2. URL of EPO website
   Future facility; NYA.
3. URL(s) of any brief overviews of project/facility
   
   • http://lwa.nrl.navy.mil/,
   • http://lwa.unm.edu,
     and links therein.
4. URL(s) of miscellaneous documentation
   
   • http://nrl.navy.mil/
   • http://www.arlut.utexas.edu/
   • http://www.unm.edu
   • http://www.lanl.gov
5. URL's of related web sites:
   
   • UNM Center for High Performance Computing: http://www.hpc.unm.edu/
   • LANL Center for Space Science and Exploration: http://www.lanl.gov/orgs/isr/csse
   • Space Science and Applications: http://www.lanl.gov/orgs/isr/isr1
   • Space and Remote Sensing Sciences: http://www.lanl.gov/orgs/isr/isr2
   • Space Data Systems: http://www.lanl.gov/orgs/isr/isr3
   • Space Instrumentation and Systems Engineering: http://www.lanl.gov/orgs/isr/isr4
   • Computer and Computational Sciences: http://www.ccs.lanl.gov/
   • LANL Physics Division: http://www.lanl.gov/orgs/p/
   • LANL space science http://www.lanl.gov/worldview/news/releases/space.shtml
   • FORTE: http://www.forte.lanl.gov/index.shtml