LWA - Key Science Drivers
- Acceleration of Relativistic Particles in:
- Hundreds of supernova remnants in normal galaxies at energies up to 1015 eV
- Thousands of radio galaxies & clusters at energies up to 1019 eV
- Ultra-high energetic cosmic rays at energies up to 1021 ev and beyond
- Evolution of Dark Matter & Energy by differentiating relaxed and merging clusters
- Study of the 1st black holes & the search for HI during Epoch of Reionization (EOR) & beyond
- Ionospheric Waves & Turbulence
- Acceleration, Turbulence, & Propagation in the interstellar medium (ISM) of Milky Way & normal galaxies
- Solar, Planetary, & Space Weather Science
- Possible new classes of sources (coherent transients like GCRT J1745-3009)
- Magnetar Giant Flares
- Extrasolar planets
- Prompt emission from gamma ray bursts (GRBs)
LWA - Science Drivers - Details
A New Window for Exploration
The greatest discoveries in astronomy have been the result of technological innovations that open new windows of the electromagnetic spectrum. The Long Wavelength Array (LWA) will explore the relatively neglected frequency regime between 10 and 90 MHz with unprecedented angular resolution and sensitivity, making it uniquely suited to serendipitous discovery, and also able to address a variety of scientific problems ranging in scale from the most distant objects in the Universe to the earth's ionosphere. Five key science areas have been identified for the LWA: cosmic evolution, transient objects, the interstellar medium of the Milky Way Galaxy, solar and extra-solar planets, and ionospheric, solar and space weather sciences. Our confidence that the LWA can explore these science topics has been increased by the 74 MHz system at the Very Large Array (VLA), which, although much less capable, has acted as a pathfinder for both the technical and scientific aspects of the LWA.
The Early Universe
The LWA will be able to take advantage of the generally steep spectral slope of distant radio objects to probe the Universe throughout its evolution. This includes detecting the first radio galaxies and black holes in the high redshift, or very young, universe, and tracing out the large scale structure of the universe via cluster radio haloes, relics, and radio galaxies which can be observed from present day out to the very earliest times in the universe. Issues of galactic evolution will be addressed through studies of the nonthermal gas associated with massive star-forming regions in the interstellar medium (ISM) of normal nearby galaxies. And finally, it will be possible to study the epoch of reionization with a search for HI 21cm absorption against the most distant radio-loud quasars and galaxies identified using the LWA.
Radio Transient Sky
In comparison to higher energies (X- and gamma-ray), the radio transient sky is poorly explored, primarily because of the lack of wide-field radio telescopes. Nonetheless, the variety of known radio transients suggests that the radio sky may be quite dynamic. With its wide field of view, the LWA will be ideal for exploring the radio transient sky. Expected sources of emission include millisecond-period pulsars, black-hole neutron star binaries, and other similar exotic systems. The LWA will also be able to study the variable but coherent radio emission from SNe, GRBs, and AGN, helping to better define the emitting mechanisms for these sources. Finally, the LWA will be able to detect radio emission from ultra-high-energy cosmic ray air showers, and may detect new classes of radio transients.
The LWA will provide an excellent probe of the interstellar medium (ISM) of the Milky Way Galaxy. It will trace Galactic electron cosmic rays, from their presumed origin in supernova remnants to their three-dimensional spatial distribution as measured by thermal absorption to objects of known distance. Using the broadband capacity of the LWA it will also be possible to study the energy distributions of the cosmic rays. Using interstellar scattering, the LWA will also probe the possible coupling between dilute relativistic gas formed by the Galactic electron cosmic rays and the more substantial warm ionized medium. A complete census of supernova remnants will be made and targeted for study of their interaction with the Galactic environment. Finally, thermal absorption measured over a variety of optical depths will provide excellent radial distance information.
Within our solar system, it is known that Jupiter emits bursts of nonthermal emission at very long wavelengths, which would be visible to the LWA for detailed study, helping to pinpoint their location and origin. Extra-solar planets which, like Jupiter, have strong coherent cyclotron emission would be directly delectable with the LWA as well.
Ionosphere, Sun, and Space Weather
A final area of interest for LWA measurements is ionospheric, solar, and space weather science. The ionosphere will necessarily contribute phase turns to every observation made by the proposed instrument. Thus the LWA will be a sensitive probe of ionospheric turbulence, and especially traveling ionospheric disturbances (TIDs). The LWA will be able to study both the quiet sun and the bright active sun, including measurements of Coronal Mass Ejections, solar bursts, interplanetary shocks and scintillations. With the use of an appropriate transmitter, this could possibly be extended to solar radar experiments to predict geomagnetic storms.
The LWA will be able to address all of these science issues and more. Due to the relatively poorly explored spectral regime in which it will operate, serendipitous discoveries are to be expected. The design of the instrument will be flexible enough that it can be easily adapted to new scientific aims as they become known, allowing the instrument to become a long-lived contributor to radio-astronomical science.