From NRAO: “VLITE First Fringes”
August 20, 2014
Namir Kassim (Naval Research Laboratory)
The Naval Research Laboratory (NRL) and NRAO have successfully teamed to obtain first fringes on the Very Large Array (VLA) Low Frequency and Ionosphere Transient Experiment (VLITE). VLITE is a 10-antenna commensal system continuously accessing 64 MHz from the new 236-492 MHz Low Band system. Its backend includes dedicated samplers, fiber optics, and a DiFX-based software correlator. By harvesting data from the VLA’s prime focus, VLITE can provide 5000+ hours of “free” observing time a year, effectively making the VLA “two telescopes in one”. VLITE is a multi-year project commencing this fall, and could pave the road towards a full VLA Low Band Observatory, or LOBO system, in the future.
VLITE became sentient at ~20h 30m UT on 17 July 2014, soon after the first antennas came on line in early July. The left side of the Figure shows the phase of the cross-correlation function as a function of time (vertical) and frequency (horizontal) between VLITE antennas 1 and 3, corresponding to VLA antennas 14 and 23, after the quasar 3C273 enters the field-of-view. The length of the scan is about 10 minutes, and the ~6.5 fringes seen across the 64 MHz bandwidth (λ~1 meter) correspond to a residual delay error of ~100 nsec. Since then, more antennas have been added and simple images of calibrators – including 3C273 (see Figure, right side), made from 5 antennas – are starting to emerge.
VLITE has two main scientific drivers, and one ethereal one. The first is to provide continuous, near real-time monitoring of ionospheric waves over the VLA. VLITE is significantly more sensitive to tiny fluctuations in ionospheric total electron content than GPS, opening a new field of ionospheric remote sensing. The second scientific goal is a continuous, blind search for astronomical transients, both fast (pulsars and fast radio bursts) and slow (supernovae, gamma-ray bursts, etc.). VLITE plays to the strength of transient observations by accessing a wide field-of-view (~5 square degrees) nearly continuously. Finally, VLITE challenges the paradigm of targeted observations catering to a priori science. Its exploration-driven model seeks to reinforce the value of serendipity in a landscape increasingly dominated by perceived “transformational” science goals.
VLITE is an NRL-funded project supported by NRAO; Namir Kassim is the PI.
See the full article here.
The NRAO operates a complementary, state-of-the-art suite of radio telescope facilities for use by the scientific community, regardless of institutional or national affiliation: the Very Large Array (VLA), the Robert C. Byrd Green Bank Telescope (GBT), and the Very Long Baseline Array (VLBA)*.
The NRAO is building two new major research facilities in partnership with the international community that will soon open new scientific frontiers: the Atacama Large Millimeter/submillimeter Array (ALMA), and the Expanded Very Large Array (EVLA). Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).
*The Very Long Baseline Array (VLBA) comprises ten radio telescopes spanning 5,351 miles. It’s the world’s largest, sharpest, dedicated telescope array. With an eye this sharp, you could be in Los Angeles and clearly read a street sign in New York City!
Astronomers use the continent-sized VLBA to zoom in on objects that shine brightly in radio waves, long-wavelength light that’s well below infrared on the spectrum. They observe blazars, quasars, black holes, and stars in every stage of the stellar life cycle. They plot pulsars, exoplanets, and masers, and track asteroids and planets.
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