An External Calibrator for HI Observatories Summary: In modern astronomy, one edge of the unknown is the Epoch of Reionization (6<z<12), when the first stars ionized the intergalactic medium. Understanding this period of ``Cosmic Dawn"was singled out during the Astro2010 decadal review as a key goal of the decade and potential area for major new discoveries. Observations of this period push the limits of modern observatories and challenge theories of star and galaxy formation in the early universe. Optical and IR observations of this period are sparse and highly localized in space and time. One promising new technique is the direct observation of the cosmological scale intergalactic medium via the 21 cm hyperfine transition redshifted into the 100 -200 MHz band. New arrays like the Murchison Widefield Array (MWA) and the Precision Array for Probing the Epoch of Reionization (PAPER) have been purpose-built to detect and characterize this emission. Here we propose to build a new type of calibration system that will make high precision maps of the wide-field primary beam, information essential to EoR foreground removal. Intellectual Merit: MWA and PAPER provide unprecedented collecting area at very low cost by using phased arrays of dipoles in place of large steerable dishes. Analysis of commissioning observations has indicated that one primary source of uncertainty is in the model of the very wide beam pattern that often extends from zenith to the horizon. At the same time, simulations suggest that precise knowledge of the beam is necessary for removing the bright foregrounds from the faint EoR signal. Several methods have been employed to understand the response of the MWA phased array. Laboratory an-echoic chamber measurements are very expensive and difficult at EoR band frequencies. Direct beam holography of a traditional dish is usually accomplished by raster scanning across a known source, but with antennae fixed to the earth, we are limited to the drift scan pattern of the sky. Satellites may also be used to map the beam but provide little in the way of direct experimental control (timing, frequency, etc). Here we propose to develop an External Calibrator for HI Observatories (ECHO) to directly map the primary beam at high precision. ECHO consists of a programmable transmitter and a compact broadband antenna mounted to a computer controlled drone helicopter. The drone is able to fly many repeated tracks over the antenna under test allowing for direct control of experimental variables. Current beam models are uncertain at the 20% level, our goal is to measure the beam of MWA and PAPER elements to within 1% with a particular focus on the horizon response where the largest chromatic aberrations are known to present bright foregrounds to EoR signals. Broader Impacts: The broader impact of the ECHO project is in training and recruiting undergraduates with interests in electronics and field experiments into a rapidly growing field of astronomy. The ASU Low frequency Cosmology lab specializes in recruiting, training, and mentoring undergraduates for hands on projects with students working on several projects at any one time including the Experiment to Detect the Global Epoch of Reionization Signal (EDGES), the proposed Dark Ages Radio Explorer (DARE) mission, and several student initiated projects including a Very Small Radio Telescope (VSRT) station. ECHO is staffed exclusively by undergraduates who are majoring in Physics, Astronomy and Space Systems Design. Students have tested, designed and built the transmitter payload and integrated it into the drone as a functional subsystem. They fly experimental missions and will eventually travel to telescope sites for in-situ calibration. The helicopter drone system is popular with the public and is featured prominently at outreach events, several times per month.
|Effective start/end date||6/15/14 → 5/31/16|
- National Science Foundation (NSF): $69,042.00
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