PAPER (telescope)

PAPER (telescope)
Name	PAPER
Caption	Precision Array for Probing the Epoch of Reionization (PAPER)
Organization	Harvard University; South African Radio Astronomy Observatory; Cornell University; University of California, Berkeley
Country	United States; South Africa
Established	2006
Wavelength	Radio (centimetre to metre)
Type	Interferometric radio array

PAPER (telescope) The Precision Array for Probing the Epoch of Reionization (PAPER) was a ground-based interferometric radio array designed to measure the redshifted 21-centimetre line from neutral hydrogen during the Epoch of Reionization, the cosmic era probed by telescopes including Murchison Widefield Array, Low-Frequency Array, Hydrogen Epoch of Reionization Array, and Square Kilometre Array. Developed through partnerships among institutions such as Harvard University, Cornell University, Brown University, and University of California, Berkeley, PAPER operated at remote sites including Green Bank Observatory and the Karoo region near the MeerKAT site, contributing important constraints on early-universe models explored alongside missions like Planck and experiments such as WMAP.

Overview

PAPER was conceived to address questions central to observations pursued by projects like James Webb Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, Spitzer Space Telescope, and theoretical efforts by teams at Caltech, Princeton University, MIT, and Institute for Advanced Study. The array targeted the high-redshift 21-cm signal predicted in modeling by researchers affiliated with NASA, European Space Agency, Max Planck Institute for Astrophysics, and Harvard–Smithsonian Center for Astrophysics. PAPER supplemented contemporaneous studies by arrays such as LOFAR and GMRT while influencing designs for future instruments including SKA1-Low.

Design and Instrumentation

PAPER’s hardware drew on heritage from experiments at facilities like Very Large Array and Arecibo Observatory, integrating technologies tested by groups at Jet Propulsion Laboratory, National Radio Astronomy Observatory, and CSIRO. The array used dipole-style elements and simple analog beamformers developed at laboratories including MIT Lincoln Laboratory and National Institute of Standards and Technology to achieve wide fields comparable to those used by Allen Telescope Array. Backends employed digital correlators inspired by designs from CASPER collaborators and firmware work at Xilinx and NVIDIA partners. Calibration strategies referenced catalogs from NRAO and survey data from Gaia, Sloan Digital Sky Survey, and Two Micron All Sky Survey teams to mitigate systematics.

Observational Strategy and Deployment

PAPER adopted a drift-scan strategy similar to approaches used by CHIME and OVRO to maximize sky coverage and sensitivity to diffuse emission mapped by Planck and WMAP. Initial deployments were staged at the National Radio Quiet Zone near Green Bank Observatory before relocating main operations to the Karoo, colocated with infrastructure supporting MeerKAT and SKA pathfinder efforts coordinated with South African Radio Astronomy Observatory. Logistics involved collaborations with institutions such as University of the Western Cape and Rhodes University for site support, and scheduling interfaces with timekeeping standards like International Atomic Time and services from USNO.

Data Processing and Analysis

PAPER’s analysis pipelines incorporated algorithms and software concepts aligned with packages from CASA, HEALPix, and work by groups at Lawrence Berkeley National Laboratory and Argonne National Laboratory. Foreground removal strategies built on techniques developed in studies by Johns Hopkins University, Princeton, and University of Chicago, referencing spectral models of sources cataloged by Culgoora, Texas Survey, and GLEAM. Power spectrum estimation and statistical validation employed methods used in analyses from Planck and theoretical frameworks advanced at Cambridge University, Oxford University, and Caltech. High-performance computing resources at National Center for Supercomputing Applications and NERSC supported map-making and Monte Carlo simulations.

Scientific Results

PAPER provided upper limits on the 21-cm power spectrum that informed reionization models developed by researchers at Columbia University, University of Pennsylvania, Imperial College London, and University of Cambridge. Its constraints intersected with interpretations of cosmic microwave background anisotropies measured by Planck and with Lyman-alpha forest results from surveys led by Keck Observatory and VLT. PAPER’s systematics studies influenced instrument design and foreground mitigation approaches later used by HERA, LOFAR, and the SKA project, while its data contributed to joint analyses involving teams from NASA and ESA.

Collaborations and Legacy

PAPER was a collaboration among many institutions including Harvard University, Cornell University, Brown University, University of California, Berkeley, University of the Western Cape, and South African Radio Astronomy Observatory, and it engaged with infrastructure programs like MeerKAT and SKA. The experiment’s engineering, software, and analytic outputs seeded techniques adopted by successor efforts such as Hydrogen Epoch of Reionization Array and informed international consortia associated with SKA Organization, NRAO, and the International Astronomical Union. Its legacy persists in instrument concepts, pipeline codebases, and personnel who moved to projects at Caltech, MIT, Princeton University, and University of Cambridge working on next-generation 21-cm cosmology.

Category:Radio telescopes