The Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) is a radio interferometer funded by the

National Science Foundation The U.S. National Science Foundation (NSF) is an Independent agencies of the United States government#Examples of independent agencies, independent agency of the Federal government of the United States, United States federal government that su ...

to detect 21 cm hydrogen (HI) fluctuations occurring when the first galaxies ionized intergalactic gas at around 500 million years after the Big Bang. PAPER is a focused experiment aimed toward making the first statistical detection of the 21 cm

reionization In the fields of Big Bang theory and physical cosmology, cosmology, reionization is the process that caused electrically neutral atoms in the primordial universe to reionize after the lapse of the "Timeline of the Big Bang#Dark Ages, dark ages". ...

signal. Given the stringent

dynamic range Dynamics (from Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' " power") or dynamic may refer to: Physics and engineering * Dynamics (mechanics), the study of forces and their effect on motion Brands and ent ...

requirements for detecting reionization in the face of foregrounds that are five orders of magnitude brighter, the PAPER project is taking a carefully staged engineering approach, optimizing each component in the array to mitigate, at the outset, any potentially debilitating problems in subsequent data calibration and analysis. This staged approach addresses the observational challenges that arise from very-wide-field, high-dynamic-range imaging over wide bandwidths in the presence of transient terrestrial interference. PAPER began as a collaboration between Don Backer of the UC Berkeley Radio Astronomy Laboratory and Richard Bradley of the

National Radio Astronomy Observatory The National Radio Astronomy Observatory (NRAO) is a federally funded research and development center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc. for the purpose of radi ...

. With Backer's passing in 2010, Aaron Parsons has assumed leadership of PAPER on the side of

UC Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a public land-grant research university in Berkeley, California, United States. Founded in 1868 and named after the Anglo-Irish philosopher George Berkele ...

. The two fundamental concerns that most influence the design of any HI reionization detection instrument are removing foregrounds and achieving the requisite sensitivity. The PAPER approach heavily emphasizes the former; the level of instrumental calibration and foreground characterization that will be required to model and remove polarized galactic

synchrotron A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The strength of the magnetic field which bends the particle beam i ...

emission, continuum point-sources, and galactic/extra-galactic free-free emission is unprecedented in the 100–200

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

band expected to encompass reionization. PAPER consists of two distinct arrays: one located at the NRAO site in Green Bank, WV, which is used primarily for engineering investigations and field testing, and another located at the South African SKA site in the

Meerkat National Park Meerkat National Park is a large South African National Parks, National Park in the Northern Cape, South Africa, that encompasses the Square Kilometre Array's MeerKAT, Precision Array for Probing the Epoch of Reionization, PAPER and Hydrogen ...

located in the

Karoo The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe Khoemana (also known as !Orakobab or Korana) word is a semidesert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is ...

desert of the Northern Cape, South Africa, which is used for science observations.

In Green Bank, West Virginia, US

PAPER in Green Bank has evolved over a few years from exploring basic systematics in a rudimentary four-element array to the more comprehensive system performance testing with the thirty-two element array that is currently deployed there. PAPER activities at the NRAO site near Green Bank, WV began in 2005 with the deployment of a 4-antenna, single-polarization interferometer. After substantial testing and improvement of the PAPER design, we deployed eight antennas in a nearby field in April, 2008. This new system incorporated antenna elements with ground-screen flaps and a digital correlator based on CASPER hardware.

In South Africa

The South African array is aimed toward realizing our primary science objective: detecting reionization. The instrument is located at the P2 site on the Square Kilometre Array South Africa (SKA-SA) in the

near the small town of Carnarvon. Deployments at the SKA-South Africa site in the Karoo desert began with ground breaking and the deployment of 16 antennas in October 2009, continued with an increase to 32 antennas in April 2010, followed by commissioning and observing in May 2010. The array was expanded again in July 2011 to 64 elements. An expansion to 128 antennas is planned for 2013.

In the HERA roadmap

PAPER, along with the

Murchison Widefield Array The Murchison Widefield Array (MWA) is a joint project between an international consortium of organisations to construct and operate a low-frequency radio array. 'Widefield' refers to its very large field of view (on the order of 30 degrees ac ...

, are frontier projects within the Hydrogen Epoch of Reionization Array (HERA) program. The HERA road map for exploring reionization was organized into three sequential phases. Phase I has as its goal the first statistical detection of the HI 21 cm signal from reionization. HERA II entails applying lessons learned during Phase I to define and build a larger array capable of detailed characterization of the statistical signal and imaging the brightest reionization structures. The final stage of HERA, Phase III, will address the challenges of full tomographic imaging using an SKA-scale facility with capabilities informed by the earlier work. The HERA program was the highest ranked of the Decadal Survey RMS Panel scientific recommendations.

Project partners

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a Public university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...

* The

University of Pennsylvania The University of Pennsylvania (Penn or UPenn) is a Private university, private Ivy League research university in Philadelphia, Pennsylvania, United States. One of nine colonial colleges, it was chartered in 1755 through the efforts of f ...

* The

Square Kilometre Array The Square Kilometre Array (SKA) is an intergovernmental organisation, intergovernmental international radio telescope project being built in Australia (low-frequency) and South Africa (mid-frequency). The combining infrastructure, the Square ...

(SKA South Africa)

References

{{reflist Interferometric telescopes Radio telescopes