PAPER’s Sweet Sixteen: Imaging the Low Frequency Sky

with a Sixteen Element Array

Nicole Gugliucci for the PAPER Team*USNC/URSI National Radio Science Meeting 2009

*Richard Bradley, Don Backer, Aaron Parsons, James Aguirre, Abhirup Datta, Chris Carilli, Griffin Foster,

Chaitali Parashare, Erin Mastrantonio, Jason Manley

Outline

• PAPER science objectives• Overview of PAPER-16• Calibration and Imaging• Early results!• Near and long-term plans

Epoch of Reionization

Signal vs. Foregrounds at 140 MHz

EoRE-gal free-free

MW free-free

Point Sources

CMB

MW synchrotron

(Multipole Moment)

(Pow

er)

Assuming accurate removal of bright foreground sources!

Epoch of Reionization

Projected sensitivity of full array in Western Australia, compared to subtracted foregrounds

PWA-128 Uniform

Synchrotron/1000

Cosmic Variance of Power Spec

PWA-128 Gaussian

21-cm Power Spectrum

Point Sources/1000

PAPER-16 in Green Bank, WV

• Green Bank engineering array as part of the staged approach

• Array design for ease of surveying while minimizing sidelobes of synthesized beam

PAPER-16 Correlator

• Flexible, FPGA-based packetized correlator

• Wide-band, scalable

PAPER-16 Goals

• Testing of array components and for stability• Early imaging to improve on PWA-4 and PGB-8

results• Explore ionospheric effects• Begin all-sky survey 120-180 MHz with fluxes

and spectral indices• Explore full-stokes imaging

Calibration and Imaging

• AIPY (Astronomical Imaging in Python) • Basic calibration (correlator effects, RFI

removal)• Fit and model antenna positions, delays,

passbands, crosstalk removal• Wide field-of-view imaging with HEALPix

functionality (http://healpix.jpl.nasa.gov)

Cyclic Calibration

Simple pipeline using prior knowledge of array and sources, and is a cyclic process

A. Parsons

Into the data…

• RFI environment

Tim

e

Frequency

Amplitude

Into the data…

• RFI environment• Rotating phases

Tim

e

Frequency

Amplitude Phase

Frequency

Into the data…

• RFI environment• Rotating phases• Fit primary beam

Tim

e

Frequency

Amplitude Phase

All-Sky Map

• Example map combining GB and WA data• 138.8 – 174 MHz, log(Jy) scale, noise to .15 Jy/beam

Measuring Fluxes… Ionosphere?Fr

om K

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n, A

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phys

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Tec

hniq

ues

Isoplanatic Patch Kassim et al. (2007) defines the isoplanatic patch as more specifically as the region of with a phase difference less than one radian at a particular observing frequency

Work at the VLA at 74 MHz probed different ionospheric disturbances

Instantaneous amplitude or apparent defocusing (weak scintillation) of Vir A over 8 hours. Sunrise occurred at +3hr.

Amplitude vs. Time

Ionospheric EffectsFr

om K

itchi

n, A

stro

phys

ical

Tec

hniq

ues

Isoplanatic Patch Kassim et al. (2007) defines the isoplanatic patch as more specifically as the region of with a phase difference less than one radian at a particular observing frequency

Work at the VLA at 74 MHz probed different ionospheric disturbances

Position vs. Time for RA and Dec

Refraction (or apparent position wander in both right ascension and declination) of Virgo A over the same timescale as before, 8 hours.

Ionospheric Effects

• Position wander over one hour

Time (samples)

Time (samples)

Ionospheric Effects

• Position wander over 24 hours

Cas A

Vir A

Summary and Future Work

• Calibration scheme in progress, includes fitting the primary beam and leads to generating all-sky maps and source fitting to visibilities

• Ionosphere becomes a new challenge with source wander and scintillation

• Future work will lead to survey with fluxes and spectral indices

• Start taking dual-polarization data• PGB stability and ionosphere studies• PWA deployment in 2009!