The C-Band All-Sky Survey A Progress Report Tim Pearson

2011 May 26 C-BASS

• A full-sky 5 GHz survey – single dish, with matched antennas in north and south – Northern Survey from OVRO 6.1 m dish (California) – Southern Survey from 7.6 m Telkom dish Karoo (SA MeerKAT/SKA site) • Total intensity and linear polarization (I, Q, U) • Resolution comparable to 30 GHz and Haslam 408 MHz • Minimal corruption by Faraday rotation and depolarization

• Primary goal: improved understanding of synchrotron foreground for CMB experiments (e.g., “WMAP haze”) • Improve accuracy of foreground subtraction in polarization • Contribute to studies of Galactic ISM and magnetic field • Motivation: see talks by Jo Dunkley and Clive Dickinson.

Pearson FGC2011 Zadar, May 26, 2011 2 C-BASS Collaboration

• Caltech/JPL – Tim Pearson, Stephen Muchovej, Oliver King, Matthew Stevenson, Tony Readhead, Russ Keeney, Dayton Jones • Oxford – Mike Jones, Angela Taylor, Charles Copley, Jamie Leech, Matthew Brock, Christian Holler [Esslingen], Jaya John John, Joe Zuntz • Manchester – Clive Dickinson, J Patrick Leahy, , Richard Davis, Melis Irfan • South Africa (HartRAO, Rhodes) – Justin Jonas, Roy Booth • Saudi Arabia (KACST) – Yaser Hafez

Pearson FGC2011 Zadar, May 26, 2011 3 Why 5 GHz?

WMAP 23 GHz polarized intensity

DRAO/Villa Elisa 1.4 GHz

Pearson FGC2011 Zadar, May 26, 2011 4 Sun et al. A&A 477, 573–592 (2008) Why 5 GHz?

• Halfway (in log ν) between surveys at 1.4 GHz (Stockert, Reich & Reich) and 23 GHz (WMAP). • Expected high-latitude Faraday rotation a few degrees, c.f. ~30° at 2.3 GHz. – residual correction at high latitude via 1.4 GHz polarization survey from Penticton (Wolleben) / Villa Elisa (Testori, Reich & Reich) • Below main emission from anomalous dust, so predominantly synchrotron. – helps to constrain AME models • Signal still strong enough (few mK) to measure in a reasonable time (< 1 year) with a single receiver.

Pearson FGC2011 Zadar, May 26, 2011 5 Survey Parameters

• FWHM resolution 48 arcmin – Same as Haslam et al. 408 MHz survey • Accurate to lowest multipoles

– At scan speed 4 deg/s needs fknee < 10 mHz (plus destriping) • Frequency 4.5 – 5.5 GHz • Target sensitivity: 0.1 mK / beam rms, i.e., will detect polarized brightness of 0.5 mK – Corresponds to ~1 μK at 23 GHz (β = 3) – 99% of pixels in WMAP 23 GHz pol intensity are detected at this level

• Tsys ~ 20 K – gives NET ~ 0.45 mK s1/2 – 20s/beam → 14 days to survey a hemisphere (night-time only) • 6 months to give complete night-time coverage – factor of 12 in hand for overheads

Pearson FGC2011 Zadar, May 26, 2011 6 Impact on Planck results

• Typical high latitude 1 deg pixel

Planck Planck+CBASS • Mean synch amplitude 80 µK@ 23 GHz Stokes I • MCMC reconstruction CMB mean error (µK) 5.4 4.0 Synch amp error (µK) 1.4 0.44 • 25% improvement Synch index error 0.29 0.03 • × 3 improvement Dust amp error (µK) 3.4 2.8 • × 10 improvement Dust index error 0.29 0.29

Stokes Q,U • 25% improvement CMB mean error (µK) 3.6 2.7 • × 4 improvement Synch amp error (µK) 0.67 0.17 • × 10 improvement Synch index error 0.29 0.03

Dust amp error (µK) 0.29 0.97 Dust index error 0.29 0.29

Pearson FGC2011 Zadar, May 26, 2011 7 Constraining synchrotron spectral index

Pearson FGC2011 Zadar, May 26, 2011 8 Receiver Architecture: 1

Internal cold load reference for I Analog correlation polarimeter LCP/RCP for Q,U

Pearson FGC2011 Zadar, May 26, 2011 9 Receiver Architecture: 2

• Digital correlation polarimeter – two downconverted channels of 500 MHz sampled in 1st and 2nd Nyquist zones • 2 x ROACH FPGA board each with 4 x 1 GS/s ADC inputs • 64-channel spectrometer

Pearson FGC2011 Zadar, May 26, 2011 10 Challenges

• Stray radiation – novel optics design • Stability – temperature control, component selection, power supplies, etc. – use of digital techniques • Radio Frequency Interference (RFI) – choose a radio-quiet location – careful shielding – notch filters • 1/f noise (map stripes) – rapid scanning to modulate sky signal – map-making algorithms • Calibration

Pearson FGC2011 Zadar, May 26, 2011 11 Telescope Optics

California South Africa

Pearson FGC2011 Zadar, May 26, 2011 12 Telescope Optics

Simulation

Measurement Bare optics Secondary baffle Primary baffle

Pearson FGC2011 Zadar, May 26, 2011 13 Receiver noise power spectra

• E-Merlin C-band LNAs

– intrinsic fknee ~1 Hz: • Intensity channel, balanced

– fknee ~ 30 mHz • Polarization

– fknee ~ 10 mHz • Should be minimal polarization 1/f receiver noise at fscan = 11 mHz • Scan in az at constant el at ~ 4°/s

Pearson FGC2011 Zadar, May 26, 2011 14 Descart Destriping Map Maker

• Model timestream as sum of: – Signal projected by pointing P – 1/f noise modeled by baseline offsets a – purely white noise w • Solve for a with conjugate gradient and subtract to make problem purely white noise

Sutton et al 2010, MNRAS, 407, 1387

Pearson FGC2011 Zadar, May 26, 2011 15 Preliminary Results

Moon I

Geo satellites Galaxy

Fixed RFI source Ground (mountaIn)

P

Transient RFI

Pearson FGC2011 Zadar, May 26, 2011 16 Preliminary Results

C-BASS 5 GHz

A few weeks’ data… no RFI removal, opacity correction, calibration…

Pearson FGC2011 Zadar, May 26, 2011 17 Preliminary Results

Reich & Reich 1.4 GHz

Pearson FGC2011 Zadar, May 26, 2011 18 Preliminary Results

Pearson FGC2011 Zadar, May 26, 2011 19 Preliminary Results

Pearson FGC2011 Zadar, May 26, 2011 20 Preliminary Results

Pearson FGC2011 Zadar, May 26, 2011 21 Status

• Northern Survey – Upgrade in progress at OVRO • Improved stability • Better RFI rejection – Survey complete in late 2011/early 2012 • Southern Survey – Antenna ready at Klerefontein – Receiver under construction in Oxford and Manchester – Survey complete in 2012 • Full data release in 2013 - for Planck public release

Pearson FGC2011 Zadar, May 26, 2011 22 OMT and feedhorn

Pearson FGC2011 Zadar, May 26, 2011 23 RFI

Pearson FGC2011 Zadar, May 26, 2011 24