University of Oxford B. R. Johnson 1 Title Slide MAXIPOL: A Bolometric, Balloon-Borne Half-Wave...

1University of OxfordB. R. Johnson

Title SlideMAXIPOL: A Bolometric, Balloon-Borne Half-Wave PlatePolarimeter for Measuring the Polarization of the CMB

Bradley R. JohnsonNSF and PPARC Postdoctoral Fellow

University of Oxford

The MAXIPOL payload on the launch pad at the NSBF in Ft. Sumner, New Mexico, September 2002.


MAXIPOL Collaboration

Matthew Abroe1 Peter Ade3 Jamie Bock4 Julian Borrill5,6

Jeff Collins2 Pedro Ferreira7 Shaul Hanany1

Andrew Jaffe8 Bradley Johnson7 Terry Jones1 Adrian Lee2,9 Tomotake Matsumura1 Paul Oxley1 Bahman Rabii2 Tom Renbarger1

Paul Richards2 George Smoot2,6,9 Radek Stompor5 Huan Tran2 Celeste Winant2 Proty Wu10 Joe Zuntz8

1) School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA2) Department of Physics, University of California, Berkeley, CA, USA

3) Department of Physics and Astronomy, Cardiff University, Cardiff, UK 4) Jet Propulsion Laboratory, Pasadena, CA, USA

5) Computational Research Division, Lawrence Berkeley National Lab, Berkeley, CA, USA6) Space Sciences Laboratory, University of California, Berkeley, CA, USA

7) Astrophysics, University of Oxford, Oxford, UK8) Astrophysics Group, Blackett Lab, Imperial College, London, UK

9) Physics Division, Lawrence Berkeley National Lab, Berkeley, CA, USA10) Department of Physics, National Taiwan University, Taipei, Taiwan


What are the Science Goals of MAXIPOL?

1) Implement half-wave plate (HWP) polarimetry in a CMB experiment.

- MAXIPOL is a pathfinder experiment -- HWP polarimeter techniques and

data analysis algorithms will be useful for B-mode experiments.

- MAXIPOL is a reimplementation of the MAXIMA hardware

- MAXIMA reported best receiver NET -- 40 K sec.

- We wanted to develop a polarization modulator -- HWP polarimeter is the best.

• Attempt detection of E-mode signal.

- Even with the high receiver sensitivity, predictions showed unambiguous

E-mode detection would be challenging -- long integration time was required.

- We collected data and data analysis is now concluding.


MAXIPOL Instrument

• Flight proven MAXIMA hardware.

• Sun shields not illustrated.


Cross-Section of MAXIPOL Instrument


Half-Wave Plate (HWP) Polarimeter

• signal amplitude corresponds to polarization magnitude.

• signal phase corresponds to polarization orientation.

• Q,U sky signals in the frequencydomain are away from 1/f noise

in sidebands of 4f

Q,U signal bandHWP rotation frequency


HWP Polarimeter Advantages

• Proven astronomical technique (see Astronomical Polarimetry by Tinbergen).

• 4f modulation provides strong rejection of systematic error.

• I, Q and U maps from ONE detector.

• Therefore, not susceptible to differential bolometer gain problems.

• Q, U signal is far from typical 1/f noise.

• Therefore, best noise performance is achieved.


HWP Polarimeter Hardware

HWP construction:

3.2 mm thick sapphire anti-reflection coated with Herasil.


MAXIPOL Payload on Launch Pad

sun shield

sun-facing surfacespainted white

terrestrialemission

baffleballoon

light fromthe sky


HWP synchronous

instrumental signals

ie. instrumental polarization

Signals in the Time Domain

time ordered data is comprised of four primary signals

these signals must be rejected

note: i is time index

modulated sky signals

cosmic rays, etc.

Reference: B. R. Johnson, J. S. Collins Ph.D. theses


Signals in the Frequency Domain

power spectrum of TOD with hi and gi removed



telescope scan frequency


HWP rotation frequency

frequencydomain

representationof thebeam





HWP rotation frequency

frequencydomain


Q and Usignalbands

T signalband


Q,U Demodulation

• HWP polarimeter works.

• Nominal noise level is recovered in the Q,U signal band.

• Maps from demodulated data show no systematic error.


Polarimeter Characterization



• receiver cross-polarization and HWP encoder offset

• modulation efficiency

• similar measurement limits instrumental polarization to < 1%



0.92 0.93 0.90

0.93 0.93 0.93

0.93 0.93 0.94

0.95 0.93 0.92

Results agree with predicted performance

assuming Pin = 0.97 and normal incidence for radiation

Modulation Efficiency Across the Array

error in measured

modulation efficiency = 1%

for all array elements


MAXIPOL-1 Flight

• 26 hour flight from Ft. Sumner, New Mexico, USA in May 2003.

• Four regions of the sky were observed.

• Jupiter was mapped twice. - beam shape - calibration

• CMB dipole was scanned.


Primary MAXIPOL-1 Scan Regions

SFD Dust Map Extrapolated to 140 GHz

PrimaryDust scan:

1.9 hourscentered on

Polaris:

Dust signal =38 ± 5 K

PrimaryCMB scan:

7.6 hourscentered onBeta Ursae

Minoris.

Expecteddust signal =4.4 ± 0.7 K

• MAXIPOL Pointing Illustrated.

Schlegel, Finkbeiner and Davis. 1998. ApJ, 500:525-553.


Intensity Calibration from Jupiter

beam map from one 140 GHz photometer

• Primary calibration from Jupiter observations.

• Map and best-fit Gaussian contours overplotted (1, 10, 50 and 90%)

• Some photometer beams were not sampled in every pixel

• Final calibration results from maximum-likelihood analysis


Data Analysis

• Data analysis is near completion.

• Two analysis algorithms are being used -- MADCAP and frequentist approach.

• Both methods are producing consistent results.

• Q,U maps are Gaussian, contain no detectable systematic error.


Conclusion

• MAXIPOL demonstrated HWP polarimetry works for CMB experiments to the sensitivity limit of the instrument.

• Data analysis is near completion.

• Results papers are currently being written.

• Papers will include Q, U maps and power spectrum estimates.

• Experiences from MAXIPOL are advising future B-mode HWP experiments -- EBEX, Polarbear.

MAXIPOL-0 Launch

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.


EBEX

expected EBEX performance

• NASA funded LDB balloon experiment

• achromatic HWP polarimeter

• 1476 detectors

• sensitivity: 0.7 K per pixel Q,U


END


Wrong Way


Instrumental Signals

16 minutes of MAXIPOL TOD

HWP synchronous instrumental signallargest contributor is instrumental polarization

same data plotted vs. HWP angle


Instrumental Signal Removal


power spectrum of TOD

differential transmission

HWP rotationfrequency

frequencydomain


instrumentalpolarization

University of Oxford B. R. Johnson 1 Title Slide MAXIPOL: A Bolometric, Balloon-Borne Half-Wave...

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