Precision measurements of CMB polarization rotation with post Planck missions Paolo de Bernardis. Dipartimento di Fisica, Sapienza Università di Roma

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1 Precision measurements of MB polarization rotation with post Planck missions Paolo de Bernardis Dipartimento di Fisica, Sapienza Università di Roma osmic Polarization Rotation From Galilean Principles to osmology Firenze, 8 Sep 2015

2 PR and B modes Detection of osmic Polarization Rotation using the MB is a difficult business. Detecting primordial B modes in MB polarization is also difficult. The two targets share most of the technical difficulties, even if an experiment optimized to detect PR in the MB might be a bit different from the optimal experiment to detect B modes. In the following I ll basically assume that the «final» MB polarization mission will also make a very good job for PR.

3 The final MB polarization measurement? MB polarization measurements of B modes at the required level of precision and accuracy are very difficult Sensitivity: Large format arrays of detectors Accuracy: Excellent foreground monitoring and removal capabilities > multi frequency! Full sky Thorough calibration ontrol and Mitigation of systematic effects Probably a combination of experiments, necessarily including a space mission.

4 Foreground complexity Other dust component? Bennett et al., ApJSS 208, 20 (2013)

5 Foregrounds are complex and polarized

6 Polarized emission of the ISM B 1 MB T 1 T 2 Often the result of superposition of several clouds along the line of sight Different temperature distribution for dust, different magnetic field orientation in different clouds, different electron populations, For example, the orientation of linear polarization resulting from the superposition of dust grains differently aligned and with different temperatures changes with frequency. For this reason, scalar extrapolation, based on the brightness spectrum alone, is only a zero order approximation. Has worked to some extent to point out the presence of ISD emission in BIEP2 data (using 350GHz data from Planck extrapolated to 150GHz, see arxiv: ). But this is just a rough approximation. For the final mission we need to carry out precise corrections. Similar arguments apply to synchrotron emission at low frequencies. Extrapolation of dust to long wavelengths and of synchrotron to high frequencies is non trivial, unless you have a number of high and low frequency channels. B 2

7 We need more bands than components ount components (or parameters) MB Thermal SZ 2 component thermal dust 2 component synchrotron Free free Spinning dust IB Zodiacal light Radio source background Surprises TOTAL I a few many 1 3 a few? P ?? 0? 0? a few? In cleaner regions of the sky, less parameters are needed, but this depends on the sensitivity of the survey. October 28, 2014 J. Delabrouille Planck and future MB obs. 7

8 Need for space based measurements Extrapolation of dust to long wavelengths and of synchrotron to high frequencies is non trivial, unless you have a number of highly sensitive channels at high and at low frequencies, basically filling the range 30 to 700 GHz. Because of the earth atmosphere, this frequency coverage cannot be obtained entirely from the ground. In addition, operation in space (L2) Permits the use of cold telescopes, reducing the radiative background on the detectors and improving their sensitivity enhances the stability of the instrument reduces ground spillover signals. September 8, 2015 P. de Bernardis PR post Planck 8

9 Atmospheric fluctuations : quantum 2 mm PWV 0.5 mm PWV 240K =2% 40 km space 240K =0.1% 26/11/2014 OrE+ 9

10 J. Delabrouille Just taking into account photon background from the atmophere and its noise, you need many more detectors in a ground based experiment than in a space based experiment, to obtain the same instantaneous sensitivity. Integration time can be longer for a ground based experiment, but not for a large factor. High frequency measurements are necessary, and require space based observations.

11 Atmospheric fluctuations : Turbulence Extremely difficult to measure MB fluctuations from the ground at f > 300 GHz, even in the best sites

12 Space is not enough Operating the instrument in space is not enough to solve the problem. A number of difficult technical issues must be taken into account, some of which are due to the operation in space. In the case of PR in particular: Polarimeter calibration Beam calibration (shape, co polar, cross polar..).. and their stability! 19 Novembre 2014 OrE+ 12

13 ) (2 sin ) (2 cos ) sin(4 2 1 ) sin(4 ) (2 sin ) (2 cos ) sin(4 ) (2 sin ) (2 cos ) cos(2 ) sin(2 ) sin(2 ) cos(2 2 2 ' 2 2 ' 2 2 ' ' ' EB BB EE EB EB EE BB BB EB BB EE EE TB TE TB TB TE TE For around =0: See e.g. Pagano et al. PRD (2009) EB BB EE EB EB EE BB EB BB EE TE TB TB TE

14 ' TE ' TB ' EE ' BB ' EB 1 2 TE TE EE BB cos(2 ) sin(2 ) cos cos 2 2 TB TB (2 ) (2 ) sin(2 ) cos(2 ) BB EE sin sin 2 2 (2 ) (2 ) EB EB sin(4 ) sin(4 ) EE BB EB 2 2 sin(4 ) cos (2 ) sin (2 ) For around =0: TE TB EE BB EB TE TB BB EB EE EB EE BB EB 4 See e.g. Pagano et al. PRD (2009) So, in the standard scenario, an error produces spurious B-modes at the same level as primordial B-modes with r around 0.01 (and shape not too far at large scales, with reionization and recombination bumps), + EB&TB signals.

15 EE BB So, in the standard scenario, an error produces spurious B-modes at the same level as primordial B-modes with r around 0.01 (and shape not too far at large scales, with reionization and recombination bumps), + EB&TB signals.

16 Self calibration? TB and EB must vanish in the absence of PR Approximate way to proceed: Estimate the rotation of the focal plane by computing TB() and find *: TB(*)=0 Use EB(*) to constrain B modes and PR Iterate to refine * (but will this converge? May be good enough for B modes, but not enough for PR if totally degenerate with angle calibration) Having a precise estimate of * from calibration would be much better: No need of dubious iterative processes Two independent spectra to constrain PR Possibility to calibrate all detectors individually. Why is calibrating * so difficult?

17 How much is a 1 rotation in practice 35m mm 2mm 75 mm In an array of discrete elements (e.g. Planck HFI): difficult to achieve. = O(1 ) In a photolitograph array high precision within a tile. Good precision for the tile : = o(0.1 ) High precision for a discrete array can be recovered using a large polarizer (LSPE: 50 cm diameter polarizer)

18 Mechanical Assembly Planck HFI: Individual PSBs : Positioning angle error of each wafer in its metal housing of the order of 1 orresponding to <100m! arxiv: annot place polarizer in front. Polarization effects of off axis telescope can be estimated reliably.

19 Mechanical Assembly Planck LFI: Individual horns & OMTs: LFI Positioning angle error of each horn in its metal housing of the order of 0.1 orresponding to <100m annot place polarizer in front. Polarization effects of off axis telescope can be estimated reliably.

20 BIEP: focal plane arrays Positioning angle error of wafer in its housing of the order of 0.1, corresponding to 100m) Polarizer in front not needed. Polarization effects of refractive telescope can be computed reliably. Ground based calibration of orientation possible with external beamfilling polarized source. Mechanical Assembly

21 LSPE: individual multi mode detectors with large polarizer Mechanical Assembly From telescope Reflected focal plane Positioning angle error of polarizer in its housing of the order of 0.02, corresponding to 200m) Ground based calibration of orientation possible with external beamfilling polarized source. Wire-grid polarizer Transmitted focal plane

22 Thermo mechanical problems All detectors must be cooled cryogenically Focal plane arrays thermally insulated from surrounding cryostat via dielectric structural elements (made of carbon fiber, fiberglass, vespel ) Differential contraction from 300K down < 1K : large effects. Example: a 0.5m high stainless steel vessel contracts by 1.5mm, a 0.5m long fiberglass strut contracts by 3.6mm, a 0.5m long teflon tube contracts by 11 mm! Several mm differences, can produce huge stresses and consequent deformations. areful design required to avoid anisotropic differential contraction effects, producing stress and misalignment. Symmetric structures & thermal effects compensations must be engineered in system design from the very beginning. For space missions, additional problem of environment change (external pressure, temperature) For all these reasons, the measurement and verification of the main axis is difficult. In addition, it mixes with beam effects.

23 Beam effects In principle, the measured polarization direction is the result of a «beam weighted convolution» of the source polarization directions cross the local polarization axis. Both co polar and cross polar responses of the full optical system must be measured accurately, since the cross polar response can be important, especially in the sidelobes. Stokes parameters of the beam: Power absorbed by the bolometer: Errors in the calibration of the beam Stokes parameters can produce Leakage of intensity into polarization Leakage of polarization into intensity Polarization mixing: Q into U and U into Q Integrals over frequency and over direction. Simplifying assumption: ideal optical system, cross pol only in detector: See arxiv: Rosset et al. Planck HFI pre flight calibration; See also Shimon et al. 2008, O Dea et al

24 In principle, the measured polarization direction is the result of a «beam weighted convolution» of the source polarization directions cross the local polarization axis. Both co polar and cross polar responses of the full optical system must be measured accurately, since the cross polar response can be important, especially in the sidelobes. A beam filling, polarization pure source is needed for calibration. Polarized artificial planet Distant oscillator with perfect antenna and well known orientation Sky source (tau A probably not good enough, as far as we know it!) Before deployment, AND during operations! Beam effects Stokes parameters of the beam: Power absorbed by the bolometer: Integrals over frequency and over direction. Simplifying assumption: ideal optical system, cross pol only in detector: See arxiv: Rosset et al. Planck HFI pre flight calibration; See also Shimon et al. 2008, O Dea et al. 2007, Hu et al

25 Beam effects A&A 458, (2006) xpol

26 Heritage of Planck Ground: Sub-system-level: thermal, vacuum and cryo facilities (Terni, TAS, INAF-IASF- Bo, INAF-IAPS) System level: definition, planning, sources, data processing and reduction In-flight planning On-board sources On-sky sources selection data processing and reduction System alibration

27 Beam measurements This kind of measurements is difficult, long, boring.., but possible for room temperature telescopes of reasonable size (B03, bicep ) It is very difficult for cryogenically cooled space telescopes (was not done for Planck at system level was done at subsystem level) Moreover, instrument configuration in space can differ from instrument configuration in the lab. In the «final» MB mission, a calibrator will be needed. Either a source on an ancillary satellite (large mission) or a sky source.

28 Polarized sky sources AGNs : point like, polarized, but variable Moon : edge polarized too bright Mars : edge polarized too small Tau A (rab nebula): complex structure known to 0.5 Detailed mapping in polarization with dedicated ground based telescopes (with good polarization properties ) worth to do at least at 90, 140 and 220 GHz Other radio sources to be properly measured (Galluzzi s talk..) Dedicated balloon/satellite: proposed several times required stability, attitude and pointing to be confirmed. Worth to investigate anyway. (Kaufman talk ) On board full beam calibrator can do a good job for beamaveraged polarization angles and cross pol. an be a single point failure in a space mission.

29 Two future missions LSPE : balloon borne mission targeting large angular scales OrE++ : ambitious satellite mission

30 (List is slightly outdated)

31 LSPE in a nutshell The Large Scale Polarization Explorer is: an instrument to measure the polarization of the osmic Microwave Background at large angular scales (reionization peak) A spinning stratospheric balloon payload to avoid atmospheric noise Flying long duration, in the polar night (large sky fraction, very stable environment) using a polarization modulator to achieve high stability 3

32 The Large Scale Polarization Explorer is: an instrument to measure the polarization of the osmic Microwave Background at large angular scales (reionization peak) A spinning stratospheric balloon payload to avoid atmospheric noise Flying long duration, in the polar night (large sky fraction, very stable environment) usinga polarization modulator to achieve high stability Frequency coverage: GHz 5 channels, 2 instruments: STRIP & SWIPE LSPE in a nutshell 3

33 LSPE in a nutshell The Large Scale Polarization Explorer is: an instrument to measure the polarization of the osmic Microwave Background at large angular scales (reionization peak) A spinning stratospheric balloon payload to avoid atmospheric noise Flying long duration, in the polar night (large sky fraction, very stable environment) using a polarization modulator to achieve high stability Frequency coverage: GHz Angular resolution: 1.3 o FWHM Sky coverage: 20 25% of the sky per flight ombined sensitivity: 5 K arcmin per flight urrent collaboration: Sapienza, UNIMI, UNIMIB, IASFBO INAF, IFA NR, Uni.ardiff, Uni.Manchester. INFN GE, INFN PI, INFN RM1, INFN RM2 See astro ph/ , , and forthcoming updates 3

34 LSPE gondola : frame + pivot + STRIP + SWIPE Preliminary sketch of the LSPE experiment, without thermal protections. The total mass is around 2.5 tons, the overall dimensions are 5.8m(w) x 3.2m(d) x 4.6m (h). A m 3 balloon is used to lift the instrument at 37 km of altitude. SWIPE to balloon PIVOT STAR SENSORS STRIP AS block diagram TM T Actuators: Azimuth pivot with torque motors Linear elevation actuators RAK Processor: P104 with AD in / PWM out H-bridges for motors Attitude sensors: Star sensors (Nati et al. RSI 2003) Laser Gyroscopes Elevation Encoders BATTERIES BALLAST FRAME 5

35 STRIP STRIP is the STRatospheric Italian Polarimeter, aimed at accurate measurements of the low frequency (44 and 90 GHz) polarized emission, dominated by Galactic synchrotron. Its sensitivity at 44 GHz in a single flight is twice better than the final sensitivity of the Planck LFI survey. The correlation radiometers are contained in a large cryostat and cooled at 20K by evaporating 4 He mm (PI: M. Bersanelli) 7

36 The STRIP Telescope The beam is defined by a 600 mm aperture side fed crossed Dragone telescope, selected for best polarization purity hallenging for spillover, stray light and obscuration Modular Primary and secondary mirrors to reduce fabrication costs Lightened structure to reduce weight 8

37 The STRIP Instrument In the focal plane, an array of 44 GHz platelet feedhorns feeds high performance OMTs and LNAs derived from the QUIET exp. The measured response of the corrugated feedhorns confirms the expected performance down to 55 db 9

38 SWIPE 10 SWIPE is the Short Wavelength Instrument for the Polarization Explorer It is a Stokes Polarimeter, based on a simple 50 cm aperture refractive telescope, a cold HWP polarization modulator, a beamsplitting polarizer, and two large focal planes, filled with multimode bolometers at 140, 220, 240 GHz. Everything is cooled by a large L 4 He cryostat and a 3 He refrigerator, for operation of the bolometers at 0.3K (PI: P. de Bernardis)

39 SWIPE: A cryogenic Stokes polarimeter Low input window thermal fliters stack cold, stepping HWP UHMWPE lens polarizer arrays of multimode feedhorns and bolometers SWIPE He tank (290L) 3 He fridge

40 SWIPE polarization modulator Is a cold (2K), large (50 cm useful dia.), wide band metamaterials HWP, placed immediately behind the window and thermal filters stack. HWP characteristics for the ordinary and extraordinary rays are well matched: (T o T e )/T o < 0.001, X pol <0.01, over the GHz band. Its orientation is stepped by or 22.5 every few scans. 500 mm 11 The cryogenic HWP rotator made for the PILOT experiment. The LSPE one will be based on the same design, and scaled up in dimensions (see Salatino et al. A&A 528 A )

41 SWIPE optical system Single lens AR coating, D=480, f=800 Two curved focal planes populated with multimode bolometric detectors, resulting in 1.3 FWHM beams M. De Petris Band (GHz) Width (%) Total # detectors # 2 modes 140 GHz GHz GHz reflected focal plane 1.2 transmitted focal plane Scan direction 12

42 SWIPE multimode feedhorns 20 mm aperture High efficiency coupling structure, easy to machine Nice top hat beams 12, 30, , 220, 240 GHz Feedhorn + detector assembly Tested Prototype 150 GHz Lamagna et al., Proc. IEAA 2013 Feedhorn + detector assembly Final design 23g each db G. oppi T. Marchetti cold aperture stop

43 SWIPE multimode absorbers & TESs The absorbers are large Si 3 N 4 spider webs (8 mm diameter, multimode) Sensors are Ti Au TES Photon noise limited = 2 ms

44 Observations and alibration Plan Scanning strategy: payload spin in azimuth, at 3 rpm (18 /s) overage of the same sky area by the two instruments Elevation changes once a day, at the same time for both instruments Specific calibration observations of Jupiter (to map the main beam, see figure below, samples = white dots) LSPE coverage for different sets of elevation changes. The first column reports the boresight elevation range in degrees for the two instruments. Second column, the full coverage. Third column, the coverage after masking the galaxy with the WMAP polarization mask. Source ulmination (deg) Elevation overage Unmasked SWIPE [30 40] 31% 23% SWIPE [40 50] 27% 20% SWIPE 35 24% 19% SWIPE 45 22% 18% SWIPE [30 50] 35% 26% STRIP 45 27% 20% STRIP 30 33% 24% STRIP S/N per sample at 44 GHz S/N per sample at 90 GHz S/N per sample at 145 GHz SWIPE S/N per sample at 245 GHz Moon rab Mars the rab nebula and the Moon Limb (to calibrate the main axis of the polarimeters) the Moon can be used to map sidelobes Jupiter Saturn Uranus Sources culmination angle, and expected S/N per sample. Sampling rate is set at 60 Hz. We assume full Moon, as it is when it is observable by LSPE. The rab flux is based on the free free spectrum reported in Macías Pérez, et al. Ap. J., 711, 417 (2010) 13

45 Sky coverage of LSPE (Launch from Longyearbyen, Svalbard) North South B-modes from GHz, as estimated from Planck 343 GHz dust polarization - Planck PIP XXX

46 SWIPE Performance Forecast (1 st flight) L. Pagano, F. Piacentini

47 SWIPE Performance Forecast (1 st flight) L. Pagano, F. Piacentini

48 urrent Status LSPE is fully funded by the Italian Space Agency (Detector development co funded by INFN) STRIP and SWIPE in due course of development, consistent with a 1st launch opportunity from Svalbard (78 N) in Winter 2016/2017. Baseline science expected from one flight is competitive with current gen B mode experiments and contributions to pol. foreground science will provide a great complement the MB science. The schedule is tight and there are lots of things still to do but we ll make it happen.

49 OrE, PRISM, OrE+, OrE++ Ambitious missions proposed to ESA See: mission.org mission.org

50 An ambitious, comprehensive space mission, should not target just B modes z<2x10 6 Thermal history, energy injection MB 6<z<11 reionization 0<z<1 Integrated SW Accelerated expansion Inflation Physics at GeV E OrE+ > E LH 1<z<3 Gravitational lensing Dark matter distribution 0<z<2 SZ effect, distribution of hot gas and velocity fields 50

51 An ambitious polarization mission Sensitivity between 1.5 and 2.5 μk.arcmin detectors Angular resolution for MB between 4' and 6 (1m 1.5m class telescope) Enough frequency channels (15) for an efficient extraction of the MB from the foregrounds Simplified, optimized OrE+ (see mission.org) Similar to Planck, with many more polarization sensitive detectors, and optimized scanning strategy OrE+ 51

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56 ryo chain OPTIONS 100 mk done for Planck, several options 15 20K Sorption cooler Planck: 15K pulse tubes Air Liquide + EA Specific JT 2 4K JT He4: 4K for closed cycle dilution need an additional 1.7K stage JT He3: 2K RAL (TRL TB); Japan 100 mk losed cysle dilution including 1.7K stage if necessary (Sorption Univ. Twente, Netherlands) ADR (EA): Good TRL, not continuous Strategy Keep several options and decide in phase A ontinue developments OrE+ 56

57 Wide Focal Plane Four solid shields Off axis Gregorian 1 m aperture radiators Solar panels Soyuz Fairing 3.8m OrE+ 57

58 Wide Focal Plane Three solid shields Off axis Gregorian 1.5 m aperture Telescope size can be reduced ompact Range Telescope also being considered radiators Soyuz Fairing 3.8m One deployable outer shield (kapton) Solar panels OrE+ 58

59 OrE+ light OBJETIVE: Most of the MB polarization science, at reduced cost and low risk. Optical axis OPTION: ESA mission (ESA member states only) 2100 detectors total ( 75% in MB channels); 3 years of observation; > 15 frequency channels MB polarization sensitivity 2.2 μk.arcmin; Budget 550 M. 1.0 m Non deployable shields Solar panels Significantly simpler mission than OrE /3 the detectors; no moving parts. Acceptable solar illumination OrE+ 59

60 OrE+ light (possible configuration) ore MB cience mission Freq beam N det per arcmin 2 pixel 5σ PS or SZ ore MB science mission Freq beam N det per arcmin 2 pixel 5σ PS or SZ GHz arcmin σ P μk MB σ I kjy/sr 5σ P mjy 5σ I 10 5 Y SZ GHz arcmin σ P μk MB σ I kjy/sr 5σ P mjy 5σ I 10 5 Y SZ OrE+ 60

61 OrE+ extended OBJETIVE: Ultimate MB polarization mission, and extensive non MB science. Optical axis 1.5m OPTION: ESA mission with substantial international contribution, e.g. NASA Solid inner shield Deployable shields 5800 detectors total ( 65% in MB channels); 3 years of observation; > 18 channels MB polarization sensitivity 1.3 μk.arcmin; Budget 700 M. Deployable solar panels Acceptable solar illumination OrE+ 61

62 OrE+ extended (possible configuration) Extended science mission Freq beam N det per arcmin 2 pixel 5σ PS or SZ Extended science mission Freq beam N det per arcmin 2 pixel 5σ PS or SZ GHz arcmin σ P μk MB σ I kjy/sr 5σ I mjy 5σ I 10 5 Y SZ GHz arcmin σ P μk MB σ I kjy/sr 5σ I mjy 5σ I 10 5 Y SZ /11/2014 OrE+ 62

63 No Pol modulator option? The modulation of polarized signals can be obtained using a sky scan strategy more elaborated than the Planck one (similar to WMAP). Big advatage: no moving parts in the instrument Possible disadvantages: Requires more energy (or gas mass) for the AS Ellipticity of beams generates T P leakage Reduced thermal stability (sun aspect modulated)

64 No Pol modulator option? Optimization of scan parameters (Desert, Ponthieu, Delabrouille et al.) Scan parameters affect sky coverage (total and per precession), angle coverage, redundancy Are constrained by the data sampling and data rate, the number of cycles in case of a gimbaled antenna, the energy(mass) required to control the scan, sun and earth directions and illumination of solar panels, etc Good tradeoffs : Thermal simulation: on going

65 Temperature to Polarization leakage due to elliptical beams etc. can be mitigated using appropriate scan strategy and advanced (iterative) map making Iterative method: J. Delabrouille Simulations by L. Pagano, F. Piacentini Works OK for small beams No Pol modulator option? Beam: Gaussian, e= No B-modes in simulation

66 Polarization modulator development going on in parallel ESA ITT No Pol modulator option? Beam: Gaussian, e= No B-modes in simulation

67 Pol modulator option? In OrE the polarization modulator was large and was the first optical element. On-going study ESA ITT AO/1-7136, Large Radii Half- Wave Plate (HWP) Development for the reflective option A smaller polarization modulator (reflective or refractive) can be placed between the telescope and the focal plane. Option under study. PILOT (NES) ESA- ITT

68 19 Novembre 2014 OrE+ 68

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70 PR expectations Statistical error: negligible (order of 0.01 ) Systematic error: minimized using large photolitographed detector «tiles», large polarizers, careful design of thermo mechanical structure. Most probably in the 0.1 range. In flight commissioning: high S/N measurements on the rab nebula, provided that ground based measurements have progressed by 2030! Good S/N on MB structures in polarization helps

71 OrE+ summary Well identified science case Primary objective : new generation mission for MB primordial B modes & lensing DM Well defined requirements (sensitivity, resolution, ) The need to remove foregrounds produces rich ancillary astrophysics science Mission similar to Planck, but >100 times more detectors and better distributed for different frequencies mission optimized for polarization measurements (observation strategy and calibration) European expertise and TRL much better than for Planck in 1994 Nice synergy netween OrE+ and ground based MB telescopes (S4) : same angular resolution at different frequencies ollaboration: heritage of Planck, enriched by the interst of extra EU scientists Well tested European consortium, playing a key role internationally on a mission very interesting also for USA, Brazil and Japan potential partners We need your support for M5! Visit OrE+ 71

72 Slide from J. Delaboruille