Detectors. Detectors. α 10. Cryogenic Bolometers

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1 Detectors Detectors Coherent detectors measure ampitude and phase of the em wave Therma detectors measure the energy of the em wave On both sides, astrophysica and CMB research drove the deveopment of new devices: Cryogenic, utra-ow noise HEMT ampifiers (coherent) Cryogenic Spider Web and Poarization Sensitive Boometers (therma) Low sideobe corrugated antennas.. Aso, the two words are progressivey mixed: for exampe waveguides and stripines are now used with cryogenic boometers Cryogenic Boometers The CMB spectrum is continuum and boometers are wide band detectors. That s why they are so sensitive. Load resistor ΔV Integrating Radiation cavity Absorber (ΔT) Thermometer (Ge thermistor (ΔR) at ow T) Feed Horn (ange seective) Incoming Photons (ΔB) fiter (frequency seective) Fundamenta noise sources are Johnson noise in the thermistor (<ΔV > 4kTRΔf), temperature fuctuations in the thermistor ((<ΔW > 4kGT Δf), background radiation noise (T bkg5 ) need to reduce the temperature of the detector and the radiative background. Cryogenic Boometers In steady conditions the temperature rise of the sensor is due to the background radiative power absorbed Q and to the eectrica bias power P: G T T ) Q + P ( The effect of the background power is thus equivaent to an increase of the reference temperature: T Q.8K P G T ( T + ) G T T G ( ').7K Q T ' T + Q(pW) G.6K 1 Cryogenic Boometers In presence of an additiona signa ΔQ e jωt (from the sky) dδt C + Geff ΔT ΔQ dt There is a tradeoff between high sensitivity and fast response. The heat capacity C shoud be minimized to optimize both. Using a current biased thermistor to readout the temperature change: 1 dr( T ) Responsivity α R( T ) R dv dq dt iαr dt dq G eff dt dq G C τ G iαr eff 1 + τ ω 1 1+ τ ω Sma sensor at ow temperature dv idr iαrdt Cryogenic Boometers 1 dr( T ) α R( T ) dt R G eff iαr 1+ τ ω A argeα is important for high responsivity. Ge thermistors: Superconducting transition edge thermistors: α α 1 K 1 K 1 1 S.F. Lee et a. App.Opt (1998) 1

2 Cryogenic Boometers Johnson noise in the thermistor d ΔV J 4kTR df Temperature noise d ΔWT 4kT G eff df G ( fc ) eff + π Photon noise d ΔW x Ph 4k TBG x ( e 1+ ε) dx df c h ε 3 x ( e 1) Tota NEP (fundamenta): d V d W d W 1 Δ J Δ T Δ NEP + + R df df df Ph Q Again, need of ow temperature and ow background time required to make a measurement (seconds) 1 17 Langey's boometer Goay Ce 1 1 Goay Ce Boye and Rodgers boometer 1 7 1year F.J.Low's cryogenic boometer 1day Composite boometer 1 hour Composite boometer at.3k 1 Deveopment of therma detectors for far IR and mm-waves 1 second Spider web boometer at.3k Spider web boometer at.1k Photon noise imit for the CMB year The absorber is micro machined as a web of Spider-Web Boometers metaized Si 3 N 4 wires, μm thick, with.1 mm Buit by JPL Signa wire pitch. Absorber This is a good absorber for mm-wave photons and features a very ow cross section for cosmic rays. Aso, the heat capacity is reduced by a arge factor with respect to the soid absorber. NEP ~ 1-17 W/Hz.5 is 15μK CMB in 1 s Mauskopf et a. App.Opt. Thermistor 36, , (1997) mm Cri et a., 3 BOOMERanG 1998 boometers, 3 mk Cryogenic Boometers Ge thermistor boometers have been used in many CMB experiments: COBE-FIRAS, ARGO, MAX, BOOMERanG, MAXIMA, ARCHEOPS Ge thermistor boometers are extremey sensitive, but sow: the typica time constant C/G is of the order of 1 3mK Transition Edge Superconductor (TES) thermistors can do much better using eectro-therma feedback (1 μs) Recent deveopment (Hear Pau Richards..) Boometer Arrays Once boometers reach BLIP conditions (CMB BLIP), the mapping speed can ony be increased by creating arge boometer arrays. BOLOCAM and MAMBO are exampes of arge arrays with hybrid components (Si wafer + Ge sensors) Techniques to buid fuy itographed arrays for the CMB are being deveoped. TES offer the natura sensors. (A. Lee, D. Benford, Boocam Wafer (CSO) A. Goding..hear Richards..) MAMBO (MPIfR for IRAM)

3 TES arrays Are the future of this fied. See recent reviews from Pau Richards, Adrian Lee, Jamie Bock, Harvey Moseey et a. In Proc. of the Far-IR, sub-mm and mm detector technoogy workshop, Monterey. Coherent Detectors Here the CMB em waves interact with an antenna, and a seected mode is propagated in a waveguide to a probe, wherea votageproportionatothe incoming fied is generated. The votage is ampified by means of a fast, ow noise ampifier (direct receivers) Very ow noise HEMT ampifiers, cooed at K have been deveoped (NRAO). They have been used in many CMB experiments: TOCO, DASI, CBI, WMAP and wi be used in Panck-LFI. NET CMB (μk s 1/ ) SINGLE From HORN J.Bock POLARIMETER (SPIE 3) SENSITIVITY HEMTs Boometers Space Based, 1 Sensitivity J. BOCK SPIE frequency (GHz) Sensitivity to CMB anisotropy A map of CMB anisotropy is a samped image ΔT i ΔT( i,b i ) for i1,n pix, where ΔT( i,b i ) is the average of ΔT(,b) over the pixe area, for the pixe centered in ( i,b i ). Knowing : the instantaneous sensitivity (NET), the instrument anguar resoution θ, the sky coverage of the survey Ω we can compute the standard error for the estimate of ΔT i of each pixe, for a given tota observation time t. Assuming uniform coverage and square pixes with side θ, we have simpy σ ΔT NET t pix NET θ Ω t Sensitivity to CMB anisotropy Numerica exampe: assume NET 15μK s 5 t 5 days s θ 1' o o Ω 1' 1' NET NET Ω σ ΔT 7μK t θ t Youget pix Per pixe, over 144 pixes: a arge dataset, with a S/N ratio per pixe of the order of 3. 3

4 Sensitivity to CMB anisotropy An array of n detectors optimay used wi simpy mutipy by n the observation time avaiabe for each pixe. NET NET Ω 1 So we get σ ΔT nt t θ pix n The use of a arge array can give more that just an improvement of sqrt(n). For ground based observations, atmospheric noise can be significanty reduced by expoiting the correations of the noise over different pixes. : First reease of BOOMERanG data: one 15 GHz detector, 5 days nd reease of BOOMERANG data 4 x 15 GHz Data ceaning de-spiking Dec[deg] 1.8% 1% Ra[deg] Data ceaning data sice Data ceaning naive combination 4

5 Data ceaning optima map-making Interdiscipinary appications: Here a component separation technique has been appied to recover some of the hidden writing in the Archimedes paimpsest, an ancient manuscript in which faint remnants of severa treatises by the great phiosopher and mathematician are partiay hidden under a more recent text. (Istituto di Scienza e Tecnoogia de'informazione, ISTI-CNR) Sensitivity to the Power Spectrum Knowing : the instantaneous sensitivity, the anguar resoution, the sky coverage we can compute the sensitivity to the different mutipoes of the power spectrum, for a given survey duration T. A first part of the fuctuation comes from the statistica nature of the observabe c. Since the a m are gaussian, c is distributed as a χ with +1 DOF, so that Δc c + 1 Cosmic Variance Sensitivity to the Power Spectrum If ony a fraction f of the sky is surveyed, the cosmic variance becomes Δc f The second contribution to the errors comes from detector noise. If a tota of N pixes is observed, the error in the determination of the temperature in each pixe wi be of the order of c σ NET N T Cosmic / Samping Variance Sensitivity to the Power Spectrum And the error on the c becomes Δc 1 Aσ Knox s c 1 + formua + 1 f Ncw (1995) When severa mutipoes are binned in a band-power < c > with bin-width Δ, we have roughy Δ c 1 1 Aσ c 1 + Δ + 1 f Ncw Since the power spectrum of CMB anisotropy and poarization is smooth, a binning with Δ -3 is perfecty acceptabe. WMAP 1st year TT Power Spectrum - Unbinned data (+1)c TT /π (μk ) mutipoe 5

6 WMAP 1st year TT Power Spectrum - binned data Δ (+1)c TT /π (μk ) mutipoe (+1)c TT /π (μk ) WMAP 3 BOOMERanG Best fit of BOOMERanG data mutipoe At arge anguar scaes WMAP is cosmic variance imited (f ->1) whie BOOM (f.3) is not. (+1)c TT /π (μk ) WMAP 3 BOOMERanG Best fit of BOOMERanG data mutipoe At intermediate anguar scaes WMAP and BOOM have comparabe power (+1)c TT /π (μk ) WMAP 3 BOOMERanG Best fit of BOOMERanG data mutipoe Δc 1 Aσ c f Ncw Δc 1 Aσ c f Ncw At sma anguar scaes BOOM is more sensitive than WMAP, due to the arger w (higher anguar resoution). Δc (+1)c TT /π (μk ) WMAP 3 BOOMERanG Best fit of BOOMERanG data mutipoe 1 Aσ c f Ncw w ' FWHM 1' FWHM 5' FWHM 7 o FWHM mutipoe FWHM BOOM 1 1 A FWHM Δc c f WMAP 15 Nc σ w 6

7 Sensitivity to the Power Spectrum Exampe of appication: measurement of the B- modes of CMB poarization with an array of detectors. Input parameters: 55 cm diameter teescope 94 GHz f.5 years in space HEMTs vs BOLOMETERS Δ c 1 1 Aσ c 1 + Δ + 1 f Ncw Exampe 1: an array of 94 GHz 55 cm teescope, years in space B-POL S. Ricciardi Exampe : an array of 94 GHz 55 cm teescope, years in space Systematics B-POL S. Ricciardi The bonus of higher sensitivity aows to sampe the part of the B-modes power spectrum dominated by ensing Systematics ARE there. Knox s formua assumes simpe white gaussian noise. In the rea word noise is not gaussian and we have drifts, spikes, events of different kind in the raw data. Detectors characteristics (responsivity, noise) can change with time during the survey. Moreover, ow-eve oca emission can contaminate the sky signa in a non gaussian way. Evident features are easiy identified and rejected. Features smaer than the noise cannot be removed, and contaminate the resuts. The experiment needs to have interna redundancy in order to make tests for the presence of systematics. Systematics ARE there. The experiment needs to have interna redundancy in order to make tests for the presence of systematics. A. Severa detectors at the same frequency B. Severa different frequencies The experimenta conditions must be changed, to check the reiabiity of the resut C. Experiment different scan speeds D. Experiment different sideobes conditions E. Experiment different ocations of sun, moon, strong sources. F. Resuts must be compare to resuts of simiar, independent experiments. Caibration shoud be carried out severa times during the survey 7

8 [B15A+(B15A1+B15A)/]/ [B15A-(B15A1+B15A)/]/ Test A: Exampe: BOOMERanG Compare independent channes at the same frequency. Different boometers have different noise performance. Two channes with simiar performance are B15A and (B15A1+B15A)/ Sum and difference maps: Test B: The spectra test shows that the structures present in the maps are CMB anisotropies. In fact: The maps at different frequencies are potted in thermodynamic temperature units for the CMB (mk) so that structures with the spectrum of the CMB wi appear the same at a frequencies. Structures with the spectrum of the CMB are evident in the maps and have high S/N at 9, 15, 4 GHz. The dust monitor channe at 41 GHz shows no CMB and very itte dust. 8

9 x14.8 x14.8 1% Region 9

10 The rms fuctuations ΔT rms {Σ (+1) c w /4π} 1/ are spectray distributed as the derivative of a.73k backbody. A other astrophysica sources of confusion do not fit the data. This means that the buk of the observed fuctuations has a cosmoogica origin. -D and 3-D scatter pots confirm this concusion Astro-ph/11469 Are these genuine CMB fuctuations? rms Brightness fuctuations (W/m /sr/hz) -1 BOOMERanG-LDB dust (spinning) CMB frequency (GHz) dust (therma) Free-free Synchrotron 4GHz 15GHz Astro-ph/11469 scatter pots of high atitude data 9GHz Test C We have a powerfu too: data were taken at two different scan speeds: 1 dps and dps. At dps the sky signa is converted into an eectrica signa at twice the frequency, whie instrument reated effects (transfer function, 1/f noise, microphonic ines etc.) remain at the same frequency. For the same detectors compare maps from data taken at 1dps and from data taken at dps 1 dps map + dps map 1 dps map - dps map 1

11 Test F: BOOMERanG vs. WMAP Pixe size 7 (heapix 51) WMAP: 94 GHz Pixe size 7 (heapix 51) BOOM/98: 15 GHz Pixe size 7 (heapix 51) BOOM/98: 15 GHz 11

12 Pixe size 7 (heapix 51) WMAP: 94 GHz Pixe size 7 (heapix 51) WMAP: 94 GHz Pixe size 7 (heapix 51) BOOM/98: 15 GHz Pixe size 7 (heapix 51) WMAP: 94 GHz Pixe size 7 (heapix 51) BOOM/98: 15 GHz BOOMERanG vs. WMAP This ooks promising. But there are important differences between the two datasets shown: 94 vs 15 GHz The BOOMERanG maps do not incude structures arger than 1 o whie WMAP maps are accurate at a scaes. In this pixeization, the noise of BOOMERanG is around 3 μk per pixe, whie the noise of WMAP is around 8 μk. The beams of BOOMERanG and WMAP are different. Let s take a coser ook 1

13 B98-15GHz 13 Gaussian 11 Gaussian B98 15 GHz 13 Gaussian WMAP 1st yr WMAP 94GHz 41GHz (deg) 6GHz (deg) 94GHz (deg) WMAP 94GHz 11 Gaussian BOOMERanG 98 GHz (deg) 15GHz (deg) 9GHz (deg) PKS GHz (deg) 6GHz (deg) 94GHz (deg) BOOMERanG 98 WMAP 1st yr PMNJ GHz (deg) 6GHz (deg) 94GHz (deg) BOOMERanG 98 WMAP 1st yr GHz (deg) 15GHz (deg) 9GHz (deg) GHz (deg) 15GHz (deg) 9GHz (deg) 1 PKS GHz (deg) 6GHz (deg) 94GHz (deg) GHz (deg) 15GHz (deg) 9GHz (deg) WMAP 1st yr BOOMERanG 98 μk CMB in a ' beam CMB rms 1 frequency (GHz) PKS PMNJ PKS F / Ω μk ' CMB ν 43 1GHz.55 13

14 There are additiona AGNs ost in the confusion of the CMB fuctuations. WOMBAT cataog The WOMBAT cataogue and toos predict quite we the fux observed for the 3 detected 1 AGN, and can be used to estimate the contamination due to unresoved AGNs. In the 3% of the sky mapped by B98 the contamination of 1 the PS at 15 GHz is ess than.3% at, and ess than 8% at 6. This is reduced by 5% if the resoved sources (at 15 GHz) are removed, and by 8% if Fux 15 GHz are removed those resoved at 41 GHz. counts (+1)c /π (μk ) 6 CMB a sources 5 removed removed mutipoe 15GHz 41GHz (deg) 6GHz (deg) 94GHz (deg) GHz (deg) 15GHz (deg) 9GHz (deg) WMAP 1st yr BOOMERanG 98 Spectrum of CMB anisotropy [from the correations map(ν) vs map(94ghz), corrected for beam and sky coverage] [db/dt](ν)/[db/dt](94ghz) 1 db/dt(.75k) WMAP & B frequency (Hz) The sky maps are so consistent at different frequencies because they are dominated by CMB anisotropy. It is then possibe to subtract two maps to remove the CMB, eaving any diffuse emission with a non-cmb spectrum. In this way we have detected thin cirrus couds at high Gaactic atitudes, as confirmed by B98 measurements at 41 GHz, by IRAS/DIRBE at 3 GHz and by the HI survey (HIPASS) at 1 cm. WehaveasodetectedSZ custers. 1 cm - HI 1 μm - 3 GHz 14

15 Extrapoation of dust fuctuations at CMB waveengths The IRAS correated dust fuctuations detected at 41 GHz by BOOMERanG can be extrapoated to 4, 15, 9 GHz using the measured sopes: c (ν)[s(ν)/s(41)] c (41). The contamination from IRAScorreated dust at 15 GHz is two orders of magnitude beow the measured power spectrum The contamination from the uncorreated component depends on its spectrum. For reasonabe spectra, it is smaer than the correated part Masi et a. Ap.J., 553, L93-L96, (1) BOOMERanG and SZ Custers In the BOOMERanG map there are about 3 known rich custers (evident in X rays). We have sorted the custers according to the SZ brightness predicted from X, and searched the CMB temperature difference map (4-15 GHz) for positive signas. The beam of BOOMERanG was 1, the pointing reconstruction uncertainty was.5 rms, and the pixe size is 7. We spent ony a few seconds per pixe (!) The three brightest custers are a detected (S/N ) The ikeihood of this detection to be random is < 1-3. (F. Piacentini) S/N (4-15)GHz AGN S59 A366 3 brightest Custers (4-15)GHz 41GHz F. Piacentini DUST Fina Remarks Wehavea goodunderstandingof how to buid instruments abe to measure the anisotropy of the CMB. A this experience wi give its definitive resut with the operation of the Panck sateite The chaanges are now high precision anisotropy measurements, reducing the systematics beow the μk eve (!!!) CMB poarization measurements Surveys of SZ custers 15