ABOUT LAMBDA

Milano Polarimeter Data Products at LAMBDA

The MIPOL Collaboration made measurements of CMB circular polarization at 33 GHz.


MIPOL image

MIPOL (Milano Polarimeter)


  • Measurements of the CMB polarization at 33 GHz
  • Two channel, phase modulated, correlation radiometer
  • Outputs: two differential plus total power channels
    Linear polarization mode
    Out1 = c1 { Q cos(χ) – U sin(χ) } + o1
    Out2 = c2 { Q sin(χ) + U cos(χ) } + o2
    TP1 and TP2
    Circular polarization mode
    Out3 = c3 { Q cos(χ) – V sin(χ) } + o3
    Out4 = c4 { Q sin(χ) + V cos(χ) } + o4
    TP3 and TP4
    (Q,U,V Stokes parameters, χ = phase difference)
    (Sx = sensitivity, ox =offset, TPx=Total Power)
  • Corrugated conical horn (HPBW 7° and 14°) steerable on the meridian
  • Cooled front end (mechanical cryocooler)
  • System housed in a thermally stabilized tent
  • Prototypes tested in Antarctica at Terra Nova Bay (1993) and Dome C (1998)
  • In the waiting list of experiments of the Italian Antarctic Program for Dome C up to 2002
  • In 2002 withdrawn from the Antarctic Program and installed on the Italian Alps at the
    Testa Grigia Observatory (lat. 45.93 N, long=7.7 E, 3480 m altitude)

References:

Sironi G. et al. (1998): New Astronomy, 3, 1-13, ADS
Sironi G. et al. (1998) ASP Conf. Ser. 141, 116, ADS
Gervasi M. et al. (2000) SIF Conf. Proc. 68,165
Spiga D. et al. (2002): New Astronomy, 7, 125-134, ADS
Gervasi M. et al. (2002): SPIE, 4843, 336-347, ADS
Mainini R. et al. (2013) JCAP, 08, 033, arXiv: 1307.6090v2, ADS


Radiometer properties

MIPOL sensitivity, gain stability, correlator offsets

Type Quantity Circular Polariz. Linear Polariz. Unit
Total power Sensitivity ch. 1 1165.8±20.0 1220.3±20.8 adu/K
  Sensitivity ch. 2 1474.0±25.4 1457.8±23.9 adu/K
  Stability ch. 1 8.0 10-9 4.3 10-9 s-1
  Stability ch.2 6.4 10-9 4.4 10-9 s-1
         
Correlator Sensitivity ch. 1 (2.9±0.9) 105 (3.0±0.9) 105 adu/K
  Sensitivity ch. 2 (2.9±0.9) 105 (3.0±0.9) 105 adu/K
Offset ch. 1 -(0.36±0.04) 105 (1.85±0.07) 105 adu
  Offset ch. 2 -(1.79±0.08) 105 -(1.06±0.06) 105 adu
  Stability ch. 1 4.3 10-9 4.0 10-9 s-1
  Stability ch. 2 4.4 10-9 8.5 10-9 s-1


Observations of CMB in Circular Polarization mode

  • Site : Testa Grigia Observatory
  • Between Nov. 10th and Dec. 9th 2009 observation in circular polarization mode followed (Dec.17th 2009 – Jan. 20th 2010) by tests of the system performance in linear polarization mode.
  • Half Power Beam Width: 7°, system time constant: 6 s, sampling of the system outputs: every 2 s
  • Continuous drift scans, while the radiometer beam moved at a constant pace along the meridian from declination δin=(41.1±0.1)
    to δfin=(15.8±0.1) in 300 s, went back to δin in 18 s then the cycle was repeated.
  • Data collected at night time (1 hour after sunset - 1 hour before sunrise) with clear sky were arranged in (2o x 2o) pixels of a (α,δ) map
  • Resulting map covers almost uniformly the sky region (-30o ≤ α ≤ +165o, 15o N ≤ δ ≤ 41o N)

Summary of results
An improved upper limit to the CMB circular polarization
at large angular scales
Mainini R. et al. (2013) JCAP, 08, 033, arXiv: 1307.6090v2, ADS


Atmospheric and system temperatures from Total Power measurements with the horn aimed at the zenith

  Linear mode
full sample
Circular mode
full sample
Circular mode
sub sample(o)
Unit
Tch1atm 9.55±0.21 7.91±0.04 8.45±0.04 K
Tch2atm 7.25±0.26 8.70±0.05 9.49±0.06 K
Tch1sys 83.6±1.4 82.9±1.4 75.36±0.05 K
Tch2sys 89.7±1.5 84.1±1.5 76.05±0.07 K

(o) data collected between Julian days 40136 and 40137 when the observing conditions were particularly good


  • contribution of atmospheric and ground emission to the correlator outputs
    with the horn aimed at the zenith

  • tan (χatm) = – (1.68±0.09)  Tatm = (0.087±0.002) K
    tan (χgr) = - (0.24±0.06)  Tgr = (0.006±0.046) K

Mean <V> , standard deviation σV, average rms per pixel σVpix, average standard
deviation of the mean per pixel σ<V>pix of V, the circular polarization Stokes parameter

Pixel size Number of pixels <V> σV σVpix σ<V>pix Unit
2° x 2° unbinned data 518 -(0.02±0.06) 1.29 -- -- mK
8° x 8° 64 -(0.02±0.08) 0.64 1.14 0.43 mK
12° x 12° 32 -(0.02±0.07) 0.38 1.27 0.35 mK
24° x 24° 9 -(0.02±0.06) 0.15 1.37 0.21 mK


Test for the gaussianity of the data

Pixel size f μ=<V>     σ=σV
χ2    P
Best fit
χ2    P
Simulations
χ2    P
8° x 8° 5 6.04    0.70 3.90    0.44 9.95    0.92
12° x 12° 1 1.96    0.76 0.79    0.55 2.81    0.83
2° x 2° 55 46.60    0.20 -- --

f = degree of freedom, P = probability of the assumed Gaussian model



Upper limits to the degree of circular polarization of the CMB by classical, Bayesian and spherical harmonics analysis methods

Method Classical Bayesian Spherical harmonics
Pixel size ΠVCMB ΠVCMB ΠVCMB
8° x 8° 5.0 10-4 4.0 10-4 4.3 10-4
<θ>=7.5°
12° x 12° 2.7 10-4 3.2 10-4 2.4 10-4
<θ>=10.6°
24° x 24° 0.7 10-4 2.1 10-4 2.7 10-4
<θ>=18.0°

A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
Goddard Space Flight Center, National Aeronautics and Space Administration
HEASARC Director: Dr. Alan P. Smale
LAMBDA Director: Dr. Eric R. Switzer
NASA Official: Dr. Eric R. Switzer
Web Curator: Mr. Michael R. Greason