Updated Design of the CMB Polarization Experiment Satellite LiteBIRD

JOURNAL OF LOW TEMPERATURE PHYSICS Springer Science and Business Media LLC 199:3-4 (2020) 1107-1117

Authors:

H Sugai, Par Ade, Y Akiba, D Alonso, K Arnold, J Aumont, J Austermann, C Baccigalupi, Aj Banday, R Banerji, Rb Barreiro, S Basak, J Beall, S Beckman, M Bersanelli, J Borrill, F Boulanger, Ml Brown, M Bucher, A Buzzelli, E Calabrese, Fj Casas, A Challinor, V Chan, Y Chinone

Abstract:

© 2020, The Author(s). Recent developments of transition-edge sensors (TESs), based on extensive experience in ground-based experiments, have been making the sensor techniques mature enough for their application on future satellite cosmic microwave background (CMB) polarization experiments. LiteBIRD is in the most advanced phase among such future satellites, targeting its launch in Japanese Fiscal Year 2027 (2027FY) with JAXA’s H3 rocket. It will accommodate more than 4000 TESs in focal planes of reflective low-frequency and refractive medium-and-high-frequency telescopes in order to detect a signature imprinted on the CMB by the primordial gravitational waves predicted in cosmic inflation. The total wide frequency coverage between 34 and 448 GHz enables us to extract such weak spiral polarization patterns through the precise subtraction of our Galaxy’s foreground emission by using spectral differences among CMB and foreground signals. Telescopes are cooled down to 5 K for suppressing thermal noise and contain polarization modulators with transmissive half-wave plates at individual apertures for separating sky polarization signals from artificial polarization and for mitigating from instrumental 1/f noise. Passive cooling by using V-grooves supports active cooling with mechanical coolers as well as adiabatic demagnetization refrigerators. Sky observations from the second Sun–Earth Lagrangian point, L2, are planned for 3 years. An international collaboration between Japan, the USA, Canada, and Europe is sharing various roles. In May 2019, the Institute of Space and Astronautical Science, JAXA, selected LiteBIRD as the strategic large mission No. 2.

The C-Band All-Sky Survey (C-BASS): Simulated parametric fitting in single pixels in total intensity and polarization

Monthly Notices of the Royal Astronomical Society Oxford University Press 490:2 (2019) 2958-2975

Authors:

Luke Jew, AC Taylor, Michael Jones, A Barr, HC Chiang, C Dickinson, RDP Grumitt, HM Heilgendorff, J Hill-Valler, JL Jonas, JP Leahy, J Leech, TJ Pearson, MW Peel, ACS Readhead, J Sievers

Abstract:

The cosmic microwave background (CMB) B-mode signal is potentially weaker than the diffuse Galactic foregrounds over most of the sky at any frequency. A common method of separating the CMB from these foregrounds is via pixel-based parametric-model fitting. There are not currently enough all-sky maps to fit anything more than the most simple models of the sky. By simulating the emission in seven representative pixels, we demonstrate that the inclusion of a 5 GHz data point allows for more complex models of low-frequency foregrounds to be fitted than at present. It is shown that the inclusion of the C-BASS data will significantly reduce the uncertainties in a number of key parameters in the modelling of both the galactic foregrounds and the CMB. The extra data allow estimates of the synchrotron spectral index to be constrained much more strongly than is presently possible, with corresponding improvements in the accuracy of the recovery of the CMB amplitude. However, we show that to place good limits on models of the synchrotron spectral curvature will require additional low-frequency data.

Gain stabilization for radio intensity mapping using a continuous-wave reference signal

Monthly Notices of the Royal Astronomical Society Oxford University Press 489:1 (2019) 548-554

Authors:

Alexander Pollak, CM Holler, ME Jones, AC Taylor

Abstract:

Stabilizing the gain of a radio astronomy receiver is of great importance for sensitive radio intensity mapping. In this paper we discuss a stabilization method using a continuous-wave reference signal injected into the signal chain and tracked in a single channel of the spectrometer to correct for the gain variations of the receiver. This method depends on the fact that gain fluctuations of the receiver are strongly correlated across the frequency band, which we can show is the case for our experimental set-up. This method is especially suited for receivers with a digital back-end with high spectral resolution and moderate dynamic range. The sensitivity of the receiver is unaltered except for one lost frequency channel. We present experimental results using a new 4–8.5 GHz receiver with a digital back-end that shows substantial reduction of the 1/f noise and the 1/f knee frequency.

The C-Band All-Sky Survey (C-BASS): constraining diffuse Galactic radio emission in the North Celestial Pole region

Monthly Notices of the Royal Astronomical Society Oxford University Press 485:2 (2019) 2844-2860

Authors:

C Dickinson, A Barr, HC Chiang, C Copley, Richard DP Grumitt, HM Heilgendorff, LRP Jew, JL Jonas, Michael E Jones, JP Leahy, J Leech, EM Leitch, SJC Muchovej, TJ Pearson, MW Peel, ACS Readhead, J Sievers, MA Stevenson, Angela Taylor

Abstract:

The C-Band All-Sky Survey (C-BASS) is a high sensitivity all-sky radio survey at an angular resolution of 45 arcmin and a frequency of 4.7 GHz. We present a total intensity map of the North Celestial Pole (NCP) region of sky, above declination >+80°, which is limited by source confusion at a level of ≈0.6 mK rms. We apply the template-fitting (cross-correlation) technique to WMAP and Planck data, using the C-BASS map as the synchrotron template, to investigate the contribution of diffuse foreground emission at frequencies ∼20–40 GHz. We quantify the anomalous microwave emission (AME) that is correlated with far-infrared dust emission. The AME amplitude does not change significantly (⁠<10 per cent⁠) when using the higher frequency C-BASS 4.7 GHz template instead of the traditional Haslam 408 MHz map as a tracer of synchrotron radiation. We measure template coefficients of 9.93 ± 0.35 and 9.52±0.34 K per unit τ353 when using the Haslam and C-BASS synchrotron templates, respectively. The AME contributes 55±2μK rms at 22.8 GHz and accounts for ≈60 per cent of the total foreground emission. Our results show that a harder (flatter spectrum) component of synchrotron emission is not dominant at frequencies ≳5 GHz; the best-fitting synchrotron temperature spectral index is β = −2.91 ± 0.04 from 4.7 to 22.8 GHz and β = −2.85 ± 0.14 from 22.8 to 44.1 GHz. Free–free emission is weak, contributing ≈7μK rms (⁠≈7 per cent⁠) at 22.8 GHz. The best explanation for the AME is still electric dipole emission from small spinning dust grains.

The C-Band All-Sky Survey (C-BASS): Digital backend for the northern survey

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2019)

Authors:

MA Stevenson, TJ Pearson, Michael E Jones, CJ Copley, C Dickinson, JJ John, OG King, SJC Muchovej, Angela C Taylor