LiteBIRD is a next-generation space telescope which aims to measure primordial gravitational waves in the polarisation of the cosmic microwave background. The level of the primordial (tensor, or B-mode) signal in relation to the scalar (or E-mode) only has a known upper limit, and the instrument requirement is to measure a tensor-to-scalar ratio sensitivity δr<0.001. Systematic effects arising from cosmic radiation are expected to play a significant role, and our prior work has focused on the development of an end-to-end simulation tool for evaluating the scale of this in LiteBIRD’s Low Frequency Telescope (LFT). We present an updated forecasting method which makes use of event tables generated by a new Geant4 mass model of LFT. We will compare the previously used simplified model with that of the updated mass model, and project these differences into an expected effect of the cosmic ray effect δr. Lastly, we will examine the use of a simple filtering method for removing direct detector impacts by cosmic rays, which have been shown previously to play the largest role in this systematic effect.
LiteBIRD is a space-borne experiment dedicated to detecting large-scale B-mode anisotropies of the linear polarization of the cosmic microwave background (CMB) predicted by the theory of inflation. It is planned to be launched in the late 2020s to the second Lagrangean point of the Sun-Earth system and map the sky in 15 frequency bands using thousands of transition edge sensor bolometers. LiteBIRD will be exposed to the cosmic-ray radiation throughout its lifetime, which may lead to the degradation of the scientific performance. Energy deposition by cosmic rays upon the focal plane bolometer detectors is considered a serious source of systematic effects. For a quantitative assessment of the effect, we present the result of Geant4 simulations to estimate the energy deposited by cosmic rays into the focal plane. We simulated different cosmic-ray components using CAD-based spacecraft models. We derive the spatial and energy distribution of the particles in the focal plane.
Resolve onboard the x-ray satellite X-Ray Imaging and Spectroscopy Mission (XRISM) is a cryogenic instrument with an x-ray microcalorimeter in a Dewar. A lid partially transparent to x-rays (called gate valve or GV) is installed at the top of the Dewar along the optical axis. Because observations will be made through the GV for the first few months, the x-ray transmission calibration of the GV is crucial for initial scientific outcomes. We present the results of our ground calibration campaign of the GV, which is composed of a Be window and a stainless steel mesh. For the stainless steel mesh, we measured its transmission using the x-ray beamline at ISAS. For the Be window, we used synchrotron facilities to measure the transmission and modeled the data with (i) photoelectric absorption and incoherent scattering of Be, (ii) photoelectric absorption of contaminants, and (iii) coherent scattering of Be changing at specific energies. We discuss the physical interpretation of the transmission discontinuity caused by the Bragg diffraction in polycrystal Be, which we incorporated into our transmission phenomenological model. We present the x-ray diffraction measurement on the sample to support our interpretation. The measurements and the constructed model meet the calibration requirements of the GV. We also performed a spectral fitting of the Crab nebula observed with Hitomi SXS and confirmed improvements of the model parameters.
LiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. JAXA selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with its expected launch in the late 2020s using JAXA's H3 rocket. LiteBIRD plans to map the cosmic microwave background (CMB) polarization over the full sky with unprecedented precision. Its main scientific objective is to carry out a definitive search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with an insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. To this end, LiteBIRD will perform full-sky surveys for three years at the Sun-Earth Lagrangian point L2 for 15 frequency bands between 34 and 448 GHz with three telescopes, to achieve a total sensitivity of 2.16 μK-arcmin with a typical angular resolution of 0.5° at 100 GHz. We provide an overview of the LiteBIRD project, including scientific objectives, mission requirements, top-level system requirements, operation concept, and expected scientific outcomes.
LiteBIRD has been selected as JAXA’s strategic large mission in the 2020s, to observe the cosmic microwave background (CMB) B-mode polarization over the full sky at large angular scales. The challenges of LiteBIRD are the wide field-of-view (FoV) and broadband capabilities of millimeter-wave polarization measurements, which are derived from the system requirements. The possible paths of stray light increase with a wider FoV and the far sidelobe knowledge of -56 dB is a challenging optical requirement. A crossed-Dragone configuration was chosen for the low frequency telescope (LFT : 34–161 GHz), one of LiteBIRD’s onboard telescopes. It has a wide field-of-view (18° x 9°) with an aperture of 400 mm in diameter, corresponding to an angular resolution of about 30 arcminutes around 100 GHz. The focal ratio f/3.0 and the crossing angle of the optical axes of 90◦ are chosen after an extensive study of the stray light. The primary and secondary reflectors have rectangular shapes with serrations to reduce the diffraction pattern from the edges of the mirrors. The reflectors and structure are made of aluminum to proportionally contract from warm down to the operating temperature at 5 K. A 1/4 scaled model of the LFT has been developed to validate the wide field-of-view design and to demonstrate the reduced far sidelobes. A polarization modulation unit (PMU), realized with a half-wave plate (HWP) is placed in front of the aperture stop, the entrance pupil of this system. A large focal plane with approximately 1000 AlMn TES detectors and frequency multiplexing SQUID amplifiers is cooled to 100 mK. The lens and sinuous antennas have broadband capability. Performance specifications of the LFT and an outline of the proposed verification plan are presented.
LiteBIRD is a JAXA-led Strategic Large-Class mission designed to search for the existence of the primordial gravitational waves produced during the inflationary phase of the Universe, through the measurements of their imprint onto the polarization of the cosmic microwave background (CMB). These measurements, requiring unprecedented sensitivity, will be performed over the full sky, at large angular scales, and over 15 frequency bands from 34 GHz to 448 GHz. The LiteBIRD instruments consist of three telescopes, namely the Low-, Medium-and High-Frequency Telescope (respectively LFT, MFT and HFT). We present in this paper an overview of the design of the Medium-Frequency Telescope (89{224 GHz) and the High-Frequency Telescope (166{448 GHz), the so-called MHFT, under European responsibility, which are two cryogenic refractive telescopes cooled down to 5 K. They include a continuous rotating half-wave plate as the first optical element, two high-density polyethylene (HDPE) lenses and more than three thousand transition-edge sensor (TES) detectors cooled to 100 mK. We provide an overview of the concept design and the remaining specific challenges that we have to face in order to achieve the scientific goals of LiteBIRD.
KEYWORDS: Polarization, Satellites, Earth observing sensors, Bolometers, Space operations, Signal detection, Digital filtering, Signal processing, Sensors, Microwave radiation
The LiteBIRD satellite is planned to be launched by JAXA in the late 2020s. Its main purpose is to observe the large-scale B-mode polarization in the Cosmic Microwave Background (CMB) anticipated from the Inflation theory. LiteBIRD will observe the sky for three years at the second Lagrangian point (L2) of the Sun-Earth system. Planck was the predecessor for observing the CMB at L2, and the onboard High Frequency Instrument (HFI) suffered contamination by glitches caused by the cosmic-ray (CR) hits. We consider the CR hits can also be a serious source of the systematic uncertainty for LiteBIRD. Thus, we have started a comprehensive end-to-end simulation study to assess impact of the CR hits for the LiteBIRD detectors. Here, we describe procedures to make maps and power spectra from the simulated time-ordered data, and present initial results. Our initial estimate is that ClBB by CR is ~ 2 ×10−6 μK2CMB in a one-year observation with 12 detectors assuming that the noise is 1 aW/ √ Hz for the differential mode of two detectors constituting a polarization pair.
Resolve onboard the X-ray satellite XRISM is a cryogenic instrument with an X-ray microcalorimeter in a Dewar. A lid partially transparent to X-rays is installed at the top of the Dewar along the optical axis, which is called the gate valve (GV). Because observations will be made through the GV for the first few months, the X-ray transmission calibration of the GV is crucial for initial scientific outcomes. We present the results of our ground calibration campaign of the GV, which is composed of a Be window and a stainless steel mesh. For the stainless steel mesh, we measured its transmission using the X-ray beamline at ISAS for the first time. For the Be window, we used synchrotron facilities to measure the transmission and modeled the data with (i) photoelectric absorption and incoherent scattering of Be, (ii) photoelectric absorption of contaminants, and (iii) coherent scattering of Be. We discuss the physical interpretation of the transmission discontinuity caused by the Bragg diffraction in poly-crystal Be, which we incorporated into our phenomenological model. The measurements and the constructed model meet the calibration requirements of the GV. We also performed a spectral fitting of the Crab nebula data observed with Hitomi SXS and confirmed improvements of the model.
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