Weekly Overview | Day 1 | Day 2 | Day 3 | Day 4 | Day 5
Day 1 – Monday, Nov. 4th
Weekly Overview | Day 1 | Day 2 | Day 3 | Day 4 | Day 5
9:30-11:00, Welcome Breakfast and Registration
Chair: Josquin Errard, APC/CNRS, Paris, France
11:00 – Introduction
Speaker: Federico Nati, University of Milano-Bicocca, Italy
Abstract: The ambitious scientific goals of current and next-generation Cosmic Microwave Background experiments demand exceptional calibration accuracy. This workshop, supported by the ERC POLOCALC project, will explore the current state and future directions of calibration methods. Topics will include gain calibration, telescope pointing, beam characterization, polarization angle, detectors, bandpass calibration, as well as the challenges posed by galactic foregrounds and the potential to measure Cosmic Birefringence. Special emphasis will be placed on calibration technologies such as far-field sources, wire grids, holography setups, and their interplay. The workshop will feature a combination of talks and hands-on sessions.
11:20 – Calibration Methods for Next-Generation CMB Experiments
Speaker: Sara Simon, Fermilab, Chicago, USA
Abstract: Formed 400,000 years after the beginning of the universe, the cosmic microwave background (CMB) offers an unparalleled window into the earliest moments of the universe and its subsequent evolution. Improved measurements of the CMB could indicate if there was a period of inflation in the early universe, constrain the existence of relativistic particles beyond the standard model, and improve our understanding of the formation and dynamics of structure in the universe, dark energy, dark matter, and neutrino properties. To reach new thresholds in cosmology, our instruments need increasingly more sensitivity. As we make our instruments more sensitive, we also become more susceptible to systematic effects. The next generation of CMB instruments will require improved calibration and systematic modeling to mitigate systematic effects and reach their science goals. I will give a general overview of calibration strategies and give an overview of the strategies targeted for use on Simons Observatory.
11:50 – Calibration Challenges for CMB-S4
Speaker: Johanna Nagy, Case Western Reserve University, USA
Abstract: CMB-S4 is a ground-based next-generation CMB experiment being designed to cross critical thresholds in several key science topics. These include searching for evidence of primordial gravitational waves, probing the dark Universe and neutrino sector, mapping the matter distribution of the cosmos, and exploring the transient millimeter-wave sky. These require a combination of dedicated telescopes small- and large-aperture telescopes each optimized for deep and wide surveys of the microwave sky. However, planning for such measurements with unprecedented sensitivity and broad science goals poses many calibration challenges. I’ll discuss these challenges for measuring bandpasses, beams, gain, and other instrument parameters and give an overview of CMB-S4’s early calibration plans.
12:20 – Data calibration perspective for dust polarization and component separation
Speaker: François Boulanger, LPENS, Paris, France
Abstract: Dust polarization is a key means of studying the role of magnetic fields in the formation of the filamentary structure of the cold ISM. Planck’s observations have had a major impact in this field, and future CMB experiments will continue to provide invaluable data. Conversely, understanding the dust foreground is a major challenge for the success of CMB experiments.
Of particular interest to both fields is the analysis of the spectral energy distribution of dust polarization, including frequency-dependent variations of polarization angles. In this perspective, I will argue that the accuracy with which we can measure dust polarization angles is essential for probing the three-dimensional structure of the dusty magnetized ISM, as well as component separation.
12:50 – Planck calibration: lessons learned
Speaker: M. Bersanelli, University of Milano, Italy
Abstract: A key element in the success of the Planck mission was the careful calibration plan that was established and executed over several years in advance to launch, as well as during flight operations. Nevertheless, in some cases, the instrumental characterization was sub-optimal and led to limiting factors in the data analysis. I will review the main features of the optical, radiometric, and photometric calibration of the Planck instruments, particularly of the LFI, with the aim of identifying lessons learned potentially useful for future projects.
13:20 – 14:20, Lunch, U6 Building
Chair: Rolando Dünner, PUC, Chile
14:20 – Calibration strategies for the Cosmology Large Angular Scale Surveyor (CLASS)
Speaker: John Appel, Johns Hopkins University, USA
Abstract: The Cosmology Large Angular Scale Surveyor (CLASS) is a set of four ground-based telescopes designed to measure and characterize the polarization signal of the cosmic microwave background (CMB) on the largest angular scales (> 1 degree) in order to probe the epochs of inflation and reionization. Located in a high altitude site in the Atacama Desert, CLASS covers over 75% of the sky in frequency bands centered at 40, 90, 150, and 220 GHz. To produce high fidelity maps CLASS employs various calibration strategies, from I-V curves to set the per-detector gain and time constant calibration, to observing astrophysical sources such as the Moon, planets and tauA to constrains the instrument beam, absolute gain and polarization angle. In collaboration with the HoverCal + PoloCalC project we are expanding and improving the CLASS calibration by conducting dedicated scans of drones in-flight, equipped with polarized microwave sources.
14:50 – Performance overview of the BICEP/Keck CMB Polarimeters
Speaker: James Cornelison, Argonne National Laboratory / University of Chicago, USA
Abstract: The Bicep/Keck collaboration operates a series of small aperture refracting telescopes that observe the degree-scale Cosmic Microwave Background from the South Pole, each which contribute to our search for primordial B-mode polarization signals that would serve as a unique signature of Cosmic Inflation. In this presentation, we give an overview of the most recent techniques and results from our calibration efforts on our 95GHz platform, BICEP3, as well as results from our 35GHz & 150GHz platforms within BICEP Array. Included in these efforts are far-field beam mapping which constrain temperature-to-polarization leakage; near-field beam mapping to identify optical anomalies; and sidelobe mapping as well as the mapping of the local mm-wave environment to study the importance and efficacy of ground radiation shielding. Within the context of each of these calibrations, we shall discuss the measurement procedure, analysis results, and the subsequent impacts on our overall experimental approach as well as constraining ability of the tensor-to-scalar ratio.
15:20 – Calibration for precision cosmology with the South Pole Telescope
Speaker: Federica Guidi, Institut d’Astrophysique de Paris, France
Abstract: SPT-3G is an experiment to observe the CMB temperature and polarisation anisotropies at small angular scales from the South Pole. The high sensitivity of SPT-3G will allows us to uncover new critical information on the composition and evolution of the universe, and to shed light on the cosmological tensions. Test observations carried out in 2018 provided cosmological constraints compatible with Planck’s, but with lower sensitivity. The analysis of more data taken in 2019/20 is ongoing, with the goal of achieving new and much more stringent cosmological constraints, requiring a significant improvement on the characterisation of the data (calibration, beams, …). In this talk I will give a quick overview on the latest SPT-3G results, and I will present the ongoing work on 2019/20 data analysis. In particular, I will focus on some specific calibration aspects and challenges, including calibration of absolute temperature and polarisation, effect of detectors time-contacts, characterisation of the beam, calibration of the polarisation angle.
15:50 – Calibration strategy for the Atacama Cosmology Telescope
Speaker: Adri Duivenvoorden, Max Planck Institute for Astrophysics, Garching, Germany
Abstract: This talk will present the calibration strategy for the 2017-2022 data release (DR6) of the Atacama Cosmology Telescope (ACT), covering the absolute gain, relative detector gains, polarization angles and beam calibration. The updated beam estimation methodology will be introduced and it will be demonstrated that, due to the color corrections needed for accurate sky component separation, passband errors must be considered during beam calibration. In addition, the estimate of the temperature-to-polarization leakage, which is one of the largest sources of systematic error for ACT, will be discussed. Finally, the impact of subtle, often overlooked model errors, which can result in significant biases during mapmaking, will be addressed, along with considerations for future ground-based CMB experiments when planning their instrument calibration strategies.
16:20 – 16:40, Coffee Break, U6 Building
Chair: Mario Zannoni, Milano-Bicocca, Italy
16:40 – QUBIC: Calibration using Bolometric Interferometry
Speaker: Steve Torchinsky, APC/Observatoire de Paris, France
Abstract: QUBIC is the Q & U Bolometric Interferometer for Cosmology. It is similar to an imaging interferometer with multiple antennas pointing in the same direction, combining the signals interferometrically. QUBIC uses an optical combiner to add the signals together while in
traditional radio aperture synthesis the signals are digitized and multiplied together in a digital correlator. The main advantage of
bolometric interferometry as implemented in QUBIC is the bandwidth, and with the use of cryogenic TES bolometers, the sensitivity of the
measurement is comparable to direct imagers. Advanced calibration techniques developed for radio aperture synthesis are available to
QUBIC, including self-calibration which will be done by scanning an artificial millimetre-wave source placed on a tower in the QUBIC
farfield. I will describe the QUBIC instrument with emphasis on the setup for calibration.
17:10 – The calibration of MISTRAL at SRT
Speaker: Elia Battistelli, Sapienza University of Rome, Italy
Abstract: In this contribution, I will present the MISTRAL instrument (MIllimetric Sardinia radio Telescope Receiver based on an Array of Lumped element kinetic inductance detectors), a cryogenic camera operating in the W-band with a bandwidth range of 77 GHz to 100 GHz. When coupled to the Sardinia Radio Telescope (SRT), MISTRAL achieves a 12″ angular resolution over a 4′ field of view (FOV). I will discuss the design and fabrication of the instrument, as well as its laboratory calibration. Additionally, I will highlight the instrument’s performance and the ongoing astronomical calibration currently being carried out in Sardinia. Both forecasted and measured sensitivities, as well as mapping
speed, will be presented.
17:40 – SPIDER Balloon-borne Experiment Calibration
Speaker: Elle Shaw, University of Texas at Austin, USA
Abstract: SPIDER is a balloon-borne instrument designed to map the cosmic microwave background at degree-angular scales in the presence of Galactic foregrounds. SPIDER mapped a large area of the Southern sky at 95, 150, and 280 GHz during two NASA Long-Duration Balloon flights above the Antarctic continent in 2015 and 2022-2023. In this talk, I will give a brief overview of the SPIDER 1 and SPIDER 2 instruments, describe the pre-flight spectroscopic and polarimetric detector calibration measurements, and describe the post-flight analyses used for absolute calibration, monitoring gain, and refining pointing offsets and beam response.
18:10 – Calibration of the GroundBIRD Telescope: Current Status and Future Prospects
Speaker: Miku Tsuji, Astronomical Instisute, Tohoku University, Japan
Abstract: GroundBIRD is a ground-based Cosmic Microwave Background (CMB) experiment for observing the polarization pattern imprinted on large angular scales (6 < ℓ < 300) at the Teide Observatory in Tenerife, Spain. One of our primary scientific objectives is a precise measurement of the optical depth τ (σ(τ) ~ 0.01) to the reionization epoch of the Universe after the Planck satellite for the first time. GroundBIRD observes a large sky region (~40% of full-sky) while continuously rotating the telescope at a high speed of 20 rotation-per-minute at an elevation of 70° to overcome the fluctuations of atmospheric radiation. These features enable us to observe the reionization bump in the E-mode power spectrum of CMB polarization appeared in low ℓ.
Our calibration efforts encompass pointing model, detector responsivities, beam profiles, and polarization angles. We constructed our pointing model using the Moon’s signal, taking advantage of our Microwave Kinetic Inductance Detectors’ (MKIDs) wide dynamic range compared to Transition Edge Sensors (TESes). The Moon and Jupiter serve as calibration sources for detector responsivities and beam profiles and we are continuously refining these methods. For polarization angle calibration, we employ a sparse wire grid technique.
In May 2023, we installed MKID arrays (138 at 145GHz, 23 at 220GHz) featuring NbTiN/Al hybrid technology. We have confirmed by a performance verification test at laboratory that the noise levels of the detectors are below the optical loading due to atmospheric radiation at our site and the time responses are fast enough for achieving diffraction-limited resolution while rapidly rotating the GroundBIRD telescope.
We will present our calibration strategy, with a particular focus on the current status and future prospects of detector polarization angle calibration.
Day 2, Tuesday, Nov. 5th
Weekly Overview | Day 1 | Day 2| Day 3| Day 4| Day 5
9:00-9:30, Breakfast
Chair: Sara Simon, Fermilab, Chicago, USA
9:30 – Dipole Based Calibration for Planck
Speaker: Mathew Galloway, University of Oslo, Norway
Abstract: Space-based CMB missions have many advantages over the ground, but one major complication is the difficulty in accessing external calibration data with sufficent precision to constrain the instrumental gain. Planck solved this issue by calibrating off the CMB itself, using the solar and orbital dipoles. Calibrating this way requires an iterative process of gain and sky signal estimation to obtain the best results, which adds additional complications but makes it well suited for iterative end-to-end analysis pipelines like Commander3.
9:50 – The Simons Observatory: Gain Calibration in the Small-Aperture Telescopes
Speaker: Kevin T. Crowley, UC San Diego, USA
Abstract: The Simons Observatory (SO) is a set of state-of-the-art instruments designed to measure the Cosmic Microwave Background (CMB) across a wide range of frequencies and angular scales. Currently, three small-aperture telescope (SATs) are pursuing the possible primordial gravitational-wave signal in the linear polarization anisotropies of the CMB that may have been induced by a theorized period of inflationary expansion in the very early universe. In this talk, I will describe progress in calibrating SO detectors operating in one of the three SATs to produce gain estimates that can be used to understand signals produced within the instrument or from sources like the atmosphere or the ground, and eventually to make highly-sensitive, low-contamination maps of the CMB linear polarization.
10:10 – Fast modulated thermal radiator “Stimulator” for gain & time-constant calibration in Simons Observatory
Speaker: Yudai Seino, Princeton University, USA
Abstract: The stimulator is a hot blackbody radiator with a fast modulation which enables us to calibrate detectors’ gain and time constant simultaneously. The stimulator will be used for important repetitive hourly calibration for Simons Observatory Large Aperture Telescope. In this talk, I will introduce the stimulator’s design, calibration method, lab test, and installation progress.
10:30 – Setting instrumental requirements to perform an effective gain calibration of the LiteBIRD satellite
Speaker: Alessandro Novelli, Sapienza University of Rome, Italy
Abstract: Next generation CMB experiments aim to measure primordial B-modes in order to set constraints on the tensor-to-scalar ratio and on inflationary theories. However, the faintness of this signal and the contamination by foregrounds make instrument calibration a critical factor to perform a detection. The objective of this study is to define the gain calibration requirements for LiteBIRD, a space-based mission that aims to measure r to an accuracy of 0.001.
The approach taken to set the requirements is based on a general and flexible calibration method that relies on a small number of assumptions that can be extended and refined in different ways. This allows for the future development of multiple calibration pipelines that can be benchmarked and tested against each other.
Through a first set of numerical simulations, we identified the optimal calibration strategy for the satellite. We then use this result together with the analysis of Ghigna et al (2020) and Carralot et al (2024) to set requirements for the gain stability and the thermal fluctuation of the detectors. The gain stability simulations focused on the maximum acceptable deviation of the gain from ideality and the Amplitude Spectral Density of the gain fluctuations. With regards to the detectors, the requirements were set on the maximum acceptable noise level at the dipole frequency and the thermal fluctuations of the focal plane. A comparison of the results obtained with the current state of the art in detector technology shows that the gain stability required for gain calibration can be easily achieved. On the other hand, the requirements for thermal stability of the focal plane under the most stringent conditions are just within the reach of current technology.
10:50 – Polarization Calibration and Frequency bandpass of the BICEP/Keck CMB Polarimeters
Speaker: James Cornelison, Argonne National Laboratory / University of Chicago, USA
Abstract: We use a custom-made quasi-thermal source to measure individual detectors’~polarization angles of BICEP3, a small aperture telescope observing the cosmic microwave background (CMB) at 95GHz from the South Pole. We describe our calibration strategy and the statistical and systematic uncertainties associated with the measurement. We reach an unprecedented precision for such measurement on a CMB experiment, with a repeatability for each detector pair of $0.02 \deg$. We show that the relative angles measured using this method are in excellent agreement with those extracted from CMB data. Because the absolute measurement is currently limited by a systematic uncertainty, we do not derive cosmic birefringence constraints from BICEP3 data in this work. Rather, we forecast the sensitivity of BICEP3 sky maps for our current analysis. We also present our calibration techniques for measuring the frequency bandpass of our instruments and discuss other methods for constraining out-of-band coupling.
11:10 – 11:40, Coffee Break, U6 Building
Chair: Federico Nati, Milano-Bicocca, Italy
11:40 – Absolute Polarization Angle Calibration With HoverCal+POLOCALC
Speaker: Rolando Dünner, PUC, Chile
Abstract: In this talk, we will present the current status and preliminary results from the HoverCal + POLOCALC calibration system. This system introduces a novel method for providing a polarized millimeter-wave reference signal, with a polarization angle known to within 0.1 degrees of absolute accuracy, with with potential to improve it. Specially designed to serve Cosmic Microwave Background (CMB) telescopes, the system uses a drone to fly the RF sources into the far field of small-aperture CMB telescopes, such as SO-SATs and CLASS, at elevations above 30 degrees, which is critical for avoiding ground pickup. The polarization accuracy is achieved through a novel metrology system, which combines Real-Time Kinematic (RTK) GPS with inverse photogrammetry to precisely determine the position and attitude of the source during flight. This system has been successfully tested with CLASS and SO-SAT telescopes, demonstrating the quality of the metrology and providing the first beam shape and polarization angle measurements, validating the system’s capabilities.
12:00 – The COSMOCal (COSmological Microwave Observations
Calibrator) project
Speaker: Alessia Ritacco, University of Rome Tor Vergata, Italy
Abstract: In the context of the next generation of microwave polarization experiments, I will present the COSMOCal project which aim to produce an unified calibration model between large and small aperture telescopes.
12:20 – UAV-Based Artificial Source for LSPE-Strip and Overview of First Tests on QUIJOTE
Speaker: Fabio Paonessa, CNR-IEIIT, Turin, Italy
Abstract: Unmanned Aerial Vehicles (UAVs) have revolutionized in-situ antenna measurements by providing versatile platforms for characterizing radiation patterns across various frequency bands. While UAV-based systems ability to perform accurate and reliable measurements has been widely documented for low-frequency radio astronomy, the applicability of UAVs for antenna characterization in higher frequency bands, including those necessary for advanced microwave cosmological research, still presents challenges. An innovative UAV-mounted test source operating in the Q-band has been developed by CNR-IEIIT within the Large-Scale Polarization Explorer (LSPE) project. The RF payload design addressed critical challenges such as frequency instability caused by thermal variations and motor vibrations. This technology will be used to validate the ground-based cluster of Q-band coherent polarimeters that compose the Strip instrument of LSPE, specifically targeting the measurement of B-modes in the polarized cosmic microwave background. In preparation for the future characterization of LSPE-Strip, a measurement campaign took place in 2022 on the QUIJOTE telescope located at the Teide Observatory, Tenerife, in collaboration with the Instituto de Astrofísica de Canarias (IAC). The relevant measured results will be shown and discussed.
12:40 – Initial Result of the Polarization Angle Calibration using Sparse Wire Grid with a Small Aperture Telescope in SO
Speaker: Hironobu Nakata, Kyoto University, Japan
Abstract: Absolute polarization angle calibration is one of the biggest challenges to detect the primordial B-mode polarization in the Cosmic Microwave Background. Small Aperture Telescopes (SATs) in Simons Observatory have an automatic calibration system, Grid Loader, which uses Sparse Wire Grids as the artificial polarization source. In this talk, we will report the method of calibration as well as its initial result.
13:00 – Using beam-filling polarized radio lobes of CenA to calibrate polarization angles
Speaker: Allen Foster, Princeton University, USA
Abstract: The bright radio lobes of Centaurus A are highly polarized and beam-filling for large aperture mm-wave telescopes. They will allow for the relative calibration of polarization angle for each detector given a dedicated calibration campaign. Such a procedure has been used in SPT-pol and SPT-3G to successfully measure the relative polarization angles of each detector to high precision. SPT does not have boresight rotation and so cannot constrain gain-angle degeneracy, however the SO-LAT does, and will be able to break the degeneracy for a very accurate measurement of angle.
13:20 – 14:20, Lunch at SottoSopra Restaurant
14:20 – 16:00: Hands-on Tutorial – A New Pipeline for Beam Simulation Studies
Speaker: Lauren Saunders, Fermilab, Chicago, USA
Abstract: One of the most important factors in CMB instrument systematics is understanding our beams. Many prior beam systematics pipelines use proprietary software, and only offer the option of analytic inputs. In this tutorial, we will introduce a new map-based beam systematic pipeline that uses simulated or measured beams as an input for studying the spectral leakage. We will use this pipeline alongside the open-source Map Multi-Tool software, which is designed to analyze map-based beams and find the T→E, T→B, and E→B leakage spectra. The Map Multi-Tool is a powerful tool for studying leakage spectra in the map domain, and this tutorial will provide a baseline for working with the software in the beam application.
16:00 – 16:30, Coffee Break
Chair: Gabriele Coppi, Milano-Bicocca, Italy
16:30 – A CubeSat-Based Instrument for Calibrating Ground-Based Millimeter-Wave Polarimeters (CalSat)
Speaker: Bradley R. Johnson, University of Virginia, USA
Abstract: CalSat is a CubeSat-based polarization-angle calibration instrument for cosmic microwave background (CMB) studies, designed to provide the critical relationship between the coordinate system of the polarimeter in the instrument frame and the coordinate system on the sky that defines the astrophysical Q and U Stokes parameters. A sufficiently precise celestial calibration sources do not exist, and a calibration tool like the instrument we propose to build also does not currently exist, so CalSat is specifically designed to fill a unique and emerging need. By decreasing the orientation-angle uncertainty in CMB polarization measurements, we will decrease systematic errors, and thereby (i) expand the search for the inflationary gravitational wave signal to lower energy scales, (ii) enable a variety of cosmic polarization rotation studies, and (iii) possibly allow searches for primordial magnetic fields. A CubeSat-based solution to the polarization-angle calibration problem is necessary because the Fraunhofer distance for the large telescopes that will be used in next generation CMB studies — like Simons Observatory and CMB-S4 — is typically between 25 and 100 km, so any calibration source must be placed more than 25 to 100 km away from the telescope for the needed far-field beam characterization measurement. At the same time, the calibration source needs to be high in the sky so the radiative loading on the detector system is appropriate. The combination of these two requirements leads to a CubeSat-based solution. In our current design, CalSat includes five amplitude-modulated, linearly-polarized tones that are well matched to (i) the observation windows in the atmospheric transmittance spectra, (ii) the spectral bands commonly used in polarimeters by the CMB community, and (iii) The Amateur Satellite Service bands for broadcasting that are defined by the Federal Communications Commission (FCC)..
16:50 – Tenerife Microwave Spectrometer (TMS): absolute spectral measurements in the 10–20GHz range
Speaker: Jose Alberto Rubiño-Martin, Instituto de Astrofisica de Canarias, Spain
Abstract: The Tenerife Microwave Spectrometer (TMS) is a new absolute spectrometer in the 10–20GHz range that will be installed at the Teide Observatory (Tenerife, Spain), next to the QUIJOTE CMB experiment. Its main scientific driver is to accurately measure absolute spectral distortions of the sky spectrum in this frequency range, with special emphasis on the characterization of the absolute synchrotron monopole from our Galaxy, and the possible deviations of the CMB spectrum from a pure blackbody law. TMS will also provide an absolute calibration for the QUIJOTE experiment. In this talk, I will present the current status of the project, describing in particular the reference cold load, the analytical model of the instrument and its data acquisition system. I will discuss the main challenges in the relation to the absolute calibration of the instrument.
17:10 – Beyond Chern-Simons: Detecting Cosmic Birefringence in the CMB’s Polarization
Speaker: Brian Keating, UC San Diego, CA, USA
Abstract: Cosmic birefringence, a rotation of the polarization plane of the Cosmic Microwave Background (CMB), offers a powerful probe of new physics beyond the Standard Model, including potential violations of parity symmetry and axion-like fields. In this talk, we will explore the theoretical framework and experimental efforts to detect the four types of cosmic birefringence signatures: isotropic static, isotropic time-varying, anisotropic static, and anisotropic time-varying. I will review the current status of calibrating for and detecting cosmic birefringence, including isotropic cosmic birefringence, focusing on recent constraints from Planck and ground-based experiments like POLARBEAR. Additionally, I will discuss the search for time-varying birefringence, highlighting theoretical motivations such as axion fields and how these affect millimeter wave polarization in compact objects like Tau A. These static and time-varying signatures present distinct challenges and opportunities for the next generation of CMB experiments, requiring advanced methods in data analysis and precision measurements. Looking forward, I will outline the potential of future missions, such as the Simons Array and the Simons Observatory, designed to push the sensitivity and calibration accuracy required to detect these subtle signatures. These efforts promise to deepen our understanding of the early universe and the fundamental forces governing its evolution.
17:30 – Forecasting Isotropic Cosmic Birefringence with the Simons Observatory Large Aperture Telescope
Speaker: Anto Lonappan, UC San Diego, CA, USA
Abstract:
In this study, we present a forecast on the detection of isotropic cosmic birefringence using the Simons Observatory Large Aperture Telescope (SO LAT). We implement the Minami-Komatsu method to estimate the birefringence angle and the frequency miscalibration angle simultaneously. Our analysis incorporates complexities such as 1/f noise and bandpass integration in foreground modelling. We also evaluate the method’s robustness against varying levels of foreground complexity. Based on our findings, we project that SO LAT could achieve a 5σ detection of isotropic cosmic birefringence with five years of observation.
Slides
17:50 – In-Situ Optical Characterization of the Simons Observatory Large-Aperture Telescope Receiver
Speaker: Claire Lessler, University of Chicago, USA
Abstract: The Simons Observatory is a new ground-based CMB experiment located in the Atacama Desert of Northern Chile. It includes a Large-Aperture Telescope, or LAT, which aims to measure the CMB at arcminute angular resolution and at a noise level of 6 uK-arcmin. This level of precision demands careful characterization and calibration of the entire instrument. We present the design of a robotically controlled optical-coupling system capable of measuring the LAT’s detector bandpasses, beam maps, and time constants in-situ in the Atacama, where 30,000 TES detectors are already deployed. Our design relies on a set of off-axis aspherical mirrors to match the beam of the telescope receiver and on a robotic stage to move the optics in three orthogonal directions. To make measurements, the optics will couple to a variety of calibration sources, including a Fourier-Transform Spectrometer, frequency-tunable laser source, and chopped thermal source. We also present the results of preliminary optical testing on the LAT conducted in the Atacama in August 2024.
18:30 – Poster Session
Day 3, Wednesday, Nov. 6th
Weekly Overview | Day 1 | Day 2 | Day 3 | Day 4 | Day 5
9:00-9:30, Breakfast
Chair: Nadia Dachlythra, Milano-Bicocca, Italy
9:30 – Challenges in optics design, calibration, and systematic control for CMB experiments
Speaker: Jón E. Guðmundsson, University of Iceland
Abstract: In this talk, I will provide an overview of the many optics-related challenges that face researchers trying to design, build, calibrate, and analyse data from telescopes observing the cosmic microwave background. Along the way, I will highlight past successes and underline unanswered questions.
9:50 – Antenna pattern measurements of millimeter-wave telescopes for LiteBIRD
Speaker: Hayato Takakura, Japan Aerospace Exploration Agency
Abstract: Characterization of the antenna beam patterns is one of the key issues in the development of a wide-field telescope for the next-generation CMB experiments. Laboratory measurements of the telescope antennas can be conducted using compact antenna test range (CATR) or near-field methods. The former uses a plane-wave source rotated near the telescope aperture and enables quick measurements of the main beams, near sidelobes and polarization angles (H. Takakura+, JATIS 2023). The latter method, which measures the electric field (amplitude and phase) near the aperture and decomposes it into plane waves with different angular direction, enables antenna pattern measurements including the far sidelobes in a small, controlled environment.
For the case of LiteBIRD, a JAXA-led space-borne CMB experiment for the early 2030s, we performed experimental verification of the wide-field optical designs by near-field measurements of prototype antennas. Both for reflective and refractive designs, we obtained the antenna patterns with a 70 dB dynamic range, with their far-sidelobe features consistent with simulations (H. Takakura+, IEEE TST 2019; E. Carinos+, SPIE 2024). In addition, by measuring the frequency spectra of the aperture field and converting them into time domain, we separated stray light components with different arrival time at ~0.1 ns resolution (corresponding to 30 mm path length difference) and identified the ones reduced but still reflected by millimeter-wave absorbers (H. Takakura+, SPIE 2022). By applying the near-field measurement method to absorber reflection measurements, we enabled two-dimensional diffuse-reflection measurements, in addition to characterizing specular reflection (F. Miura+, AO 2024).
We also investigated the technical feasibility of near-field measurements in a cryogenic chamber. We implemented a cryogenic-compatible millimeter-wave circuit and motorized stages inside a chamber and scanned the aperture fields of the LFT so that we could measure the aperture fields without being affected by a vacuum window (H. Takakura+, SPIE 2024). By combining a phase-retrieval technique (R. Nakano+ JATIS 2023; R. Takahashi+ SPIE 2024), we expect that measurements of telescopes combined with bolometric detectors are feasible.
10:10 – Holographic field-retrieval method of near-field measurements of wide field-of-view millimeter-wave telescopes using reference phase steps
Speaker: Rion Takahashi, The University of Tokyo, ISAS/JAXA, Japan
Abstract: For observation of cosmic microwave background (CMB), antenna patterns of telescopes including far sidelobes should be carefully characterized. To evaluate far-field antenna patterns at short distances, the near-field measurements have been demonstrated (H. Takakura et al., IEEE TST, 9, 6, 598, 2019). This method requires measuring the phase and amplitude of the electric field on the aperture plane. It can be performed with a compact setup and is advantageous for cryogenic measurements. To perform near-field measurements of telescopes that employ bolometers, several variations of holographic field-retrieval methods have been proposed (e.g. R. Nakano et al., J. Astron. Telesc. Instrum. Syst., 9, 2, 2023).
We present the one using phase steps of the reference waves, which does not require a fine frequency sweeping nor fine-tuning of the phase steps. We demonstrated the proposed method using a LiteBIRD LFT 1/4-scaled antenna, which is a crossed Dragone telescope with a field of view of 18 degrees x 9 degrees. The antenna patterns computed from the retrieved aperture fields and those directly measured by the vector near-field measurements agreed mostly down to the -60 dB level, even at the edges of the focal plane (R. Takahashi et al., Proc SPIE 13102-120, 2024). In this presentation, we present the details of the proposed method and the experimental results.
10:30 – POLARBEAR: calibration strategy, systematics simulations and lessons learned
Speaker: Giulio Fabbian, Kavli Institute of Cosmology Cambridge, UK
Abstract: POLARBEAR was one of the leading polarization experiment in the 2010s that delivered the first direct measurement of B-mode of CMB polarization at sub-degree scales. In this talk I will review the approach adopted by the collaboration to characterize the instrument, focusing in particular on the detector and beam calibration. I will show how the instrumental systematics uncertainties have been incorporated in the final measurement through numerical simulations and how similar level of uncertainties are expected to scale for the scientific target of the next generation experiment (e.g. B-modes power spectrum, CMB lensing).
10:50 – Impact of beam far-sidelobes: a calibration related approach
Speaker: Davide Maino, University of Milan, Italy
Abstract: We present a study on the impact of beam far-sidelobes on CMB polarisation measurements with particular attention to B-modes detection. Using the latest up-to-date optical simulations for LiteBird project including also the effects of some of the payload structures – namely V-Grooves – we perform full mission galactic signal convolution, assuming no Half-wave plate, with different kind of cuts in the beam response. These are based either on the angular distance from the main pointing direction or on the beam power level which is much more related to the actual beam calibration measurements. We consider all the MHFT frequencies selecting three pixels at each frequency that would be representative of the expected variations in the beam shape along the focal plane. Residual B-modes power spectra induced by unaccounted signal from galactic sidelobes are compared to the expected cosmic variance which is our actual knowledge limit. A final impact on the expected bias in the estimation of r tensor-to-scalar ration is also presented.
11:10 – 11:40, Coffee Break, U6 Building
Chair: Alexandre Adler, USA
11:40 – Is beam chromaticity important for the large-scale B-mode spectra of the SO SATs?
Speaker: Nadia Dachlythra, University of Milano-Bicocca, Italy
Abstract: The telescopes employed by CMB experiments are sensitive to a finite range of frequencies. A single bolometric detector can have a frequency bandwidth of approximately 20%. This means that it is sensitive to photons with frequencies spanning a ±10% frequency range around a nominal band-center frequency. The spatial response of our instrument, the beam, which is largely determined by the telescope, also varies with frequency. Standard analysis of CMB data will frequently ignore the frequency dependence of the beam response, so-called beam chromaticity. This can cause issues when the analysis needs to account for signal components coming from sources with different spectral energy distributions (SEDs), such as thermal emission from dust, synchrotron radiation, or the cosmic microwave background. To assess the overall beam chromaticity impact on the forecasted accuracy of the cosmological analysis, we employ a parametric power-spectrum-based foreground component separation algorithm, namely BBPower [Wolz et al., 2023], to which we provide beam-convolved time domain simulations performed with beamconv [Duivenvoorden et al., 2018]. We evaluate the resulting bias on the tensor-to-scalar ratio and the foreground parameters as a function of the complexity of the assumed foreground model and introduce some degree of bandpass uncertainty, which we approximate with a straightforward error model for the bandpass shape. The work presented in this talk focuses specifically on the Simons Observatory (SO) Small Aperture Telescopes (SATs) but can, in principle, be generalized to any ground-based or satellite instrument.
12:00 – Observations of the early Universe at millimeter wavelengths: The Grenoble GIS Contribution
Speaker: Andrea Catalano, LPSC – CNRS, Grenoble, France
Abstract: After two decades of great advances in the observation of the Universe at millimeter wavelengths, our understanding of the standard cosmology model makes it possible to constrain the cosmological parameters. However, the current model remains unsatisfactory. The next generation of experiments must therefore not only achieve greater precision and unambiguous detection of the B modes of the cosmic microwave background, but also precisely measure its spectral distortion. The LPSC, Institut Néel, IPAG and IRAM laboratories are driving forces in the preparation of this new generation, particularly with regard to Kinetic Inductance Detectors (KID), their photometric and polarisation validation, related instrumentation and calibration. In this talk, we will review the main results of the operational instruments as NIKA2 and Concerto and the perspectives on the incoming activities.
12:20 – Polarization measurements and calibration strategies with KIDs for the next generation of CMB telescopes
Speaker: Sofia Savorgnano, LPSC – CNRS, Grenoble, France
Abstract: The ambitious goal of detecting CMB B-modes of polarization, pursued by experiments like the Simons Observatory and LiteBIRD, demands thorough characterization of systematic effects. The PolarKID project, funded by CNES (2023–2025), aims to address this challenge by testing filled array LEKIDs for controlling these effects in polarimetry. In this presentation, I will discuss polarization measurements at 2 mm and 1 mm bandwidths using LEKIDs cooled to 150 mK, arranged perpendicularly with the beam split by a 45º linear polarizer. The cryostat housing the arrays is optically coupled to a 30 K sky simulator, in front of which we scan extended polarized sources and we retrieve their polarization angles. By analyzing the systematic effects impacting these measurements, we demonstrate the setup’s validity for future experiments. In the context of polarization calibration, I will also present preliminary results from the COSMOCal project, focusing on the first tests of the interface between the NIKA2 instrument and the COSMOCal calibrator for large ground-based telescopes.
12:40 – Simulation and analysis of HWP and TES non-idealities for CMB space missions
Speaker: Silvia Micheli, Sapienza University of Rome, Italy
Abstract: A common feature of next generation CMB experiments is the use of a large number of high-sensitive detectors over a range of frequencies and rotating half-wave plates to measure the B-modes polarization. As our target signal is extremely faint, it is also crucial to properly model and correct instrumental systematic effects that can contaminate polarization measurements. We consider a LiteBIRD-like experiment to develop a simulation pipeline which can be used to build timestreams including some of the HWP and detectors non-idealities. In this way, we can propagate systematic effects up to the final sky maps and to the estimation of the tensor-to-scalar ratio. Following a conventional approach, which relies on comparing ideal CMB maps with contaminated CMB maps, we are able to understand the impact of several systematics and develop appropriate mitigation techniques.
13:00 – TES bolometer non-linearity: an (incomplete) review
Speaker: Tommaso Ghigna, QUP-KEK, Japan
Abstract: Several upcoming CMB (Cosmic Microwave Background) experiments are planning to deploy between a few thousand and a few hundred thousand antenna-coupled TES (Transition-Edge Sensors) bolometers in order to drastically increase sensitivity and unveil the B-mode signal. Traditionally we rely on a linear approximation to convert the electronic readout data to optical power incident on the TES detector. However, this approximation is only true under perfect voltage bias conditions and for small signals. In recent years, results from a few experiments (for example POLARBEAR and EBEX) have found non-zero non-linearity levels that need to be properly accounted for to avoid biasing the data. Moreover, TES non-linear response may couple to other spurious signals and even further contaminate the data. While these effects are not fully understood yet and are dependent on the exact experiment implementation, in this talk we will review the current understanding of TES bolometer physics and recent results concerning TES non-linearity and some proposed methods to mitigate these effects.
13:20 – 14:20, Lunch at SottoSopra Restaurant
14:20 – 16:00: Hands-on Tutorial – CMB data analysis and calibration on rectangular pixels with Python
Speaker: Andrea Zonca, San Diego Supercomputer Center, USA
Abstract: In this tutorial we will cover the basics of simulating toy datasets for a CMB instrument using tools provided by the Python library pixell (2D-array maps with rectangular pixels), we will simulate CMB emission, foregrounds, include the effect of beam and noise and then calibrating the transfer function and the noise bias. Basic knowledge of Python is required to follow along. Attendees will execute code in Jupyter Notebooks.
16:00 – 16:30, Coffee Break
14:20 – 16:00: Hands-on Tutorial – Time-domain calibration using simulated planet scans
Speaker: Alexandre Adler (UC Berkeley/LBNL, USA) & Nadia Dachlythra (Uni. of Milano-Bicocca, Italy)
Abstract: In this tutorial, we will use simulated planet scans to fit the telescope’s pointing, beam parameters, and gain. We will do so step-by-step by running a Jupyter notebook but we will also have all the outputs precomputed and stored. We will experiment with different sources and noise levels and discuss important factors that one needs to consider when designing a time-domain calibration pipeline. Note that, even though the simulated data we will employ have been produced assuming specifically the SO SAT telescope, the tutorial will only require the use of standard open-access Python modules.
16:00 – 16:30, Coffee Break
18:30 – Poster Session
19:30 – Social Dinner
Day 4, Thursday, Nov. 7th
Weekly Overview | Day 1 | Day 2 | Day 3 | Day 4 | Day 5
9:00-9:30, Breakfast
Chair: Alessia Ritacco, Roma Tor Vergata, Italy
9:30 – Simons Observatory Pointing from Template Fitting
Speaker: Saianeesh Harridas, University of Pennsylvania, USA
Abstract: The Simons Observatory is a CMB experiment nominally consisting of three Small Aperture Telescopes (SATs) and one Large Aperture Telescope (LAT). In order to produce high quality maps and fully characterize the instruments, well-understood pointing for each detector is required. Here we show how templates derived from physical optics are used to constrain the pointing of the currently commissioning SATs
9:50 – Calibration techniques for a CMB polarimeter using a cryogenic continuously-rotating half-wave plate
Speaker: Samuel Day-Weiss, Princeton University, USA
Abstract: The Simons Observatory Small Aperture Telescopes (SATs) are a new set of three 0.5m refractive polarimeters now operating on the Chajnantor Plateau in the Atacama desert in Chile to measure the polarization anisotropy of the CMB at degree scales. In contrast to experiments on satellite missions and in the South Pole, atmospheric fluctuations at the observation site on Chajnantor are difficult to model, requiring mitigation techniques to measure low ell modes on the sky, for which the SATs employ a continuously-rotating half-wave plate polarization modulator (CHWP). This talk will present an overview of preliminary calibration efforts for one of the 90/150 GHz SATs, focusing on advantages and challenges unique to the SATs’ implementation of the CHWP. Topics covered will include polarization beam and pointing systematics, polarization efficiency and absolute angle calibration, and detector gain and responsivity tracking.
10:10 – Probing frequency-dependent half-wave plate systematics for CMB experiments with beamconv full-sky simulations
Speaker: Matteo Billi, Università di Catania, Catania, Italy
Abstract: An attractive approach for reducing spurious polarisation and accurately measuring the weak CMB polarisation is the use of a half-wave plate (HWP). However, real HWPs impede perfectly controlled modulation and indirectly cause a spurious polarised signal of their own. In this talk we use full-sky time-domain simulation produced with the extended version of beamconv code to investigate the interplay between HWP non-idealities and the beams in forthcoming CMB polarisation experiments. Using an optical model for a fiducial spaceborne two-lens refractor telescope, we show how different HWP configurations optimised for dichroic detectors centred at 95 and 150 GHz affect the reconstruction of primordial B-mode polarisation. Particular attention is paid to possible biases arising from the interaction of frequency dependent HWP non-idealities with polarised Galactic dust emission and the interaction between the HWP and the instrumental beam. To this end, we have extended the capabilities of the publicly available beamconv code to produce time-domain simulations that include both HWP non-idealities and realistic full-sky beam convolution. Our analysis shows how certain achromatic HWP configurations produce significant systematic polarisation angle offsets that vary for sky components with different frequency dependence. Our analysis also demonstrates that once we account for interactions with HWPs, realistic beam models with non-negligible cross-polarisation and sidelobes will cause significant B-mode residuals that will have to be extensively modelled in some cases.
10:30 – Polarization Modulator Unit: angular accuracy and wobbling characterization
Speaker: Giulia Barbieri Ripamonti, Sapienza University of Rome, Italy
Abstract: The main target of the most recent CMB surveys is the detection of the polarized signal of the Cosmic Microwave Background. Since the polarized component is very weak, it is mandatory to modulate the signal. Thus, the Polarization Modulator Unit (PMU) is a fundamental component for reducing 1/ f noise and mitigating spurious polarization.
We are currently developing the PMU for both the balloon-borne LSPE/SWIPE experiment, and the Mid- and High- Frequency Telescopes (MHFT) of the LiteBIRD space mission. The PMU consists of a half-wave plate, levitating and rotating on superconducting magnetic bearing, operating in a cryogenic environment. It is crucial to monitor the dynamical behaviour of the system during the rotation, as deviations from ideal motion can introduce systematic effects during the measurements. In our implementation, two optical encoders and three capacitive sensors allow us to monitor the rotation and to retrieve the HWP angular position during the rotation. In order to minimize systematic effects, the rotation must be kept as stable as possible, but it is even more critical to reconstruct the HWP angle with high fidelity. Specifically, the angular position of the HWP must be reconstructed with an accuracy of the order of ∼ 0.1′, to minimize the leakage from E-modes to B-modes. We obtained this level of reconstruction accuracy for rotation frequencies between 0.3 Hz and 1 Hz, which is the typical range for the measurements.
10:50 – Towards a parametric model to describe half-wave-plate non idealities for primordial B-modes detection
Speaker: Ema Tsang King Sang, APC Paris, France
Abstract: I’ll present a parametric model of the continuously rotating half-wave plate (HWP) used in cutting-edge CMB polarization experiments like the Simons Observatory and LiteBIRD. We explore how the frequency- and geometry-dependent response of these optics is characterized by deriving their Mueller matrices. Our analysis reveals that simplifying the extraction of Stokes parameters through basic demodulation of raw time-ordered data can introduce biases, especially if the color-dependence of the HWP response is neglected. This oversight leads to polarization leakage, which can have a significant impact on the precision of component separation and ultimately on the estimation of cosmological parameters, such as the tensor-to-scalar ratio. To address this challenge, I’ll discuss a JAX-based time-domain approach to component separation that models both the sky components and their spectral energy distributions, incorporating the non-ideal HWP response while allowing for marginalization over uncertain hardware parameters
11:10 – 11:40, Coffee Break
Chair: Johanna Nagy, Case Western Reserve University, USA
11:30 – Impact of half-wave plate non-idealities on the observed CMB polarization
Speaker: Marta Monelli, Max Planck Institute for Astrophysics, Garching, Germany
Abstract: Half-wave plates (HWPs) are becoming a popular choice of polarization modulator in CMB experiments due to several advantages, but their non-idealities represent an additional source of systematics. Understanding how the non-idealities can affect the information we aim to extract from CMB polarization is a necessary step towards developing sound design recommendations, calibration requirements and mitigation strategies. One way to achieve this goal is to perform end-to-end simulations, followed by comprehensive analysis. Another way is to develop analytical descriptions that are, by definitions, approximate but better suited to gain some intuition about the problem at hand. In this talk, I’ll focus on the latter and present a simple semi-analytical framework to propagate HWP non-idealities through map-making and component separation, and show how this approach can help us better understand how they affect the inferred cosmological parameters.
12:00 – Bandpass calibration using a Frequency-selectable Laser Source (FLS)
Speaker: Shreya Sutariya, University of Chicago, USA
Abstract: The advances in sensitivity being brought about by projects like Simons Observatory and CMB-S4 will require improvements on bandpass uncertainties to levels as small as 0.1% to fully realize the astrophysical potential of the data. The current state of the art calibration instrument in the field, the Fourier Transform Spectrometer (FTS), provides bandpass uncertainties at the few percent level. We present a new approach to millimeter wave bandpass calibration. This calibration system, called the Frequency-selectable
Laser Source (FLS) uses an ultra-broadband coherent source which is capable of emitting from 20 GHz to 1.2 THz with a step size as small as 10 MHz. We feed this output into an achromatic attenuator built from absorbing prisms that allows for power variability. We present the design of this system, a spectral calibration of a 220/280 GHz detector from Simons Observatory including a comparison to FTS measurements, and a characterization of the source’s power variation with frequency. These results show that this system compliments measurements using the FTS, particularly in the investigation of small signals and for the complimentary systematics. This approach offers a promising avenue toward the sub-percent calibration accuracy needed for future measurements.
12:20 – Setting requirements on out-of-band rejection for next generation CMB experiments
Speaker: Louise Mousset, LPENS, Paris, France
Abstract: Next generation CMB experiments have very stringent constraints to achieve the required sensitivity to target polarization B-modes. In this work, we intend to set requirements on out-of-band rejection level, meaning frequencies outside the telescope band-pass. We follow a global approach, taking into account thermal aspects and detector chain constraints. The method developed is applied to the Medium- and High-Frequency Telescopes (MHFT) of the LiteBIRD satellite. I will first present the performance code used in this study which computes the sensitivity on the tensor-to-scalar ratio for a given instrument design. Then I will focus on the requirements that we derived for out-of-band rejection level.
12:40 – Crosstalk in Microwave Frequency Multiplexing Readout Systems
Speaker: Toby Satterthwaite, Stanford University, USA
Abstract: Construction of next-generation CMB telescopes has necessitated constructing receivers with a high density of superconducting bolometers. Reading out this unprecedented number of detectors requires breakthrough technology to reach high multiplexing factors. The SLAC Microresonator RF (SMuRF) readout system has been developed to achieve this goal using microwave SQUID multiplexing. The Simons Observatory, a set of CMB telescopes located at 5200 m in Chile’s Atacama Desert, is the largest deployment of this technology for astronomy to date. However, with this large-scale deployment comes unique challenges in understanding new systematic effects; crosstalk in the system may present in new ways. This talk will discuss ongoing work of modeling this type of crosstalk, and understanding its implications for CMB science.
13:00 – LEO-CalSat for the Calibration of W-band Ground-Based CMB Polarization Experiments
Speaker: Francisco Javier (Patxi) Casas, Instituto de Física de Cantabria (IFCA), Spain
Abstract: The new generation of ground- and space-based CMB telescopes requires very precise calibration processes. In general, celestial polarized sources like Tau-A are not characterized with the required accuracy. This is the main motivation of several proposals to develop well-known artificial signal sources onboard flying platforms, to have the possibility of observing them from the telescopes’ far-field.
In this communication we propose the use of an W-band polarized signal source onboard a calibration satellite, flying in a Low-Earth Orbit (LEO). This will allow the calibration of ground-based CMB polarization experiments with an improved accuracy considering celestial sources like Tau-A. During calibration, the sources on-board LEO-CalSat can emit purely polarized microwave radiation from the far field towards the CMB telescopes. Additionally, LEO-CalSat can also help for the calibration of space-missions, thanks to a better characterization of the polarized celestial sources, while increasing the TRL for the future development of a calibration satellite at L2.
Several possibilities in terms of launchers (Spectrum suttles and/or MIURA) and satellite options (microSATs like UPMSat-4 or cubeSATs) are being considered. Currently we have an expected launching date of a 400Km altitude LEO-CalSat, during the first half of 2026.
In our collaboration the UPM group is in charge of the satellite design and development, while the IFCA group is in charge of the payload signal source.
13:20 – 14:20, Lunch at SottoSopra Restaurant
15:30 – 19:00: ORGANIZED VISITS
Day 5, Friday, Nov. 8th
Weekly Overview | Day 1 | Day 2 | Day 3 | Day 4 | Day 5
9:00-9:30, Breakfast
Chair: François Boulanger, LPENS, Paris, France
9:30 – Self-calibration of instrumental polarization angles in the case of LiteBIRD
Speaker: Patricia Diego Palazuelos, Max Planck Institute for Astrophysics, Garching, Germany
Abstract: The success of current- and next-generation CMB experiments will demand unparalleled accuracy in the calibration of the detectors’ polarization angle. As opposed to calibrating against astrophysical or artificial sources, in this talk, we will review the self-calibration of polarisation angles by nulling the measured EB spectra. We will focus on the specific case of the LiteBIRD mission, a JAXA-led satellite for measurement of the CMB polarization at large angular scales in the full sky from 34 to 448 GHz. Nevertheless, this methodology also applies to the calibration of ground-based experiments. After presenting the methodology, we will assess the impact of Galactic synchrotron and dust EB in polarization angle estimation, discussing the advantages and disadvantages of dealing with foreground emission in a model-independent or model-dependent way. Finally, we will also comment on the challenges of self-calibrating polarization angles in the presence of other instrumental systematics.
9:50 – The SciPol project: caracterizing and mitigating the instrumental, astrophysical and environmental systematics effects
Speaker: Josquin Errard, APC/CNRS, Paris, France
Abstract: I present some of the studies we currently undertake in Paris, within the ERC SciPol project, on the interaction between calibration (systematics) and Galactic foregrounds cleaning in the context of inflationary B-modes characterization.
10:10 – Requirements on systematic effects calibration with component separation
Speaker: Florie Carralot, SISSA, Trieste, Italy
Abstract: The presence of systematic effects is one of the major challenges for the measurement of CMB B-modes. Some systematic effects are subject to on-flight calibration with astrophysical observables, such as polarization angles. For other systematic effects, it is needed to set calibration requirements beforehand, these allowing to mitigate the impact on the tensor-to-scalar ratio estimation and reach the scientific goal of the mission. In this presentation, we propose general way to derive calibration requirements, that could be applied to any systematic effects. Furthermore, we assess to what extent the component separation approach we consider influences the calibration requirements.
10:30 – Cosmic Birefringence and the calibration requirements necessary by next generation of CMB experiments
Speaker: Toshiya Namikawa, Kavli IPMU, Japan
Abstract: Cosmic birefringence — a rotation of the linear polarization plane of the CMB as they travel through space — is a key observational effect on CMB as it provides a way to search for parity-violating physics in cosmology. Recent measurements of the EB cross-power spectrum from the Planck polarization map suggest a tantalizing hint of cosmic birefringence. A possible candidate for the origin of cosmic birefringence is pseudoscalar “axionlike” fields. In this talk, I will first brifely review the current status of cosmic birefringence measurements and required accuracy of the miscalibration angle to confirm the signal. I will also discuss the cases if axionlike fields have time evolution where the required accuracy of the miscalibration angle could be significantly relaxed.
10:50 – A Framework to Mitigate Foregrounds and Systematic Effects for Tensor-to-Scalar Ratio and Birefringence Angle Measurements using Calibration Priors Optimally
Speaker: Baptiste Joste, Kavli IPMU, Japan
Abstract: Precise measurements of the faint primordial B-modes originating from cosmological inflation (parameterized by r), or of EB correlations coming from parity-violating mechanisms in the Universe (parameterized by the isotropic cosmic birefringence angle, β), require meticulous attention to the removal of Galactic foregrounds and the mitigation of systematic effects, as well as the interplay between the two.
In this talk I will present the method developed in Jost et al. 2023 (PRD), where we address this interplay by developing a map-based parametric component separation approach that considers polarization angle miscalibration and incorporates calibration priors. This framework propagates statistical and systematic errors from spectral and instrumental parameters to estimate r and β. It also makes the most out of prior information by combining different measurements on different frequency channels, and allows retrieving r without being impacted by polarization angle miscalibration.
11:10 – 11:40, Coffee Break
11:40 – 12:50: Hands-on Tutorial and Final Discussions
12:50 – Concluding remarks
Speaker: Federico Nati, University of Milano-Bicocca, Italy
Weekly Overview | Day 1 | Day 2 | Day 3 | Day 4 | Day 5