arXiv subjects

F. Pajot

Publications and source records attributed to F. Pajot.

At least 19 recordsLinked to original sources

arXiv2023

Measuring the CMB primordial B-modes with Bolometric Interferometry

The Q&U Bolometric Interferometer for Cosmology (QUBIC) is the first bolometric interferometer designed to measure the primordial B-mode polarization of the Cosmic Microwave Background (CMB). Bolometric interferometry is a novel technique that combines the sensitivity of bolometric detectors with the control of systematic effects that is typical of interferometry, both key features in the quest for the faint signal of the primordial B-modes. A unique feature is the so-called "spectral imaging", i.e., the ability to recover the sky signal in several sub-bands within the physical band during data analysis. This feature provides an in-band spectral resolution of \Delta{\nu}/{\nu} \sim 0.04 that is unattainable by a traditional imager. This is a key tool for controlling the Galactic foregrounds contamination. In this paper, we describe the principles of bolometric interferometry, the current status of the QUBIC experiment and future prospects.

astro-ph.CO↗

arXiv2023

A case study of early galaxy cluster with the Athena X-IFU

Context: Observations of the hot gas in distant clusters of galaxies, though challenging, are key to understand the role of intense galaxy activity, super-massive black hole feedback and chemical enrichment in the process of massive halos assembly. Aims: We assess the feasibility to retrieve, using X-ray hyperspectral data only, the thermodymamical hot gas properties and chemical abundances of a $z=2$ galaxy cluster of mass M500=7 x $10^{13} M_{\odot}$, extracted from the Hydrangea hydrodynamical simulation. Methods: We create mock X-ray observations of the future X-ray Integral Field Unit (X-IFU) onboard the Athena mission. By forward-modeling the measured 0.4-1 keV surface brightness, the projected gas temperature and abundance profiles, we reconstruct the three-dimensional distribution for the gas density, pressure, temperature and entropy. Results: Thanks to its large field-of-view, high throughput and exquisite spectral resolution, one X-IFU exposure lasting 100ks enables reconstructing density and pressure profiles with 20% precision out to a characteristic radius of R500, accounting for each quantity's intrinsic dispersion in the Hydrangea simulations. Reconstruction of abundance profiles requires both higher signal-to-noise ratios and specific binning schemes. We assess the enhancement brought by longer exposures and by observing the same object at later evolutionary stages ($z=1-1.5$). Conclusions: Our analysis highlights the importance of scatter in the radially binned gas properties, which induces significant effects on the observed projected quantities. The fidelity of the reconstruction of gas profiles is sensitive to the degree of gas components mixing along the line-of-sight. Future analyses should aim at involving dedicated hyper-spectral models and fitting methods that are able to grasp the complexity of such three-dimensional, multi-phase, diffuse gas structures.

astro-ph.CO↗

arXiv2022

Status of QUBIC, the Q&U Bolometer for Cosmology

The Q&U Bolometric Interferometer for Cosmology (QUBIC) is a novel kind of polarimeter optimized for the measurement of the B-mode polarization of the Cosmic Microwave Back-ground (CMB), which is one of the major challenges of observational cosmology. The signal is expected to be of the order of a few tens of nK, prone to instrumental systematic effects and polluted by various astrophysical foregrounds which can only be controlled through multichroic observations. QUBIC is designed to address these observational issues with a novel approach that combines the advantages of interferometry in terms of control of instrumental systematics with those of bolometric detectors in terms of wide-band, background-limited sensitivity.

astro-ph.IM↗

arXiv2022

X-IFU/Athena view of the most distant galaxy clusters in the Universe

The X-ray Integral Field Unit (X-IFU) on-board the second large ESA mission ''Athena'' will be a high spatial (5'') and spectral (2.5eV) resolution X-ray imaging spectrometer, operating in the 0.2-12 keV energy band. It will address the science question of the assembly and evolution through cosmic time of the largest halos of matter in the Universe, groups and clusters of galaxies. To this end, we present an on-going feasibility study to demonstrate the X-IFU capabilities to unveil the physics of massive halos at their epoch of formation. Starting from a distant (z=2) group of galaxies ($M_{500} = 7\cdot 10^{13} M_\odot/h$) extracted from the HYDRANGEA cosmological and hydrodynamical numerical simulations, we perform an end-to-end simulation of X-IFU observations. From the reconstruction of the global, 1D and 2D quantities, we plan to investigate the various X-IFU science cases for clusters of galaxies, such as the chemical enrichment of the intra-cluster medium (ICM), the dynamical assembly of groups and clusters and the impact of feedback from galaxy and super-massive black hole evolution.

astro-ph.CO↗

arXiv2022

Performance of the polarization leakage correction in the PILOT data

The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (PILOT) is a balloon-borne experiment that aims to measure the polarized emission of thermal dust at a wavelength of 240 um (1.2 THz). The PILOT experiment flew from Timmins, Ontario, Canada in 2015 and 2019 and from Alice Springs, Australia in April 2017. The in-flight performance of the instrument during the second flight was described in Mangilli et al. 2019. In this paper, we present data processing steps that were not presented in Mangilli et al. 2019 and that we have recently implemented to correct for several remaining instrumental effects. The additional data processing concerns corrections related to detector cross-talk and readout circuit memory effects, and leakage from total intensity to polarization. We illustrate the above effects and the performance of our corrections using data obtained during the third flight of PILOT, but the methods used to assess the impact of these effects on the final science-ready data, and our strategies for correcting them will be applied to all PILOT data. We show that the above corrections, and in particular that for the intensity to polarization leakage, which is most critical for accurate polarization measurements with PILOT, are accurate to better than 0.4 % as measured on Jupiter during flight#3.

astro-ph.IM↗

arXiv2021

QUBIC IV: Performance of TES Bolometers and Readout Electronics

A prototype version of the Q & U bolometric interferometer for cosmology (QUBIC) underwent a campaign of testing in the laboratory at Astroparticle Physics and Cosmology laboratory in Paris (APC). The detection chain is currently made of 256 NbSi transition edge sensors (TES) cooled to 320 mK. The readout system is a 128:1 time domain multiplexing scheme based on 128 SQUIDs cooled at 1 K that are controlled and amplified by an SiGe application specific integrated circuit at 40 K. We report the performance of this readout chain and the characterization of the TES. The readout system has been functionally tested and characterized in the lab and in QUBIC. The low noise amplifier demonstrated a white noise level of 0.3 nV.Hz^-0.5. Characterizations of the QUBIC detectors and readout electronics includes the measurement of I-V curves, time constant and the noise equivalent power. The QUBIC TES bolometer array has approximately 80% detectors within operational parameters. It demonstrated a thermal decoupling compatible with a phonon noise of about 5.10^-17 W.Hz^-0.5 at 410 mK critical temperature. While still limited by microphonics from the pulse tubes and noise aliasing from readout system, the instrument noise equivalent power is about 2.10^-16 W.Hz^-0.5, enough for the demonstration of bolometric interferometry.

astro-ph.IM↗

arXiv2020

QUBIC I: Overview and ScienceProgram

The Q $\&$ U Bolometric Interferometer for Cosmology (QUBIC) is a novel kind of polarimeter optimized for the measurement of the B-mode polarization of the Cosmic Microwave Background (CMB), which is one of the major challenges of observational cosmology. The signal is expected to be of the order of a few tens of nK, prone to instrumental systematic effects and polluted by various astrophysical foregrounds which can only be controlled through multichroic observations. QUBIC is designed to address these observational issues with a novel approach that combines the advantages of interferometry in terms of control of instrumental systematic effects with those of bolometric detectors in terms of wide-band, background-limited sensitivity. The QUBIC synthesized beam has a frequency-dependent shape that results in the ability to produce maps of the CMB polarization in multiple sub-bands within the two physical bands of the instrument (150 and 220 GHz). These features make QUBIC complementary to other instruments and makes it particularly well suited to characterize and remove Galactic foreground contamination. In this article, first of a series of eight, we give an overview of the QUBIC instrument design, the main results of the calibration campaign, and present the scientific program of QUBIC including not only the measurement of primordial B-modes, but also the measurement of Galactic foregrounds. We give forecasts for typical observations and measurements: with three years of integration on the sky and assuming perfect foreground removal as well as stable atmospheric conditions from our site in Argentina, our simulations show that we can achieve a statistical sensitivity to the effective tensor-to-scalar ratio (including primordial and foreground B-modes) $\sigma(r)=0.015$.

astro-ph.IM↗

arXiv2020

QUBIC II: Spectro-Polarimetry with Bolometric Interferometry

Bolometric interferometry is a novel technique that has the ability to perform spectral imaging. A bolometric interferometer observes the sky in a wide frequency band and can reconstruct sky maps in several sub-bands within the physical band in post-processing of the data. This provides a powerful spectral method to discriminate between the cosmic microwave background (CMB) and astrophysical foregrounds. In this paper, the methodology is illustrated with examples based on the Q \& U Bolometric Interferometer for Cosmology (QUBIC) which is a ground-based instrument designed to measure the B-mode polarization of the sky at millimeter wavelengths. We consider the specific cases of point source reconstruction and Galactic dust mapping and we characterize the point spread function as a function of frequency. We study the noise properties of spectral imaging, especially the correlations between sub-bands, using end-to-end simulations together with a fast noise simulator. We conclude showing that spectral imaging performance are nearly optimal up to five sub-bands in the case of QUBIC.

astro-ph.IM↗

arXiv2020

Constraining the origin and models of chemical enrichment in galaxy clusters using the Athena X-IFU

The chemical enrichment of the Universe at all scales is related to stellar winds and explosive supernovae phenomena. Metals produced by stars and later spread at the mega-parsec scale through the intra-cluster medium (ICM) become a fossil record of the chemical enrichment of the Universe and of the dynamical and feedback mechanisms determining their circulation. As demonstrated by the results of the soft X-ray spectrometer onboard Hitomi, high resolution X-ray spectroscopy is the path to to differentiate among the models that consider different metal production mechanisms, predict the outcoming yields, and are function of the nature, mass, and/or initial metallicity of their stellar progenitor. Transformational results shall be achieved through improvements in the energy resolution and effective area of X-ray observatories to detect rare metals (e.g. Na, Al) and constrain yet uncertain abundances (e.g. C, Ne, Ca, Ni). The X-ray Integral Field Unit (X-IFU) instrument onboard the next-generation European X-ray observatory Athena is expected to deliver such breakthroughs. Starting from 100 ks of synthetic observations of 12 abundance ratios in the ICM of four simulated clusters, we demonstrate that the X-IFU will be capable of recovering the input chemical enrichment models at both low ($z = 0.1$) and high ($z = 1$) redshifts, while statistically excluding more than 99.5% of all the other tested combinations of models. By fixing the enrichment models which provide the best fit to the simulated data, we also show that the X-IFU will constrain the slope of the stellar initial mass function within $\sim$12%. These constraints will be key ingredients in our understanding of the chemical enrichment of the Universe and its evolution.

astro-ph.GA↗

arXiv2020

QUBIC VII: The feedhorn-switch system of the technological demonstrator

We present the design, manufacturing and performance of the horn-switch system developed for the technological demonstrator of QUBIC (the $Q$\&$U$ Bolometric Interferometer for Cosmology). This system is constituted of 64 back-to-back dual-band (150\,GHz and 220\,GHz) corrugated feed-horns interspersed with mechanical switches used to select desired baselines during the instrument self-calibration. We manufactured the horns in aluminum platelets milled by photo-chemical etching and mechanically tightened with screws. The switches are based on steel blades that open and close the wave-guide between the back-to-back horns and are operated by miniaturized electromagnets. We also show the current development status of the feedhorn-switch system for the QUBIC full instrument, based on an array of 400 horn-switch assemblies.

astro-ph.IM↗

arXiv2020

QUBIC V: Cryogenic system design and performance

Current experiments aimed at measuring the polarization of the Cosmic Microwave Background (CMB) use cryogenic detector arrays and cold optical systems to boost the mapping speed of the sky survey. For these reasons, large volume cryogenic systems, with large optical windows, working continuously for years, are needed. Here we report on the cryogenic system of the QUBIC (Q and U Bolometric Interferometer for Cosmology) experiment: we describe its design, fabrication, experimental optimization and validation in the Technological Demonstrator configuration. The QUBIC cryogenic system is based on a large volume cryostat, using two pulse-tube refrigerators to cool at ~3K a large (~1 m^3) volume, heavy (~165kg) instrument, including the cryogenic polarization modulator, the corrugated feedhorns array, and the lower temperature stages; a 4He evaporator cooling at ~1K the interferometer beam combiner; a 3He evaporator cooling at ~0.3K the focal-plane detector arrays. The cryogenic system has been tested and validated for more than 6 months of continuous operation. The detector arrays have reached a stable operating temperature of 0.33K, while the polarization modulator has been operated from a ~10K base temperature. The system has been tilted to cover the boresight elevation range 20 deg -90 deg without significant temperature variations. The instrument is now ready for deployment to the high Argentinean Andes.

astro-ph.IM↗

arXiv2020

QUBIC VI: cryogenic half wave plate rotator, design and performances

Inflation Gravity Waves B-Modes polarization detection is the ultimate goal of modern large angular scale cosmic microwave background (CMB) experiments around the world. A big effort is undergoing with the deployment of many ground-based, balloon-borne and satellite experiments using different methods to separate this faint polarized component from the incoming radiation. One of the largely used technique is the Stokes Polarimetry that uses a rotating half-wave plate (HWP) and a linear polarizer to separate and modulate the polarization components with low residual cross-polarization. This paper describes the QUBIC Stokes Polarimeter highlighting its design features and its performances. A common systematic with these devices is the generation of large spurious signals synchronous with the rotation and proportional to the emissivity of the optical elements. A key feature of the QUBIC Stokes Polarimeter is to operate at cryogenic temperature in order to minimize this unwanted component. Moving efficiently this large optical element at low temperature constitutes a big engineering challenge in order to reduce friction power dissipation. Big attention has been given during the designing phase to minimize the differential thermal contractions between parts. The rotation is driven by a stepper motor placed outside the cryostat to avoid thermal load dissipation at cryogenic temperature. The tests and the results presented in this work show that the QUBIC polarimeter can easily achieve a precision below 0.1{\deg} in positioning simply using the stepper motor precision and the optical absolute encoder. The rotation induces only few mK of extra power load on the second cryogenic stage (~ 8 K).

astro-ph.IM↗

arXiv2020

QUBIC III: Laboratory Characterization

A prototype version of the Q & U Bolometric Interferometer for Cosmology (QUBIC) underwent a campaign of testing in the laboratory at Astroparticle Physics and Cosmology in Paris. We report the results of this Technological Demonstrator which successfully shows the feasibility of the principle of Bolometric Interferometry. Characterization of QUBIC includes the measurement of the synthesized beam, the measurement of interference fringes, and the measurement of polarization performance. A modulated and frequency tunable millimetre-wave source in the telescope far-field is used to simulate a point source. The QUBIC pointing is scanned across the point source to produce beam maps. Polarization modulation is measured using a rotating Half Wave Plate. The measured beam matches well to the theoretical simulations and gives QUBIC the ability to do spectro imaging. The polarization performance is excellent with less than 0.5\% cross-polarization rejection. QUBIC is ready for deployment on the high altitude site at Alto Chorillo, Argentina to begin scientific operations.

astro-ph.IM↗

arXiv2020

QUBIC VIII: Optical design and performance

The Q and U Bolometric Interferometer for Cosmology (QUBIC) is a ground-based experiment that aims to detect B-mode polarisation anisotropies in the CMB at angular scales around the l=100 recombination peak. Systematic errors make ground-based observations of B modes at millimetre wavelengths very challenging and QUBIC mitigates these problems in a somewhat complementary way to other existing or planned experiments using the novel technique of bolometric interferometry. This technique takes advantage of the sensitivity of an imager and the systematic error control of an interferometer. A cold reflective optical combiner superimposes there-emitted beams from 400 aperture feedhorns on two focal planes. A shielding system composedof a fixed groundshield, and a forebaffle that moves with the instrument, limits the impact of local contaminants. The modelling, design, manufacturing and preliminary measurements of the optical components are described in this paper.

astro-ph.IM↗

arXiv2020

QUBIC: the Q & U Bolometric Interferometer for Cosmology

The Q & U Bolometric Interferometer for Cosmology, QUBIC, is an innovative experiment designed to measure the polarization of the Cosmic Microwave Background and in particular the signature left therein by the inflationary expansion of the Universe. The expected signal is extremely faint, thus extreme sensitivity and systematic control are necessary in order to attempt this measurement. QUBIC addresses these requirements using an innovative approach combining the sensitivity of Transition Edge Sensor cryogenic bolometers, with the deep control of systematics characteristic of interferometers. This makes QUBIC unique with respect to others classical imagers experiments devoted to the CMB polarization. In this contribution we report a description of the QUBIC instrument including recent achievements and the demonstration of the bolometric interferometry performed in lab. QUBIC will be deployed at the observation site in Alto Chorrillos, in Argentina at the end of 2019.

astro-ph.IM↗

arXiv2019

Towards mapping turbulence in the intra-cluster medium -- II. Measurement uncertainties in the estimation of structure functions

X-ray observations of the hot gas filling the intra-cluster medium provide a wealth of information on the dynamics of clusters of galaxies. The global equilibrium of the ICM is believed to be partially ensured by non-thermal pressure support, notably the dissipation of energy through turbulent motions. Accurate mapping of turbulence using X-ray emission lines is challenging due to the lack of spatially-resolved spectroscopy. Only future instruments such as the X-ray Integral Field Unit (X-IFU) on Athena will have the spatial and spectral resolution to quantitatively investigate the ICM turbulence at all scales. Powerful diagnostics for these studies are line shift and the line broadening maps, and the second-order structure function. When estimating these quantities, instruments will be limited by uncertainties of their measurements, and by the sample variance (aka cosmic variance) of the observation. We extend here the formalism started in our companion paper I to include the effect of statistical uncertainties in the estimation of these line diagnostics, in particular for structure functions. We demonstrate that statistics contribute to the total variance through different terms, which depend on the geometry of the detector, the spatial binning and the nature of the turbulent field. These terms are important when probing the small scales of the turbulence. An application of these equations is performed for the X-IFU, using synthetic turbulent velocity maps of a Coma-like cluster of galaxies. Results are in excellent agreement with the formulas both for the structure function estimation (<3%) and its variance (<10%). The expressions derived here and in paper I are generic, and ensure an estimation of the total errors in any X-ray measurement of turbulent structure functions. They also open the way for optimisations in the upcoming instrumentation and in observational strategies.

astro-ph.CO↗

arXiv2019

The geometry of the magnetic field in the Central Molecular Zone measured by PILOT

We present the first far infrared (FIR) dust emission polarization map covering the full extent Milky Way's Central molecular zone (CMZ). The data, obtained with the PILOT balloon-borne experiment, covers the Galactic Center region $-2\,^\circ<l<2\,^\circ$, $-4\,^\circ<b<3\,^\circ$ at a wavelength of 240 $μ$m and an angular resolution $2.2\,'$. From our measured dust polarization angles, we infer a magnetic field orientation projected onto the plane of the sky that is remarkably ordered over the full extent of the CMZ, with an average tilt angle of $\simeq 22\,^\circ$ clockwise with respect to the Galactic plane. Our results confirm previous claims that the field traced by dust polarized emission is oriented nearly orthogonal to the field traced by GHz radio synchrotron emission in the Galactic Center region. The observed field structure is globally compatible with the latest Planck polarization data at 353 GHz and 217 GHz. Upon subtraction of the extended emission in our data, the mean field orientation that we obtain shows good agreement with the mean field orientation measured at higher angular resolution by the JCMT within the 20 km/s and 50 km/s molecular clouds. We find no evidence that the magnetic field orientation is related to the 100 pc twisted ring structure within the CMZ. We propose that the low polarization fraction in the Galactic Center region and the highly ordered projected field orientation can be reconciled if the field is strong, with a 3D geometry that is is mostly oriented $\simeq 15\,^\circ$ with respect to the line-of-sight towards the Galactic center. Assuming equipartition between the magnetic pressure and ram pressure, we obtain magnetic field strengths estimates as high as a few mG for several CMZ molecular clouds.

astro-ph.GA↗

arXiv2019

PILOT balloon-borne experiment in-flight performance

The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (PILOT) is a balloon-borne experiment aiming at measuring the polarized emission of thermal dust at a wavelength of 240 mm (1.2 THz). A first PILOT flight (flight#1) of the experiment took place from Timmins, Ontario, Canada, in September 2015 and a second flight (flight#2) took place from Alice Springs, Australia in april 2017. In this paper, we present the inflight performance of the instrument during these two flights. We concentrate on performances during flight#2, but allude to flight#1 performances if significantly different. We first present a short description of the instrument and the flights. We determine the time constants of our detectors combining inflight information from the signal decay following high energy particle impacts (glitches) and of our internal calibration source. We use these time constants to deconvolve the data timelines and analyse the optical quality of the instrument as measured on planets. We then analyse the structure and polarization of the instrumental background. We measure the detector response flat field and its time variations using the signal from the residual atmosphere and of our internal calibration source. Finally, we analyze the detector noise spectral and temporal properties. The in-flight performances are found to be satisfactory and globally in line with expectations from ground calibrations. We conclude by assessing the expected in-flight sensitivity of the instrument in light of the above in-flight performances.

astro-ph.IM↗