Context.
Future weak lensing surveys, such as the
Euclid
mission, will attempt to measure the shapes of billions of galaxies in order to derive cosmological information. These surveys will attain ...very low levels of statistical error, and systematic errors must be extremely well controlled. In particular, the point spread function (PSF) must be estimated using stars in the field, and recovered with high accuracy.
Aims.
The aims of this paper are twofold. Firstly, we took steps toward a nonparametric method to address the issue of recovering the PSF field, namely that of finding the correct PSF at the position of any galaxy in the field, applicable to
Euclid
. Our approach relies solely on the data, as opposed to parametric methods that make use of our knowledge of the instrument. Secondly, we studied the impact of imperfect PSF models on the shape measurement of galaxies themselves, and whether common assumptions about this impact hold true in an
Euclid
scenario.
Methods.
We extended the recently proposed resolved components analysis approach, which performs super-resolution on a field of under-sampled observations of a spatially varying, image-valued function. We added a spatial interpolation component to the method, making it a true 2-dimensional PSF model. We compared our approach to
PSFEx
, then quantified the impact of PSF recovery errors on galaxy shape measurements through image simulations.
Results.
Our approach yields an improvement over
PSFEx
in terms of the PSF model and on observed galaxy shape errors, though it is at present far from reaching the required
Euclid
accuracy. We also find that the usual formalism used for the propagation of PSF model errors to weak lensing quantities no longer holds in the case of an
Euclid
-like PSF. In particular, different shape measurement approaches can react differently to the same PSF modeling errors.
The cosmological surveys that are planned for the current decade will provide us with unparalleled observations of the distribution of galaxies on cosmic scales, by means of which we can probe the ...underlying large-scale structure (LSS) of the Universe. This will allow us to test the concordance cosmological model and its extensions. However, precision pushes us to high levels of accuracy in the theoretical modelling of the LSS observables so that no biases are introduced into the estimation of the cosmological parameters. In particular, effects such as redshift-space distortions (RSD) can become relevant in the computation of harmonic-space power spectra even for the clustering of the photometrically selected galaxies, as has previously been shown in literature. In this work, we investigate the contribution of linear RSD, as formulated in the Limber approximation by a previous work, in forecast cosmological analyses with the photometric galaxy sample of the survey. We aim to assess their impact and to quantify the bias on the measurement of cosmological parameters that would be caused if this effect were neglected. We performed this task by producing mock power spectra for photometric galaxy clustering and weak lensing as is expected to be obtained from the survey. We then used a Markov chain Monte Carlo approach to obtain the posterior distributions of cosmological parameters from these simulated observations. When the linear RSD is neglected, significant biases are caused when galaxy correlations are used alone and when they are combined with cosmic shear in the so-called 3times 2pt approach. These biases can be equivalent to as much as $5\ when an underlying Lambda CDM cosmology is assumed When the cosmological model is extended to include the equation-of-state parameters of dark energy, the extension parameters can be shifted by more than $1\ sigma$.
The development of a new generation of soft gamma-ray telescopes should allow polarimetric measurements of astrophysical sources to be associated with the results from spectroscopy and imaging due to ...the promising developments in polarimetry achieved over the last decade. In this perspective, the advanced surveyor of transient events and nuclear astrophysics mission which includes a narrow field telescope (NFT) that comprises a wide band Laue lens (60-600 keV) associated with a high performance thick and stacked CdZnTe focal plane operating as spectrometer, imager, and scattering polarimeter has been submitted for the ESA Voyage 2050 long term scientific planning preparation. In this context, and with the aim of optimizing the focal plane configuration of an instrument such as NFT, several studies are underway. In particular, with this work we study some performance issues such as polarimeters of segmented semiconductor detectors at room temperature, such as CdZnTe and cadmium telluride (CdTe), by means of a prototype based on two planar CdTe spectroimagers operating in coincidence. The two CdTe detectors are 2-mm-thick crystals with the anode segmented in <inline-formula> <tex-math notation="LaTeX">8\times8 </tex-math></inline-formula> pixels with 2-mm pitch. This prototype configuration allows the Compton polarimetric performance of a spectroimager to be assessed by changing the distance between the two detection layers while operating in the 100-600-keV energy range, thereby allowing the analysis of Compton polarimetry 3-D dependence. The results obtained provide relevant input to the design of large sensitive volume multilayer and 3-D sensitive focal planes.
Nuclear astrophysics, and particularly nuclear emission line diagnostics from a variety of cosmic sites, has remained one of the least developed fields in experimental astronomy, despite its central ...role in addressing a number of outstanding questions in modern astrophysics. Radioactive isotopes are co-produced with stable isotopes in the fusion reactions of nucleosynthesis in supernova explosions and other violent events, such as neutron star mergers. The origin of the 511 keV positron annihilation line observed in the direction of the Galactic Center is a 50-year-long mystery. In fact, we still do not understand whether its diffuse large-scale emission is entirely due to a population of discrete sources, which are unresolved with current poor angular resolution instruments at these energies, or whether dark matter annihilation could contribute to it. From the results obtained in the pioneering decades of this experimentally-challenging window, it has become clear that some of the most pressing issues in high-energy astrophysics and astro-particle physics would greatly benefit from significant progress in the observational capabilities in the keV-to-MeV energy band. Current instrumentation is in fact not sensitive enough to detect radioactive and annihilation lines from a wide variety of phenomena in our and nearby galaxies, let alone study the spatial distribution of their emission. In this White Paper (WP), we discuss how unprecedented studies in this field will become possible with a new low-energy gamma-ray space experiment, called
ASTENA
(Advanced Surveyor of Transient Events and Nuclear Astrophysics), which combines new imaging, spectroscopic and polarization capabilities. In a separate WP (Guidorzi et al.
39
), we discuss how the same mission concept will enable new groundbreaking studies of the physics of Gamma–Ray Bursts and other high-energy transient phenomena over the next decades.
This article reports the proton radiation sensitivity of two 1.0-mm-thick EURORAD ohmic CdTe detectors, irradiated with a low energy proton beam generated in a positron emission tomography (PET) ...cyclotron facility. The CdTe crystals were exposed to a proton radiation field composed of energies of <inline-formula> <tex-math notation="LaTeX">\approx 13.8 </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">\approx 9.7 </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">\approx 5.7 </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">\approx 3.3 </tex-math></inline-formula> MeV, at an average flux of ~<inline-formula> <tex-math notation="LaTeX">10^{8} </tex-math></inline-formula> protons cm −2 s −1 , a total fluence from <inline-formula> <tex-math notation="LaTeX">\approx 2.1 \times 10^{9} </tex-math></inline-formula> up to <inline-formula> <tex-math notation="LaTeX">\approx 4.5 \times 10^{10} </tex-math></inline-formula> protons cm −2 , and an average dose from <inline-formula> <tex-math notation="LaTeX">\approx 5.9 </tex-math></inline-formula> up to <inline-formula> <tex-math notation="LaTeX">\approx 130 </tex-math></inline-formula> Gy, equivalent to the proton fluence accumulated in ~1 up to ~20 years in a low earth orbit (LEO). The impact of the proton radiation field was analyzed through its charge transport properties-the mobility-lifetime product for electrons, (<inline-formula> <tex-math notation="LaTeX">\mu \tau </tex-math></inline-formula>) e , and holes, (<inline-formula> <tex-math notation="LaTeX">\mu \tau </tex-math></inline-formula>) h ,-and spectroscopic properties-the energy resolution and the peak-to-valley ratio, for <inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-ray lines within 60-662 keV. The tested CdTe detectors, with (<inline-formula> <tex-math notation="LaTeX">\mu \tau </tex-math></inline-formula>)<inline-formula> <tex-math notation="LaTeX">_{e} \sim 5 \times 10^{-4} </tex-math></inline-formula> cm 2 V −1 and (<inline-formula> <tex-math notation="LaTeX">\mu \tau </tex-math></inline-formula>)<inline-formula> <tex-math notation="LaTeX">_{h} \sim 3\times \,\,10^{-5} </tex-math></inline-formula> cm 2 V −1 , showed good radiation hardness, with the measured upper-limit of (<inline-formula> <tex-math notation="LaTeX">\mu \tau </tex-math></inline-formula>) e and (<inline-formula> <tex-math notation="LaTeX">\mu \tau </tex-math></inline-formula>) h proton fluence (average dose) sensitivity of <inline-formula> <tex-math notation="LaTeX">\sim 2\times 10^{-15} </tex-math></inline-formula> cm 2 V −1 /protons cm −2 (<inline-formula> <tex-math notation="LaTeX">\sim 7 \times 10^{-7} </tex-math></inline-formula> cm 2 V −1 /Gy) and <inline-formula> <tex-math notation="LaTeX">\sim 3 \times 10^{-16} </tex-math></inline-formula> cm 2 V −1 /protons cm −2 (<inline-formula> <tex-math notation="LaTeX">\sim 1 \times 10^{-7} </tex-math></inline-formula> cm 2 V −1 /Gy), respectively. Up to <inline-formula> <tex-math notation="LaTeX">\approx 130 </tex-math></inline-formula> Gy, no significant degradation of the energy resolution and the peak-to-valley ratio was observed.
CZT drift strip detectors for high energy astrophysics Kuvvetli, I.; Budtz-Jørgensen, C.; Caroli, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2010, Letnik:
624, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Requirements for X- and gamma ray detectors for future High Energy Astrophysics missions include high detection efficiency and good energy resolution as well as fine position sensitivity even in ...three dimensions.
We report on experimental investigations on the CZT drift detector developed DTU Space. It is operated in the planar transverse field (PTF) mode, with the purpose of demonstrating that the good energy resolution of the CZT drift detector can be combined with the high efficiency of the PTF configuration. Furthermore, we demonstrated and characterized the 3D sensing capabilities of this detector configuration.
The CZT drift strip detector (10
mm×10
mm×2.5
mm) was characterized in both standard illumination geometry, Photon Parallel Field (PPF) configuration and in PTF configuration. The detection efficiency and energy resolution are compared for both configurations . The PTF configuration provided a higher efficiency in agreement with calculations. The detector energy resolution was found to be the same (3
keV FWHM at 122
keV) in both in PPF and PTF .
The depth sensing capabilities offered by drift strip detectors was investigated by illuminating the detector using a collimated photon beam of
57Co radiation in PTF configuration. The width (
300
μ
m
FWHM at 122
keV) of the measured depth distributions was almost equal to the finite beam size. However, the data indicate that the best achievable depth resolution for the CZT drift detector is
90
μ
m
FWHM at 122
keV and that it is determined by the electronic noise from the setup.
Two-inch-diameter CdZnTe crystals doped with indium were grown by the boron oxide encapsulated vertical Bridgman technique. The crystals showed large single crystalline yield and low etch pit ...density. The background impurity content was dominated by boron in concentration lower than 1 ppm. High resistivity was obtained and a procedure for contact preparation was developed. The mobility-lifetime product of the material was determined by both X-ray irradiation and photocurrent spectroscopy. The X-ray detector prepared with this material showed good spectroscopic performance.
Great efforts are being presently devoted to the development of CdTe and CdZnTe detectors for a large variety of applications, such as the basic, medical, industrial, and space research. The purpose ...of this work is to present the spectroscopic proper ties of some CZT crystals grown by the boron oxide encapsulated vertical Bridgman method, which has been recently implemented at IMEM-CNR. By this technique the crystal, during the growth, is fully encapsulated by a thin layer of liquid boron oxide, so that the crystal-crucible contact is prevented, thus allowing larger single grains with lower dislocation density to be obtained. Several detectors were realized about 4 mm x 4 mm x 1 mm in size, with two planar gold contacts on both the surfaces realized by an electroless technique. The behavior of these detectors was studied as a function of the bias voltage, irradiation geometry and energy of the interacting photons. Good electron charge collection properties have been demonstrated and electric field distribution has been investigated using the Pockels effect.
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