The Imaging X-ray Polarimetry Explorer (IXPE) will expand the information space for study of cosmic sources, by adding polarization to the properties (time, energy, and position) observed in x-ray astronomy. Selected in 2017 January as a NASA Astrophysics Small Explorer (SMEX) mission, IXPE will be launched into an equatorial orbit in 2021. The IXPE observatory includes three identical x-ray telescopes, each comprising a 4-m-focal-length (grazing-incidence) mirror module assembly (MMA) and a polarization-sensitive (imaging) detector unit (DU). The optical bench separating the MMAs from the DUs is a deployable boom with a tip/tilt/rotation stage for DU-to-MMA (gang) alignment, similar to the configuration used for the NuSTAR observatory. The IXPE mission will provide scientifically meaningful measurements of the x-ray polarization of a few dozen sources in the 2-8 keV band, over the first two years of the mission. For several bright, extended x-ray sources (pulsar wind nebulae, supernova remnants, and an active-galaxy jet), IXPE observations will produce polarization maps indicating the magnetic structure of the synchrotron emitting regions. For many bright pulsating x-ray sources (isolated pulsars, accreting x-ray pulsars, and magnetars), IXPE observations will produce phase-resolved profiles of the polarization degree and position angle.
The Gas Pixel Detector (GPD) is an X-ray polarimeter that exploits the photoelectric effect to measure the polarization and to obtain the image of astrophysical sources. This detector is on board the IXPE (Imaging X-ray Polarimetry Explorer) mission selected by NASA in the framework of the Explorer program scheduled for the launch in 2021. We report on tests carried out with a laboratory prototype of the GPD to verify the performance as a function of the temperature in a large temperature range between 15°C and 40°C.
We present a new simulation framework, XIMPOL, based on the python programming language and the Scipy stack, specifically developed for X-ray polarimetric applications. XIMPOL is not tied to any specific mission or instrument design and is meant to produce fast and yet realistic observation-simulations, given as basic inputs: (i) an arbitrary source model including morphological, temporal, spectral and polarimetric information, and (ii) the response functions of the detector under study, i.e., the effective area, the energy dispersion, the point-spread function and the modulation factor. The format of the response files is OGIP compliant, and the framework has the capability of producing output files that can be directly fed into the standard visualization and analysis tools used by the X-ray community, including XSPEC which make it a useful tool not only for simulating physical systems, but also to develop and test end-to-end analysis chains.
The Imaging X-ray Polarimetry Explorer (IXPE) will be the next SMEX mission launched by NASA in 2021 in collaboration with the Italian Space Agency (ASI). IXPE will perform groundbreaking measurements of imaging polarization in X-rays for a number of different classes of sources with three identical telescopes, finally (re)opening a window in the high energy Universe after more than 40 years since the first pioneering results. The unprecedented sensitivity of IXPE to polarization poses peculiar requirements on the payload calibration, e.g. the use of polarized and completely unpolarized radiation, both on ground and in orbit, and can not rely on a systematic comparison with results obtained by previous observatories. In this paper, we will present the IXPE calibration plan, describing both calibrations which will be performed on the detectors at INAF-IAPS in Rome (Italy) and the calibration on the mirror and detector assemblies which will be carried out at Marshall Space Flight Center in Huntsville, Alabama. On orbit calibrations, performed with calibrations sources mounted on a filter wheel and placed in front of each detector when necessary, will be presented as well.
eXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. Primary goals are the determination of the equation of state of matter at supra-nuclear density, the measurement of QED effects in highly magnetized star, and the study of accretion in the strong-field regime of gravity. Primary targets include isolated and binary neutron stars, strong magnetic field systems like magnetars, and stellar-mass and supermassive black holes. The mission carries a unique and unprecedented suite of state-of-the-art scientific instruments enabling for the first time ever the simultaneous spectral-timing-polarimetry studies of cosmic sources in the energy range from 0.5-30 keV (and beyond). Key elements of the payload are: the Spectroscopic Focusing Array (SFA) - a set of 11 X-ray optics for a total effective area of ∼0.9 m<sup>2</sup> and 0.6 m<sup>2</sup> at 2 keV and 6 keV respectively, equipped with Silicon Drift Detectors offering <180 eV spectral resolution; the Large Area Detector (LAD) - a deployable set of 640 Silicon Drift Detectors, for a total effective area of ∼3.4 m<sup>2</sup>, between 6 and 10 keV, and spectral resolution better than 250 eV; the Polarimetry Focusing Array (PFA) – a set of 2 X-ray telescope, for a total effective area of 250 cm<sup>2</sup> at 2 keV, equipped with imaging gas pixel photoelectric polarimeters; the Wide Field Monitor (WFM) - a set of 3 coded mask wide field units, equipped with position-sensitive Silicon Drift Detectors, each covering a 90 degrees x 90 degrees field of view. The eXTP international consortium includes major institutions of the Chinese Academy of Sciences and Universities in China, as well as major institutions in several European countries and the United States. The predecessor of eXTP, the XTP mission concept, has been selected and funded as one of the so-called background missions in the Strategic Priority Space Science Program of the Chinese Academy of Sciences since 2011. The strong European participation has significantly enhanced the scientific capabilities of eXTP. The planned launch date of the mission is earlier than 2025.
XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to X-ray Astronomy. At the time of
writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the
polarimetry window in high energy Astrophysics after more than 4 decades thanks to a detector that efficiently
exploits the photoelectric effect and to X-ray optics with large effective area. XIPE uniqueness is time-spectrally-spatially-
resolved X-ray polarimetry as a breakthrough in high energy astrophysics and fundamental physics.
Indeed the payload consists of three Gas Pixel Detectors at the focus of three X-ray optics with a total effective
area larger than one XMM mirror but with a low weight. The payload is compatible with the fairing of the Vega
launcher. XIPE is designed as an observatory for X-ray astronomers with 75 % of the time dedicated to a Guest
Observer competitive program and it is organized as a consortium across Europe with main contributions from
Italy, Germany, Spain, United Kingdom, Poland, Sweden.
X-ray polarimetry is a hot topic and, as a matter of fact, a number of missions dedicated to the measurement of the polarization in the ∼2-8 keV energy range with photoelectric devices are under advanced study by space agencies. The Gas Pixel Detector (GPD), developed and continuously improved in Italy by Pisa INFN in collaboration with INAF-IAPS, is the only instrument able to perform imaging polarimetry; moreover, it can measure photon energy and time of arrival. In this paper, we report on the performance of a GPD prototype assembled with flight-like materials and procedures. The remarkably uniform operation over a long period of time assures a straightforward operation in orbit and support the high readiness level claimed for this instrument.
The High Energy cosmic-Radiation Detection (HERD) facility is one of several space astronomy payloads of the cosmic light house program onboard China's Space Station, which is planned for operation starting around 2020 for about 10 years. Beam test with a HERD prototype, to verify the HERD specifications and the reading out method of wavelength shifting fiber and image intensified CCD, was taken at CERN SPS in November, 2015. The prototype is composed of an array of 5*5*10 LYSO crystals, which is 1/40th of the scale of HERD calorimeter. Experimental results on the performances of the calorimeter are discussed.
The Lightweight Asymmetry and Magnetism Probe (LAMP) is a micro-satellite mission concept dedicated for astronomical X-ray polarimetry and is currently under early phase study. It consists of segmented paraboloidal multilayer mirrors with a collecting area of about 1300 cm2 to reflect and focus 250 eV X-rays, which will be detected by position sensitive detectors at the focal plane. The primary targets of LAMP include the thermal emission from the surface of pulsars and synchrotron emission produced by relativistic jets in blazars. With the expected sensitivity, it will allow us to detect polarization or place a tight upper limit for about 10 pulsars and 20 blazars. In addition to measuring magnetic structures in these objects, LAMP will also enable us to discover bare quark stars if they exist, whose thermal emission is expected to be zero polarized, while the thermal emission from neutron stars is believed to be highly polarized due to plasma polarization and the quantum electrodynamics (QED) effect. Here we present an overview of the mission concept, its science objectives and simulated observational results.
We show that meaningful, highly sensitive x-ray polarimetry with imaging capability is possible with a small
mission tailored to the NASA Explorer program. Such a mission—derived from the Imaging X-ray Polarimetry
Explorer (IXPE) proposed to a previous NASA call—takes advantage of progress in light-weight x-ray optics
and in gas pixel detectors to achieve sensitive time-resolved, spectrometric, imaging polarimetry. We outline the
main characteristics and requirements of this mission and provide a realistic assessment of its scientific utility
for modeling point-like and extended x-ray sources and for studying physical processes (including questions of
The Large Area Telescope (LAT) is the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi),
an orbital astronomical observatory that was launched on 11 June 2008. Its tracker is a solid-state instrument
that converts the gamma rays into electron-positron pairs which it then tracks in order to measure the incoming
gamma-ray direction. The tracker comprises 36 planes of single-sided silicon strip detectors, for a total of 73
square meters of silicon, read out by nearly 900,000 amplifier-discriminator channels. The system operates on
only 160 W of conditioned power while achieving > 99% single-plane efficiency within its active area and better
than 1 channel per million noise occupancy. We describe the tracker's design and performance, and discuss in
particular the excellent stability of the hardware response during the first two years of operation on orbit.
The development of micropixel gas detectors, capable to image tracks produced in a gas by photoelectrons,
makes possible to perform polarimetry of X-ray celestial sources in the focus of grazing incidence X-ray telescopes.
HXMT is a mission by the Chinese Space Agency aimed to survey the Hard X-ray Sky with Phoswich detectors, by
exploitation of the direct demodulation technique. Since a fraction of the HXMT time will be spent on dedicated
pointing of particular sources, it could host, with moderate additional resources a pair of X-ray telescopes, each
with a photoelectric X-ray polarimeter (EXP<sup>2</sup>, Efficient X-ray Photoelectric Polarimeter) in the focal plane. We
present the design of the telescopes and the focal plane instrumentation and discuss the performance of this
instrument to detect the degree and angle of linear polarization of some representative sources. Notwithstanding
the limited resources, the proposed instrument can represent a breakthrough in X-ray Polarimetry.
XEUS is a large area telescope aiming to rise X-ray Astronomy to the level of Optical Astronomy in terms of
collecting areas. It will be based on two satellites, locked on a formation flight, one with the optics, one with
the focal plane. The present design of the focal plane foresees, as an auxiliary instrument, the inclusion of a
Polarimeter based on a Micropattern Chamber. We show how such a device is capable to solve open problems
on many classes of High Energy Astrophysics objects and to use X-ray sources as a laboratory for a substantial
progress on Fundamental Physics.
Development of multi-layer optics makes feasible the use of X-ray telescope at energy up to 60-80 keV: in this paper we discuss the extension of photoelectric polarimeter based on Micro Pattern Gas Chamber to high energy X-rays. We calculated the sensitivity with Neon and Argon based mixtures at high pressure with thick absorption gap: placing the MPGC at focus of a next generation multi-layer optics, galatic and extragalactic X-ray polarimetry can be done up till 30 keV.
We report on a large active area (15x15mm2), high channel density (470 pixels/mm2), self-triggering CMOS analog chip that we have developed as pixelized charge collecting electrode of a Micropattern Gas Detector. This device, which represents a big step forward both in terms of size and performance, is the last version of three generations of custom ASICs of increasing complexity. The CMOS pixel array has the top metal layer patterned in a matrix of 105600 hexagonal pixels at 50μm pitch. Each pixel is directly connected to the underneath full electronics chain which has been realized in the remaining five metal and single poly-silicon layers of a standard 0.18μm CMOS VLSI technology. The chip has customizable self-triggering capability and includes a signal pre-processing function for the automatic localization of the event coordinates. In this way it is possible to reduce significantly the readout time and the data volume by limiting the signal output only to those pixels belonging to the region of interest. The very small pixel area and the use of a deep sub-micron CMOS technology has brought the noise down to 50 electrons ENC.
Results from in depth tests of this device when coupled to a fine pitch (50μm on a triangular pattern) Gas Electron Multiplier are presented. The matching of readout and gas amplification pitch allows getting optimal results. The application of this detector for Astronomical X-Ray Polarimetry is discussed. The experimental detector response to polarized and unpolarized X-ray radiation when working with two gas mixtures and two different photon energies is shown. Results from a full MonteCarlo simulation for several galactic and extragalactic astronomical sources are also reported.
We discuss a new class of Micro Pattern Gas Detectors, the Gas Pixel Detector (GPD), in which a complete integration between the gas amplification structure and the read-out electronics has been reached. An Application-Specific Integrated Circuit (ASIC) built in deep sub-micron technology has been developed to realize a monolithic device that is, at the same time, the pixelized charge collecting electrode and the amplifying, shaping and charge measuring front-end electronics. The CMOS chip has the top metal layer patterned in a matrix of 80 μm pitch hexagonal pixels, each of them directly connected to the underneath electronics chain which has been realized in the remaining five layers of the 0.35 μm VLSI technology. Results from tests of a first prototype of such detector with 2k pixels and a full scale version with 22k pixels are presented. The application of this device for Astronomical X-Ray Polarimetry is discussed. The experimental detector response to polarized and unpolarized X-ray radiation is shown. Results from a full MonteCarlo simulation for two astronomical sources, the Crab Nebula and the Hercules X1, are also reported.
X-Ray Polarimetry can be now performed by using a Micro Pattern Gas Chamber in the focus of a telescope. It
requires large area optics for most important scientific targets. But since the technique is additive a dedicated
mission with a cluster of small telescopes can perform many important measurements and bridge the 40 year gap
between OSO-8 data and future big telescopes such as XEUS. POLARIX has been conceived as such a pathfinder.
It is a Small Satellite based on the optics of JET-X. Two telescopes are available in flight configuration and three
more can be easily produced starting from the available superpolished mandrels. We show the capabilities of such
a cluster of telescopes each equipped with a focal plane photoelectric polarimeter and discuss a few alternative
We report on the development of a new higly efficient polarimeter, based on the photoelectric effect in gas, for the 2-10 keV energy range, a particularly interesting band for x-ray astronomy. We derive the polarization information by reconstructing the direction of photoelectron emission with a pixel gas detector. Attention is focused on the algorithms used in data analysis in order to maximize the sensitivity of the instrument. Monte Carlo simulation is also discussed in details.
We report on a new instrument that brings high efficiency to x-ray polarimetry, which is the last unexplored field of x-ray astronomy. It derives the polarization information from the tracks of the photoelectrons imaged by a finely subdivided gas pixel detector. The device can also do simultaneously good imaging, moderate spectroscopy and fast, high rate timing down to 150 eV. Moreover, being truly 2D, it is non dispersive and does not require rotation. The great immprovement of sensitivity will allow direct exploration of the most dramatic objects of the x-ray sky; with integrations of the order of one day we could perform polarimetry of Active Galactic Nuclei at the percent level, a breakthrough in this fascinating window of high energy astrophysics.
A Micropattern detector in the focus of a grazing incidence telescope is nowadays the most powerful tool to perform a sensitive and reliable measurement of the linear polarization of celestial X-ray sources. The actual implementation of such a completely new device results from a trade-off of various factors and can provide a break-through increase of sensitivity with respect to traditional instrumental approaches. The sensitivity depends on the effective area of the optics and the modulation factor and efficiency of the detector. The latter strongly depends on the filling gas through various factors, including the absorption probability, the length of track versus the pixel size, the blurring introduced by the lateral diffusion during the drift. We discuss the impact of the choice of the filling gas on the sensitivity and on the operative band of the instrument, while the noble gases drive the efficiency, the organic quenching gases impact both in reducing the scattering and producing most straight tracks and on reducing diffusion. Some design solution are discussed both for a low energy oriented and high energy oriented polarimeters.
This paper reports the experimentation of a joint use of ground-based radar and satellite radiometer to calibrate and validate passive microwave data for rainfall monitoring. In particular, the utilization of radar vertical profile maps in order to figure out the passive microwave signatures is outlined. The experimentation has been conducted utilizing active microwave data acquired from the Chilbolton radar and passive microwave data acquired from the DMSP SSM/I instruments. The two microwave data type have been processed in order to be overlayable in time and space, and several parameters have been estimated from the SSM/I data. Radar vertical profile maps have been classified to outline the cloud structure and the obtained information have been utilized to make statistical analysis of passive microwave parameters related to rainfall over land. In particular, an attempt to divide the cloud structure into three meaningful layers has been worked out; this is important as the different channels of SSM/I can penetrate in a diverse way cloud structure. The result are in accordance to theory and outline the importance of utilizing radar vertical profiles in order to figure out the passive microwave measurements.
The present work empirically deals with the challenging problem of the integration of data obtained from passive and active microwave sources, in order to develop procedures to suitably calibrate and validate satellite-based passive microwave rainfall algorithms by means of multiparameter radar information over midlatitude areas. SSM/I passive microwave radiometer precipitation related parameters have been analysed against multiparameter radar Zh and Zdr three dimensional maps, obtained from the POLAR-55C multiparameter radar set near Florence, Italy. The main objectives of this work are: to try to better analyse the satellite beam-filling problem and its different channel penetration topic; to design and validate an operational procedure in order to integrate SSMfl and the POLAR -55C data. Starting from radar-derived volumetric information and passive microwave multi-frequency data, we have faced several statistical analyses of the obtained data sets. Results report the effectiveness of Montagnana radar and SSM/I data fusion. In particular, it was outlined the· diverse influence that different vertical profile layers have on radiometer channels. Radar measurements versus SSM/I parameters correlation values may be improved by filtering radar data according to several parameters thresholds, in order to tackle beam-filling problem and statistical issues. Eventually, utilised hydrometeor classification schemes seems not to work properly for a whole stack of CAPPis. Keywords: Microwave, Radar, Data Integration, Vertical structure, Statistical Analysis