Compton polarimeters are typically designed to be sensitive only to the azimuthal angle of the scattered photon, ignoring the scattering angle. Such a 2-dimensional reconstruction of the event is pursued for both simplicity and because the polarization of the incident photon influences only the azimuthal response of the instrument. While this is true for on-axis sources, when the source starts to be off-axis of several degrees the azimuthal response of the instrument is effectively a convolution of the azimuthal and polar scattering angles: measuring the latter would provide a better sensitivity and smaller systematic effects. In this contribution, we will present a design which allows to estimate the scattering angle in a Compton polarimeter through the read-out of the light signal at the two ends of scintillator bars. Such a design is being tested with a representative set-up and first results on the performance are presented.
IXPE has been a highly successful mission, opening a new window in X-ray astronomy. IXPE observations have highlighted the importance of polarimetry along with spectroscopy in determining the geometry and physics behind many high-energy emissions from black hole X-ray binaries (BHXRBs), Pulsar Wind Nebulae (PWN), Active Galactic Nuclei (AGN) etc. However, IXPE is just the first step towards future wide band (0.1 to 100 keV) X-ray polarimetry. The future of this field demands larger effective areas, better energy resolution, and broader energy bands. IXPE is barely capable to address key scientific cases such as reflection features in X-ray binaries, molecular clouds around the Galactic Center, radio-quiet AGNs, non-thermal emission regions in supernova remnants etc. To take advantage of the recent advances in X-ray optics, gaseous detectors with different thickness, pressures and gas mixtures would be required. Using next-generation ASICs, like Timepix3, it is possible to have parallel fast readout, providing simultaneous time and charge information for each pixel, enabling 3D imaging of photoelectron tracks. In this article, we explore such a possibility using GridPix detectors.
A new generation of 3D gas detectors is available and applied today, for example, to track particles in accelerator vertex detectors. They apply the concept of Time Projection Chambers to 2D devices. When coupled with a gas system, Timepix3, or the most recent Timepix4, allows for 3D track reconstruction. Such capability promises to improve by far the sensitivity of the present 2D Gas Pixel Detector (GPD) on board the Imaging X-ray Polarimeter Explorer (IXPE), also solving the issue of its large dead time thanks to its parallel read-out. In this framework, we are developing a new simulation software based on the Geant4 tool to be used to develop these devices as a new generation of X-ray polarimeters for astrophysics. Moreover, a new read-out software capable of obtaining a 3D track reconstruction, taking advantage of the Timepix3 time capabilities and using the IXPE GPD legacy, has been developed, which helps improve the polarimetric sensitivity in view of future X-ray missions having on board this kind of detectors.
We have, at last, an observatory dedicated to X-ray polarimetry that has been operational since December 9th, 2021. The Imaging X-ray Polarimetry Explorer (IXPE) is a NASA SMEX mission, in partnership with ASI, based on three X-ray telescopes, each equipped with a polarization-sensitive detector in the focus. An extending boom was deployed in orbit, positioning the detectors at the optimal distance from the optics, which have a 4-meter focal length. The spacecraft is three-axis stabilized, providing power, attitude determination and control, transmission, and commanding capabilities.
After two and a half years of observation, IXPE has detected positive polarization from nearly all classes of celestial sources that emit X-rays. In this report, we describe the IXPE mission, detailing the performance of the scientific instrumentation after 2.5 years of operation. We also present the main astrophysical results and a few examples of scientific performance during flight.
IXPE, the first observatory dedicated to imaging x-ray polarimetry, was launched on Dec 9, 2021 and is operating successfully. A partnership between NASA and the Italian Space Agencey (ASI) IXPE features three x-ray telescopes each comprised of a mirror module assembly with a polarization sensitive detector at its focus. An extending boom was deployed on orbit to provide the necessary 4 m focal length. A three-axis-stabilized spacecraft provides power, attitude determination and control, and commanding. After one year of observation IXPE has measured statistically significant polarization from almost all the classes of celestial sources that emit X-rays. In the following we describe the IXPE mission, reporting on its performance after 1.5 year of operations. We show the main astrophysical results which are outstanding for a SMEX mission.
The Imaging X-ray Polarimetry Explorer (IXPE) mission, done in collaboration between NASA and the Italian Space Agency (ASI), has been successfully detecting x-ray polarization from celestial sources for more than one year. This mission comprises three x-ray optics and three x-ray polarization sensitive detectors. Four calibration sources based on 55Fe nuclides, one producing polarized radiation (at two energies) and three producing unpolarized radiation, are present on board with each detector. In this contribution we present the in-flight monitoring and calibration of IXPE using these sources, with particular regard to the calibrations of the spectral and polarization response. We also show the monitoring of the optics half-power diameter.
In this work, we measured the polarization properties of the X-rays emitted from the X-ray tubes, which were used during the calibration of the instrument onboard Imaging X-ray Polarimetry Explorer (IXPE). X-ray tubes are used as a source of unpolarized X-rays to calibrate the response of the gas pixel detectors to unpolarized radiation. However, even though the characteristic fluorescent emission lines are unpolarized, continuum bremsstrahlung emission can be polarized based on the geometry of the accelerated electrons and emitted photons. Hence, characterizing the contribution of polarized X-rays from bremsstrahlung emission is of interest, also for future measurements. We find that, when accelerated electrons are parallel to the emitted photons, the bremsstrahlung emission is unpolarized, and when they are perpendicular, the polarization increases with energy, as expected from the theoretical predictions. A comparison with the theoretical predictions is also shown.
On December 9, 2021, the imaging x-ray polarimetry explorer (IXPE) observatory was launched, carrying three x-ray polarimeters based upon the gas pixel detector (GPD). These devices measure the photoelectron’s ionization track following absorption of an x-ray, from which the photoelectron’s initial direction (correlated to the polarization position angle) is determined. Here we describe a method for event-by-event correction of pixel-by-pixel gain variations, which are found to be +/-20%, by comparing the charge in each pixel with the average at the same relative position inside tracks of the same shape. Using the large dataset acquired during on-ground calibration of the IXPE detectors, we have individually calibrated each of the 300×352 pixels of each detector’s ASIC. We discuss the performance improvements obtained using this method, which may be relevant to other instruments that detect individual events through images.
The imaging x-ray polarimetry explorer (IXPE) was launched on December 9, 2021, from Cape Canaveral into a low-Earth equatorial orbit. The mission, led by NASA in collaboration with the Italian Space Agency (ASI), features three identical telescopes, each with an imaging x-ray photoelectric polarimeter at the focus of an x-ray mirror assembly. Each focal-plane detector includes a set of four calibration sources powered by a 55Fe nuclide to monitor the detector’s performance. Of these sources, one produces polarized x-rays at two energies and the remaining three generate unpolarized radiation. Here we present the status of this monitoring program, starting from installation of the flight nuclides before on-ground environmental testing of the observatory through recent on-orbit measurements during science operations.
The Imaging X-ray Polarimetry Explorer (IXPE), launched 2021 December 9, will enable meaningful x-ray polarimetry of several types of astronomical sources. Aiming to improve the polarimetric sensitivity of Gas Pixel Detectors, track-reconstruction algorithms based upon machine learning have been proposed in the literature. In particular, a neural-network approach recently developed at Stanford University seems very promising. Here, we describe results obtained using this neural-network approach to analyze IXPE ground calibration data; we then compare those results with results obtained using the current moments-based analysis approach.
This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation, 2022.
The CubeSat solar polarimeter (CUSP) project aims to develop a constellation of two CubeSats orbiting the Earth to measure the linear polarisation of solar flares in the hard x-ray band by means of a Compton scattering polarimeter on board of each satellite. CUSP will allow to study the magnetic reconnection and particle acceleration in the flaring magnetic structures. CUSP is a project approved for a Phase A study by the Italian Space Agency in the framework of the Alcor program aimed to develop CubeSat technologies and missions.
Launched on 2021 December 9, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Small Explorer Mission in collaboration with the Italian Space Agency (ASI). The mission will open a new window of investigation—imaging x-ray polarimetry. The observatory features three identical telescopes, each consisting of a mirror module assembly with a polarization-sensitive imaging x-ray detector at the focus. A coilable boom, deployed on orbit, provides the necessary 4-m focal length. The observatory utilizes a three-axis-stabilized spacecraft, which provides services such as power, attitude determination and control, commanding, and telemetry to the ground. During its 2-year baseline mission, IXPE will conduct precise polarimetry for samples of multiple categories of x-ray sources, with follow-on observations of selected targets.
Scheduled to launch in late 2021 the Imaging X-ray Polarimetry Explorer (IXPE) is a Small Explorer Mission designed to open up a new window of investigation -- X-ray polarimetry. The IXPE observatory features 3 identical telescope each consisting of a mirror module assembly with a polarization-sensitive imaging x-ray detector at its focus. An extending beam, deployed on orbit provides the necessary 4 m focal length. The payload sits atop a 3-axis stabilized spacecraft which among other things provides power, attitude determination and control, commanding, and telemetry to the ground. During its 2-year baseline mission, IXPE will conduct precise polarimetry for samples of multiple categories of x-ray sources, with follow-on observations of selected targets. IXPE is a partnership between NASA and the Italian Space Agency (ASI).
IXPE (Imaging X-ray Polarimetry Explorer) is the next Nasa Small Explorer mission foreseen for the lunch in 2021. It is a partnership with the Italian Space Agency (ASI). IXPE is devoted to X-ray polarimetry in the 2-8 keV energy band. The IXPE telescope comprises three grazing incidence mirror modules coupled to three detector units hosting each one a Gas Pixel Detector (GPD) polarimeter. The GPD exploits the photoelectric effect to measure the linear polarization of the X-ray emission from astrophysical sources. A wide and accurate on ground calibration was carried out on the IXPE detector units at INAF-IAPS in Italy. A dedicated facility was set-up to calibrate the detector units with polarized and unpolarised X-rays at different energies before Instrument integration.
IXPE (Imaging X-ray Polarimetry Explorer) is a NASA SMEX in a partnership with ASI. The focal plane Detector Units (DUs) and the Detector Service Unit (DSU) were developed by the Italian research Institutes INAF-IAPS and INFN and were manufactured by OHB-I. IXPE will investigate X-ray polarimetry in the 2-8 keV energy band. The payload comprises three identical telescopes, each composed of a mirror and a detector unit with an X-ray polarimeter based on the Gas Pixel Detector (GPD). A stray-light collimator (SLC) is mounted on the top of the DU to shield the GPD from background X-rays not coming from the optics. At the bottom of the SLC, an ions-UV filter is mounted to reduce the thermal load and to prevent ions and UV from entering the DU. The ions-UV filters consist mainly of 1 um LUXFilm (based on polyimide). During on-ground calibration activities of the IXPE DUs, X-ray transparency of DU-FM ions-UV filters was measured with monochromatic X-ray at 2.7 keV and 6.4 keV at INAF-IAPS.
The Imaging X-ray Polarimetry Explorer (IXPE) is a scientific observatory with the purpose of expand observation space adding polarization property to the X-ray sourceƒ_Ts currently measured characteristics. The mission, selected in the context of NASA Small Explorer (SMEX) is a collaboration between NASA and ASI that will provide to observatory the instrumentation of focal plane. IXPE instrument is composed by three photoelectric polarimeter based on the Gap Pixel Detector (GPD) design, integrated by INFN inside detector unit (DU) that comprises all the electrical interfaces required to control and communicate with GPD. The three DUs are interfaced with spacecraft through a de-tector service unit (DSU) that collect scientific and ancillary data and provides a basically data handling and interfaces to manage the three DUs. AIV has been planned to combine calibration of DUs and Instrument integration and veri-fication activities. Due the tight schedule and the scientific and functional requirements to be verified, in IAPS/INAF have been assembled two equipments that work in parallel. The flight model of each DU after the environmental tests campaign was calibrated on-ground using Instrument Calibration Equipment (ICE) and subsequently integrated in the instrument in the AIV-T process on a AIV and Calibration Equipment (ACE), both the facilities managed by Electrical Ground Support Equipment (EGSE) that emulate the spacecraft interfaces of power supply, functional and thermal control and scientific data collection. AIV activities test functionalities and nominal/off-nominal orbits activities of IXPE instrument each time a calibrated DU is connected to DSU flight model completing step by step the full instrument. Here we describe the details of instrumentation and procedures adopted to make possible the full integration and test activities compatibly with calibration of IXPE Instrument.
IXPE, the Imaging X-ray Polarimetry Explorer, is a NASA SMEX mission with an important contribution of ASI that will be launched with a Falcon 9 in 2021 and will reopen the window of X-ray polarimetry after more than 40 years. The payload features three identical telescopes each one hosting one light-weight X-ray mirror fabricated by MSFC and one detector unit with its in-orbit calibration system and the Gas Pixel Detector sensitive to imaging X-ray polarization fabricated by INAF/IAPS, INFN and OHB Italy. The focal length after boom deployment from ATK-Orbital is 4 m, while the spacecraft is being fabricated by Ball Aerospace. The sensitivity will be better than 5.5% in 300 ks for a 1E-11 erg/s/cm2 (half mCrab) in the energy band of 2-8 keV allowing for sensitive polarimetry of extended and point-like X-ray sources. The focal plane instrument is completed, calibrated and it is going to be delivered at MSFC. We will present the status of the mission at about one year from the launch.
The NASA/ASI imaging x-ray polarimetry explorer, which will be launched in 2021, will be the first instrument to perform spatially resolved x-ray polarimetry on several astronomical sources in the 2- to 8-keV energy band. These measurements are made possible owing to the use of a gas pixel detector (GPD) at the focus of three x-ray telescopes. The GPD allows simultaneous measurements of the interaction point, energy, arrival time, and polarization angle of detected x-ray photons. The increase in sensitivity, achieved 40 years ago, for imaging and spectroscopy with the Einstein satellite will thus be extended to x-ray polarimetry for the first time. The characteristics of gas multiplication detectors are subject to changes over time. Because the GPD is a novel instrument, it is particularly important to verify its performance and stability during its mission lifetime. For this purpose, the spacecraft hosts a filter and calibration set (FCS), which includes both polarized and unpolarized calibration sources for performing in-flight calibration of the instruments. We present the design of the flight models of the FCS and the first measurements obtained using silicon drift detectors and charge-coupled device cameras, as well as those obtained in thermal vacuum with the flight units of the GPD. We show that the calibration sources successfully assess and verify the functionality of the GPD and validate its scientific results in orbit; this improves our knowledge of the behavior of these detectors in x-ray polarimetry.
The Imaging X-ray Polarimetry Explorer (IXPE) will add polarization to the properties (time, energy, and position) observed in x-ray astronomy. A NASA Astrophysics Small Explorer (SMEX) in partnership with the Italian Space Agency (ASI), IXPE will measure the 2–8-keV polarization of a few dozen sources during the first 2 years following its 2021 launch. The IXPE Observatory includes three identical x-ray telescopes, each comprising a 4-m-focal-length (grazingincidence) mirror module assembly (MMA) and a polarization-sensitive (imaging) detector unit (DU), separated by a deployable optical bench. The Observatory’s Spacecraft provides typical subsystems (mechanical, structural, thermal, power, electrical, telecommunications, etc.), an attitude determination and control subsystem for 3-axis stabilized pointing, and a command and data handling subsystem communicating with the science instrument and the Spacecraft subsystems.
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