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Gloria Spandre

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Oberto Citterio

Francesco Lazzarotto

Istituto Nazionale di Astrofisica

GianLuca Israel

University of Victoria

Istituto Nazionale di Astrofisica, FIRENZE, ITALY

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Papers by Gloria Spandre

The Study of PWNe with a photoelectric polarimeter

Proceedings of Polarimetry days in Rome: Crab status, theory and prospects — PoS(CRAB2008)

The measurement of the polarization of Pulsar Wind Nebulae is a powerful tool to investigate the ... more The measurement of the polarization of Pulsar Wind Nebulae is a powerful tool to investigate the flow structure of the wind produced by the central pulsar and the magnetic field in the nebula. Unfortunately, polarimeters in the X-ray range where these sources are easily observed are not available yet. However, the recent development of instruments based on photoelectric absorption is opening the possibility to observe a large number of PWNe with sufficient sensitivity to measure a degree of polarization at the level of % and resolve the closer sources. Here we present the first simulations of the angular resolution of the Gas Pixel Detector, one of the most advanced project in the field of photoelectric polarimeters. We assume that it will be placed in orbit in the context of a pathfinder mission, like POLARIX, or in the focal plane of a large mission like the International X-ray Observatory (IXO).

Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar

Science advances, 2018

Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appea... more Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appear to pulsate as their emission beams cross our line of sight. To date, radio pulsations have been detected from all rotation-powered MSPs. In an attempt to discover radio-quiet gamma-ray MSPs, we used the aggregated power from the computers of tens of thousands of volunteers participating in the Einstein@Home distributed computing project to search for pulsations from unidentified gamma-ray sources in Fermi Large Area Telescope data. This survey discovered two isolated MSPs, one of which is the only known rotation-powered MSP to remain undetected in radio observations. These gamma-ray MSPs were discovered in completely blind searches without prior constraints from other observations, raising hopes for detecting MSPs from a predicted Galactic bulge population.

Limits on dark matter annihilation signals from the Fermi LAT 4-year measurement of the isotropic gamma-ray background

Journal of Cosmology and Astroparticle Physics

We search for evidence of dark matter (DM) annihilation in the isotropic gamma-ray background (IG... more We search for evidence of dark matter (DM) annihilation in the isotropic gamma-ray background (IGRB) measured with 50 months of Fermi Large Area Telescope (LAT) observations. An improved theoretical description of the cosmological DM annihilation signal, based on two complementary techniques and assuming generic weakly interacting massive particle (WIMP) properties, renders more precise predictions compared to previous work. More specifically, we estimate the cosmologicallyinduced gamma-ray intensity to have an uncertainty of a factor ∼ 20 in canonical setups. We consistently include both the Galactic and extragalactic signals under the same theoretical framework, and study the impact of the former on the IGRB spectrum derivation. We find no evidence for a DM signal and we set limits on the DM-induced isotropic gamma-ray signal. Our limits are competitive for DM particle masses up to tens of TeV and, indeed, are the strongest limits derived from Fermi LAT data at TeV energies. This is possible thanks to the new Fermi LAT IGRB measurement, which now extends up to an energy of 820 GeV. We quantify uncertainties in detail and show the potential this type of search offers for testing the WIMP paradigm with a complementary and truly cosmological probe of DM particle signals.

Tests of MSGCs with Pestov-glass coatings

The Gamma-Ray Large-Area Space Telescope: An Astro-Particle Mission to Explore the High-Energy Gamma-Ray Sky

ABSTRACT

Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications

Medical Physics, 2016

High-resolution, photon-counting, energy-resolved detector with fast-framing capability can facil... more High-resolution, photon-counting, energy-resolved detector with fast-framing capability can facilitate simultaneous acquisition of precontrast and postcontrast images for subtraction angiography without pixel registration artifacts and can facilitate high-resolution real-time imaging during image-guided interventions. Hence, this study was conducted to determine the spatial resolution characteristics of a hexagonal pixel array photon-counting cadmium telluride (CdTe) detector. A 650 μm thick CdTe Schottky photon-counting detector capable of concurrently acquiring up to two energy-windowed images was operated in a single energy-window mode to include photons of 10 keV or higher. The detector had hexagonal pixels with apothem of 30 μm resulting in pixel pitch of 60 and 51.96 μm along the two orthogonal directions. The detector was characterized at IEC-RQA5 spectral conditions. Linear response of the detector was determined over the air kerma rate relevant to image-guided interventional procedures ranging from 1.3 nGy/frame to 91.4 μGy/frame. Presampled modulation transfer was determined using a tungsten edge test device. The edge-spread function and the finely sampled line spread function accounted for hexagonal sampling, from which the presampled modulation transfer function (MTF) was determined. Since detectors with hexagonal pixels require resampling to square pixels for distortion-free display, the optimal square pixel size was determined by minimizing the root-mean-squared-error of the aperture functions for the square and hexagonal pixels up to the Nyquist limit. At Nyquist frequencies of 8.33 and 9.62 cycles/mm along the apothem and orthogonal to the apothem directions, the modulation factors were 0.397 and 0.228, respectively. For the corresponding axis, the limiting resolution defined as 10% MTF occurred at 13.3 and 12 cycles/mm, respectively. Evaluation of the aperture functions yielded an optimal square pixel size of 54 μm. After resampling to 54 μm square pixels using trilinear interpolation, the presampled MTF at Nyquist frequency of 9.26 cycles/mm was 0.29 and 0.24 along the orthogonal directions and the limiting resolution (10% MTF) occurred at approximately 12 cycles/mm. Visual analysis of a bar pattern image showed the ability to resolve close to 12 line-pairs/mm and qualitative evaluation of a neurovascular nitinol-stent showed the ability to visualize its struts at clinically relevant conditions. Hexagonal pixel array photon-counting CdTe detector provides high spatial resolution in single-photon counting mode. After resampling to optimal square pixel size for distortion-free display, the spatial resolution is preserved. The dual-energy capabilities of the detector could allow for artifact-free subtraction angiography and basis material decomposition. The proposed high-resolution photon-counting detector with energy-resolving capability can be of importance for several image-guided interventional procedures as well as for pediatric applications.

ADAHELI+: exploring the fast, dynamic Sun in the x-ray, optical, and near-infrared

Journal of Astronomical Telescopes, Instruments, and Systems, 2015

Advanced Astronomy for Heliophysics Plus (ADAHELI+) is a project concept for a small solar and sp... more Advanced Astronomy for Heliophysics Plus (ADAHELI+) is a project concept for a small solar and space weather mission with a budget compatible with an European Space Agency (ESA) S-class mission, including launch, and a fast development cycle. ADAHELI+ was submitted to the European Space Agency by a European-wide consortium of solar physics research institutes in response to the "Call for a small mission opportunity for a launch in 2017," of March 9, 2012. The ADAHELI+ project builds on the heritage of the former ADAHELI mission, which had successfully completed its phase-A study under the Italian Space Agency 2007 Small Mission Programme, thus proving the soundness and feasibility of its innovative low-budget design. ADAHELI+ is a solar space mission with two main instruments: ISODY+: an imager, based on Fabry-Pérot interferometers, whose design is optimized to the acquisition of highest cadence, long-duration, multiline spectropolarimetric images in the visible/near-infrared region of the solar spectrum. XSPO: an x-ray polarimeter for solar flares in x-rays with energies in the 15 to 35 keV range. ADAHELI+ is capable of performing observations that cannot be addressed by other currently planned solar space missions, due to their limited telemetry, or by ground-based facilities, due to the problematic effect of the terrestrial atmosphere.

Photoelectric polarimeterse

The Imaging Properties of the Gas Pixel Detector as a Focal Plane Polarimeter

The Astrophysical Journal Supplement Series, 2014

X-rays are particularly suited to probe the physics of extreme objects. However, despite the enor... more X-rays are particularly suited to probe the physics of extreme objects. However, despite the enormous improvements of X-ray Astronomy in imaging, spectroscopy and timing, polarimetry remains largely unexplored. We propose the photoelectric polarimeter Gas Pixel Detector (GPD) as an instrument candidate to fill the gap of more than thirty years of lack of measurements. The GPD, in the focus of a telescope, will increase the sensitivity of orders of magnitude. Moreover, since it can measure the energy, the position, the arrival time and the polarization angle of every single photon, allows to perform polarimetry of subsets of data singled out from the spectrum, the light curve or the image of source. The GPD has an intrinsic very fine imaging capability and in this work we report on the calibration campaign carried out in 2012 at the PANTER X-ray test facility of the Max-Planck-Institut für extraterrestrische Physik of Garching (Germany) in which, for the first time, we coupled it to a JET-X optics module with a focal length of 3.5 m and an angular resolution of 18 arcsec at 4.5 keV. This configuration was proposed in 2012 aboard the X-ray Imaging Polarimetry Explorer (XIPE) in response to the ESA call for a small mission. We derived the imaging and polarimetric performance for extended sources like Pulsar Wind Nebulae and Supernova Remnants as case studies for the XIPE configuration, discussing also possible improvements by coupling the detector with advanced optics, having finer angular resolution and larger effective area, to study with more details extended objects.

WE-G-204-03: Photon-Counting Hexagonal Pixel Array CdTe Detector: Optimal Resampling to Square Pixels

Medical Physics, 2015

ABSTRACT Detectors with hexagonal pixels require resampling to square pixels for distortion-free ... more ABSTRACT Detectors with hexagonal pixels require resampling to square pixels for distortion-free display of acquired images. In this work, the presampling modulation transfer function (MTF) of a hexagonal pixel array photon-counting CdTe detector for region-of-interest fluoroscopy was measured and the optimal square pixel size for resampling was determined. A 0.65mm thick CdTe Schottky sensor capable of concurrently acquiring up to 3 energy-windowed images was operated in a single energy-window mode to include ≥10 KeV photons. The detector had hexagonal pixels with apothem of 30 microns resulting in pixel spacing of 60 and 51.96 microns along the two orthogonal directions. Images of a tungsten edge test device acquired under IEC RQA5 conditions were double Hough transformed to identify the edge and numerically differentiated. The presampling MTF was determined from the finely sampled line spread function that accounted for the hexagonal sampling. The optimal square pixel size was determined in two ways; the square pixel size for which the aperture function evaluated at the Nyquist frequencies along the two orthogonal directions matched that from the hexagonal pixel aperture functions, and the square pixel size for which the mean absolute difference between the square and hexagonal aperture functions was minimized over all frequencies up to the Nyquist limit. Evaluation of the aperture functions over the entire frequency range resulted in square pixel size of 53 microns with less than 2% difference from the hexagonal pixel. Evaluation of the aperture functions at Nyquist frequencies alone resulted in 54 microns square pixels. For the photon-counting CdTe detector and after resampling to 53 microns square pixels using quadratic interpolation, the presampling MTF at Nyquist frequency of 9.434 cycles/mm along the two directions were 0.501 and 0.507. Hexagonal pixel array photon-counting CdTe detector after resampling to square pixels provides high-resolution imaging suitable for fluoroscopy.

Fourth Workshop on Science with the New Generation of High Energy Gamma-ray Experiments

ABSTRACT

Gleam: the GLAST Large Area Telescope Simulation Framework

This paper presents the simulation of the GLAST high energy gammaray telescope. The simulation pa... more This paper presents the simulation of the GLAST high energy gammaray telescope. The simulation package, written in C++, is based on the Geant4 toolkit, and it is integrated into a general framework used to process events. A detailed simulation of the electronic signals inside Silicon detectors has been provided and it is used for the particle tracking, which is handled by a dedicated software. A unique repository for the geometrical description of the detector has been realized using the XML language and a C++ library to access this information has been designed and implemented.

Observations of the Large Magellanic Cloud with

Gamma ray large area space telescope balloon flight engineering model: overview

2001 IEEE Nuclear Science Symposium Conference Record (Cat. No.01CH37310), 2002

... SM Williams, D. Lauben, P. Michelson, PL Nolan, J. Wallace, Stanford University ... batteries... more

Photoelectric X-ray Polarimetry with Gas Pixel Detectors

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2013

The Gas Pixel Detector, recently developed and continuously improved by Pisa-INFN in collaboratio... more The Gas Pixel Detector, recently developed and continuously improved by Pisa-INFN in collaboration with IASF-Roma (INAF), can visualize the tracks produced within a low Z gas by photoelectrons of few keV. By reconstructing the impact point and the original direction of the photoelectrons, the GPD can measure the polarization plane of X-Ray photons, while preserving the information on the absorption point, the energy and the time of arrival of individual photons. Applied to X-ray Astrophysics, in the focus of grazing incidence telescopes, it can perform angular and energy resolved polarimetry with a large improvement of sensitivity, when compared with the conventional techniques of Bragg diffraction at 451 and Compton scattering around 901. This configuration has been the basis of POLARIX and HXMT, two pathfinder missions, and was included in the baseline design of IXO, the very large X-ray telescope under study by NASA, ESA and JAXA. We have recently improved the design of this low energy polarimeter (2-10 keV) by modifying the geometry of the absorption cell to minimize any systematic effect that could leave a residual polarization signal for nonpolarized source. We will report on the testing of this new concept.

Title: The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks

Science

Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse ... more Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 s is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.

A79Glast trk

Recent development on photoelectric X-ray polarimeters

ABSTRACT A position-sensitive Gas Pixel Detector was proposed for the first time by Pisa-INFN in ... more ABSTRACT A position-sensitive Gas Pixel Detector was proposed for the first time by Pisa-INFN in collaboration with IASF-Roma to image with high accuracy the photoelectron tracks produced in the interaction of low energy X-ray photons with the gas molecules inside the active volume of the detector. By reconstructing the impact point and the original direction of the photoelectrons, the GPD can measure the linear polarization of X-rays, while preserving the information on the absorption point, the energy and the arrival time of each individual photon. In the time, the performance of the GPD have been continuously improved by incresing the complexity, the functionality and the pixel density of the microelectronics implemented in the CMOS VLSI developed to readout the detector. Recently new modifications of the detector design have been implemented to improve the sensitivity of the device as X-ray polarimeter in the 2-10 keV energy range. The transverse dimensions of the absorption and drift volume have been increased to minimize any systematic effect that could leave a residual polarization signal for non-polarized source. We believe this new geometry the GPD, in the focus of grazing incidence telescopes, can perform angular and energy resolved polarimetry with higher sensitivity when compared with the conventional techniques. We will report on test and results on prototypes of this new concept obtained with two different gas mixture fillings.

$Research paper thumbnail of Inferred cosmic-ray spectrum from ${\ it Fermi} $-LAT $\ gamma $-ray observations of the Earth's limb$

Inferred cosmic-ray spectrum from ${\ it Fermi} $-LAT $\ gamma $-ray observations of the Earth's limb

Recent accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA reveal an un... more Recent accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA reveal an unexpected hardening in the proton and He spectra above a few hundred GeV, a gradual softening of the spectra just below a few hundred GeV, and a harder spectrum of He compared to that of protons. These newly-discovered features may offer a clue to the origin of high-energy CRs. We use the Fermi Large Area Telescope observations of the γ-ray emission from the Earth's limb for an indirect measurement of the local spectrum of CR protons in the energy range ∼ 90 GeV-6 TeV 3 (derived from a photon energy range 15 GeV-1 TeV). Our analysis shows that single power law and broken power law spectra fit the data equally well and yield a proton spectrum with index 2.68 ± 0.04 and 2.61 ± 0.08 above ∼ 200 GeV, respectively. PACS numbers: 96.50.sb, 95.85.Ry, 98.70.Sa

A solar flares X-ray polarimeter

ABSTRACT The measurement of X-ray polarization from solar flares is a scientific challenge which ... more ABSTRACT The measurement of X-ray polarization from solar flares is a scientific challenge which did not give any exhaustive result so far. X-ray polarimetry would be a probe of the solar flares physics making possible to study directly the magnetic reconnection and particle acceleration in the solar atmosphere of active regions where flares take place. New instrumentation specifically developed to measure the polarization of X-ray is needed to obtain results with adequate significance. The photoelectric polarimeter Gas Pixel Detector (GPD), originally developed to observe astrophysical sources other then the Sun, can address also solar science. The recent development of a new detector prototype effective in the hard X-rays makes suitable this polarimeter to examine the solar flares spectral region in which typically the non-thermal bremsstrahlung emission, expected to be highly polarized, arises with respect to the thermal bremsstrahlung whose polarization is expected to be marginal. The GPD versatility and small size make such an instrument suitable to fly on board of small space missions.

The Study of PWNe with a photoelectric polarimeter

Proceedings of Polarimetry days in Rome: Crab status, theory and prospects — PoS(CRAB2008)

The measurement of the polarization of Pulsar Wind Nebulae is a powerful tool to investigate the ... more The measurement of the polarization of Pulsar Wind Nebulae is a powerful tool to investigate the flow structure of the wind produced by the central pulsar and the magnetic field in the nebula. Unfortunately, polarimeters in the X-ray range where these sources are easily observed are not available yet. However, the recent development of instruments based on photoelectric absorption is opening the possibility to observe a large number of PWNe with sufficient sensitivity to measure a degree of polarization at the level of % and resolve the closer sources. Here we present the first simulations of the angular resolution of the Gas Pixel Detector, one of the most advanced project in the field of photoelectric polarimeters. We assume that it will be placed in orbit in the context of a pathfinder mission, like POLARIX, or in the focal plane of a large mission like the International X-ray Observatory (IXO).

Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar

Science advances, 2018

Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appea... more Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appear to pulsate as their emission beams cross our line of sight. To date, radio pulsations have been detected from all rotation-powered MSPs. In an attempt to discover radio-quiet gamma-ray MSPs, we used the aggregated power from the computers of tens of thousands of volunteers participating in the Einstein@Home distributed computing project to search for pulsations from unidentified gamma-ray sources in Fermi Large Area Telescope data. This survey discovered two isolated MSPs, one of which is the only known rotation-powered MSP to remain undetected in radio observations. These gamma-ray MSPs were discovered in completely blind searches without prior constraints from other observations, raising hopes for detecting MSPs from a predicted Galactic bulge population.

Limits on dark matter annihilation signals from the Fermi LAT 4-year measurement of the isotropic gamma-ray background

Journal of Cosmology and Astroparticle Physics

We search for evidence of dark matter (DM) annihilation in the isotropic gamma-ray background (IG... more We search for evidence of dark matter (DM) annihilation in the isotropic gamma-ray background (IGRB) measured with 50 months of Fermi Large Area Telescope (LAT) observations. An improved theoretical description of the cosmological DM annihilation signal, based on two complementary techniques and assuming generic weakly interacting massive particle (WIMP) properties, renders more precise predictions compared to previous work. More specifically, we estimate the cosmologicallyinduced gamma-ray intensity to have an uncertainty of a factor ∼ 20 in canonical setups. We consistently include both the Galactic and extragalactic signals under the same theoretical framework, and study the impact of the former on the IGRB spectrum derivation. We find no evidence for a DM signal and we set limits on the DM-induced isotropic gamma-ray signal. Our limits are competitive for DM particle masses up to tens of TeV and, indeed, are the strongest limits derived from Fermi LAT data at TeV energies. This is possible thanks to the new Fermi LAT IGRB measurement, which now extends up to an energy of 820 GeV. We quantify uncertainties in detail and show the potential this type of search offers for testing the WIMP paradigm with a complementary and truly cosmological probe of DM particle signals.

Tests of MSGCs with Pestov-glass coatings

The Gamma-Ray Large-Area Space Telescope: An Astro-Particle Mission to Explore the High-Energy Gamma-Ray Sky

ABSTRACT

Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications

Medical Physics, 2016

High-resolution, photon-counting, energy-resolved detector with fast-framing capability can facil... more High-resolution, photon-counting, energy-resolved detector with fast-framing capability can facilitate simultaneous acquisition of precontrast and postcontrast images for subtraction angiography without pixel registration artifacts and can facilitate high-resolution real-time imaging during image-guided interventions. Hence, this study was conducted to determine the spatial resolution characteristics of a hexagonal pixel array photon-counting cadmium telluride (CdTe) detector. A 650 μm thick CdTe Schottky photon-counting detector capable of concurrently acquiring up to two energy-windowed images was operated in a single energy-window mode to include photons of 10 keV or higher. The detector had hexagonal pixels with apothem of 30 μm resulting in pixel pitch of 60 and 51.96 μm along the two orthogonal directions. The detector was characterized at IEC-RQA5 spectral conditions. Linear response of the detector was determined over the air kerma rate relevant to image-guided interventional procedures ranging from 1.3 nGy/frame to 91.4 μGy/frame. Presampled modulation transfer was determined using a tungsten edge test device. The edge-spread function and the finely sampled line spread function accounted for hexagonal sampling, from which the presampled modulation transfer function (MTF) was determined. Since detectors with hexagonal pixels require resampling to square pixels for distortion-free display, the optimal square pixel size was determined by minimizing the root-mean-squared-error of the aperture functions for the square and hexagonal pixels up to the Nyquist limit. At Nyquist frequencies of 8.33 and 9.62 cycles/mm along the apothem and orthogonal to the apothem directions, the modulation factors were 0.397 and 0.228, respectively. For the corresponding axis, the limiting resolution defined as 10% MTF occurred at 13.3 and 12 cycles/mm, respectively. Evaluation of the aperture functions yielded an optimal square pixel size of 54 μm. After resampling to 54 μm square pixels using trilinear interpolation, the presampled MTF at Nyquist frequency of 9.26 cycles/mm was 0.29 and 0.24 along the orthogonal directions and the limiting resolution (10% MTF) occurred at approximately 12 cycles/mm. Visual analysis of a bar pattern image showed the ability to resolve close to 12 line-pairs/mm and qualitative evaluation of a neurovascular nitinol-stent showed the ability to visualize its struts at clinically relevant conditions. Hexagonal pixel array photon-counting CdTe detector provides high spatial resolution in single-photon counting mode. After resampling to optimal square pixel size for distortion-free display, the spatial resolution is preserved. The dual-energy capabilities of the detector could allow for artifact-free subtraction angiography and basis material decomposition. The proposed high-resolution photon-counting detector with energy-resolving capability can be of importance for several image-guided interventional procedures as well as for pediatric applications.

ADAHELI+: exploring the fast, dynamic Sun in the x-ray, optical, and near-infrared

Journal of Astronomical Telescopes, Instruments, and Systems, 2015

Advanced Astronomy for Heliophysics Plus (ADAHELI+) is a project concept for a small solar and sp... more Advanced Astronomy for Heliophysics Plus (ADAHELI+) is a project concept for a small solar and space weather mission with a budget compatible with an European Space Agency (ESA) S-class mission, including launch, and a fast development cycle. ADAHELI+ was submitted to the European Space Agency by a European-wide consortium of solar physics research institutes in response to the "Call for a small mission opportunity for a launch in 2017," of March 9, 2012. The ADAHELI+ project builds on the heritage of the former ADAHELI mission, which had successfully completed its phase-A study under the Italian Space Agency 2007 Small Mission Programme, thus proving the soundness and feasibility of its innovative low-budget design. ADAHELI+ is a solar space mission with two main instruments: ISODY+: an imager, based on Fabry-Pérot interferometers, whose design is optimized to the acquisition of highest cadence, long-duration, multiline spectropolarimetric images in the visible/near-infrared region of the solar spectrum. XSPO: an x-ray polarimeter for solar flares in x-rays with energies in the 15 to 35 keV range. ADAHELI+ is capable of performing observations that cannot be addressed by other currently planned solar space missions, due to their limited telemetry, or by ground-based facilities, due to the problematic effect of the terrestrial atmosphere.

Photoelectric polarimeterse

The Imaging Properties of the Gas Pixel Detector as a Focal Plane Polarimeter

The Astrophysical Journal Supplement Series, 2014

X-rays are particularly suited to probe the physics of extreme objects. However, despite the enor... more X-rays are particularly suited to probe the physics of extreme objects. However, despite the enormous improvements of X-ray Astronomy in imaging, spectroscopy and timing, polarimetry remains largely unexplored. We propose the photoelectric polarimeter Gas Pixel Detector (GPD) as an instrument candidate to fill the gap of more than thirty years of lack of measurements. The GPD, in the focus of a telescope, will increase the sensitivity of orders of magnitude. Moreover, since it can measure the energy, the position, the arrival time and the polarization angle of every single photon, allows to perform polarimetry of subsets of data singled out from the spectrum, the light curve or the image of source. The GPD has an intrinsic very fine imaging capability and in this work we report on the calibration campaign carried out in 2012 at the PANTER X-ray test facility of the Max-Planck-Institut für extraterrestrische Physik of Garching (Germany) in which, for the first time, we coupled it to a JET-X optics module with a focal length of 3.5 m and an angular resolution of 18 arcsec at 4.5 keV. This configuration was proposed in 2012 aboard the X-ray Imaging Polarimetry Explorer (XIPE) in response to the ESA call for a small mission. We derived the imaging and polarimetric performance for extended sources like Pulsar Wind Nebulae and Supernova Remnants as case studies for the XIPE configuration, discussing also possible improvements by coupling the detector with advanced optics, having finer angular resolution and larger effective area, to study with more details extended objects.

WE-G-204-03: Photon-Counting Hexagonal Pixel Array CdTe Detector: Optimal Resampling to Square Pixels

Medical Physics, 2015

ABSTRACT Detectors with hexagonal pixels require resampling to square pixels for distortion-free ... more ABSTRACT Detectors with hexagonal pixels require resampling to square pixels for distortion-free display of acquired images. In this work, the presampling modulation transfer function (MTF) of a hexagonal pixel array photon-counting CdTe detector for region-of-interest fluoroscopy was measured and the optimal square pixel size for resampling was determined. A 0.65mm thick CdTe Schottky sensor capable of concurrently acquiring up to 3 energy-windowed images was operated in a single energy-window mode to include ≥10 KeV photons. The detector had hexagonal pixels with apothem of 30 microns resulting in pixel spacing of 60 and 51.96 microns along the two orthogonal directions. Images of a tungsten edge test device acquired under IEC RQA5 conditions were double Hough transformed to identify the edge and numerically differentiated. The presampling MTF was determined from the finely sampled line spread function that accounted for the hexagonal sampling. The optimal square pixel size was determined in two ways; the square pixel size for which the aperture function evaluated at the Nyquist frequencies along the two orthogonal directions matched that from the hexagonal pixel aperture functions, and the square pixel size for which the mean absolute difference between the square and hexagonal aperture functions was minimized over all frequencies up to the Nyquist limit. Evaluation of the aperture functions over the entire frequency range resulted in square pixel size of 53 microns with less than 2% difference from the hexagonal pixel. Evaluation of the aperture functions at Nyquist frequencies alone resulted in 54 microns square pixels. For the photon-counting CdTe detector and after resampling to 53 microns square pixels using quadratic interpolation, the presampling MTF at Nyquist frequency of 9.434 cycles/mm along the two directions were 0.501 and 0.507. Hexagonal pixel array photon-counting CdTe detector after resampling to square pixels provides high-resolution imaging suitable for fluoroscopy.

Fourth Workshop on Science with the New Generation of High Energy Gamma-ray Experiments

ABSTRACT

Gleam: the GLAST Large Area Telescope Simulation Framework

This paper presents the simulation of the GLAST high energy gammaray telescope. The simulation pa... more This paper presents the simulation of the GLAST high energy gammaray telescope. The simulation package, written in C++, is based on the Geant4 toolkit, and it is integrated into a general framework used to process events. A detailed simulation of the electronic signals inside Silicon detectors has been provided and it is used for the particle tracking, which is handled by a dedicated software. A unique repository for the geometrical description of the detector has been realized using the XML language and a C++ library to access this information has been designed and implemented.

Observations of the Large Magellanic Cloud with

Gamma ray large area space telescope balloon flight engineering model: overview

2001 IEEE Nuclear Science Symposium Conference Record (Cat. No.01CH37310), 2002

... SM Williams, D. Lauben, P. Michelson, PL Nolan, J. Wallace, Stanford University ... batteries... more

Photoelectric X-ray Polarimetry with Gas Pixel Detectors

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2013

The Gas Pixel Detector, recently developed and continuously improved by Pisa-INFN in collaboratio... more The Gas Pixel Detector, recently developed and continuously improved by Pisa-INFN in collaboration with IASF-Roma (INAF), can visualize the tracks produced within a low Z gas by photoelectrons of few keV. By reconstructing the impact point and the original direction of the photoelectrons, the GPD can measure the polarization plane of X-Ray photons, while preserving the information on the absorption point, the energy and the time of arrival of individual photons. Applied to X-ray Astrophysics, in the focus of grazing incidence telescopes, it can perform angular and energy resolved polarimetry with a large improvement of sensitivity, when compared with the conventional techniques of Bragg diffraction at 451 and Compton scattering around 901. This configuration has been the basis of POLARIX and HXMT, two pathfinder missions, and was included in the baseline design of IXO, the very large X-ray telescope under study by NASA, ESA and JAXA. We have recently improved the design of this low energy polarimeter (2-10 keV) by modifying the geometry of the absorption cell to minimize any systematic effect that could leave a residual polarization signal for nonpolarized source. We will report on the testing of this new concept.

Title: The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks

Science

Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse ... more Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 s is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.

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Recent development on photoelectric X-ray polarimeters

ABSTRACT A position-sensitive Gas Pixel Detector was proposed for the first time by Pisa-INFN in ... more ABSTRACT A position-sensitive Gas Pixel Detector was proposed for the first time by Pisa-INFN in collaboration with IASF-Roma to image with high accuracy the photoelectron tracks produced in the interaction of low energy X-ray photons with the gas molecules inside the active volume of the detector. By reconstructing the impact point and the original direction of the photoelectrons, the GPD can measure the linear polarization of X-rays, while preserving the information on the absorption point, the energy and the arrival time of each individual photon. In the time, the performance of the GPD have been continuously improved by incresing the complexity, the functionality and the pixel density of the microelectronics implemented in the CMOS VLSI developed to readout the detector. Recently new modifications of the detector design have been implemented to improve the sensitivity of the device as X-ray polarimeter in the 2-10 keV energy range. The transverse dimensions of the absorption and drift volume have been increased to minimize any systematic effect that could leave a residual polarization signal for non-polarized source. We believe this new geometry the GPD, in the focus of grazing incidence telescopes, can perform angular and energy resolved polarimetry with higher sensitivity when compared with the conventional techniques. We will report on test and results on prototypes of this new concept obtained with two different gas mixture fillings.

$Research paper thumbnail of Inferred cosmic-ray spectrum from ${\ it Fermi} $-LAT $\ gamma $-ray observations of the Earth's limb$

Inferred cosmic-ray spectrum from ${\ it Fermi} $-LAT $\ gamma $-ray observations of the Earth's limb

Recent accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA reveal an un... more Recent accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA reveal an unexpected hardening in the proton and He spectra above a few hundred GeV, a gradual softening of the spectra just below a few hundred GeV, and a harder spectrum of He compared to that of protons. These newly-discovered features may offer a clue to the origin of high-energy CRs. We use the Fermi Large Area Telescope observations of the γ-ray emission from the Earth's limb for an indirect measurement of the local spectrum of CR protons in the energy range ∼ 90 GeV-6 TeV 3 (derived from a photon energy range 15 GeV-1 TeV). Our analysis shows that single power law and broken power law spectra fit the data equally well and yield a proton spectrum with index 2.68 ± 0.04 and 2.61 ± 0.08 above ∼ 200 GeV, respectively. PACS numbers: 96.50.sb, 95.85.Ry, 98.70.Sa

A solar flares X-ray polarimeter

ABSTRACT The measurement of X-ray polarization from solar flares is a scientific challenge which ... more ABSTRACT The measurement of X-ray polarization from solar flares is a scientific challenge which did not give any exhaustive result so far. X-ray polarimetry would be a probe of the solar flares physics making possible to study directly the magnetic reconnection and particle acceleration in the solar atmosphere of active regions where flares take place. New instrumentation specifically developed to measure the polarization of X-ray is needed to obtain results with adequate significance. The photoelectric polarimeter Gas Pixel Detector (GPD), originally developed to observe astrophysical sources other then the Sun, can address also solar science. The recent development of a new detector prototype effective in the hard X-rays makes suitable this polarimeter to examine the solar flares spectral region in which typically the non-thermal bremsstrahlung emission, expected to be highly polarized, arises with respect to the thermal bremsstrahlung whose polarization is expected to be marginal. The GPD versatility and small size make such an instrument suitable to fly on board of small space missions.