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G. Weidenspointner

Publications and source records attributed to G. Weidenspointner.

At least 19 recordsLinked to original sources
arXiv2016

INTEGRAL upper limits on gamma-ray emission associated with the gravitational wave event GW150914

Using observations of the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), we put upper limits on the gamma-ray and hard X-ray prompt emission associated with the gravitational wave event GW150914, discovered by the LIGO/Virgo collaboration. The omni-directional view of the INTEGRAL/SPI-ACS has allowed us to constrain the fraction of energy emitted in the hard X-ray electromagnetic component for the full high-probability sky region of LIGO trigger. Our upper limits on the hard X-ray fluence at the time of the event range from $F_γ=2 \times 10^{-8}$ erg cm$^{-2}$ to $F_γ=10^{-6}$ erg cm$^{-2}$ in the 75 keV - 2 MeV energy range for typical spectral models. Our results constrain the ratio of the energy promptly released in gamma-rays in the direction of the observer to the gravitational wave energy E$_γ/$E$_\mathrm{GW}<10^{-6}$. We discuss the implication of gamma-ray limits on the characteristics of the gravitational wave source, based on the available predictions for prompt electromagnetic emission.

astro-ph.HE↗
arXiv2013

The Hot and Energetic Universe: The Wide Field Imager (WFI) for Athena+

The Wide Field Imager (WFI) is one of the two scientific instruments proposed for the Athena+ X-ray observatory. It will provide imaging in the 0.1-15 keV band over a wide field, simultaneously with spectrally and time-resolved photon counting. The instrument is designed to make optimal use of the grasp (collecting area times solid angle product) provided by the optical design of the Athena+ mirror system (Willingale et al. 2013), by combining a sensitive approx. 40' diameter field of view (baseline; 50' goal) DEPFET detector with a pixel size properly sampling the angular resolution of 5 arc sec on-axis (half energy width).This synthesis makes the WFI a very powerful survey instrument, significantly surpassing currently existing capabilities (Nandra et al. 2013; Aird et al. 2013). In addition, the WFI will provide unprecedented simultaneous high-time resolution and high count rate capabilities for the observation of bright sources with low pile-up and high efficiency. In this paper, we summarize the instrument design, the status of the technology development, and the baseline performance.

astro-ph.IM↗
arXiv2011

Quantifying the unknown: issues in simulation validation and their experimental impact

The assessment of the reliability of Monte Carlo simulations is discussed, with emphasis on uncertainty quantification and the related impact on experimental results. Methods and techniques to account for epistemic uncertainties, i.e. for intrinsic knowledge gaps in physics modeling, are discussed with the support of applications to concrete experimental scenarios. Ongoing projects regarding the investigation of epistemic uncertainties in the Geant4 simulation toolkit are reported.

physics.comp-ph↗
arXiv2010

New Physics Data Libraries for Monte Carlo Transport

The role of data libraries as a collaborative tool across Monte Carlo codes is discussed. Some new contributions in this domain are presented; they concern a data library of proton and alpha ionization cross sections, the development in progress of a data library of electron ionization cross sections and proposed improvements to the EADL (Evaluated Atomic Data Library), the latter resulting from an extensive data validation process.

physics.comp-ph↗
arXiv2010

The 511 keV emission from positron annihilation in the Galaxy

The first gamma-ray line originating from outside the solar system that was ever detected is the 511 keV emission from positron annihilation in the Galaxy. Despite 30 years of intense theoretical and observational investigation, the main sources of positrons have not been identified up to now. Observations in the 1990's with OSSE/CGRO showed that the emission is strongly concentrated towards the Galactic bulge. In the 2000's, the SPI instrument aboard ESA's INTEGRAL gamma-ray observatory allowed scientists to measure that emission across the entire Galaxy, revealing that the bulge/disk luminosity ratio is larger than observed in any other wavelength. This mapping prompted a number of novel explanations, including rather "exotic ones (e.g. dark matter annihilation). However, conventional astrophysical sources, like type Ia supernovae, microquasars or X-ray binaries, are still plausible candidates for a large fraction of the observed total 511 keV emission of the bulge. A closer study of the subject reveals new layers of complexity, since positrons may propagate far away from their production sites, making it difficult to infer the underlying source distribution from the observed map of 511 keV emission. However, contrary to the rather well understood propagation of high energy (>GeV) particles of Galactic cosmic rays, understanding the propagation of low energy (~MeV) positrons in the turbulent, magnetized interstellar medium, still remains a formidable challenge. We review the spectral and imaging properties of the observed 511 keV emission and we critically discuss candidate positron sources and models of positron propagation in the Galaxy.

astro-ph.HE↗
arXiv2010

New models for PIXE simulation with Geant4

Particle induced X-ray emission (PIXE) is a physical effect that is not yet adequately modelled in Geant4. The current status as in Geant4 9.2 release is reviewed and new developments are described. The capabilities of the software prototype are illustrated in application to the shielding of the X-ray detectors of the eROSITA telescope on the upcoming Spectrum-X-Gamma space mission.

physics.comp-ph↗
arXiv2010

R&D on co-working transport schemes in Geant4

A research and development (R&D) project related to the extension of the Geant4 toolkit has been recently launched to address fundamental methods in radiation transport simulation. The project focuses on simulation at different scales in the same experimental environment; this problem requires new methods across the current boundaries of condensed-random-walk and discrete transport schemes. The new developments have been motivated by experimental requirements in various domains, including nanodosimetry, astronomy and detector developments for high energy physics applications.

physics.comp-ph↗
arXiv2010

Design and performance evaluations of generic programming techniques in a R&D prototype of Geant4 physics

A R&D project has been recently launched to investigate Geant4 architectural design in view of addressing new experimental issues in HEP and other related physics disciplines. In the context of this project the use of generic programming techniques besides the conventional object oriented is investigated. Software design features and preliminary results from a new prototype implementation of Geant4 electromagnetic physics are illustrated. Performance evaluations are presented. Issues related to quality assurance in Geant4 physics modelling are discussed.

physics.comp-ph↗
arXiv2009

Research in Geant4 electromagnetic physics design, and its effects on computational performance and quality assurance

The Geant4 toolkit offers a rich variety of electromagnetic physics models; so far the evaluation of this Geant4 domain has been mostly focused on its physics functionality, while the features of its design and their impact on simulation accuracy, computational performance and facilities for verification and validation have not been the object of comparable attention yet, despite the critical role they play in many experimental applications. A new project is in progress to study the application of new design concepts and software techniques in Geant4 electromagnetic physics, and to evaluate how they can improve on the current simulation capabilities. The application of a policy-based class design is investigated as a means to achieve the objective of granular decomposition of processes; this design technique offers various advantages in terms of flexibility of configuration and computational performance. The current Geant4 physics models have been re-implemented according to the new design as a pilot project. The main features of the new design and first results of performance improvement and testing simplification are presented; they are relevant to many Geant4 applications, where computational speed and the containment of resources invested in simulation production and quality assurance play a critical role.

physics.comp-ph↗
arXiv2009

Geant4-related R&D for new particle transport methods

A R&D project has been launched in 2009 to address fundamental methods in radiation transport simulation and revisit Geant4 kernel design to cope with new experimental requirements. The project focuses on simulation at different scales in the same experimental environment: this set of problems requires new methods across the current boundaries of condensed-random-walk and discrete transport schemes. An exploration is also foreseen about exploiting and extending already existing Geant4 features to apply Monte Carlo and deterministic transport methods in the same simulation environment. An overview of this new R&D associated with Geant4 is presented, together with the first developments in progress.

physics.comp-ph↗
arXiv2009

Recent Developments on PIXE Simulation with Geant4

Particle induced X-ray emission (PIXE) is an important physical effect that is not yet adequately modelled in Geant4. This paper provides a critical analysis of the problem domain associated with PIXE simulation and describes a set of software developments to improve PIXE simulation with Geant4. The capabilities of the developed software prototype are illustrated and applied to a study of the passive shielding of the X-ray detectors of the German eROSITA telescope on the upcoming Russian Spectrum-X-Gamma space mission.

physics.comp-ph↗
arXiv2009

Inter-Comparison and Validation of Geant4 Photon Interaction Models

A R&D project, named Nano5, has been recently launched to study an architectural design in view of addressing new experimental issues related to particle transport in high energy physics and other related physics disciplines with Geant4. In this frame, the first step has involved the redesign of the photon interaction models currently available in Geant4; this task has motivated a thorough investigation of the physics and computational features of these models, whose first results are presented here.

physics.comp-ph↗
arXiv2009

The Twin Magnetars: SGR 1627-41 and 1E 1547-5408

We report on recent results obtained thanks to Target of Opportunity observations of the two galactic sources SGR 1627-41 and 1E 1547-5408. These two transient sources present several similarities which support the interpretation of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters as a single class of strongly magnetized neutron stars.

astro-ph.HE↗
arXiv2009

Strong bursts from the anomalous X-ray pulsar 1E 1547.0-5408 observed with the INTEGRAL/SPI Anti-Coincidence Shield

In January 2009, multiple short bursts of soft gamma-rays were detected from the direction of the anomalous X-ray pulsar 1E 1547.0-5408 by different satellites. Here we report on the observations obtained with the INTEGRAL SPI-ACS detector during the period with the strongest bursting activity. More than 200 bursts were detected at energies above 80 keV in a few hours on January 22. Among these, two remarkably bright events showed pulsating tails lasting several seconds and modulated at the 2.1 s spin period of 1E 1547.0-5408. The energy released in the brightest of these bursts was of a few 10^43 erg, for an assumed distance of 10 kpc. This is smaller than that of the three giant flares seen from soft gamma-ray repeaters, but higher than that of typical bursts from soft gamma-ray repeaters and anomalous X-ray pulsars.

astro-ph.HE↗
arXiv2007

SPI observations of the diffuse 60Fe emission in the Galaxy

Gamma-ray line emission from radioactive decay of 60Fe provides constraints on nucleosynthesis in massive stars and supernovae. The spectrometer SPI on board INTEGRAL has accumulated nearly three years of data on gamma-ray emission from the Galactic plane. We have analyzed these data with suitable instrumental-background models and sky distributions to produce high-resolution spectra of Galactic emission. We detect the gamma-ray lines from 60Fe decay at 1173 and 1333 keV, obtaining an improvement over our earlier measurement of both lines with now 4.9 sigma significance for the combination of the two lines. The average flux per line is (4.4 \pm 0.9) \times 10^{-5} ph cm^{-2} s^{-1} rad^{-1} for the inner Galaxy region. Deriving the Galactic 26Al gamma-ray line flux with using the same set of observations and analysis method, we determine the flux ratio of 60Fe/26Al gamma-rays as 0.148 \pm 0.06. The current theoretical predictions are still consistent with our result.

astro-ph↗
arXiv2007

The sky distribution of 511 keV positron annihilation line emission as measured with INTEGRAL/SPI

The imaging spectrometer SPI on board ESA's INTEGRAL observatory provides us with an unprecedented view of positron annihilation in our Galaxy. The first sky maps in the 511 keV annihilation line and in the positronium continuum from SPI showed a puzzling concentration of annihilation radiation in the Galactic bulge region. By now, more than twice as many INTEGRAL observations are available, offering new clues to the origin of Galactic positrons. We present the current status of our analyses of this augmented data set. We now detect significant emission from outside the Galactic bulge region. The 511 keV line is clearly detected from the Galactic disk; in addition, there is a tantalizing hint at possible halo-like emission. The available data do not yet permit to discern whether the emission around the bulge region originates from a halo-like component or from a disk component that is very extended in latitude.

astro-ph↗