Context.
Despite over 50 years of research, many open questions remain about the origin and nature of gamma-ray bursts (GRBs). Linear polarization measurements of the prompt emission of these extreme ...phenomena have long been thought to be key to answering a range of these questions. The POLAR detector was designed to produce the first set of detailed and reliable linear polarization measurements in the 50 − 500 keV energy range. During late 2016 and early 2017, POLAR detected a total of 55 GRBs. The analysis results of 5 of these GRBs have been reported, and were found to be consistent with a low or unpolarized flux. However, previous reports by other collaborations found high levels of linear polarization, including some as high as 90%.
Aims.
We study the linear polarization for the 14 GRBs observed by POLAR for which statistically robust inferences are possible. Additionally, time-resolved polarization studies are performed on GRBs with sufficient apparent flux.
Methods.
A publicly available polarization analysis tool, developed within the Multi-Mission Maximum Likelihood framework (
3ML
), was used to produce statistically robust results. The method allows spectral and polarimetric data from POLAR to be combined with spectral data from the
Fermi
Gamma-ray Burst Monitor (
Fermi
-GBM) and the
Neil Gehrels Swift
Observatory to jointly model the spectral and polarimetric parameters.
Results.
The time-integrated analysis finds all results to be compatible with low or zero polarization with the caveat that, when time-resolved analysis is possible within individual pulses, we observe moderate linear polarization with a rapidly changing polarization angle. Therefore, time-integrated polarization results, while pointing to lower polarization, are potentially an artifact of summing over the changing polarization signal and thus washing out the true moderate polarization. We therefore caution against overinterpretation of any time-integrated results inferred herein and encourage the community to wait for more detailed polarization measurements from forthcoming missions such as POLAR-2 and LEAP.
The LHCb simulation application, Gauss, consists of two independent phases, the generation of the primary event and the tracking of particles produced in the experimental setup. For the LHCb ...experimental program it is particularly important to model B meson decays: the EvtGen code developed in CLEO and BABAR has been chosen and customized for non-coherent B production as occuring in pp collisions at the LHC. The initial proton-proton collision is provided by a different generator engine, currently PYTHIA 6 for massive production of signal and generic pp collisions events. Beam gas events, background events originating from proton halo, cosmics and calibration events for different detectors can be generated in addition to pp collisions. Different generator packages as available in the physics community or specifically developed in LHCb are used for the different purposes. Running conditions affecting the generated events such as the size of the luminous region, the number of collisions occuring in a bunch crossing and the number of spill-over events from neighbouring bunches are modeled via dedicated algorithms appropriately configured. The design of the generator phase of Gauss will be described: a modular structure with well defined interfaces specific to the various tasks, e.g. pp collisions, particle decays, selections, etc. has been chosen. Different implementations are available for the various tasks allowing selecting and combining them as most appropriate at run time as in the case of PYTHIA 6 for pp collisions or HIJING for beam gas. The advantages of such structure, allowing for example to adopt transparently new generators packages, will be discussed.
The LHCb simulation application. Gauss, consists or two independent phases, the generation of the primary event and the tracking of particles produced in the experimental setup. For the LHCh ...experimental program it is particularly important to model B meson decays: the EvtGcn code developed in CLEO and BaBah has been chosen and customized for non-coherent B production as occurring in pp collisions at the LHC, The initial proton-proton collision is provided by a different generator engine, currently PYTHIA 6 for massive production of signal and generic pp collisions events. Beam gas events, background events originating from proton halo, cosmics and calibration events for different detectors can be generated in addition to pp collisions. Different generator packages as available in the physics community or specifically developed in LHCb are used for the different purposes. Running conditions affecting the events generated such as the size of the luminous region, the number of collisions occuring in a bunch crossing and the number of spill-over events from neighbouring bunches are modeled via dedicated algorithms appropriately configured. The design of the generator phase of Gauss will be described: a modular structure with well defined interfaces specific to the various tasks, e.g. pp collisions, particles' decays, selections, etc. has been chosen. Different implementations are available for the various tasks allowing selecting and combining them as most appropriate at run time as in the case of Pythia 6 im pp collisions or HIJING for beam gas. The advantages of such structure, allowing for example to adopt transparently new generators packages will be discussed.
As a space-borne detector POLAR is designed to conduct hard X-ray polarization measurements of gamma-ray bursts on a statistically significant sample of events and with an unprecedented accuracy. ...During its development phase a number of tests, calibrations and verification measurements were carried out in order to validate instrument functionality and optimize operational parameters. In this article we present results on gain optimization together with verification data obtained in the course of broad laboratory and environmental tests. In particular we focus on exposures to the 137Cs radioactive source and determination of the gain dependence on the high voltage for all 1600 detection channels of the polarimeter. Performance of the instrument is described in detail with respect to the dynamic range, energy resolution and temperature dependence. Gain optimization algorithms and response non-uniformity studies are also discussed. Results presented below are important for the development of the POLAR calibration and operation database.
Design and construction of the POLAR detector Produit, N.; Bao, T.W.; Batsch, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2018, Letnik:
877
Journal Article
Recenzirano
Odprti dostop
The POLAR detector is a space based Gamma Ray Burst (GRB) polarimeter with a wide field of view, which covers almost half the sky. The instrument uses Compton scattering of gamma rays on a plastic ...scintillator hodoscope to measure the polarization of the incoming photons. The instrument has been successfully launched on board of the Chinese space laboratory Tiangong 2 on September 15, 2016. The construction of the instrument components is described in this article. Details are provided on problems encountered during the construction phase and their solutions. Initial performance of the instrument in orbit is as expected from ground tests and Monte Carlo simulation.
Allpix2: A modular simulation framework for silicon detectors Spannagel, S.; Wolters, K.; Hynds, D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2018, Letnik:
901
Journal Article
Recenzirano
Odprti dostop
Allpix2 (read: Allpix Squared) is a generic, open-source software framework for the simulation of silicon pixel detectors. Its goal is to ease the implementation of detailed simulations for both ...single detectors and more complex setups such as beam telescopes from incident radiation to the digitised detector response. Predefined detector types can be automatically constructed from simple model files describing the detector parameters.
The simulation chain is arranged with the help of intuitive configuration files and an extensible system of modules, which implement separate simulation steps such as realistic charge carrier deposition with the Geant4 toolkit or propagation of charge carriers in silicon using a drift–diffusion model. Detailed electric field maps imported from TCAD simulations can be used to precisely model the drift behaviour of charge carriers within the silicon, bringing a new level of realism to Monte Carlo based simulations of particle detectors.
This paper provides an overview of the framework and a selection of different simulation modules, and presents a comparison of simulation results with test beam data recorded with hybrid pixel detectors. Emphasis is placed on the performance of the framework itself, using a first-principles simulation of the detectors without addressing secondary ASIC-specific effects.
POLAR is a new satellite-born detector aiming to measure the polarization of an unprecedented number of Gamma-Ray Bursts in the 50–500 keV energy range. The instrument, launched on-board the ...Tiangong-2 Chinese Space lab on the 15th of September 2016, is designed to measure the polarization of the hard X-ray flux by measuring the distribution of the azimuthal scattering angles of the incoming photons. A detailed understanding of the polarimeter and specifically of the systematic effects induced by the instrument’s non-uniformity are required for this purpose. In order to study the instrument’s response to polarization, POLAR underwent a beam test at the European Synchrotron Radiation Facility in France. In this paper both the beam test and the instrument performance will be described. This is followed by an overview of the Monte Carlo simulation tools developed for the instrument. Finally a comparison of the measured and simulated instrument performance will be provided and the instrument response to polarization will be presented.
The main performance challenge of POLAR - a novel hard X-ray polarimeter, is to achieve high statistical accuracy and large modulation factors. Both require great level of response uniformity. ...Though, typical sensitivity of multi-anode PMTs may vary between its channels up to the factor of two to three. Moreover, the measured signal can be further altered by light coupling quality. We investigate response equalization based on utilizing of an optical mask with light-blocking diaphragms. It is placed between scintillator bars and the PMT photo-cathode. Each PMT channel-pad is equipped with the unique diaphragm with its area related to the initial sensitivity of the corresponding channel. We present module/mask construction details, test setup and measurement results done before and after applying of the mask corrections. Applicability of the method is discussed with respect to the instrument dynamic range, low energy threshold requirements and aging effects due to the in-space utilization.
Introduction
The aim of this study was to better understand the family resilience process following a severe traumatic brain injury during adolescence.
Case Presentation
Inspired by the humanistic ...model of nursing care as a disciplinary perspective, this study used a qualitative and inductive case study design.
Management and Outcome
The data analysis yielded six themes as well as four subthemes that illustrate this family’s resilience process. The most important factors that emerged are (a) family characteristics (i.e., a fighter personality, cultural and spiritual beliefs, presence of hope, keeping a sense of humor), (b) support of family members, (c) support of friends, (d) practicing sports and leisure activities, (e) back-to-school support, and (f) feeling helpful to the adolescent.
Discussion
This study provides interesting avenues with regard to the implementation of strategies to foster the resilience process in families during particularly difficult situations in their lives, such as a traumatic brain injury during adolescence.
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