86 research outputs found
Runaway stars and the Galactic supernova remnant landscape: non-thermal emission and observational evidence
No full textContext. A significant fraction (~30%) of massive stars in our Galaxy are moving supersonically through the interstellar medium, which strongly governs their location at the time they end their lives, e.g. die as a supernova and give birth to a supernova remnant (SNR). These dead stellar environments accelerate particles, emitting by non-thermal mechanisms up to the TeV range, and they are considered as a major contributor to the very-high-energy band of the local cosmic-ray spectrum.
Aims. This study investigates the effect of the runaway motion of supernova progenitors on the spatial distribution of SNRs in the Milky Way and how this influences the deduced properties of the population.
Methods. We construct Galactic populations of SNRs by Monte Carlo simulation, taking into account the bulk motion and the evolution history of their progenitor stars once ejected from their parent clusters. The gamma-ray domain emission of each population is then calculated, to be compared with the High Energy Stereoscopic System (H.E.S.S.) Galactic Plane Survey.
Results. We find that including the runaway motion of supernova progenitors strongly modifies the detectability of the simulated emission of their remnants in the very-high-energy band. Particularly, our best fit model using a Reid Milky Way model for core-collapse supernova progenitors requires 33% of massive runaway stars, which is close to the known fraction of runaway high-mass stars, to be in accordance with the H.E.S.S. Galactic Plane Survey data.
Conclusions. Our results show that the runaway nature of supernova progenitors must be taken into account in the study of the Galactic population of SNRs within the H.E.S.S. Galactic Plane Survey and the forthcoming Galactic Plane Survey of the Cherenkov Telescope Array Observatory, as it is a governing factor of the detectability of non-thermal emission of their subsequent SNRs.The authors would like to give the referee a big thank-you, their suggestions and comments significantly improved the work. The authors are grateful for the computing time on the high-performance computer “Lise” at the NHR Center NHR@ZIB, jointly supported by the Federal Ministry of Education and Research and the state governments participating in the NHR (https://www.nhr-verein.de/unsere-partner). This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) with the grant 500120112 and supported by the grant PID2021-124581OB-I00 funded by MCIN/AEI/10.13039/501100011033 and 2021SGR00426 of the Generalitat de Catalunya. This work is also supported by the Spanish program Unidad de Excelencia María de Maeztu CEX2020-001058-M. This work is also supported by MCIN with funding from European Union NextGeneration EU (PRTR-C17.I1).With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (CEX2020-001058-M)Peer reviewe
Estimating the performance gain achievable by the H. E. S. S. I camera upgrade
No full textThe High Energy Stereoscopic System (H.E.S.S.) is an array of four 12-m and one 28-m Imaging Atmospheric Cherenkov Telescopes (IACT) that is used to study the emission of cosmic gamma-rays at very-high energies (100 GeV − 100 TeV). In 2015/2016 the H. E. S. S. collaboration undertook an upgrade of the more than 10-year-old cameras of the four 12-m-telescopes. The upgrade aims for an increase of the rate of gamma-ray events that are observed by more than one telescope (stereo events) by reducing the dead time of the telescopes. Especially at low energies, where currently most gamma-ray events are recorded only by the 28-m-telescope (mono events), the more accurate reconstruction of stereo events will improve the performance of the system.In the course of this thesis Monte Carlo simulations are used to estimate the performance gain that can be achieved with the camera upgrade. The standard simulation chain has been adjusted for this purpose. The adjustments include the implementation of the effect of the dead time of the cameras, the reduction of the pixel trigger threshold and the read-out of additional information related to the signal timing in each pixel. Based on the signal timing a new image cleaning approach is introduced.An optimisation of analysis parameters is performed in order to yield the maximal perfor- mance for the upgraded system. The performance of a Hillas-based stereo event analysis of simulated data for the upgraded cameras, using the optimised parameters, is compared to the performance of the original cameras with the standard analysis parameters being applied. Furthermore, the performance of a mono event analysis is compared to the stereo event anal- yses. The comparison reveals that the camera upgrade can reduce the energy threshold for a Hillas-based stereo event analysis by 25 % down to 100 GeV. For the same analysis param- eters the reduction of the dead time improves the sensitivity by a factor of 30 % in the core energy range around 1TeV. It is also shown that stereo event analyses with the upgraded cameras provide a higher angular resolution, a more accurate energy reconstruction and a better sensitivity than a mono event analysis.The new image cleaning approach is demonstrated to be able to reduce the impact of elec- tronic noise and the night sky background in event images notably when low pixel intensity thresholds are applied for the cleaning. Since applying low pixel intensity thresholds could ad- ditionally reduce the energy threshold of the system, further investigations are recommended to test whether this method can be optimised to yield an improved image quality compared to a standard cleaning with high pixel intensity thresholds.Finally, this work proves that the camera upgrade enhances the performance of H. E. S. S. sig- nificantly, which will allow for more precise analyses of cosmic gamma-ray source at very-high energies
Modelling the Galactic very-high-energy
No full textContext. The High Energy Stereoscopic System Galactic plane survey (HGPS) is to date the most comprehensive census of Galactic γ-ray sources at very high energies (VHE; 100 GeV ≤ E ≤ 100 TeV). As a consequence of the limited sensitivity of this survey, the 78 detected γ-ray sources comprise only a small and biased subsample of the overall population. The larger part consists of currently unresolved sources, which contribute to large-scale diffuse emission to a still uncertain amount.
Aims. We study the VHE γ-ray source population in the Milky Way. For this purpose population-synthesis models are derived based on the distributions of source positions, extents, and luminosities.
Methods. Several azimuth-symmetric and spiral-arm models are compared for spatial source distribution. The luminosity and radius function of the population are derived from the source properties of the HGPS data set and are corrected for the sensitivity bias of the HGPS. Based on these models, VHE source populations are simulated and the subsets of sources detectable according to the HGPS are compared with HGPS sources.
Results. The power-law indices of luminosity and radius functions are determined to range between −1.6 and −1.9 for luminosity and −1.1 and −1.6 for radius. A two-arm spiral structure with central bar is discarded as spatial distribution of VHE sources, while azimuth-symmetric distributions and a distribution following a four-arm spiral structure without bar describe the HGPS data reasonably well. The total number of Galactic VHE sources is predicted to be in the range from 800 to 7000 with a total luminosity and flux of (1.6 − 6.3) × 1036 ph s−1 and (3 − 15) × 10−10 ph cm−2 s−1, respectively.
Conclusions. Depending on the model, the HGPS sample accounts for (68 − 87)% of the emission of the population in the scanned region. This suggests that unresolved sources represent a critical component of the diffuse emission measurable in the HGPS. With the foreseen jump in sensitivity of the Cherenkov Telescope Array, the number of detectable sources is predicted to increase by a factor between 5 and 9
Probing Galaxy structure with VHE rays
No full textAs an observer from within the Milky Way, it is difficult to determine its
global structure. Despite extensive observational data from surveys at
different wavelengths, we have no conclusive description of the structure of
our own Galaxy. For very-high-energy (VHE) rays, the most
comprehensive catalogue of Galactic sources resulting from the H.E.S.S.
Galactic Plane Survey (HGPS) shows a striking asymmetry in the distribution of
the sources in the latitudinal direction. This could be the result of a local
feature in the spatial distribution of the sources or it could be due to the
position of the Sun above the Galactic plane. In this contribution, we estimate
the position of the Sun based on the latitudinal flux profile of VHE
-ray sources, assuming three mirror-symmetric models for the spatial
distribution of the sources in three-dimensional space and taking into account
the observational bias of the HGPS. We verify our method using simulations and
find values for between and
depending on the considered model. Our results show that the position of the
Sun has a significant impact on the observed source distribution and must
therefore be taken into account when modelling the population of Galactic VHE
sources. However, it is not conclusive whether the Sun's offset from
the Galactic plane is the only factor leading to the asymmetry in the
latitudinal profile.Comment: 6 pages, 3 figures, Proceedings of the 7th Heidelberg International
Symposium on High-Energy Gamma-Ray Astronomy (-2022), Barcelona,
Spai
Modellierung der Population galaktischer Quellen von sehr hochenergetischer Gammastrahlung
No full textThe current generation of ground-based instruments has rapidly extended the limits of the range accessible to us with very-high-energy (VHE) gamma-rays, and more than a hundred sources have now been detected in the Milky Way. These sources represent only the tip of the iceberg, but their number has reached a level that allows population studies. In this work, a model of the global population of VHE gamma-ray sources based on the most comprehensive census of Galactic sources in this energy regime, the H.E.S.S. Galactic plane survey (HGPS), will be presented. A population synthesis approach was followed in the construction of the model. Particular attention was paid to correcting for the strong observational bias inherent in the sample of detected sources. The methods developed for estimating the model parameters have been validated with extensive Monte Carlo simulations and will be shown to provide unbiased estimates of the model parameters. With these methods, five models for different spatial distributions of sources have been constructed. To test the validity of these models, their predictions for the composition of sources within the sensitivity range of the HGPS are compared with the observed sample. With one exception, similar results are obtained for all spatial distributions, showing that the observed longitude profile and the source distribution over photon flux are in fair agreement with observation. Regarding the latitude profile and the source distribution over angular extent, it becomes apparent that the model needs to be further adjusted to bring its predictions in agreement with observation. Based on the model, predictions of the global properties of the Galactic population of VHE gamma-ray sources and the prospects of the Cherenkov Telescope Array (CTA) will be presented.
CTA will significantly increase our knowledge of VHE gamma-ray sources by lowering the threshold for source detection, primarily through a larger detection area compared to current-generation instruments. In ground-based gamma-ray astronomy, the sensitivity of an instrument depends strongly, in addition to the detection area, on the ability to distinguish images of air showers produced by gamma-rays from those produced by cosmic rays, which are a strong background. This means that the number of detectable sources depends on the background rejection algorithm used and therefore may also be increased by improving the performance of such algorithms. In this context, in addition to the population model, this work presents a study on the application of deep-learning techniques to the task of gamma-hadron separation in the analysis of data from ground-based gamma-ray instruments. Based on a systematic survey of different neural-network architectures, it is shown that robust classifiers can be constructed with competitive performance compared to the best existing algorithms. Despite the broad coverage of neural-network architectures discussed, only part of the potential offered by the
application of deep-learning techniques to the analysis of gamma-ray data is exploited in the context of this study. Nevertheless, it provides an important basis for further research on this topic.Die aktuelle Generation bodengestützter Instrumente hat die Grenzen des uns mit sehr hoch-energetischer (very-high-energy, VHE) Gammastrahlung zugänglichen Bereichs rasch erweitert, so dass inzwischen bereits mehr als hundert Quellen in der Milchstraße entdeckt wurden. Diese Quellen repräsentieren zwar nur die Spitze des Eisbergs, doch ihre Anzahl hat ein Niveau erreicht, das Populationsstudien ermöglicht. In dieser Arbeit wird ein Modell der globalen Population von VHE Gammastrahlungsquellen vorgestellt, das auf den umfassendsten Zensus galaktischer Quellen in diesem Energiebereich, dem H.E.S.S. Galactic plane survey (HGPS), beruht. Bei der Erstellung des Modells wurde ein Populationssynthese-Ansatz verfolgt. Besonderes Augenmerk wurde auf die Korrektur der starken Beobachtungsverzerrung gelegt, die der Stichprobe detektierter Quellen innewohnt. Die für die Schätzung der Modellparameter entwickelten Methoden wurden mit umfangreichen Monte-Carlo-Simulationen validiert und es wird gezeigt, dass sie akkurate Schätzungen der Modelparameter ermöglichen. Mit diesen Methoden wurden fünf Modelle für verschiedene räumliche Verteilungen von Quellen erstellt. Um die Gültigkeit dieser Modelle zu prüfen, werden ihre Vorhersagen für die Zusammensetzung der Quellen innerhalb des Sensitivitätsbereichs des HGPS mit der beobachteten Stichprobe verglichen. Mit einer Ausnahme werden für alle räumlichen Verteilungen ähnliche Ergebnisse erzielt, die zeigen, dass das beobachtete Longitudenprofil und die Quellenverteilung über den Photonenfluss gut mit der Beobachtung übereinstimmen. Bezüglich des Latitudenprofils und der Quellenverteilung über die Winkelausdehnung zeigt sich, dass das Modell weiter angepasst werden muss, um dessen Vorhersagen mit den Beobachtungen in Einklang zu bringen. Auf der Grundlage des Modells werden Vorhersagen über die globalen Eigenschaften der galaktischen Population von VHE Gammastrahlungsquellen und die Perspektiven des Cherenkov Telescope Array (CTA) vorgestellt.
CTA wird unser Wissen über VHE Gammastrahlungsquellen erheblich erweitern, indem es die Detektionsschwelle für die Quellen senkt, vor allem durch einer im Vergleich zu Instrumenten der aktuellen Generation größeren Detektionsfläche. In der bodengebundenen Gammastrahlenastronomie hängt die Empfindlichkeit eines Instruments neben der Detektionsfläche jedoch auch stark von der Fähigkeit ab, Bilder von Luftschauern, die durch Gammastrahlen erzeugt werden, von denen zu unterscheiden, die durch kosmische Strahlung erzeugt werden und einen starken Hintergrund darstellen. Dies bedeutet, dass die Anzahl der detektierbaren Quellen von dem verwendeten Algorithmus zur Hintergrundunterdrückung abhängt und daher möglicherweise auch durch eine Verbesserung der Leistung solcher Algorithmen erhöht werden kann. In diesem Zusammenhang wird in dieser Arbeit zusätzlich zum Populationsmodell eine Studie über die Anwendung von Deep-Learning-Techniken für die Aufgabe der Gamma-Hadron-Trennung bei der Analyse von Daten von bodengestützten Gammastrahleninstrumenten vorgestellt. Auf der Grundlage einer systematischen Untersuchung verschiedener neuronaler Netzwerkarchitekturen wird gezeigt, dass robuste Klassifikatoren konstruiert werden können, die im Vergleich zu den besten bestehenden Algorithmen eine konkurrenzfähige Leistung aufweisen. Trotz des Umfangs der diskutierten neuronalen Netzwerkarchitekturen wird im Rahmen dieser Studie nur ein Teil des Potenzials ausgeschöpft, das die Anwendung von Deep-Learning-Techniken für die Analyse von Daten in der Gammaastronomie bietet. Dennoch bietet sie eine wichtige Grundlage für weitere Forschungen zu diesem Thema
Sexual Capital in the Public Version
No full textThe main intention of Samuel Nowak—the author of Sexual Capital—is to define “what the mass media are for men labelling themselves as gay, taking into account various, although always treated collectively, contexts: economic, political and medial”(p. 9). The sub-title of the study, which defines the direction of the whole text, is Wyobrażone wspólnotysmaku i medialne tożsamości polskich gejów (“Imagined Communities of Taste and Medial Identities of Polish Gay Persons”). In the Nowak’s study, important is the evaluation from outside (as viewed by science) and from within (as viewed by proponents of LGBT). The critical review of Sexual Capital is compatible with the structure of the original text: originally focuses on scientific theories in order to end with the examples from Polish medial realities.</p
HexagDLy—Processing hexagonally sampled data with CNNs in PyTorch
No full textHexagDLy is a Python-library extending the PyTorch deep learning framework with convolution and pooling operations on hexagonal grids. It aims to ease the access to convolutional neural networks for applications that rely on hexagonally sampled data as, for example, commonly found in ground-based astroparticle physics experiments. Keywords: Convolutional neural networks, Hexagonal grid, PyTorch, Astroparticle physic
HexagDLy - Hexagonal Convolutions with PyTorch
No full text<p>HexagDLy provides convolution and pooling methods for hexagonally sampled input data on the basis of the deep learning framework PyTorch.</p>
Exploring the population of Galactic very-high-energy gamma-ray sources
No full textAt very high energies (VHE), the emission of γ rays is dominated by discrete sources. Due to the limited resolution and sensitivity of current-generation instruments, only a small fraction of the total Galactic population of VHE γ-ray sources has been detected significantly. The larger part of the population can be expected to contribute as a diffuse signal alongside emission originating from propagating cosmic rays. Without quantifying the source population, it is not possible to disentangle these two components. Based on the H.E.S.S. Galactic plane survey, a numerical approach has been taken to develop a model of the population of Galactic VHE γ-ray sources, which is shown to account accurately for the observational bias. We present estimates of the absolute number of sources in the Galactic Plane and their contribution to the total VHE γ-ray emission for five different spatial source distributions. Prospects for CTA and its ability to constrain the model are discussed. Finally, first results of an extension of our modelling approach using machine learning to extract more information from the available data set are presented
Seksualny kapitał w wersji publicznej
No full textThe main intention of Samuel Nowak—the author of Sexual Capital—is to define “what the mass media are for men labelling themselves as gay, taking into account various, although always treated collectively, contexts: economic, political and medial”(p. 9). The sub-title of the study, which defines the direction of the whole text, is Wyobrażone wspólnotysmaku i medialne tożsamości polskich gejów (“Imagined Communities of Taste and Medial Identities of Polish Gay Persons”). In the Nowak’s study, important is the evaluation from outside (as viewed by science) and from within (as viewed by proponents of LGBT). The critical review of Sexual Capital is compatible with the structure of the original text: originally focuses on scientific theories in order to end with the examples from Polish medial realities
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