Gamma-Hadron Separation in Very-High-Energy gamma-ray astronomy using a multivariate analysis method

In recent years, Imaging Atmospheric Cherenkov Telescopes (IACTs) have discovered a rich diversity of very high energy (VHE, > 100 GeV) gamma-ray emitters in the sky. These instruments image Cherenkov light emitted by gamma-ray induced particle cascades in the atmosphere. Background from the much more numerous cosmic-ray cascades is efficiently reduced by considering the shape of the shower images, and the capability to reduce this background is one of the key aspects that determine the sensitivity of a IACT. In this work we apply a tree classification method to data from the High Energy Stereoscopic System (H.E.S.S.). We show the stability of the method and its capabilities to yield an improved background reduction compared to the H.E.S.S. Standard Analysis.Comment: 10 pages, 9 figures, accepted for publication in Astroparticle Physic

Very High Energy Gamma-Ray Observations with H.E.S.S

The H.E.S.S. Imaging Atmospheric Cherenkov Telescope Array is currently the most sensitive instrument for Very High Energy (VHE) gamma-ray observations in the energy range of about 0.1-10 TeV. During more than two years of operation with the complete 4-telescope array, many galactic and extragalactic VHE gamma-ray sources have been discovered. With its superior sensitivity and its large field-of-view camera, H.E.S.S. is particularly suited for surveys and detailed studies of extended sources. A selection of recent H.E.S.S. results is presented in this proceeding.Comment: 8 pages, 4 figures, to appear in the proceedings of the 41st Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Aosta Valley, Italy, 11-18 March 200

The very-high-energy gamma-ray view of the Galactic Centre as of early 2010

Progress in the Imaging Atmospheric Cherenkov Technique has enabled first sensitive observations of the innermost few 100 pc of the Milky Way in Very High Energy (VHE; >100 GeV) gamma rays. Observations by the H.E.S.S. instrument deliver the at date most precise data on this peculiar region, and provide an interesting view onto the acceleration and propagation of energetic particles near the Galactic Centre. Besides two point-like sources -- one coincident with the supermassive black hole (SMBH) Sgr A* -- diffuse VHE emission has been discovered within a 1 deg region around the centre. The current VHE gamma-ray view of the region is reviewed, and possible counterparts of the gamma-ray sources and the origin of the diffuse emission are discussed.Comment: 10 pages, 2 figures, invited contribution to the Galactic Center Workshop, Shanghai (2009

Subscribe to my city:Exploring Rotterdam adolescents’ urban identity construction through social media engagement

The city is the background of many people’s everyday lives. It is a space that contextualizes many of one’s experiences, memories, and ideas. Previous research has explored connections to place from a variety of perspectives (e.g., Proshansky, 1978; Relph, 1976; Tuan, 1977). The city has been found to play an important role in the everyday life, and through this, the construction of one’s identity – the urban identity (Lalli, 1992; Proshansky, 1978; Proshansky et al., 1983). This concept focuses on one’s experiences of and ideas about the city and its inhabitants. In recent decades, the city is something that is no longer only experienced offline but may also be experienced and negotiated online (e.g., Farman, 2015; Saker, 2017; Schwartz &amp; Halegoua, 2014; Wilken &amp; Humphreys, 2021; Yılmaz &amp; Kocabalkanlı, 2021). This is particularly relevant for the adolescent population, who, in this important developmental phase in which they find themselves (Erikson, 1968; Ferrer-Wreder &amp; Kroger, 2019; Marcia, 1993), are known to use the online space for identity construction (boyd, 2014; Granic et al., 2020). This process might be complicated by the superdiversity that nowadays characterizes various big cities (Vertovec, 2007). However, at the same time the city can be understood as a commonality of all kinds of different individuals in their everyday experience of place. As a space for identity construction and negotiation, social media therefore deserves our attention in light of urban identity construction, especially for adolescents who find themselves in the situation where they try to understand who they are and where they belong. Focusing on the super-diverse city of Rotterdam, this dissertation therefore aims to explore question how and to what extent Rotterdam adolescents’ social media use contribute to the creation and negotiation of their urban identity. To do so, the topic is addressed from a variety of angles and using several methods to create a broad understanding of the phenomenon.To be able to understand and contextualize the various aspects of online urban identity, one first needs to understand its various dimensions. In Chapter 2, this dissertation starts by outlining a conceptual model, the trans-spatial urban identity model, that builds on and adds to previous work on online urban identity. It emphasizes the importance of recognizing the layered hybridity and mutual influence of online and offline construction of urban identity. To provide a systematic way to understand urban identity, the model proposes several dimensions. It emphasizes the personal and social elements of urban identity, arguing that they are intertwined but both need to be actively considered. It also focuses on the difference between a user’s own expressions that they share and those that they consume from others. The Chapter also discusses a variety of unique affordances of the online environment that need to be considered in order to conduct research in this field. Finally, two cases are provided, focusing on consumption and production, that bring to light various relevant contexts and demonstrate the conceptual model’s value. The trans-spatial urban identity model provides a background to understand the focus points of the Chapters that follow.Chapter 3 sets out on a general exploration of urban identity and its presence in Rotterdam adolescents’ social media ecology by means of a survey among 324 young participants. It focuses on the relationship between various forms of social media engagement and urban identity. In this Chapter, particular attention is paid to differences between adolescents with or without a migration background in order to take into account the relevance of cultural diversity in the city, building on earlier research that emphasized the importance of a local identity to youngsters with a migrant background (e.g., Day &amp; Badou, 2019). Results show various correlations among and between social media use and urban identity, both its personal and social aspects. It was also found that (personal) urban identity was significantly higher among adolescents with a migrant background. Findings demonstrate the relevance of social media engagement in relation to urban identity, and implicate the importance of urban identity in the context of a culturally diverse city.In Chapter 4, this dissertation dives into the world of local influencers as everyday media idols for Rotterdam adolescents, and therefore focuses on what Rotterdam adolescents consume. Based on the local influencers reported in the survey study, this study explores the content of a number of these influencers in depth by means of a thematic analysis of their YouTube video content, and a network analysis of their affiliation network and related channel networks on the platform. Results show a plethora of ways in which the city appears in the content of these local influencers that could provide viewers with a recognizable framework for urban identity, including various local settings, fellow inhabitants, various cultural elements, its (super-) diversity, and references to one’s own presence in or identification with the city. The network structures further emphasized this affiliation with the city, through its various cultural themes, diversity, and local networks. The next two chapters move towards social media content production by means of a participatory action research study conducted with Rotterdam adolescents. In Chapter 5, the design of the study is explained in detail. TheChapter explains how a multiple-week video making course was created to explore urban identity construction practices during audio-visual social mediacontent production, which was carried out in collaboration with a local philanthropic initiative. The Chapter provides an illustrated approach towards designing and conducting a study in which both the process of and created materials are taken into account when investigating identity construction. Additionally, it provides an illustration of how media literacy and empowerment, as two concepts that were considered as potentially process-related results, were approached by means of conceptualizing its subcomponents as building blocks easily applicable to the study. The procedure and analysis are discussed in detail, and followed by a reflection on the lessons learned, including insights on value of collaborating, the active design for positive impact, the importance of flexibility, and the complexity of the dual role of being a researcher and teacher in the context of this study.Chapter 6 reports on the results of the PAR study. Combining a thematic and interpretative approach in interpreting the data, a thematic illustration was created of the PAR study with 10 participants. Not only did the study look at the created materials, but also at brainstorm materials, group discussions, brief interviews, and observations. The results describe how the city was presented in process as well as in the created materials (a video introducing oneself and a video about life in the city). Various spatial environments, symbolic elements, and social network elements are discussed inside and outside the videos. The predominantly personal, positive tone of the videos stood out, whereas negative and comparative expressions in videos seemed mostly absent. The presentation of the city mainly happened as a part of self-presentation. While participants identified themselves as inhabitants of the city, discussions showed various ideas existed about what characterizes inhabitants. Participants also reported ideas and behaviors outside of the course regarding urban related content, which emphasized the importance of self-presentation in urban identity related content, as well as a gap between ideas for videos and the ultimately created materials. Finally, the Chapter also provides empirical examples of how the building blocks of media literacy and empowerment could be observed in the course, and how they (inter)related to each other and to the (stimulation of) urban identity. This emphasizes the potential for applicability of this type of conceptual building blocks in future participatory action research. The dissertation is concluded by Chapter 7, where findings of the various studies are combined to draw more general conclusions, discuss limitations and opportunities, and see implications for research and society. It discusses the importance of broadening our understanding of the role of the online realm in urban identity construction, the unique findings for adolescents growing up in a trans-spatial environment both in terms of consumption and production, the relevance of online urban identity for living in a super-diverse city, and the practical and impactful implications of identity research. A discussion of limitations and related recommendations for future research include the focus on Rotterdam as a case study, the complexities of identity development and age, the need for a focus on participation, and the most important strengths and limitations of our mixed-method and multi-method approach. Recommendations for societal actors include the advice to use knowledge about online urban identity to strengthen a sense of belonging, make local social media influencers aware of their potential function as local role models, and the need for media literacy education to support a healthy and safe way of expressing urban identity online.<br/

Very High Energy Gamma-Ray Observations of the Galactic Centre Region

Recent progress in pushing the sensitivity of the Imaging Atmospheric Cherenkov Technique into the 10 mCrab regime has enabled first sensitive observations of the innermost few 100 pc of the Milky Way in Very High Energy (VHE; >100 GeV) gamma rays. These observations are a valuable tool to understand the acceleration and propagation of energetic particles near the Galactic Centre. Remarkably, besides two compact gamma-ray sources, faint diffuse gamma-ray emission has been discovered with high significance. The current VHE gamma-ray view of the Galactic Centre region is reviewed, and possible counterparts of the gamma-ray sources and the origin of the diffuse emission are discussed. The future prospects for VHE Galactic Centre observations are discussed based on order-of-magnitude estimates for a CTA type array of telescopes.Comment: 11 pages, 7 figures, Invited talk at the "4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy 2008

Subscribe to my city:Exploring Rotterdam adolescents’ urban identity construction through social media engagement

The city is the background of many people’s everyday lives. It is a space that contextualizes many of one’s experiences, memories, and ideas. Previous research has explored connections to place from a variety of perspectives (e.g., Proshansky, 1978; Relph, 1976; Tuan, 1977). The city has been found to play an important role in the everyday life, and through this, the construction of one’s identity – the urban identity (Lalli, 1992; Proshansky, 1978; Proshansky et al., 1983). This concept focuses on one’s experiences of and ideas about the city and its inhabitants. In recent decades, the city is something that is no longer only experienced offline but may also be experienced and negotiated online (e.g., Farman, 2015; Saker, 2017; Schwartz &amp; Halegoua, 2014; Wilken &amp; Humphreys, 2021; Yılmaz &amp; Kocabalkanlı, 2021). This is particularly relevant for the adolescent population, who, in this important developmental phase in which they find themselves (Erikson, 1968; Ferrer-Wreder &amp; Kroger, 2019; Marcia, 1993), are known to use the online space for identity construction (boyd, 2014; Granic et al., 2020). This process might be complicated by the superdiversity that nowadays characterizes various big cities (Vertovec, 2007). However, at the same time the city can be understood as a commonality of all kinds of different individuals in their everyday experience of place. As a space for identity construction and negotiation, social media therefore deserves our attention in light of urban identity construction, especially for adolescents who find themselves in the situation where they try to understand who they are and where they belong. Focusing on the super-diverse city of Rotterdam, this dissertation therefore aims to explore question how and to what extent Rotterdam adolescents’ social media use contribute to the creation and negotiation of their urban identity. To do so, the topic is addressed from a variety of angles and using several methods to create a broad understanding of the phenomenon.To be able to understand and contextualize the various aspects of online urban identity, one first needs to understand its various dimensions. In Chapter 2, this dissertation starts by outlining a conceptual model, the trans-spatial urban identity model, that builds on and adds to previous work on online urban identity. It emphasizes the importance of recognizing the layered hybridity and mutual influence of online and offline construction of urban identity. To provide a systematic way to understand urban identity, the model proposes several dimensions. It emphasizes the personal and social elements of urban identity, arguing that they are intertwined but both need to be actively considered. It also focuses on the difference between a user’s own expressions that they share and those that they consume from others. The Chapter also discusses a variety of unique affordances of the online environment that need to be considered in order to conduct research in this field. Finally, two cases are provided, focusing on consumption and production, that bring to light various relevant contexts and demonstrate the conceptual model’s value. The trans-spatial urban identity model provides a background to understand the focus points of the Chapters that follow.Chapter 3 sets out on a general exploration of urban identity and its presence in Rotterdam adolescents’ social media ecology by means of a survey among 324 young participants. It focuses on the relationship between various forms of social media engagement and urban identity. In this Chapter, particular attention is paid to differences between adolescents with or without a migration background in order to take into account the relevance of cultural diversity in the city, building on earlier research that emphasized the importance of a local identity to youngsters with a migrant background (e.g., Day &amp; Badou, 2019). Results show various correlations among and between social media use and urban identity, both its personal and social aspects. It was also found that (personal) urban identity was significantly higher among adolescents with a migrant background. Findings demonstrate the relevance of social media engagement in relation to urban identity, and implicate the importance of urban identity in the context of a culturally diverse city.In Chapter 4, this dissertation dives into the world of local influencers as everyday media idols for Rotterdam adolescents, and therefore focuses on what Rotterdam adolescents consume. Based on the local influencers reported in the survey study, this study explores the content of a number of these influencers in depth by means of a thematic analysis of their YouTube video content, and a network analysis of their affiliation network and related channel networks on the platform. Results show a plethora of ways in which the city appears in the content of these local influencers that could provide viewers with a recognizable framework for urban identity, including various local settings, fellow inhabitants, various cultural elements, its (super-) diversity, and references to one’s own presence in or identification with the city. The network structures further emphasized this affiliation with the city, through its various cultural themes, diversity, and local networks. The next two chapters move towards social media content production by means of a participatory action research study conducted with Rotterdam adolescents. In Chapter 5, the design of the study is explained in detail. TheChapter explains how a multiple-week video making course was created to explore urban identity construction practices during audio-visual social mediacontent production, which was carried out in collaboration with a local philanthropic initiative. The Chapter provides an illustrated approach towards designing and conducting a study in which both the process of and created materials are taken into account when investigating identity construction. Additionally, it provides an illustration of how media literacy and empowerment, as two concepts that were considered as potentially process-related results, were approached by means of conceptualizing its subcomponents as building blocks easily applicable to the study. The procedure and analysis are discussed in detail, and followed by a reflection on the lessons learned, including insights on value of collaborating, the active design for positive impact, the importance of flexibility, and the complexity of the dual role of being a researcher and teacher in the context of this study.Chapter 6 reports on the results of the PAR study. Combining a thematic and interpretative approach in interpreting the data, a thematic illustration was created of the PAR study with 10 participants. Not only did the study look at the created materials, but also at brainstorm materials, group discussions, brief interviews, and observations. The results describe how the city was presented in process as well as in the created materials (a video introducing oneself and a video about life in the city). Various spatial environments, symbolic elements, and social network elements are discussed inside and outside the videos. The predominantly personal, positive tone of the videos stood out, whereas negative and comparative expressions in videos seemed mostly absent. The presentation of the city mainly happened as a part of self-presentation. While participants identified themselves as inhabitants of the city, discussions showed various ideas existed about what characterizes inhabitants. Participants also reported ideas and behaviors outside of the course regarding urban related content, which emphasized the importance of self-presentation in urban identity related content, as well as a gap between ideas for videos and the ultimately created materials. Finally, the Chapter also provides empirical examples of how the building blocks of media literacy and empowerment could be observed in the course, and how they (inter)related to each other and to the (stimulation of) urban identity. This emphasizes the potential for applicability of this type of conceptual building blocks in future participatory action research. The dissertation is concluded by Chapter 7, where findings of the various studies are combined to draw more general conclusions, discuss limitations and opportunities, and see implications for research and society. It discusses the importance of broadening our understanding of the role of the online realm in urban identity construction, the unique findings for adolescents growing up in a trans-spatial environment both in terms of consumption and production, the relevance of online urban identity for living in a super-diverse city, and the practical and impactful implications of identity research. A discussion of limitations and related recommendations for future research include the focus on Rotterdam as a case study, the complexities of identity development and age, the need for a focus on participation, and the most important strengths and limitations of our mixed-method and multi-method approach. Recommendations for societal actors include the advice to use knowledge about online urban identity to strengthen a sense of belonging, make local social media influencers aware of their potential function as local role models, and the need for media literacy education to support a healthy and safe way of expressing urban identity online.<br/

A Pointing Solution for the Medium Size Telescopes for the Cherenkov Telescope Array

An important aspect of the calibration of the Cherenkov Telescope Array is the pointing, which enables an exact alignment of each telescope and therefore allows to transform a position in the sky to a point in the plane of the Cherenkov camera and vice versa. The favoured approach for the pointing calibration of the medium size telescopes (MST) is the installation of an optical CCD-camera in the dish of the telescope that captures the position of the Cherenkov camera and of the stars in the night sky simultaneously during data taking. The adaption of this approach is presented in this proceeding.Comment: 6 pages, 9 figures, Proceedings of the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2016