Type Ia supernovae are exploding stars that are used to measure the accelerated expansion of the Universe and are responsible for most of the iron ever produced. Although there is general agreement ...that the exploding star is a white dwarf in a binary system, the exact configuration and trigger of the explosion is unclear, which could hamper their use for precision cosmology. Two families of progenitor models have been proposed. In the first, a white dwarf accretes material from a companion until it exceeds the Chandrasekhar mass, collapses and explodes. Alternatively, two white dwarfs merge, again causing catastrophic collapse and an explosion. It has hitherto been impossible to determine if either model is correct. Here we report the discovery of an object in pre-supernova archival X-ray images at the position of the recent type Ia supernova (2007on) in the elliptical galaxy NGC 1404. Deep optical images (also archival) show no sign of this object. From this we conclude that the X-ray source is the progenitor of the supernova, which favours the accretion model for this supernova, although the host galaxy is older (6-9 Gyr) than the age at which the explosions are predicted in the accreting models.
Git is one of the most popular tools for versioning. Start your journey by understanding the Git data model and discover the numerous possibilities that Git notes has to offer. You'll also get ...various tips and tricks for everyday usage and develop knowledge of Git providers, integrations, and clients.
We present new Chandra X-ray observations and detailed astrometry of the field of the type Ia supernova 2007on, for which the detection of a likely progenitor in archival Chandra data was recently ...reported. No source is detected in the new Chandra images, taken six weeks after optical maximum. We calculate a 90–99 per cent probability that any X-ray source near the position of the supernova (SN) is fainter than in the pre-outburst images, depending on the choice of aperture, which supports the identification of the archival X-ray source with the SN. Detailed astrometry of the X-ray and new optical images, however, gives an offset between the SN and the measured X-ray source position of 1.15 ± 0.27 arcsec. Extensive simulations show that the probability of finding an offset of this magnitude is ∼1 per cent, equal to the (trial-corrected) probability of a chance alignment with any X-ray source in the field. This casts doubt on the identification of the X-ray source with the progenitor, although the scenario in which at least some of the observed X-rays are connected to the SN may be the least unlikely based on all available data. After a brief review of the auxiliary evidence, we conclude that only future X-ray observations can shed further light on the proposed connection between the X-ray source and the progenitor of SN 2007on, and thus whether an accreting white dwarf scenario is truly favoured for this SN Ia.
Git: Mastering Version Control Ferdinando Santacroce, Aske Olsson, Rasmus Voss, Jakub Narebski
2016, 2016-10-25T00:00:00
eBook
Learn everything you need to take full control of your workflow with Git with this curated Learning Path – dive in and transform the way you work About This Book * Master all the basic concepts of ...Git to protect your code and make it easier to evolve * Filled with practical recipes that will teach you how to use the most advanced features of the Git system * Harness the full power of the Git version control system to customize Git behavior, manipulate history, integrate external tools, and explore platform shortcuts Who This Book Is For This learning path is for software developers who want to become proficient at using the Git version control system. A basic understanding of any version control system would be beneficial. What You Will Learn * Transport your work to a remote repository in a centralized manner * Experiment with your code without affecting functional code files * Explore some tools used to migrate to Git from other versioning systems without losing your development history * Understand the Git data model and how you can navigate the database with simple commands * Debug with Git and use various techniques to find faulty commits * Customize Git behavior system-wide, on a per-user, per-repository, and per-file basis * Master administering and setting up Git repositories, configuring access, finding and recovering from repository errors, and performing repository maintenance * Chose a workflow and configure/set up support for the chosen workflow In Detail Git is one of the most popular types of Distributed Version Control System. Since its inception, it has attracted skilled developers due to its robust, powerful, and reliable features. Like most powerful tools, Git can be hard to approach for the newcomers. However, this learning path will help you overcome this fear and become adept at all the basic and advanced tasks in Git. This course starts with an introduction to version control systems before you delve deeply into the essentials of Git. This serves as a primer for the topics to follow such as branching and merging, creating and managing a GitHub personal repository, and fork and pull requests. You'll also learn how to migrate from SVN using Git tools or TortoiseGit and migrate from other VCSs, concluding with a collection of resources, links, and appendices. As you progress on to the next module, you will learn how you can automate the usual Git processes by utilizing the hook system built into Git. It also covers advanced repository management, including different options to rewrite the history of a Git repository before you discover how you can work offline with Git, how to track what is going on behind the scenes, and how to use the stash for different purposes. Moving forward, you will gain deeper insights into Git's architecture, its underlying concepts, behavior, and best practices. It gives a quick implementation example of using Git for a collaborative development of a sample project to establish the foundation knowledge of Git operational tasks and concepts. By exploring advanced Git practices, you will attain a deeper understanding of Git's behavior, allowing you to customize and extend existing recipes and write your own. This Learning Path is a blend of content, all packaged up keeping your journey in mind. It includes content from the following Packt products: * Git Essentials, Ferdinando Santacroce * Git Version Control Cookbook, Aske Olsson and Rasmus Voss * Mastering Git, Jakub Narebski Style and approach Its step-by-step approach with useful information makes this course the ultimate guide to understanding and mastering Git. This course will show the road to mastery example by example, while also explaining the mental model of Git.
## In Detail Starting with the Git data model, you will learn how Git stores files and how it looks at commits. You will then learn how you can recover from mistakes; from committing on the wrong ...branch to recovering lost commits/files. Next, you will discover how you can force rebase on some branches and use regular Git merge on other branches. You will also learn how to extract information from the repository. As you progress through this book, you will learn how you can automate the usual Git processes by utilizing the hook system built into Git. The book also covers advanced repository management, including different options to rewrite the history of a Git repository. Finally, you will discover how you can work offline with Git, how to track what is going on behind the scenes, and how to use the stash for different purposes. ## Approach This practical guide contains a wide variety of recipes, taking you through all the topics you need to know about to fully utilize the most advanced features of the Git system. ## Who this book is for If you are a software developer or a build and release engineer who uses Git in your daily work and want to take your Git knowledge to the next level, then this book is for you. To understand and follow the recipes included in this book, basic knowledge of Git command-line code is mandatory.
Starting with the Git data model, you will learn how Git stores files and how it looks at commits. You will then learn how you can recover from mistakes; from committing on the wrong branch to ...recovering lost commits/files. Next, you will discover how you can force rebase on some branches and use regular Git merge on other branches. You will also learn how to extract information from the repository. As you progress through this book, you will learn how you can automate the usual Git processes by utilizing the hook system built into Git. The book also covers advanced repository management, including different options to rewrite the history of a Git repository. Finally, you will discover how you can work offline with Git, how to track what is going on behind the scenes, and how to use the stash for different purposes.
Git is one of the most popular types of Distributed Version Control System. Since its inception, it has attracted skilled developers due to its robust, powerful, and reliable features. Like most ...powerful tools, Git can be hard to approach for the newcomers. However, this learning path will help you overcome this fear and become adept at all the basic and advanced tasks in Git. This course starts with an introduction to version control systems before you delve deeply into the essentials of Git. This serves as a primer for the topics to follow such as branching and merging, creating and managing a GitHub personal repository, and fork and pull requests. You'll also learn how to migrate from SVN using Git tools or TortoiseGit and migrate from other VCSs, concluding with a collection of resources, links, and appendices. As you progress on to the next module, you will learn how you can automate the usual Git processes by utilizing the hook system built into Git. It also covers advanced repository management, including different options to rewrite the history of a Git repository before you discover how you can work offline with Git, how to track what is going on behind the scenes, and how to use the stash for different purposes. Moving forward, you will gain deeper insights into Git's architecture, its underlying concepts, behavior, and best practices. It gives a quick implementation example of using Git for a collaborative development of a sample project to establish the foundation knowledge of Git operational tasks and concepts. By exploring advanced Git practices, you will attain a deeper understanding of Git’s behavior, allowing you to customize and extend existing recipes and write your own.
We report the discovery of a bright X-ray transient CXOU J132527.6-430023 in the nearby early-type galaxy NGC 5128. The source was first detected over the course of five Chandra observations in 2007, ...reaching an unabsorbed outburst luminosity of (1-2) x 10 super(38) erg s super(-1) in the 0.5-7.0 keV band before returning to quiescence. Such luminosities are possible for both stellar-mass black hole and neutron star (NS) X-ray binary transients. Here, we attempt to characterize the nature of the compact object. No counterpart has been detected in the optical or radio sky, but the proximity of the source to the dust lanes allows for the possibility of an obscured companion. The brightness of the source after a >100-fold increase in X-ray flux makes it either the first confirmed transient non-ultraluminous X-ray black hole system in outburst to be subject to detailed spectral modeling outside the Local Group, or a bright (>10 super(38) erg s super(-1)) transient NS X-ray binary, which are very rare. Such a large increase in flux would appear to lend weight to the view that this is a black hole transient. X-ray spectral fitting of an absorbed power law yielded unphysical photon indices, while the parameters of the best-fit absorbed disk blackbody model are typical of an accreting ~10 M sub(middot in circle) black hole in the thermally dominant state.
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