Python for gamma-ray astronomy

Gamma-ray astronomy is a relatively new window on the cosmos. The first source detected from the ground was the Crab nebula, seen by the Whipple telescope in Arizona in 1989. Today, about 150 sources have been detected at TeV energies using gamma-ray telescopes from the ground such as H.E.S.S. in Namibia or VERITAS in Arizona, and about 3000 sources at GeV energies using the Fermi Gamma-ray Space Telescope. Soon construction will start for the Cherenkov Telescope Array (CTA), which will be the first ground-based gamma-ray telescope array operated as an open observatory, with a site in the southern and a second site in the northern hemisphere. In this presentation I will give a very brief introduction to gamma-ray astronomy and data analysis, as well as a short overview of the software used for the various missions. The main focus will be on recent attempts to build open-source gamma-ray software on the scientific Python stack and Astropy: ctapipe as a CTA Python pipeline prototype, Fermipy and the Fermi Science Tools for Fermi-LAT analysis, Gammapy as a community-developed gamma-ray Python package and naima as a non-thermal spectral modeling and fitting package

The γ\gamma-ray Milky Way above 10 GeV: Distinguishing Sources from Diffuse Emission

One of the most prominent features of the $\gamma$-ray sky is the emission from our own Galaxy. The Galactic plane has been observed by Fermi-LAT in GeV and H.E.S.S. in TeV light. Fermi has modeled the Galactic emission as the sum of a complex 'diffuse' emission model with the predominately point source catalogs of 1FHL and 2FGL, while H.E.S.S. has primarily detected extended TeV sources. At GeV energies, Galactic diffuse emission dominates the $\gamma$-ray Milky Way but, as sources have hard spectra, it is likely their emission dominates at TeV energies. Generally the spatial shape and fraction of source emission compared to diffuse emission in the Galactic plane is not well known and is dependent on the source detection method, threshold and diffuse emission modeling methods used. We present a simple image-analysis based method applied to Fermi-LAT data from 10 GeV to 500 GeV, covering a region of +/- 5 degrees in Galactic latitude and +/- 100 degrees in Galactic longitude, to separate source and diffuse emission. This method involves elongated filter smoothing, combined with significance clipping to exclude sources. We test the method against models based on the 1FHL catalog and very simple model Galaxies to evaluate the response for an input of known fraction and shape of diffuse and source emission.Comment: 6 pages, 5 figures; Proceedings of the 10th Workshop on Science with the New Generation of High-Energy Gamma-ray experiments (SciNeGHE) - PoS(Scineghe2014)03

gamma-sky.net: Portal to the Gamma-Ray Sky

Gamma-sky.net is a novel interactive website designed for exploring the gamma-ray sky. The Map View portion of the site is powered by the Aladin Lite sky atlas, providing a scalable survey image tesselated onto a three-dimensional sphere. The map allows for interactive pan and zoom navigation as well as search queries by sky position or object name. The default image overlay shows the gamma-ray sky observed by the Fermi-LAT gamma-ray space telescope. Other survey images (e.g. Planck microwave images in low/high frequency bands, ROSAT X-ray image) are available for comparison with the gamma-ray data. Sources from major gamma-ray source catalogs of interest (Fermi-LAT 2FHL, 3FGL and a TeV source catalog) are overlaid over the sky map as markers. Clicking on a given source shows basic information in a popup, and detailed pages for every source are available via the Catalog View component of the website, including information such as source classification, spectrum and light-curve plots, and literature references. We intend for gamma-sky.net to be applicable for both professional astronomers as well as the general public. The website started in early June 2016 and is being developed as an open-source, open data project on GitHub (https://github.com/gammapy/gamma-sky). We plan to extend it to display more gamma-ray and multi-wavelength data. Feedback and contributions are very welcome!Comment: 6th International Meeting on High Energy Gamma-Ray Astronomy, Heidelberg, 2016. 6 pages, 5 figures. Website: http://gamma-sky.ne

HESS and Fermi Surveys of the Galactic Gamma-ray Source Population

Das High Energy Stereoscopic System (HESS) ist ein Array von vier atmosphärischen Cherenkov-Teleskopen in Namibia, das seit 2004 den Himmel im Bereich hochenergetischer Gammastrahlung (> 100 GeV) beobachtet. In einem erstmaligen Survey der Galaktischen Ebene (circa im Bereich GLON = -110 bis +70 deg, GLAT = -3 bis +3 deg) wurde eine Reihe neuer Gamma-Strahlungs-Quellen entdeckt. Diese Objekte sind kosmische Teilchenbeschleuniger, in denen Gamma-Strahlung durch die Wechselwirking von kosmischer Strahlung mit umgebenden Materie- und Strahlungsfeldern entsteht. In dieser Arbeit wurde der gesamte HESS-Datensatz für die galaktische Ebene benutzt um Signifikanz- und Flußkarten sowie einen Katalog von 62 Quellen zu erstellen, der ihre Position, Ausdehnung und Spektrum angibt. Neue Methoden für eine verbesserte und halb-automatische Erkennung und Analyse aller Quellen wurden entwickelt. Das Fermi Large Area Telescope (LAT) ist ein Satellit, der seit Juni 2008 das Universum kontinuierlich im Bereich von Gammastrahlung oberhalb von 100 MeV observiert. Basierend auf den Daten der ersten 2 Jahre im Bereich von 100 MeV bis 100 GeV hat die LAT-Kollaboration einen 1873 Quellen umfassenden Katalog veröffentlicht, wovon 244 Quellen, vorwiegend galaktischen Ursprungs, im Bereich des HESS-Surveys liegen. In dieser Arbeit wurden Signifikanzkarten und Kataloge von 74 Fermi-Quellen über 10 GeV und 42 Quellen über 100 GeV erstellt und ein vorläufiger Vergleich mit den HESS-Daten wirt präsentiert. Die in dieser Arbeit erstellten Daten können als Grundlage für zukünftige detaillierte Analysen der galaktischen Gamma- Quellen-Population dienen

astroplan: An Open Source Observation Planning Package in Python

We present astroplan - an open source, open development, Astropy affiliated package for ground-based observation planning and scheduling in Python. astroplan is designed to provide efficient access to common observational quantities such as celestial rise, set, and meridian transit times and simple transformations from sky coordinates to altitude-azimuth coordinates without requiring a detailed understanding of astropy's implementation of coordinate systems. astroplan provides convenience functions to generate common observational plots such as airmass and parallactic angle as a function of time, along with basic sky (finder) charts. Users can determine whether or not a target is observable given a variety of observing constraints, such as airmass limits, time ranges, Moon illumination/separation ranges, and more. A selection of observation schedulers are included which divide observing time among a list of targets, given observing constraints on those targets. Contributions to the source code from the community are welcome

Gammapy: A Python package for gamma-ray astronomy

In this article, we present Gammapy, an open-source Python package for the analysis of astronomical $\gamma$-ray data, and illustrate the functionalities of its first long-term-support release, version 1.0. Built on the modern Python scientific ecosystem, Gammapy provides a uniform platform for reducing and modeling data from different $\gamma$-ray instruments for many analysis scenarios. Gammapy complies with several well-established data conventions in high-energy astrophysics, providing serialized data products that are interoperable with other software packages. Starting from event lists and instrument response functions, Gammapy provides functionalities to reduce these data by binning them in energy and sky coordinates. Several techniques for background estimation are implemented in the package to handle the residual hadronic background affecting $\gamma$-ray instruments. After the data are binned, the flux and morphology of one or more $\gamma$-ray sources can be estimated using Poisson maximum likelihood fitting and assuming a variety of spectral, temporal, and spatial models. Estimation of flux points, likelihood profiles, and light curves is also supported. After describing the structure of the package, we show, using publicly available $\gamma$-ray data, the capabilities of Gammapy in multiple traditional and novel $\gamma$-ray analysis scenarios, such as spectral and spectro-morphological modeling and estimations of a spectral energy distribution and a light curve. Its flexibility and power are displayed in a final multi-instrument example, where datasets from different instruments, at different stages of data reduction, are simultaneously fitted with an astrophysical flux model.Comment: 26 pages, 16 figure