After three years of reflection and development, the "Astro-Colibri" application has just been launched. This digital interface, created by researchers at Irfu/DPhP, aims to make information on transient and multi-messenger phenomena easily accessible in real time. The need to react quickly to the most violent explosions in the universe and the large amount of information provided by the global network of observatories requires new approaches and new tools. Through "Astro-Colibri", several observatories now have the capacity to coordinate in monitoring and identifying the sources of physical phenomena in the transient sky.
The platform, which exists in the form of a smartphone application (IOS and Android) and a website, allows alerts to be put into their observational context by cross-referencing them with already known data. This saves researchers a considerable amount of time. In addition, the application anticipates the best possible observation periods for a given observatory. This free interface is also a fun and practical tool for astrophysics enthusiasts who will be able to easily move around this functional application.
Astronomy and astrophysics are currently undergoing several fundamental changes, such as the increasing relevance of observations of transients, i.e., short-lived astrophysical phenomena such as supernova explosions, fast radio bursts (FRBs), and gamma-ray bursts (GRBs). At the same time, an increasing number of fundamentally new cosmic messengers provide crucial information about these objects. Today, the detection of high-energy neutrinos and gravitational waves (GWs) routinely supplement traditional astronomical observations in the electromagnetic spectrum. These trends will continue in the coming years, which will see the advent of a large variety of next-generation observatories dedicated to time-domain astronomy and astrophysics. These observatories cover the full electromagnetic spectrum from the radio domain (e.g., Square Kilometer Array), optical observations (e.g., Vera Rubin Observatory), X-rays (e.g. SVOM, ATHENA), to the highest energy gamma-rays (e.g., LHAASO, Cherenkov Telescope Array (CTA)). These are complemented by significant improvements and commissioning of observatories of novel messengers from the violent universe: high-energy neutrinos (IceCube-Gen2, KM3NeT, GVD) and GWs (Virgo/LIGO/KAGRA, LISA).
The wealth of information provided by the worldwide network of observatories, combined with the need for reactions in real-time to catch the most violent explosions in the universe requires novel approaches and new tools. In this context we have developed “Astro-COLIBRI”, a platform that evaluates alerts of transient observations in real time, filters them by user-specified criteria, and puts them into their multiwavelength and multimessenger context. Through fast generation of an overview of persistent sources as well as transient events in the relevant phase space, Astro-COLIBRI contributes to an enhanced discovery potential of both serendipitous and follow-up observations of the transient sky.
Figure 1: Astro-COLIBRI is a central point for information about astrophysical sources and transient events
The software's architecture comprises an Application Programming Interface (API), both a static and a real-time database, a cloud-based alert system, as well as a website and apps for iOS and Android as clients for users. The latter provides a graphical representation with a summary of the relevant data to allow for the fast identification of interesting phenomena along with an assessment of observing conditions at a large selection of observatories around the world. Providing direct access to a large number of additional and external services, Astro-COLIBRI is a central point of accessing information about astrophysical sources and transient events (cf. Fig. 1).
Astro-COLIBRI is a complex, cloud-based computing architecture as illustrated in Fig. 2. It is centered around a RestFul API. Clients and external services can send HTML requests to the API through various public and private/protected endpoints. The API is built within the Flask framework using Python as the programming language, performs specific, computing intensive tasks and returns a JSON file with the computed and collected information. It runs in a container and can thus be flexibly deployed on any cloud-computing platform. Currently, the API is hosted on the Heroku cloud-computing service.
Figure 3: Sky view showing the position of the IceCube-170922A event in black and the position of other active sky sources for the specified time period (in green, the Fermi sources, in orange the Swift sources for example). On the right, characteristics of the event are given as well as its visibility by the HESS telescope over the next 24 hours
To notify users in the most effective way and to provide modern and mobile usage we decided to develop platform-independent Astro-COLIBRI user interfaces. Using the open-source framework Flutter, we developed a website and apps for iOS and Android natively in the programming language Dart. Since we only use one common codebase for all clients, the maintenance of the code remains effortless and the implementation of further features particularly fast. The website is accessible via various URLs (e.g. https://astro-colibri.com and https://astro-colibri.science) and is hosted in Firebase, which provides a performant, low-latency access. A screenshot of the website is shown in Figure 3. The clients are connected via streams to a real-time database hosted at Firebase Firestore. Transient events which are interesting for the user are displayed via these streams in real time and announced via push notifications on mobile devices.
Astro-COLIBRI presents the events in the context of historical data, as well as other transient events under consideration of timescales relevant for the respective event category. For this purpose, Astro-COLIBRI uses cone searches around the event of interest, in which sources and transient events are shown, the latter being filtered for the user-adjustable relevant timescale. An example cone search is presented in the smartphone view in the left image of Figure 4. The uncertainty of the localization of the selected transient event is visualized by the boundary matching the color of the marker. In this example, it is the black ellipse.
In multiwavelength and multimessenger astronomy, there is an increasing demand for rapid and multi-mission coordination for follow-up observations of transient events. Astro-COLIBRI shows the near-term and long-term visibility and observability of transient events of all major observatories or custom locations. The visibility plots contain the monitoring of source altitude, Sun and Moon altitude, Moon phase, Moon-to-source separation if available, etc. In the website and apps, the visibility for the user-selected observatory is shown immediately for the events/source selected by the user. The exact observation conditions, including observations possible during Moon time, are implemented for selected observatories already. The right image of Figure 4 shows an example of a visibility plot for H.E.S.S. that contains observatory-specific details. Via a customized link to the ESA based Tool for Observation visiBilitY and schedule (TOBY), users also have direct access to the visibility and schedule of space-based observatories like INTEGRAL, Gaia, Chandra, Insight-HXMT, XMM-Newton, and Swift.
Astro-COLIBRI is free to use for both professional and amateur astronomers. It is already regularly being using by burst advocates in several observatories (e.g. H.E.S.S., CTA/LST-1, SVOM, etc.). The website is available at https://astro-colibri.com and the smartphone apps can be found in the relevant app stores (Android / iOS). Further information, tutorials, etc. are available on our dedicated YouTube channel. Follow us on Twitter: @AstroColibri
A paper describing the functionalities has just been published in the Astrophysical Journal (P. Reichherzer et al 2021 ApJS 256 5, journal link + arXiv). Concrete examples of uses are described in (F. Schüssler et al. PoS (ICRC2021) 935 (2021), arXiv).