Gaia Early Data Release 3

Gaia photometric science alerts^★

¹ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK.
e-mail: sth@ast.cam.ac.uk; dlh@ast.cam.ac.uk
² Kavli Institute for Cosmology, Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago, Chile
⁴ RHEA Group for ESA/ESAC, Camino bajo del Castillo s/n, Urbanización Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁶ SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁷ Warsaw University, Astronomical Observatory, Department of Physics, Al. Ujazdowskie 4, 00-478, Warszawa, Poland
⁸ Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁹ Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
¹⁰ School of Physics, O’Brien Centre for Science North, University College Dublin, Belfield, Dublin 4, Ireland
¹¹ Isaac Newton Group of Telescopes, Apdo. 321, E-38700 Santa Cruz de la Palma, Canary Islands, Spain
¹² Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹³ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network, Konkoly Thege 15-17, 1121 Budapest, Hungary
¹⁴ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
¹⁵ Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí Franquès 1, 08028 Barcelona, Spain
¹⁶ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201AZ, Noordwijk, The Netherlands
¹⁷ STFC, Rutherford Appleton Laboratory, Harwell, Didcot OX11 0QX, UK
¹⁸ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
¹⁹ ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
²⁰ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078, Monte Porzio Catone (Roma), Italy
²¹ Space Science Data Center – ASI, Via del Politecnico SNC, 00133 Roma, Italy
²² ARI/ZAH, Heidelberg University, Heidlelberg, Germany
²³ School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
²⁴ Centre for Advanced Instrumentation, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
²⁵ DAPCOM for Institut de Ciències del Cosmos, Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
²⁶ School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 67AA, UK
²⁷ INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Piero Gobetti 93/3, 40129 Bologna, Italy
²⁸ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
²⁹ Astronomical Observatory (street Volgina 7, 11060 Belgrade, Serbia)
³⁰ National Science Foundation, 2415 Eisenhower Avenue, Alexandria, Virginia 22314, USA
³¹ Sorbonne Universités, UPMC Univ Paris 6 et CNRS, UMR 7095, Institut d’Astrophysique de Paris, IAP, 75014 Paris, France
³² Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
³³ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
³⁴ SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
³⁵ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
³⁶ Center for Astrophysics and Cosmology, University of Nova Gorica, Vipavska 13, 5000 Nova Gorica, Slovenia
³⁷ University of Lethbridge, 4401 University Drive, Lethbridge, Alberta T1K 3M4, Canada
³⁸ Centre for Astrophysics and Planetary Science, School of Physical Sciences, University of Kent, Canterbury CT2 7NH, UK
³⁹ ESA, ESAC, Camino Bajo del Castillo s/n, Urb. Villafranca del Castillo, 28692 Villanueva de la Cañada, Spain
⁴⁰ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁴¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁴² School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
⁴³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53111 Bonn, Germany
⁴⁴ Max Planck Institute for Astronomy, Königstuhl17, 69117 Heidelberg, Germany
⁴⁵ DiRAC Institute, Department of Astronomy, University of Washington, Seattle, WA98195, USA
⁴⁶ INAF-Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁴⁷ Faulkes Telescope Project, School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, Wales, UK
⁴⁸ Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
⁴⁹ Center for Data Driven Discovery, California Institute of Technology, Pasadena, CA 91125, USA
⁵⁰ Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, UK
⁵¹ ZARM, Center of Applied Space Technology and Microgravity, Bremen University, Germany
⁵² Ruđer Bošković Institute, Bijenička cesta 54, Zagreb, Croatia
⁵³ Instytut Astronomiczny, Uniwersytet Wrocławski, Kopernika 11, 51-622 Wrocław, Poland
⁵⁴ South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
⁵⁵ Instituto de Telecomunicações, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
⁵⁶ Departamento de Física, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
⁵⁷ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁵⁸ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
⁵⁹ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁶⁰ INAF Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁶¹ Department of Astronomy, University of Cape Town, 7701 Rondebosch, South Africa

Received: 5 March 2021
Accepted: 20 May 2021

Abstract

Context. Since July 2014, the Gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky.

Aims. We present the Gaia Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by Gaia.

Methods. We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to Gaia and (2) Gaia sources which have undergone a significant brightening or fading. Validation of the Gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours.

Results. We show that the Gaia Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae, C_E = 0.46, is dominated by the Gaia scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is C_I = 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec.

Conclusions. The per-transit photometry for Gaia transients is precise to 1% at G = 13, and 3% at G = 19. The per-transit astrometry is accurate to 55 mas when compared to Gaia DR2. The Gaia Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge.