Gaia Photometric Science Alerts

Abstract

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 per cent at $G=13$, and 3 per cent at $G=19$. The per-transit astrometry is accurate to 55 milliarcseconds 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.

26 pages, 26 figures, accepted for publication in Astronomy & Astrophysics

References in corpus (19)

• The Gaia mission
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• HyperLEDA. III. The catalogue of extragalactic distances
• Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes
• PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects
• Gaia Data Release 1, Pre-processing and source list creation
• Identification of Young Stellar Object candidates in the $Gaia$ DR2 x AllWISE catalogue with machine learning methods
• An ultraviolet excess in the superluminous supernova Gaia16apd reveals a powerful central engine
• Gaia 17bpi: An FU Ori Type Outburst
• The ALMA early science view of FUor/EXor objects - V: continuum disc masses and sizes
• Detecting stars, galaxies, and asteroids with Gaia
• Gaia 18dvy: a new FUor in the Cygnus OB3 association
• Completeness of the Gaia-verse I: when and where were Gaia's eyes on the sky during DR2?
• Gaia 19ajj: A Young Star Brightening Due to Enhanced Accretion + Reduced Extinction
• The 2014-2017 outburst of the young star ASASSN-13db: A time-resolved picture of a very low-mass star between EXors and FUors
• The New EXor Outburst of ESO-H-alpha~99 observed by Gaia ATLAS and TESS
• Extreme variability in an active galactic nucleus: Gaia16aax
• The fast transient sky with Gaia
• Short timescale variables in the Gaia era: detection and characterization by structure function analysis

Cited by in corpus (12)

• A Systematic Study of Ia-CSM Supernovae from the ZTF Bright Transient Survey
• The rise and fall of the iron-strong nuclear transient PS16dtm
• The Galactic Nova Rate: Estimates from the ASAS-SN and Gaia Surveys
• Single-lens mass measurement in the high-magnification microlensing event Gaia19bld located in the Galactic disc
• Recurrent strong outbursts of an EXor-like young eruptive star Gaia20eae
• Predicting the Yield of Small Transiting Exoplanets around Mid-M and Ultra-Cool Dwarfs in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey
• Photometric and Spectroscopic monitoring of YSOs in nearby star forming regions. I. Eruptive YSOs
• Machine Learning based search for Cataclysmic Variables within Gaia Science Alerts
• Astro-COLIBRI 2 -- an advanced platform for real-time multi-messenger discoveries
• Photometric and spectroscopic study of the burst-like brightening of two Gaia-alerted young stellar objects
• A survey for variable young stars with small telescopes: VI -- Analysis of the outbursting Be stars NSW284, Gaia19eyy, and VES263
• Automatic Detection of Accretion Bursts in Young Stellar Objects: a New Algorithm for Long--Term Sky Surveys