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The GALEX Time Domain Survey. I. Selection and Classification of Over a Thousand Ultraviolet Variable Sources

Gezari, S. and Martin, D. C. and Forster, K. and Neill, J. D. and Huber, M. and Heckman, T. and Bianchi, L. and Morrissey, P. and Neff, S. G. and Seibert, M. and Schiminovich, D. and Wyder, T. K. and Burgett, W. S. and Chambers, K. C. and Kaiser, N. and Magnier, E. A. and Price, P. A. and Tonry, J. L. (2013) The GALEX Time Domain Survey. I. Selection and Classification of Over a Thousand Ultraviolet Variable Sources. Astrophysical Journal, 766 (1). Art. No. 60. ISSN 0004-637X.

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We present the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in ∼40 deg^2 of GALEX Time Domain Survey (TDS) NUV images observed with a cadence of 2 days and a baseline of observations of ∼3 years. The GALEX TDS fields were designed to be in spatial and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which provides deep optical imaging and simultaneous optical transient detections via image differencing.We characterize the GALEX photometric errors empirically as a function of mean magnitude, and select sources that vary at the 5σ level in at least one epoch. We measure the statistical properties of the UV variability, including the structure function on timescales of days and years. We report classifications for the GALEX TDS sample using a combination of optical host colors and morphology, UV light curve characteristics, and matches to archival X-ray, and spectroscopy catalogs. We classify 62% of the sources as active galaxies (358 quasars and 305 active galactic nuclei), and 10% as variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2 cataclysmic variables). We detect a large-amplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to |Δm| = 4.6 mag and 2.9 mag, respectively. The mean amplitude of the structure function for quasars on year timescales is five times larger than observed at optical wavelengths. The remaining unclassified sources include UV-bright extragalactic transients, two of which have been spectroscopically confirmed to be a young core-collapse supernova and a flare from the tidal disruption of a star by dormant supermassive black hole. We calculate a surface density for variable sources in the UV with NUV < 23 mag and |Δm| > 0.2 mag of ∼8.0, 7.7, and 1.8 deg^(−2) for quasars, active galactic nuclei, and RR Lyrae stars, respectively. We also calculate a surface density rate in the UV for transient sources, using the effective survey time at the cadence appropriate to each class, of ∼15 and 52 deg^(−2) yr^(−1) for M dwarfs and extragalactic transients, respectively.

Item Type:Article
Related URLs:
URLURL TypeDescription 10.1088/0004-637X/766/1/60DOIArticle
Neill, J. D.0000-0002-0466-1119
Chambers, K. C.0000-0001-6965-7789
Magnier, E. A.0000-0002-7965-2815
Additional Information:© 2013 American Astronomical Society. Received 2012 November 19; accepted 2013 February 1; published 2013 March 7. We thank the anonymous referee for their constructive comments which improved the paper. GALEX (Galaxy Evolution Explorer) is a NASA Small Explorer, launched in 2003 April. We gratefully acknowledge NASA’s support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d’Etudes Spatiales of France and the Korean Ministry of Science and Technology. The Pan-STARRS1 survey has been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, and the Las Cumbres Observatory Global Telescope Network, Incorporated, the National Central University of Taiwan, and the National Aeronautics and Space Administration under grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate.
Group:Space Astrophysics Laboratory
Funding AgencyGrant Number
Subject Keywords:surveys; ultraviolet: general
Record Number:CaltechAUTHORS:20130412-100925592
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Official Citation:The GALEX Time Domain Survey. I. Selection and Classification of Over a Thousand Ultraviolet Variable Sources S. Gezari et al. 2013 ApJ 766 60
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37905
Deposited By: Ruth Sustaita
Deposited On:12 Apr 2013 17:47
Last Modified:22 Nov 2017 19:45

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