The<i>GALEX</i>Ultraviolet Variability Catalog

Welsh, Barry Y.; Wheatley, Jonathan; Heafield, Kenneth; Seibert, Mark; Browne, S. E.; Salim, Samir; Rich, R. Michael; Barlow, Tom A.; Bianchi, Luciana; Byun, Yong Ik; Donas, J.; Forster, Karl; Friedman, Peter G.; Heckman, Timothy M.; Jelinsky, Patrick; Lee, Young-Wook; Madore, Barry F.; Malina, Roger F.; Martin, D. Christopher; Milliard, B.; Morrissey, Patrick; Neff, Susan G.; Schiminovich, David; Siegmund, Oswald H. W.; Small, Todd; Szalay, Alexander S.; Wyder, Ted K.

doi:10.1086/431222

Cited by 35 publications

(35 citation statements)

References 10 publications

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“…Neither category is unexpected given that our search is based on consecutive g P1 r P1 detections with a time-span of about 0.5 hr. M dwarf flares typically exhibit blue colors indicative of T ∼ 10 4 K, with timescales of minutes to hours, and are thus ubiquitous in searches that utilize rapid observations in the ultraviolet (Welsh et al 2005(Welsh et al , 2006 or blue optical bands (Becker et al 2004;Kulkarni & Rau 2006;Rau et al 2008). Similarly, our requirement of two consecutive detections within ∼ 0.5 hr, with non-detections on preceding or subsequent nights is effective at capturing asteroids near the stationary point of their orbits (i.e., at solar elongations of about 130 deg for main-belt asteroids).…”

Section: Limits On the Rate Of Extragalactic Fastmentioning

confidence: 99%

A SEARCH FOR FAST OPTICAL TRANSIENTS IN THE Pan-STARRS1 MEDIUM-DEEP SURVEY: M-DWARF FLARES, ASTEROIDS, LIMITS ON EXTRAGALACTIC RATES, AND IMPLICATIONS FOR LSST

Berger

Leibler

Chornock

et al. 2013

ApJ

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We present a search for fast optical transients (τ ∼ 0.5 hr − 1 d) using repeated observations of the Pan-STARRS1 Medium-Deep Survey (PS1/MDS) fields. Our search takes advantage of the consecutive g P1 r P1 observations (16.5 min in each filter), by requiring detections in both bands, with non-detections on preceding and subsequent nights. We identify 19 transients brighter than 22.5 AB mag (S/N 10). Of these, 11 events exhibit quiescent counterparts in the deep PS1/MDS templates that we identify as M4-M9 dwarfs at d ≈ 0.2 − 1.2 kpc. The remaining 8 transients lack quiescent counterparts, exhibit mild but significant astrometric shifts between the g P1 and r P1 images, colors of (g − r) P1 ≈ 0.5 − 0.8 mag, non-varying light curves, and locations near the ecliptic plane with solar elongations of about 130 deg, which are all indicative of main-belt asteroids near the stationary point of their orbits. With identifications for all 19 transients, we place an upper limit of R FOT (τ ∼ 0.5 hr) 0.12 deg −2 d −1 (95% confidence level) on the sky-projected rate of extragalactic fast transients at 22.5 mag, a factor of 30 − 50 times lower than previous limits; the limit for a timescale of ∼ day is R FOT 2.4 × 10 −3 deg −2 d −1 . To convert these sky-projected rates to volumetric rates, we explore the expected peak luminosities of fast optical transients powered by various mechanisms, and find that nonrelativistic events are limited to M ≈ −10 mag (M ≈ −14 mag) for a timescale of ∼ 0.5 hr (∼ day), while relativistic sources (e.g., gamma-ray bursts, magnetar-powered transients) can reach much larger luminosities. The resulting volumetric rates are 13 Mpc −3 yr −1 (M ≈ −10 mag), 0.05 Mpc −3 yr −1 (M ≈ −14 mag) and 10 −6 Mpc −3 yr −1 (M ≈ −24 mag), significantly above the nova, supernova, and GRB rates, respectively, indicating that much larger surveys are required to provide meaningful constraints. Motivated by the results of our search we discuss strategies for identifying fast optical transients in the LSST main survey, and reach the optimistic conclusion that the veil of foreground contaminants can be lifted with the survey data, without the need for expensive follow-up observations.

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Section: Limits On the Rate Of Extragalactic Fastmentioning

confidence: 99%

A SEARCH FOR FAST OPTICAL TRANSIENTS IN THE Pan-STARRS1 MEDIUM-DEEP SURVEY: M-DWARF FLARES, ASTEROIDS, LIMITS ON EXTRAGALACTIC RATES, AND IMPLICATIONS FOR LSST

Berger

Leibler

Chornock

et al. 2013

ApJ

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“…Active galactic nuclei (AGN) and quasars demonstrate stronger variability with decreasing wavelength and longer timescales of years (Vanden Berk et al 2004). UV variability studies of GALEX data observed as part of the All-Sky, Medium, and Deep Imaging baseline mission surveys (AIS, MIS, DIS) from 2003 to 2007, yielded the detection of M-dwarf flare stars (Welsh et al 2007), RR Lyrae stars, AGN, and quasars (Welsh et al 2005;Wheatley et al 2008;Welsh et al 2011), and flares from the tidal disruption of stars around dormant supermassive black holes (Gezari et al 2006(Gezari et al , 2008a(Gezari et al , 2009. Serendipitous overlap of 4 GALEX DIS fields with the optical CFHT Supernova Legacy Survey, enabled the extraction of simultaneous optical light curves from image differencing for 2 of the tidal disruption event (TDE) candidates (Gezari et al 2008a), and enabled the association of transient UV emission with two Type IIP supernovae (SNe) within hours of shock breakout (Schawinski et al 2008;Gezari et al 2008b).…”

Section: Introductionmentioning

confidence: 99%

THEGALEXTIME DOMAIN SURVEY. I. SELECTION AND CLASSIFICATION OF OVER A THOUSAND ULTRAVIOLET VARIABLE SOURCES

Gezari

Martin

Forster

et al. 2013

ApJ

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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) N U V 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 largeamplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to |∆m| = 4.6 mag and 2.9 mag, respectively. The mean amplitude of the structure function for quasars on year timescales is 5 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 N U V < 23 mag and |∆m| > 0.2 mag of ∼ 8.0, 7.7, and 1.8 deg −2 for quasars, AGNs, 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.

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“…Thus, if a flare is observed by TAUVEX, the comparison of the theoretical flux ratios with the measured ones can help in determining the value of the plasma electron density during the flare event, in the assumption that the increase in electron pressure during the flare has a major influence on the ratios (Welsh et al 2006). In addition, since GALEX has produced a catalog of GALEX transient events (Welsh et al 2005), the predictions for the stellar-planetary collision UV flashes could be tested against the existing GALEX data set, and this topic will also be addressed in the forthcoming paper.…”

Section: Resultsmentioning

confidence: 99%

Prospects for observations of transient UV Events with the TAUVEX UV observatory

Safonova

Sivaram

Murthy

2008

Astrophys Space Sci

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Transient events have posed special problems in astronomy because of the intrinsic difficulty of their detection, and a new class of observatories such as the Pan-STARRS and LSST are coming up specifically to observe these energetic events. In this paper we discuss the UV transient events from two specific sources, such as possible collisions in extrasolar planetary systems and M dwarf flares, to find the probability of their detection by space UV observatories, in particular, by the Tel Aviv University Explorer (TAUVEX). TAUVEX is an UV imaging experiment that will image large parts of the sky in the wavelength region between 1200 and 3500 Å. TAUVEX is a collaborative effort between the Indian Institute of Astrophysics (IIA) and Tel Aviv University, and is scheduled for an early-2009 launch with at least three years of operations. The scientific instrument has been fabricated at El-Op in Israel, with the satellite interfaces, launch and flight operations provided by the Indian Space Research Organization (ISRO). The ground-based software development is the responsibility of the IIA while other aspects of the mission are the joint responsibility of IIA and Tel Aviv University. TAUVEX Science Team (TST) have created a coherent observing program to address several key science objectives, one of them is a program to study short-scale UV transient events. We have estimated that in one year of TAUVEX observations we can expect about 90 − 350 short-scale transient events. Because we obtain real-time telemetry with TAUVEX, we will be able to catch transients early in their evolution and to alert other observatories. We also present a description of TAUVEX mission, including instrument design and its estimated performance.

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TheGALEXUltraviolet Variability Catalog

Cited by 35 publications

References 10 publications

A SEARCH FOR FAST OPTICAL TRANSIENTS IN THE Pan-STARRS1 MEDIUM-DEEP SURVEY: M-DWARF FLARES, ASTEROIDS, LIMITS ON EXTRAGALACTIC RATES, AND IMPLICATIONS FOR LSST

A SEARCH FOR FAST OPTICAL TRANSIENTS IN THE Pan-STARRS1 MEDIUM-DEEP SURVEY: M-DWARF FLARES, ASTEROIDS, LIMITS ON EXTRAGALACTIC RATES, AND IMPLICATIONS FOR LSST

THEGALEXTIME DOMAIN SURVEY. I. SELECTION AND CLASSIFICATION OF OVER A THOUSAND ULTRAVIOLET VARIABLE SOURCES

Prospects for observations of transient UV Events with the TAUVEX UV observatory

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