| 1. |
- Bellm, Eric C., et al.
(författare)
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The Zwicky Transient Facility : System Overview, Performance, and First Results
- 2019
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:995
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Tidskriftsartikel (refereegranskat)abstract
- The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg(2) field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF's public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.
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| 2. |
- Frederick, Sara, et al.
(författare)
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A New Class of Changing-look LINERs
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 883:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of six active galactic nuclei (AGNs) caught turning on during the first nine months of the Zwicky Transient Facility (ZTF) survey. The host galaxies were classified as low-ionization nuclear emissionline region galaxies (LINERs) by weak narrow forbidden line emission in their archival SDSS spectra, and detected by ZTF as nuclear transients. In five of the cases, we found via follow-up spectroscopy that they had transformed into broad-line AGNs, reminiscent of the changing-look LINER iPTF16bco. In one case, ZTF18aajupnt/ AT2018dyk, follow-up Hubble Space Telescope ultraviolet and ground-based optical spectra revealed the transformation into a narrow-line Seyfert 1 with strong [Fe VII, X, XIV] and He II lambda 4686 coronal lines. Swift monitoring observations of this source reveal bright UV emission that tracks the optical flare, accompanied by a luminous soft X-ray flare that peaks similar to 60 days later. Spitzer follow-up observations also detect a luminous midinfrared flare, implying a large covering fraction of dust. Archival light curves of the entire sample from CRTS, ATLAS, and ASAS-SN constrain the onset of the optical nuclear flaring from a prolonged quiescent state. Here we present the systematic selection and follow-up of this new class of changing-look LINERs, compare their properties to previously reported changing-look Seyfert galaxies, and conclude that they are a unique class of transients well-suited to test the uncertain physical processes associated with the LINER accretion state.
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| 3. |
- Perley, Daniel A., et al.
(författare)
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The fast, luminous ultraviolet transient AT2018cow : extreme supernova, or disruption of a star by an intermediate-mass black hole?
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 484:1, s. 1031-1049
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Tidskriftsartikel (refereegranskat)abstract
- Wide-field optical surveys have begun to uncover large samples of fast (t(rise) less than or similar to 5 d), luminous (M-peak < 18), blue transients. While commonly attributed to the breakout of a supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered detailed investigation of their properties. We present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT 2018cow (ATLAS 18qqn), the first fast-luminous optical transient to be found in real time at low redshift. Our first spectra (<2 days after discovery) are entirely featureless. A very broad absorption feature suggestive of near-relativistic velocities develops between 3 and 8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R < 10 (14) cm after 1 month). This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass black hole, although this would require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT 2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.
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| 4. |
- Ye, Quanzhi, et al.
(författare)
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Toward Efficient Detection of Small Near-Earth Asteroids Using the Zwicky Transient Facility (ZTF)
- 2019
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:1001
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Tidskriftsartikel (refereegranskat)abstract
- We describe ZStreak, a semi-real-time pipeline specialized in detecting small, fast-moving, near-Earth asteroids (NEAs), which is currently operating on the data from the newly commissioned Zwicky Transient Facility (ZTF) survey. Based on a prototype originally developed by Waszczak et al. (2017) for the Palomar Transient Factory (PTF), the predecessor of ZTF, ZStreak features an improved machine-learning model that can cope with the 10x data rate increment between PTF and ZTF. Since its first discovery on 2018 February 5 (2018 CL), ZTF/ZStreak has discovered 45 confirmed new NEAs over a total of 232 observable nights until 2018 December 31. Most of the discoveries are small NEAs, with diameters less than similar to 100. m. By analyzing the discovery circumstances, we find that objects having the first to last detection time interval under 2. hr are at risk of being lost. We will further improve real-time follow-up capabilities, and work on suppressing false positives using deep learning.
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