| 1. |
- Bellm, Eric C., et al.
(författare)
-
The Zwicky Transient Facility : System Overview, Performance, and First Results
- 2019
-
Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:995
-
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.
|
|
| 2. |
- Bolin, Bryce T., et al.
(författare)
-
Characterization of the Nucleus, Morphology, and Activity of Interstellar Comet 2I/Borisov by Optical and Near-infrared GROWTH, Apache Point, IRTF, ZTF, and Keck Observations
- 2020
-
Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 160:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present visible and near-infrared (NIR) photometric and spectroscopic observations of interstellar object (ISO) 2I/Borisov taken from 2019 September 10 to 2019 December 20 using the GROWTH, the Apache Point Observatory Astrophysical Research Consortium 3.5 m, and the NASA Infrared Telescope Facility 3.0 m combined with pre- and postdiscovery observations of 2I obtained by the Zwicky Transient Facility from 2019 March 17 to 2019 May 5. Comparison with imaging of distant solar system comets shows an object very similar to mildly active solar system comets with an outgassing rate of similar to 10(27)mol s(-1). The photometry, taken in filters spanning the visible and NIR range, shows a gradual brightening trend of similar to 0.03 mag day(-1)since 2019 September 10 UTC for a reddish object becoming neutral in the NIR. The light curve from recent and prediscovery data reveals a brightness trend suggesting the recent onset of significant H2O sublimation with the comet being active with super volatiles such as CO at heliocentric distances >6 au consistent with its extended morphology. Using the advanced capability to significantly reduce the scattered light from the coma enabled by high-resolution NIR images from Keck adaptive optics taken on 2019 October 4, we estimate a diameter for 2I's nucleus of less than or similar to 1.4 km. We use the size estimates of 1I/'Oumuamua and 2I/Borisov to roughly estimate the slope of the ISO size distribution, resulting in a slope of similar to 3.4 1.2, similar to solar system comets and bodies produced from collisional equilibrium.
|
|
| 3. |
- Frederick, Sara, et al.
(författare)
-
A New Class of Changing-look LINERs
- 2019
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 883:1
-
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.
|
|
| 4. |
- Lin, Weili, et al.
(författare)
-
A superluminous supernova lightened by collisions with pulsational pair-instability shells
- 2023
-
Ingår i: Nature Astronomy. - 2397-3366. ; 7:7, s. 779-789
-
Tidskriftsartikel (refereegranskat)abstract
- Superluminous supernovae are among the most energetic stellar explosions in the Universe, but their energy sources remain an open question. Here we present long-term observations of one of the closest examples of the hydrogen-poor superluminous supernovae subclass SLSNe-I, supernova SN 2017egm, revealing the most complicated known luminosity evolution of SLSNe-I. Three distinct post-peak bumps were recorded in its light curve collected at about 100–350 days after maximum brightness, challenging current popular power models such as magnetar, fallback accretion, and interaction between ejecta and a circumstellar shell. However, the complex light curve can be well modelled by successive interactions with multiple circumstellar shells with a total mass of about 6.8–7.7 M⊙. In this scenario, large energy deposition from interaction-induced reverse shocks results in ionization of neutral oxygen in the supernova ejecta and hence a much lower nebular-phase line ratio of [O I] λ6,300/([Ca II] + [O II]) λ7,300 (~0.2) compared with that derived for other superluminous and normal stripped-envelope supernovae. The pre-existing multiple shells indicate that the progenitor of SN 2017egm experienced pulsational mass ejections triggered by pair instability within 2 years before explosion, in robust agreement with theoretical predictions for a pre-pulsation helium-core mass of 48–51 M⊙.
|
|
| 5. |
- van Velzen, Sjoert, et al.
(författare)
-
The First Tidal Disruption Flare in ZTF : From Photometric Selection to Multi-wavelength Characterization
- 2019
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 872:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present Zwicky Transient Facility (ZTF) observations of the tidal disruption flare AT2018zr/PS18kh reported by Holoien et al. and detected during ZTF commissioning. The ZTF light curve of the tidal disruption event (TDE) samples the rise-to-peak exceptionally well, with 50. days of g- and r-band detections before the time of maximum light. We also present our multi-wavelength follow-up observations, including the detection of a thermal (kT approximate to 100 eV) X-ray source that is two orders of magnitude fainter than the contemporaneous optical/UV blackbody luminosity, and a stringent upper limit to the radio emission. We use observations of 128 known active galactic nuclei (AGNs) to assess the quality of the ZTF astrometry, finding a median host-flare distance of 0.'' 2 for genuine nuclear flares. Using ZTF observations of variability from known AGNs and supernovae we show how these sources can be separated from TDEs. A combination of light-curve shape, color, and location in the host galaxy can be used to select a clean TDE sample from multi-band optical surveys such as ZTF or the Large Synoptic Survey Telescope.
|
|
