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.

The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs) centres on the origin of the short-hard class of bursts, which are suspected on theoretical grounds to result from the coalescence of neutron-star or black-hole binary systems. Numerous searches for the afterglows of short-hard bursts have been made, galvanized by the revolution in our understanding of long-duration GRBs that followed the discovery in 1997 of their broadband (X-ray, optical and radio) afterglow emission. Here we present the discovery of the X-ray afterglow of a short-hard burst, GRB 050709, whose accurate position allows us to associate it unambiguously with a star-forming galaxy at redshift z = 0.160, and whose optical lightcurve definitively excludes a supernova association. Together with results from three other recent short-hard bursts, this suggests that short-hard bursts release much less energy than the long-duration GRBs. Models requiring young stellar populations, such as magnetars and collapsars, are ruled out, while coalescing degenerate binaries remain the most promising progenitor candidates.

Over the past decade our physical understanding of gamma-ray bursts (GRBs) has progressed rapidly thanks to the discovery and observation of their long-lived afterglow emission. Longduration (T > ∼ 2 s) GRBs are associated with the explosive deaths of massive stars ("collapsars" 1 ), which produce accompanying supernovae, 2-4 while the short-duration (T < ∼ 2 s) GRBs arise from a different origin, which has been argued to be the merger of two compact objects, [5][6][7] either neutron stars or black holes. Here we present observations of GRB 060614, a 100-s long burst discovered by the Swift satellite, 8 which require the invocation of a new explosive process: 2 Gal-Yam et al.either a massive "collapsar" that powers a GRB without any associated supernova, or a new type of engine, as long-lived as the collapsar but without any such massive stellar host. We also discuss the properties of this burst's redshift z = 0.125 host galaxy, which distinguish it from other long-duration GRBs and suggest that an entirely new type of GRB progenitor may be required.On 14 June 2006, 12:43 UT, the burst alert telescope (BAT) on board the Swift satellite detected the γ-Ray Burst (GRB) 060614.8 The BAT detected γ-rays from this event for 120s, and the burst showed strong variability during much of that period, as confirmed by parallel observations by the Konus-Wind satellite. 9 Note that while some evolution in the temporal and spectral properties of this GRB were observed, the emission remained highly variable and relatively hard for tens of seconds, unlike the situation observed for a few short bursts with long, soft "tails". 10,7 This indicates sustained activity of an engine, rather than the early onset of the afterglow. The γ-ray properties of this event are similar to those of other bursts from the long-duration subgroup of GRBs. Swift autonomously slewed to the GRB position and began taking data with the X-ray telescope and UVoptical telescope. 11 We began observing this event ≈ 26 minutes later using the 40 inch telescope at Siding Springs Observatory. The evolution of the optical radiation from this event as traced by our data, augmented by Swift observations and additional data from the literature is shown in Fig. 1. As the optical source decayed, we noticed that it was apparently superposed on a faint dwarf host galaxy. On June 19, 2006 UT We obtained a spectrum of the host using the GMOS-S spectrograph mounted on the Gemini-south 8m telescope at Cerro Pachon, Chile. From this spectrum we derived the redshift of the host galaxy, and by association of the GRB, and found it to be z = 0.125, a low value for long GRBs. We confirmed this redshift with a higher quality spectrum obtained using the same instrument on July 15, 2006 UT (Fig. 2). Previous long GRBs at such low redshifts showed clear signatures of the underlying supernova (SN) explosions at comparable age post-burst. 3,12 However, such signatures were lacking in the case of this long GRB. well-detected in our first-epoch WFPC2 observations, and is apparently gone du...

The Zwicky Transient Facility (ZTF), a public–private enterprise, is a new time-domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg2 field of view and an 8 second readout time. It is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights in g and r filters and the visible Galactic plane every night in g and r. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities that provided funding (“partnership”) are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r ∼ 20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF, including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei, and tidal disruption events, stellar variability, and solar system objects.

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