The Zwicky Transient Facility: Data Processing, Products, and Archive (1902.01872v1)

Abstract: The Zwicky Transient Facility (ZTF) is a new robotic time-domain survey currently in progress using the Palomar 48-inch Schmidt Telescope. ZTF uses a 47 square degree field with a 600 megapixel camera to scan the entire northern visible sky at rates of ~3760 square degrees/hour to median depths of g ~ 20.8 and r ~ 20.6 mag (AB, 5sigma in 30 sec). We describe the Science Data System that is housed at IPAC, Caltech. This comprises the data-processing pipelines, alert production system, data archive, and user interfaces for accessing and analyzing the products. The realtime pipeline employs a novel image-differencing algorithm, optimized for the detection of point source transient events. These events are vetted for reliability using a machine-learned classifier and combined with contextual information to generate data-rich alert packets. The packets become available for distribution typically within 13 minutes (95th percentile) of observation. Detected events are also linked to generate candidate moving-object tracks using a novel algorithm. Objects that move fast enough to streak in the individual exposures are also extracted and vetted. The reconstructed astrometric accuracy per science image with respect to Gaia is typically 45 to 85 milliarcsec. This is the RMS per axis on the sky for sources extracted with photometric S/N >= 10. The derived photometric precision (repeatability) at bright unsaturated fluxes varies between 8 and 25 millimag. Photometric calibration accuracy with respect to Pan-STARRS1 is generally better than 2%. The products support a broad range of scientific applications: fast and young supernovae, rare flux transients, variable stars, eclipsing binaries, variability from active galactic nuclei, counterparts to gravitational wave sources, a more complete census of Type Ia supernovae, and Solar System objects.

• The paper presents ZTF's innovative data processing system that delivers transient alerts within 13 minutes of observation.
• It describes a distributed pipeline architecture achieving astrometric accuracy of 45–85 mas and photometric precision below 25 millimag.
• The study highlights the system’s scalability for future surveys like LSST, underscoring its impact on time-domain astronomy.

Overview of the Zwicky Transient Facility's Data Processing, Products, and Archive

The Zwicky Transient Facility (ZTF), an ongoing robotic time-domain survey, operates from the Palomar 48-inch Schmidt Telescope and is a significant advancement in transient sky surveys. This paper, published in the Publications of the Astronomical Society of the Pacific, provides a comprehensive overview of the ZTF's data processing system and its resulting products.

Data Processing Architecture

The ZTF data processing is housed at IPAC, Caltech, and consists of sophisticated data-processing pipelines, an alert production system, and an extensive data archive. The real-time pipeline features an innovative image-differencing algorithm optimized for detecting point-source transient events, which are further validated using a machine-learned classifier. This configuration enables data-rich alert packets to be distributed within thirteen minutes of observation, representing a highly efficient turnover from data capture to alert dissemination.

The processing pipeline is sustained by a robust architecture featuring 66 compute cluster nodes and a distributed file server system. This infrastructure supports parallelized data processing with capabilities to handle astrometric and photometric calibrations comprehensively. The system achieves a reconstructed astrometric accuracy of 45 to 85 milliarcseconds with respect to Gaia DR1 for well-exposed sources and a photometric precision below 25 millimag at brighter flux levels.

Archive and Access

The ZTF archive supports a diverse array of scientific studies such as fast supernovae, rare transients, and variability from active galactic nuclei. Users can access the data through various interfaces designed for flexibility and efficiency, facilitating both immediate data retrieval and more intricate exploratory analysis.

Preliminary Results and Implications

Preliminary results show that the ZTF achieves photometric calibration accuracy with respect to Pan-STARRS1 generally better than 2%. This level of precision supports a broad range of scientific applications, including tracking solar-system objects with sufficient accuracy to identify promising candidates for follow-up.

The facility's design anticipates the high data rates and large volumes of data typical in contemporary large-scale surveys. This preparation aligns with future demands anticipated from succeeding astronomical surveys such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). The results from the ZTF, bolstered by a scalable and adaptable processing paradigm, suggest that the survey is positioned as a cornerstone in the ongoing exploration of the transient universe.

Conclusion

The ZTF demonstrates a model of efficient and effective astronomical data processing. By leveraging automated pipelines for swift alert generation and maintaining high data integrity standards, the facility not only contributes vital data to the astronomical community but also lays groundwork for the future of time-domain astronomy. Anticipating the dynamic nature of celestial events, the ZTF's approach serves as a blueprint for managing large volumes of astronomical data, offering insights that extend well beyond its immediate scope.