Support ATel At Patreon

[ Previous | Next | ADS ]

The Zwicky Transient Facility Public Alert Stream

ATel #11685; F. Masci, S. R. Kulkarni, M. Graham, T. Prince, G. Helou (Caltech) on behalf of the Zwicky Transient Facility collaboration
on 5 Jun 2018; 16:14 UT
Credential Certification: Frank Masci (fmasci@ipac.caltech.edu)

Subjects: Optical, AGN, Asteroid, Cataclysmic Variable, Comet, Gamma-Ray Burst, Supernovae, Transient, Variables, Tidal Disruption Event

Referred to by ATel #: 11688, 13262

The Zwicky Transient Facility (ZTF; ATel #11266) announces the start of public alerts. These alerts will originate from the ZTF public surveys (Bellm & Kulkarni 2017; Nature Astronomy 1, 71) as described at www.ztf.caltech.edu/page/msip

Alerts are generated by the ZTF Science Data System housed at IPAC-Caltech (www.ipac.caltech.edu) using a realtime image-subtraction pipeline (Masci et al. 2018; www.ztf.caltech.edu/page/technical). Newly acquired images are differenced against a reference image to reveal candidate events from flux transients, variable stars, eclipsing binaries, AGN, and Solar System objects. The candidates are lightly filtered to remove easily identifiable instrumental artifacts. They are then packetized into files in the Apache Avro format -- a serialized binary format for efficient distribution. Each packet contains metadata on the single event that triggered the alert. This consists of a unique object identifier; a machine-learned reliability score; source and image metrics to facilitate further analysis and vetting; the nearest known Solar System object with metadata; the nearest Pan-STARRS (PS1) sources with star-galaxy classification scores and metadata inherited from the PS1 catalogs; metadata for previous positionally-coincident alerts going back 30 consecutive nights if found, otherwise, flux upper-limits if the alert position was covered during this period; and ~ 1' x 1' full-resolution cutouts from the new, reference, and subtraction images. Content details, suggestions for further filtering, and cautionary notes are described in the Data System documentation at www.ztf.caltech.edu/page/technical. Documentation on packet usage, examples, and software is available at github.com/ZwickyTransientFacility/ztf-avro-alert

We expect anywhere from a thousand to >~ 100 thousand public alerts per night, where numbers (and astrophysical types) depend on the region of sky visited, i.e., galactic and/or ecliptic latitude range covered. Numbers also depend on the available reference image coverage. Alerts are generated and delivered approximately 10 to 20 minutes following observation.

During commissioning of the ZTF alert infrastructure, 185 supernovae were discovered. Some of them were known and recovered in the alert packets. Four known supernovae from three nights are listed below. Their selection is described in ATel #11615.

 
Survey name  | IAU name | Discovery mag (r) | Discovery date 
 ZTF18aajpjdi  SN2018bfx  20.0                2018-04-14.31 
 ZTF18aajtlbf  SN2018bbz  18.2                2018-04-14.42 
 ZTF18aamfrvy  SN2018ahe  19.0                2018-04-21.36 
 ZTF18aaovbiy  SN2018bdo  19.5                2018-04-24.38 

Alert packets are transmitted from IPAC-Caltech to the University of Washington in realtime for redistribution to community brokers. These brokers will provide value-added services and are responsible for public access. The brokers who have agreed to support ZTF are ALERCE, ANTARES, and LASAIR. These brokers are presently concluding development and commissioning, and science users should consult their websites for available services and timelines. Until the broker services become available, users can download a tar file of each night's alerts the following day from ztf.uw.edu/alerts/public/. This mechanism does not currently support realtime access. Furthermore, all alert packets are archived at IPAC-Caltech. This archive will be publicly accessible following the first ZTF Public Data Release, which is anticipated in the Spring of 2019.

ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL #11266), and includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW,USA; DESY, Germany; NRC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341.