Lasair Overview

Primary Goals

  1. Ingest the ZTF public alert stream into a relational database

  2. Condense the alerts into possible objects

  3. Produce lightcurves of these objects and reliable cross-matches to star and galaxy catalogs for possible follow-up

Assorted Info

  • Lasair = “flare” or “flash” in Scots and Irish gaelic

  • The transient alerts broker for the LSST: UK collaboration

  • Currently testing using the ZTF alert stream

  • Databases saved on hardware in Edinburgh

  • Can be viewed and queried through a web browser via a full SQL search engine

  • Registration to their website is free, optional, and publically available

  • Registered users can save useful SQL queries either privately or publically; public saves are called “streams”

    • Both the Lasair team and users can curate scientifically interesting substreams

    • Ex: nuclear transients and TDE candidates

    • Ex: SNe candidates—all objects NOT classified as a variable star, AGN, or CV and are not coincident with a Pan-STARRS stellar source

Data Products

3 SQL tables as data products

  1. candidates: photometric data from each ZTF alert

  2. objects: metadata for collected alerts:

  • Group of 3+ candidates with the same object ID number

    • ZTF assigns this same object ID number if the positions agree within 1.5” (check this number)

    • Requiring 3+ is done to remove moving objects and reduce bogus detections

  • Min, Max, and Average magnitudes

  • Earliest and latest dates of detection

  • Mean coordinates

  • All objects data is in the candidates table, but not all of the candidates table makes it into the objects table

  1. sherlock_crossmatches: value-added classification info created using Sherlock

  • Crossmatches nearby sources with various catalogs for their corresponding photometry and spec/photo z’s

  • Sherlock: uses star/galaxy separation methods, estimated distances, and galaxy offsets to classify the objects into a few possible categories:

    • Supernovae

    • Nuclear transients

    • Variable stars

    • AGN (Véron-Cetty and Véron 2010)

    • CV (Downes et al. 2001, Ritter and Kolb 2003)

    • Orphans: stationary, transient sources that aren’t associated with a cataloged star or galaxy

  • Maintains an up-to-date crossmatch with the IAU Transient Name Server to quickly identify known transients within the ZTF stream

Searching Lasair

  • Can use SQL SELECT queries to search their provided tables

  • Few different types of search methods:

    • Single object, cone search using sky position or ZTF object ID

    • Stored SQL queries, whether private saves or public “streams”

    • “Watchlists”: up to a few thousand sources saved in an input list that can be crossmatched at any future time; alerts will be sent to the watchlist owners when transient activity occurs (currently in development, estimated to be minutes between the time of observation and time to alert)

  • Results can be analyzed in Jupyter notebooks, with examples provided on their website

  • An example of the query results page of the objects table is shown in the only figure. Summary:

    • ZTF lightcurve and basic astro information: # of candidates, mean RA & Dec (degrees and hours/min/sec), galactic longitude (l) and latitude (b)

    • Classification and info from Sherlock, including links to cone searches

    • User comments (including Lasair bots)

    • Sherlock’s ranked table of the likely catalogued crossmatched sources

    • An interactive AladinLite display of the region of interest

    • A table with each of the relevant candidates’ info (i.e., each lightcurve point), taken from the candidates table


  1. Smith, K. W., Williams, R. D., Young, R. D., et al. 2019, RNAAS 3:1