Lasair Overview¶
Primary Goals¶
Ingest the ZTF public alert stream into a relational database
Condense the alerts into possible objects
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
candidates: photometric data from each ZTF alert
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
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
Sources¶
Smith, K. W., Williams, R. D., Young, R. D., et al. 2019, RNAAS 3:1