Porting from Lasair-ZTF

For several years, the Lasair system has been delivering alerts from the Zwicky Transient Facility (ZTF) . But Lasair-LSST is a new system, built from the lessons of the ZTF prototype.

Account

To use Lasair-LSST, you will need to register again, with username, password, and email. Your account with Lasair-ZTF will not be copied over, and the API token from Lasair-ZTF will not work for Lasair-LSST.

Watchlists and Watchmaps

For watchlists and watchmaps, the porting process should be simple. Use the ZTF website to navigate to the resource, then do Export/Original Watchlist File, which you can import into a new resource on lasair-lsst.

Filters

But filters are more difficult, as the objects attributes, used in SQL clauses, have been rebuilt for LSST. First an example WHERE clause from Lasair-ZTF:

sherlock_classifications.classification = "AGN"
AND objects.ncand >= 1
AND objects.decmean < 10
AND objects.jdgmax > jdnow() - 7
AND (objects.rmag < 20.0 OR objects.gmag < 20.0)
AND ((objects.magrmax- objects.magrmin) > 0.5)
AND objects.dmdt_g >= 1.5

Changes needed for Lasair-LSST are: * Change ncand to nDiaSources (could also use nuSources, ngSources, nrSources, etc for the six bands) * Change decmean to decl * For the third line, aboout timing, change jdgmax to g_latestMJD, for the most recent g-band detection. There is also the time of latest detection in any band, that is lastDiaSourceMjdTai. Also notice that Lasair-LSST uses MJD instead of JD.

Magnitude 20 is about 50,000 nJ, see here for explanation and conversion table/formula. And the replacement of rmag is r_psfFlux. Perhaps the line about maximum and minimum magnitude could be replaced with something about the standard deviation of the lightcurve, the objects-ext.r_psfFluxSigma

The last line is most difficult, there is no direct replacement for the ZTF attribute dmdt_g, which has always been problematic. If you want fast risers, the bazinBlackBody set of attributes tries for a collective approach, taking the whole 6-band lightcurve and fitting both temperature on the spectral axis, and explosion models on the time axis. If the fit has converged, the attribute BBBRiseRate might work, it is an e-folding rate \(e^{kt}\) for flux (linear in magnitude), but can also be thought of as magnitudes per day, within a few percent. Perhaps we choose 0.2 magnitudes a day.

So the clause looks like:

sherlock_classifications.classification = "AGN"
AND objects.nDiaSources >= 1
AND objects.decl < 10
AND objects.g_latestMJD > mjdnow() - 7
AND (objects.r_psfFlux > 50000 OR objects.g_psfFlux > 50000)
AND (objects-ext.r_psfFluxSigma > 10000)
AND objects.BBBRiseRate > 0.2

If you have a porting problem from ZTF to LSST filters, please use the Community Forum.