jdmin meaning in Lasair

[chrisfrohmaier]

What does the jdmin column actually store?
Should it be the discovery date or the oldest date in a ZTF alert packet?

I've noticed this when using filters to find short lived transients. Filtering on say, jdmax-jdmin < N days, finds objects with loads of light curve history before jdmin.

We're also trying to search for more long-lived transients by doing jdmax-jdmin > N days in the filter, but noticed that for ZTF20abrbeie the jdmin is only 30 days ago, but the light curve has more than 800 days of history.

Without a true date of discovery or earliest detection it is impossible to do some types of archival searches in Lasair.

[RoyWilliams]

jdmin is the earliest of the candidates that are included with the alert from ZTF. That alert has 30 days of lightcurve, so jdmax - jdmin cannot be more than 30 days. When we built Lasair we assumed it would be about rapid transients, not about archival searches. There has been a lot of discussion about this at Lasair meetings, and we have petitioned Rubin to include the true number -- see here