LSST Mag discrepancy: AT 2026eqf use case

[FredDJN]

Hi
I Would like to come back on the AT 2026eqf example given in the last announcement.
I noticed an unexplained/misunderstood (for me) descrepancy in term of magnitudes between sources.

*According to the light curve of AT 2026eqf supplied by AstroColibri, the mag(r) at the time of discovery was in the range of 23
(see Astro-COLIBRI )

*More precisely, this is also what is shown in the tab

* The downloadable csv file shows the value 23.05, it’s great

* And this is also what is shown on the TNS

Up till now, all the value are the same, it’s good.

On the other hand, the data is quiet different lookink on the LSST server:

The mag(r) is given to be 21.30 at the time of dicovery (same time stamp as above).

The same kind of discrepancy could be observed if we consider the mag at the time of discovery for the i and z bands (TNS does not supply any data on these bands).

Could you help me understand why the values reported on TNS and AC differ from the source data given by the LSST?

Note:
To dig further and find any clue, I tried to compare the data supplied by ATLAS (same target, same time slot), but could not find them online.

I also tried to find another target reported by the LSST in the TNS, but no luck

[emilleishida]

hi, this is the difference between differencial and total magnitude.
Difference magnitude is the magnitude calculated in the difference stamp – it includes only the transient, since the template image has been subtracted.

Total magnitude is calculated in the science stamp, so includes transient and host.

On the top right of the Fink portal there is a configuration wheel where you can choose between the two

choosing differential magnitude you get the reported TNS value.

[FredDJN]

Thank you very much for your reply and your kind explanation.

It’s all clear now for me.

I could not find this feature on the Fink portal, although the Help tab should have warn me.

Thanks for the advice.