# Difference versus forced flux

**URL:** <https://www.rubin.community/t/difference-versus-forced-flux/11753>\
**Category:** Alerts & Brokers\
**Tags:** forcedphotometry\
**Created:** [March 17, 2026, 5:51pm UTC](https://www.rubin.community/t/difference-versus-forced-flux/11753 "2026-03-17T17:51:20Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![pjpessi](https://avatars.discourse-cdn.com/v4/letter/p/e9c0ed/32.png) [@pjpessi](https://www.rubin.community/u/pjpessi)\
**Post date:** [March 17, 2026, 5:51pm UTC](https://www.rubin.community/t/difference-versus-forced-flux/11753/1 "2026-03-17T17:51:20Z")

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I see some brokers show two panels for LSST alerts, one with difference photometry, and the other with forced photometry. I would assume the forced magnitude come from the flux of the diaForcedSource, while difference magnitude comes from the diaSource. As far as I understand, on a given date the only difference between these two should be detection or non-detection. Meaning that the event can be detected as a diaForcedSource while not being normally detected as a diaSource. However, I see that for a given date, there are small differences between the difference magnitude and the forced magnitude, does anyone know why is this?

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**Author:** ![ebellm](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/ebellm/32/771_2.png) [@ebellm](https://www.rubin.community/u/ebellm)\
**Post date:** [March 17, 2026, 6:34pm UTC](https://www.rubin.community/t/difference-versus-forced-flux/11753/2 "2026-03-17T18:34:04Z")

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Hi @pjpessi, it would be worth confirming with the brokers which measurements they are using, but the diaForcedSource measurement is forced at the `DiaObject` position, which may differ from the centroid of the `diaSource` detection, resulting in a slightly different flux value.

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**Author:** ![pjpessi](https://avatars.discourse-cdn.com/v4/letter/p/e9c0ed/32.png) [@pjpessi](https://www.rubin.community/u/pjpessi)\
**Post date:** [March 18, 2026, 5:21pm UTC](https://www.rubin.community/t/difference-versus-forced-flux/11753/3 "2026-03-18T17:21:15Z")

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I see, @ebellm that’s probably the issue. Thank you.