# Jump1 and Jump2 for flux dips?

**URL:** <https://www.rubin.community/t/jump1-and-jump2-for-flux-dips/11623>\
**Category:** Lasair\
**Created:** [February 25, 2026, 2:22am UTC](https://www.rubin.community/t/jump1-and-jump2-for-flux-dips/11623 "2026-02-25T02:22:46Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![jrad](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/jrad/32/2717_2.png) [@jrad](https://www.rubin.community/u/jrad)\
**Post date:** [February 25, 2026, 2:22am UTC](https://www.rubin.community/t/jump1-and-jump2-for-flux-dips/11623/1 "2026-02-25T02:22:46Z")

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Do the (or perhaps _could_ the) Jump1 and Jump2 parameters return negative values for flux dips? That would be very helpful for detecting (for example) dipper stars and giant eclipses.

Based on the [provided notebook](https://github.com/lsst-uk/lasair-examples/blob/main/lsst_notebooks/features/jump.ipynb) that defines the Jump parameters, there seems to be an Absolute Magnitude that removes the sign of the jump.

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**Author:** ![heloise](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/heloise/32/3680_2.png) [@heloise](https://www.rubin.community/u/heloise)\
**Post date:** [February 25, 2026, 10:30pm UTC](https://www.rubin.community/t/jump1-and-jump2-for-flux-dips/11623/2 "2026-02-25T22:30:53Z")

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That is a good point. Would a feature to directly access whether the latest diaSourceId was positive or negative helpful as well?

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**Author:** ![jrad](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/jrad/32/2717_2.png) [@jrad](https://www.rubin.community/u/jrad)\
**Post date:** [February 25, 2026, 11:31pm UTC](https://www.rubin.community/t/jump1-and-jump2-for-flux-dips/11623/3 "2026-02-25T23:31:00Z")

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That would definitely be helpful, as long as negative “jumps” are being reported (I.e. not as zeros) all we’d need is a bit that indicates the sign

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**Author:** ![roy](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/roy/32/1254_2.png) [@roy](https://www.rubin.community/u/roy)\
**Post date:** [February 26, 2026, 9:29am UTC](https://www.rubin.community/t/jump1-and-jump2-for-flux-dips/11623/4 "2026-02-26T09:29:43Z")

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Obviously the Rubin alerts program is already a jump detector – every alert comes from 5-sigma jump in flux. Therefore we see strange objects like this [anti-supernova](https://lasair.lsst.ac.uk/objects/170028527544959074/), that was very bright when the templates were acquired, but now its gone. so the difference flux is -100000 nJ.

The jump detector features are looking for changes in difference flux. You could do this yourself with a collection of six SQL clauses, one for each filter band, like this:  
`abs(objects.g_psfFlux - objects.g_psfFluxMean) / objects.g_psfFluxMeanErr > 3`

The jump features were designed as a way to find outbursts in AGN. Characteristically, the flux jumps up and down so they will generate long lightcurves in LSST, but interesting science is when they suddenly brighten over a few days. The advantages of the jump features are:

- Its much simpler than the long SQL shown above.
- The jump features use the mean and standard deviation from a specific interval from 70 days before now to 10 days before now. The ten-day standoff is to maximise the discernment of AGN flares.
- There is also the `jump2` statistic – brightening in a different filter band – that we would not expect from a measurement error.
- Note that if you have a filter using the jump features, you can fetch the results with the “lite” lightcurve in the Kafka and thus do your own analysis of the flux jumps.

Hope this helps