This page gives an overview of the process that takes DiaSources generated by difference imaging, updates the Level 1 Database, and generates alerts that are sent to the community.

Baseline Documents

The primary documents are:

Most of this is laid out in detail in the Data Products Definition Document.  As long as DiaSource measurement on the boundaries of an image area (e.g. CCD) are well-defined (TBD: how will edges be handled?), this process appears to be parallelizable.

  1. Associate the DiaSources with a (single) best-fit DiaObject or SSObject each. (TBD: exact association algorithm)
  2. For all associated DiaSources:
    1. Retrieve all past DiaSources.
  3. If DiaSource is associated with an SSObject:
    1. Update SSObject with DiaSource properties. (TBD: not mentioned explicitly in LSE-163; can this wait for DayMOPS?)
  4. If DiaSource is not associated:
    1. Create a new DiaObject
  5. For all unassociated DiaObjects:
    1. Do forced measurement on difference image, calibrated image (for fpFlux), and difference of snaps (diffFlux), generating new DiaSource
    2. Note that this is a normal DiaSource, not a ForcedDiaSource (which does not exist any more), but it may need to have a flag set to indicate that it was forced.
  6. Update all DiaSources with their associated DiaObject identifier.
  7. Insert all normal and forced measurement DiaSources into Level 1 Database.
  8. For all DiaObjects:
    1. (Re)compute DiaObject measurements from DiaSources.
  9. Ingest DiaObjects into Level 1 Database: as one transaction, invalidate previous DiaObject row and insert new DiaObject row.
  10. Issue alert for each DiaSource with contents:
    • Alert Identifier
    • Level 1 Database Identifier
    • DiaSource contents
    • DiaObject or SSObject contents
    • All previous DiaSources (including any new precovery forced measurements)
    • Difference image cutout
    • Template image cutout
    • Image metadata
    • Note that no calibrated image cutout is included.
  11. Package alerts into VOEvent or other relevant standard.
  12. Transmit VOEvents to public VOEvent brokers via pre-configured transport protocol and internal LSST filtering service.
  13. Internal LSST filtering service executes pre-configured per-user filters for each alert.
    1. If filter returns True, alert is forwarded to user via pre-configured transport protocol.
  14. During the next day, for all unassociated DiaSources
    1. Do precovery forced measurement on 30-day difference image cache, creating additional forced DiaSources.
      1. The note above about forced DiaSources applies here as well.
      2. TBD: Do we cache difference images or just calibrated images and parameters to recompute difference images?
      3. TBD: DiaSources include data from (differences of) snaps (diffFlux); those have to be cached as well
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