AIMS Provenance: Rubin Observatory / LSST Alerts

Draft for review. This page describes the current AIMS handling of Vera C. Rubin Observatory / LSST alert detections.

Source summary

Rubin Observatory describes LSST alerts as products of the Prompt Processing pipeline. Alert packets contain measurements associated with detections of time-variable sources in difference images; Rubin states that alert packets are world-public and have no proprietary period.

The LSST Alert Production Database schema describes DiaSource rows as difference-image sources detected at signal-to-noise ratio >= 5, with fields such as diaSourceId, midpointMjdTai, ra, dec, raErr, decErr, psfFlux, psfFluxErr, band, and ssObjectId.

How AIMS accesses LSST alerts

AIMS receives LSST alert data through broker-backed BigQuery tables. In production, AIMS is configured to use the Pitt alert broker source for the full LSST alert stream. Non-production environments may use simulated LSST alert tables for development and testing.

AIMS stages LSST alerts through three daily surfaces:

1. Raw-lite alerts — selected alert-packet fields are copied into a compact daily BigQuery table.
2. Candidates — raw-lite rows are filtered for moving-source relevance and PSF quality.
3. AIMS LSST — candidate rows are converted into the canonical AIMS observation schema.

AIMS date range and observatory

• AIMS LSST partition start defaults to 2025-09-01.
• AIMS treats LSST as active/continuing.
• AIMS observatory code: X05.

AIMS filtering

AIMS first copies selected alert fields for a daily kafkaPublishTimestamp window.

The candidate filter keeps rows that pass PSF quality checks and satisfy either a solar-system association or a PSF signal-to-noise threshold:

• PSF flux quality flags must pass:
  • psfFlux_flag is not set;
  • psfFlux_flag_edge is not set;
  • psfFlux_flag_noGoodPixels is not set.
• Then either:
  • ssObjectId IS NOT NULL; or
  • psfFlux / psfFluxErr >= 5.0.

The final AIMS publication step also requires:

• midpointMjdTai IS NOT NULL;
• ra IS NOT NULL;
• dec IS NOT NULL.

AIMS-derived and normalized values

Time conversion

LSST alert source times are expressed as TAI MJD. AIMS converts them to UTC using a leap-second-aware TAI-to-UTC conversion derived from Asteroid Institute time utilities. A fixed TAI-UTC offset can be configured operationally, but the preferred behavior is leap-second-aware conversion.

Photometric conversion

AIMS converts positive calibrated PSF fluxes in nJy to AB magnitudes using:

m_AB = -2.5 * log10(psfFlux_nJy) + 31.4

AIMS converts flux uncertainty to magnitude uncertainty with the first-order approximation:

sigma_mag = (2.5 / ln(10)) * psfFluxErr / psfFlux

AIMS stores null magnitudes when psfFlux <= 0, and stores null magnitude uncertainties when the flux or uncertainty is not physically usable for this conversion.

HEALPix conversion

LSST candidate rows carry a NESTED healpix19 value. AIMS stores nside=128 NESTED HEALPix by integer downsampling:

healpixel = floor(healpix19 / 16,777,216)

Known limitations and interpretation notes

• AIMS LSST rows are alert-derived prompt detections, not a full LSST data release catalog.
• Difference-image flux can be negative; AIMS only derives AB magnitude for positive PSF flux values.
• The AIMS candidate filter prioritizes moving-source relevance and operational reliability; it is not a substitute for Rubin’s full alert packet or downstream broker classifications.
• Source schema versions and broker delivery details can change over time. Version-specific changes should be added to this page as they affect AIMS fields or filters.

Source links

• Rubin Observatory alerts and brokers overview
• Rubin Prompt Products documentation
• LSST Alert Production Database schema
• Pitt-Google alert broker documentation