feat: add SNEWS2 coincidence alert schema

[medhansh29]

Summary

Adds the initial JSON schema for Supernova Early Warning System 2.0 (SNEWS2) coincidence tier alerts to the GCN schema repository.

Files Added

• gcn/notices/snews2/coincidence.schema.json — JSON schema defining the SNEWS2 CoincidenceTier alert format
• gcn/notices/snews2/coincidence.test_alert.example.json — Example payload conforming to the schema

Schema Design

The schema inherits from 5 GCN Core schemas using allOf:

• core/Alert.schema.json
• core/Event.schema.json
• core/Reporter.schema.json
• core/DateTime.schema.json
• core/Statistics.schema.json

SNEWS2-specific fields include:

• snews2_tier — The SNEWS tier (CoincidenceTier only at this stage)
• detector_names — Array of contributing detector names
• event_times_utc — Array of neutrino arrival times per detector
• tier_data — Tier-specific payload (p_values, false_alarm_prob, etc.)

Notes

• Only the CoincidenceTier alert type is published to GCN at this time
• All tests pass with npm run test

[medhansh29]

Key Changes:

Schema Versioning: Renamed schema_version to snews_schema_version to completely eliminate any ambiguity with the standard JSON $schema keyword.

Detector Status Enrichment: Replaced the simple detector_names string array with a detector_status object pattern mapping to DetectorStatus.schema.json via additionalProperties. This matches patterns established by missions like BurstCube and allows tracking whether detectors were triggered, on, or off.

Core DateTime Referencing: Updated the event_times_utc array to explicitly use a JSON Pointer $ref to ../core/DateTime.schema.json#/properties/trigger_time. By doing this, we seamlessly inherit the core schema's documentation and standard ISO 8601 constraints without duplicating logic.

[jracusin]

Is there a formal scheme for naming these SNEWS events with an event_name?

[jracusin]

In the GCN Classic notices, you also had the number of neutrinos detected and event duration. It would be interesting to have the number of neutrinos per detector.

[Vidushi-GitHub]

Additionally, run npx prettier -c .
One of the validation is failing.

[mlinvill]

In the GCN Classic notices, you also had the number of neutrinos detected and event duration. It would be interesting to have the number of neutrinos per detector.

We don't have neutrino counts in the coincidence tier. This information is reported in the timing tier, which is out of the scope of this initial effort. I expect our GCN schema will be extended to handle this information in future efforts.

[medhansh29]

Is there a formal scheme for naming these SNEWS events with an event_name?

No there is no formal event name, just the uuid passed generated which is passed into the $id field in the schema.

[medhansh29]

Additionally, run npx prettier -c . One of the validation is failing.

Fixed in latest update