NITRATES (NITRogen Analysis Tool for Rapid Event Search) is a data analysis pipeline designed to identify high-energy electromagnetic counterparts to gravitational-wave (GW) events using time-tagged data from the Swift Burst Alert Telescope (BAT). It focuses on sub-threshold searches—events that do not trigger onboard detection but may still contain astrophysical signals—thereby expanding the discovery potential for short gamma-ray bursts (GRBs) and other transients associated with compact binary mergers.
Key features
Sub-Threshold GRB Search
NITRATES analyzes BAT data streams that did not result in an onboard trigger, performing sensitive searches for faint or short-duration GRBs that could be missed by standard detection pipelines.
Integration with GUANO
Leverages the GUANO system (Gamma-ray Urgent Archiver for Novel Opportunities) to rapidly retrieve time-tagged event data from BAT following external triggers, such as GW or neutrino alerts.
High-Performance Computing Compatibility
Runs on HPC environments to perform end-to-end data analysis, including job management, execution, monitoring, and debugging—enabling fast, scalable searches across large data volumes.
Multi-Messenger Association Tools
Uses tools like RAVEN and Echo-Location to assess the significance of possible associations between BAT detections and GW events. It supports the interpretation of joint sky localization maps, including overlap with LIGO/Virgo or Fermi GRB maps.
Rapid Follow-up Capabilities
When a candidate counterpart is found with arcminute localization, NITRATES enables submission of target-of-opportunity (ToO) requests to Swift’s XRT and UVOT instruments for prompt multi-wavelength follow-up.
Sky-Position-Dependent Upper Limits
In the case of non-detections, NITRATES calculates upper limits on the gamma-ray flux as a function of sky position, supporting the interpretation of null results in a physically meaningful context.
Use case
NITRATES is a powerful tool for the low-latency identification of gamma-ray counterparts to GW events. It is primarily used by multi-messenger teams to:
- Search for faint GRBs in temporal and spatial coincidence with GW signals.
- Interpret the absence of a detection using sky-position-dependent sensitivity.
- Provide rapid, high-confidence follow-up targets for X-ray and optical observations.
- Contribute to the statistical understanding of GRB production efficiency in compact binary coalescences.
By expanding the effective sensitivity of the Swift BAT through targeted sub-threshold searches, NITRATES increases the likelihood of discovering weak or off-axis GRBs and strengthens the multi-messenger detection framework.