Interface definition for online detection pipelines¶
The BAYESTAR rapid localization algorithm is designed as a post-processing stage for compact binary merger search pipelines. The script bayestar-localize-lvalert provides rapid sky localization as a service.
Other available modes of operation for BAYESTAR that are documented
elsewhere include the script bayestar-localize-coincs for offline batch processing
and the method
ligo.skymap.bayestar.localize() for directly calling
BAYESTAR from Python code.
In online operation, search pipelines upload candidates to the Gravitational-Wave Candidate Event Database (GraceDB). The script bayestar-localize-lvalert (or the equivalent Celery task in GWCelery) listens for and intercepts LVAlert pubsub messages. For each event created, the script downloads the pipeline’s output data products from GraceDB, performs rapid sky localization, and uploads the resulting FITS file back to GraceDB.
The interactions between the search pipeline, GraceDB, and BAYESTAR are illustrated in the sequence diagram below. Line styles have the following meanings:
Solid lines directed into GraceDB represent HTTP requests.
Solid lines directed out of GraceDB represent HTTP responses.
Dashed lines represent LVAlert pubsub messages.
This section describes the interface between search pipelines and BAYESTAR. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.
The following two files MUST be uploaded to GraceDB:
coinc.xml: The event file, which SHOULD be the initial upload that creates the event.
psd.xml.gz: The power spectral density data file, which MUST be uploaded with the
The format of both files MUST be LIGO-LW (see LIGO-T990023). LIGO-LW is a legacy XML-based format used by a variety of LIGO/Virgo/KAGRA software and services for storing tabular datasets.
There are two variants of the LIGO-LW format, an old format implemented by
glue.ligolw that uses string (“ilwdchar”) row IDs, and a new format
ligo.lw that uses integer row IDs. GraceDB and
BAYESTAR can accept either format.
The ligolw_no_ilwdchar command-line tool provided by
ligo.lw can convert from the new format to the old format.
This file describes the search pipeline’s matched filter output. It MUST contain the point estimates of the time, phase, and amplitude on arrival in each detector. It MUST provide the intrinsic template parameters (masses and spins). It SHOULD contain a signal-to-noise time series for each detector.
coinc.xml file MUST contain at least the following LIGO-LW tables
(in any order):
The value of those rows’
programcolumn MUST be one of
Additional valid columns of this table MAY be populated in order to identify the pipeline software version or include other metadata. Additional unrelated rows (e.g. to identify prior analysis steps such as template bank generation) MAY be included and will be ignored.
sngl_inspiraltable MUST contain exactly one row per detector that the search analyzed.
The values of the
event_idcolumn MUST be distinct across all rows.
If the template has zero spin, then the spin columns MAY be left blank. If the template has aligned spins, then the _x_ and _y_ spin components MAY be left blank.
end_time_nscolumns MUST report the seconds and nanoseconds parts of the GPS time at which the same fiducial reference part of the signal (e.g., the time of merger, or the time at which the inspiral reaches reference frequency) is received in each detector. It SHOULD record the merger time. If the event is an “early warning” or pre-merger event, then it SHOULD record the predicted time of merger.
If the event is an early warning event, then the high-frequency cutoff frequency MUST be recorded in the
snrcolumn MUST report the absolute value of the complex matched filter SNR of the best-matching template. It MUST NOT report a modified SNR-like quantity such as newSNR.
coa_phasecolumn MUST report the argument of the complex matched filter SNR of the best-matching template.
If the search pipeline as identified by the
programcolumn in the
pycbc, then phase convention of the
coa_phasecolumn MUST be that the matched filter output is linear in terms of the data. Otherwise, the phase convention MUST be that the matched filter output is antilinear in terms of the data.
The value in each row’s
table_namecolumn must be set
coinc_inspiraltable MUST be present because it is required by GraceDB (although it is ignored by BAYESTAR).
It MUST have exactly one row.
coinc.xml file SHOULD also provide SNR time series for each
Each SNR time series MUST be stored inside a
LIGO_LWelement as a serialized
COMPLEX8TimeSeries. The function
lal.sereries.build_COMPLEX8TimeSeries()can be used to serialize a
Each of the
LIGO_LWelements for serialized SNR time series MUST contain a
Paramelement to link it to a row in the
sngl_inspiral. The param name MUST be
event_id:paramand the param value must match the
event_idcolumn in the corresponding
The SNR time series MUST have an odd number of samples, e.g., the length must be \(2 * n + 1\) for some integer \(n\).
The timestamp of the central sample (e.g. \(n\) times the sample interval plus the epoch) MUST differ from the corresponding
sngl_inspiralrow’s time (if present) by no more than one sample interval.
The timestamps of the samples of the SNR time series MUST correspond to sample boundaries. The timestamps MUST NOT have any sub-sample time shift applied to them.
For any detector that lacks an SNR time series, sub-sample interpolation SHOULD be applied by the search pipeline to obtain the values for the
end_time_nscolumns in the corresponding row of the
This file contains each analyzed detectors’ estimated noise power spectral density (PSD) series.
There MUST be exactly one PSD per detector analyzed.
Each PSD MUST be stored inside a
LIGO_LWelement as a serialized
lal.sereries.build_COMPLEX8TimeSeries()function or the
lal.sereries.make_psd_xmldoc()function can be used to serialize
LIGO_LWelement MUST contain a
Paramelement to link it to a detector. The param’s name MUST be
instrument:param, its type MUST be
instrument:param, and its value should be a detector prefix such (e.g. one of
Any samples that are invalid because their frequencies are outside of the range analyzed by the search MUST be absent or have their values set to positive infinity. Invalid values MUST NOT be set to zero.