  GW170817-GRB 170817A provided the first observation of gravitational waves
from a neutron star merger with associated transient counterparts across the
entire electromagnetic spectrum. This discovery demonstrated the
long-hypothesized association between short gamma-ray bursts and neutron star
mergers. More joint detections are needed to explore the relation between the
parameters inferred from the gravitational wave and the properties of the
gamma-ray burst signal. We developed a joint multimessenger analysis of LIGO,
Virgo, and Fermi/GBM data designed for detecting weak gravitational-wave
transients associated with weak gamma-ray bursts. As such, it does not start
from confident (GWTC-1) events only. Instead, we take the full list of existing
compact binary coalescence triggers generated with the PyCBC pipeline from the
second Gravitational-Wave Observing Run (O2), and reanalyze the entire set of
public Fermi/GBM data covering this observing run to generate a corresponding
set of gamma-ray burst candidate triggers. We then search for coincidences
between the gravitational-wave and gamma-ray burst triggers without requiring a
confident detection in any channel. The candidate coincidences are ranked
according to a statistic combining each candidate's strength in
gravitational-wave and gamma-ray data, their time proximity, and the overlap of
their sky localization. The ranking is then converted to a false alarm rate
using time shifts between the gravitational-wave and gamma-ray burst triggers.
We present the results using O2 triggers, which allowed us to check the
validity of our method against GW170817-GRB 170817A. We also discuss the
different configurations tested to maximize the significance of the joint
detection.
