  We explore a novel, exotic physics, modality in multi-messenger astronomy. We
are interested in exotic fields emitted by the mergers and their direct
detection with a network of atomic clocks. We specifically focus on the
rubidium clocks onboard satellites of the Global Positioning System. Bursts of
exotic fields may be produced during the coalescence of black hole
singularities, releasing quantum gravity messengers. To be detectable such
fields must be ultralight and ultra-relativistic and we refer to them as exotic
low-mass fields (ELFs). Since such fields possess non-zero mass, the ELF bursts
lag behind the gravitational waves emitted by the very same merger. Then the
gravitational wave observatories provide a detection trigger for the atomic
clock networks searching for the feeble ELF signals. ELFs would imprint an
anti-chirp transient across the sensor network. ELFs can be detectable by
atomic clocks if they cause variations in fundamental constants. We report our
progress in the development of techniques to search for ELF bursts with clocks
onboard GPS satellites. We focus on the binary neutron star merger GW170817 of
August 17, 2017. We find an intriguing excess in the clock noise post LIGO
gravitational wave trigger. Potentially the excess noise could be explained
away by the increased solar electron flux post LIGO trigger.
