  The ESA M3 candidate mission LOFT (Large Observatory For x-ray Timing) has
been designed to study strong gravitational fields by observing compact
objects, such as black-hole binaries or neutron-star systems and supermassive
black-holes, based on the temporal analysis of photons collected by the primary
instrument LAD (Large Area Detector), sensitive to X-rays from 2 to 50 keV,
offering a very large effective area (>10 m 2 ), but a small field of view
({\o}<1{\deg}). Simultaneously the second instrument WFM (Wide Field Monitor),
composed of 5 coded-mask camera pairs (2-50 keV), monitors a large part of the
sky, in order to detect and localize eruptive sources, to be observed with the
LAD after ground-commanded satellite repointing. With its large field of view
(>{\pi} sr), the WFM actually detects all types of transient sources, including
Gamma-Ray Bursts (GRBs), which are of primary interest for a world-wide
observers community. However, observing the quickly decaying GRB afterglows
with ground-based telescopes needs the rapid knowledge of their precise
localization. The task of the Loft Burst Alert System (LBAS) is therefore to
detect in near- real-time GRBs (about 120 detections expected per year) and
other transient sources, and to deliver their localization in less than 30
seconds to the observers, via a VHF antenna network. Real-time full resolution
data download to ground being impossible, the real-time data processing is
performed onboard by the LBOT (LOFT Burst On-board Trigger system). In this
article we present the LBAS and its components, the LBOT and the associated
ground-segment.
