Long gamma-ray bursts (GRBs) are believed to originate from core collapse of
massive stars. High-redshift GRBs can probe the star formation and reionization
history of the early universe, but their detection remains rare. Here we report
the detection of a GRB triggered in the 0.5–4 keV band by the Wide-field X-ray
Telescope (WXT) on board the Einstein Probe (EP) mission, designated as
EP240315a, whose bright peak was also detected by the Swift Burst Alert
Telescope and Konus-Wind through off-line analyses. At a redshift of z=4.859,
EP240315a showed a much longer and more complicated light curve in the soft
X-ray band than in gamma-rays. Benefiting from a large field-of-view
(∼3600 deg^2) and a high sensitivity, EP-WXT captured the earlier engine
activation and extended late engine activity through a continuous detection.
With a peak X-ray flux at the faint end of previously known high-z GRBs, the
detection of EP240315a demonstrates the great potential for EP to study the
early universe via GRBs.
