  During a 50 ks monitoring observation of the Galactic bulge performed in
September 1999 by the Wide Field Cameras on board the BeppoSAX satellite, an
X-ray burst was detected from a sky position ~3 degrees off the Galactic
centre. No previously known X-ray sources are located within the position error
circle of the observed burst. The new burster, SAX J1752.3-3138, did not show
any persistent emission during the whole observation. No other bursting events,
as well as steady emission, were reported so far by other instruments or
detected in the WFC archive, which covers ~6 Ms and ~4 Ms for burst and
persistent luminosity detection, respectively, starting from August 1996.
Unless the source is a very weak transient, this could indicate SAX
J1752.3-3138 is an atypical burster, a member of a possibly new class of
sources characterised by very low steady luminosities and accretion rates (L_x
< 10^35 erg/s) and extremely rare bursting activity. The characteristics of the
detected burst are consistent with a type I event, identifying the source as a
weakly magnetised neutron star in a low-mass X-ray binary system. Evidence for
photospheric radius expansion due to Eddington-limited burst luminosity allows
to estimate the distance to the source (~9 kpc).
