Context :

Aims : AX J1845.0 - 0433 is a transient high-mass X-ray binary discovered by ASCA .
The source displays bright and short flares observed recently with INTEGRAL .
The transient behaviour and the bright and short flares are studied in order to understand the accretion mechanisms and the nature of the source .

Methods : Public INTEGRAL data and a pointed XMM-Newton observation are used to study in details the flaring and quiescent phases .

Results : AX J1845.0 - 0433 is a persistent X-ray binary with a O9.5I supergiant companion emitting at a low 0.2–100 keV luminosity of \sim 10 ^ { 35 } \mathrm { erg } \mathrm { s } ^ { -1 } with seldom flares reaching luminosities of 10 ^ { 36 } \mathrm { erg } \mathrm { s } ^ { -1 } .
The most-accurate X-ray position is R.A. ( 2000 ) = 18 ^ { \mathrm { h } } 45 ^ { \mathrm { m } } 01.4 ^ { \mathrm { s } } and Dec . = -04 \degr 33 \arcmin 57.7 \arcsec ( 2 \arcsec ) .
Variability factors of 50 are observed on time scale as short as hundreds of seconds .
The broad-band high-energy spectrum is typical of wind-fed accreting pulsars with an intrinsic absorption of N _ { \mathrm { H } } = ( 2.6 \pm 0.2 ) \times 10 ^ { 22 } \mathrm { cm } ^ { -2 } , a hard continuum of \Gamma = ( 0.7 - 0.9 ) \pm 0.1 and a high-energy cutoff at E _ { \mathrm { cut } } = 16 _ { -3 } ^ { +5 } keV .
An excess at low energies is also observed fitted with a black body with a temperature of kT = 0.18 \pm 0.05 keV .
Optically-thin and highly-ionised iron ( Fe XVIII - XIX ) located near the supergiant star is detected during the quiescence phase .
The spectral shape of the X-ray continuum is constant .
The flare characteristics in contrast to the persistent quiescent emission suggest that clumps of mass M \sim 10 ^ { 22 } g are formed within the stellar wind of the supergiant companion .

Conclusions :