Context : AX J1749.1 - 2733 is an unclassified transient X-ray source discovered during surveys by ASCA in 1993–1999 .
The transient behaviour and the short and bright flares of the source have led to the idea that it is part of the recently revealed subclass of supergiant fast X-ray transients .

Aims : A multi-wavelength study in NIR , optical , X-rays , and hard X-rays of AX J1749.1 - 2733 is undertaken in order to determine its nature .

Methods : Public INTEGRAL data and our target of opportunity observation with XMM-Newton were used to study the high-energy source through timing and spectral analysis .
Multi-wavelength observations in optical and NIR with the ESO/NTT telescope were also performed to search for the counterpart .

Results : AX J1749.1 - 2733 is a new high-mass X-ray binary pulsar with an orbital period of 185.5 \pm 1.1 days ( or 185.5 / f with f = 2 , 3 \mathrm { or } 4 ) and a spin period of \sim 66 s , parameters typical of a Be/X-ray binary .
The outbursts last \sim 12 d. A spin-down of \dot { P } = 0.08 \pm 0.02 \mathrm { s } \mathrm { yr } ^ { -1 } is also observed , very likely due to the propeller effect .
The most accurate X-ray position is R.A. ( 2000 ) = 17 ^ { \mathrm { h } } 49 ^ { \mathrm { m } } 06.8 ^ { \mathrm { s } } and Dec . = -27 \degr 32 \arcmin 32.5 \arcsec ( \mathrm { uncertainty } 2 \arcsec ) .
The high-energy broad-band spectrum is well-fitted with an absorbed powerlaw and a high-energy cutoff with values N _ { \mathrm { H } } = 20.1 _ { -1.3 } ^ { +1.5 } \times 10 ^ { 22 } \mathrm { cm } ^ { -2 } , \Gamma = 1.0 _ { -0.3 } ^ { +0.1 } , and E _ { \mathrm { cut } } = 21 _ { -3 } ^ { +5 } keV .
The only optical/NIR candidate counterpart within the X-ray error circle has magnitudes of R = 21.9 \pm 0.1 , I = 20.92 \pm 0.09 , J = 17.42 \pm 0.03 , H = 16.71 \pm 0.02 , and K _ { \mathrm { s } } = 15.75 \pm 0.07 , which points towards a Be star located far away ( > 8.5 kpc ) and highly absorbed ( N _ { \mathrm { H } } \sim 1.7 \times 10 ^ { 22 } \mathrm { cm } ^ { -2 } ) .
The average 22–50 keV luminosity is 0.4 - 0.9 \times 10 ^ { 36 } \mathrm { ergs } \mathrm { s } ^ { -1 } during the long outbursts and 3 \times 10 ^ { 36 } \mathrm { ergs } \mathrm { s } ^ { -1 } during the bright flare that occurred on MJD 52891 for an assumed distance of 8.5 kpc .

Conclusions :