We report the results from an archival XMM-Newton observation of the Supergiant Fast X-ray Transient ( SFXT ) IGR J18483 - 0311 during its apastron passage .
The measured 0.5–10 keV luminosity state ( 1.3 \times 10 ^ { 33 } erg s ^ { -1 } ) is the lowest ever reported in the literature , it is best fitted by an absorbed black body model yielding parameters consistent with previous measurements .
In addition , we find evidence of an emission line feature at \sim 3.3 keV in the 0.5–10 keV EPIC-pn source spectrum .
We show that its physical explanation in terms of atomic emission line appears unlikely and conversely we attempt to ascribe it to an electron cyclotron emission line which would implies a neutron star magnetic field of the order of \sim 3 \times 10 ^ { 11 } G. A possible hint of the first harmonic is also found .
If firmly confirmed by future longer X-ray observations , this would be the first detection ever of a cyclotron feature in the X-ray spectrum of a SFXT , with important implications on theoretical models .