  IGR J17407-2808 is an enigmatic and poorly studied X-ray binary that was
recently observed quasi-simultaneously with NuSTAR and XMM-Newton. In this
paper we report the results of this observational campaign. During the first 60
ks of observation, the source was caught in a relatively low emission state,
characterised by a modest variability and an average flux of ~8.3E-13
erg/cm^2/s (4-60 keV). Afterwards, IGR J17407-2808 entered a significantly more
active emission state that persisted for the remaining ~40 ks of the NuSTAR
observation. During this state, IGR J17407-2808 displayed several fast X-ray
flares, featuring durations of ~1-100 s and profiles with either single or
multiple peaks. The source flux in the flaring state reached values as high as
2E-9 erg/cm^2/s (4-60 keV), leading to a measured dynamic range during the
NuSTAR and XMM-Newton campaign of >~ 10^3. We also analysed available archival
photometric near-infrared data of IGR J17407-2808 to improve the constraints
available so far on the the nature of the donor star hosted in this system. Our
analysis shows that the donor star can be either a rare K or M-type
sub-subgiant or an K type main sequence star, or sub-giant star. Our findings
support the classification of IGR J17407-2808 as a low-mass X-ray binary. We
discuss the source X-ray behaviour as recorded by NuSTAR and XMM-Newton in view
of this revised classification.
