The very faint hard state of the persistent neutron star X-ray binary SLX 1737-282 near the Galactic Centre

We report on a detailed study of the spectral and temporal properties of the neutron star low-mass X-ray binary SLX 1737-282, which is located only similar to 1 degrees away from Sgr A*. The system is expected to have a short orbital period, even within the ultracompact regime, given its persistent nature at low X-ray luminosities and the long duration thermonuclear burst that it has displayed. We have analysed a Suzaku (18 ks) observation and an XMM-Newton (39 ks) observation taken 7 yr apart. We infer (0.5-10 keV) X-ray luminosities in the range of 3-6 x 10(35)ergs(-1), in agreement with previous findings. The spectra are well described by a relatively cool (kT(bb) = 0.5 keV) blackbody component plus a Comptonized emission component with Gamma similar to 1.5-1.7. These values are consistent with the source being in a faint hard state, as confirmed by the similar to 20 per cent fractional root-mean-square amplitude of the fast variability (0.1-7 Hz) inferred from the XMM-Newton data. The electron temperature of the corona is greater than or similar to 7 keV for the Suzaku observation, but it is measured to be as low as similar to 2 keV in the XMM-Newton data at higher flux. The latter is significantly lower than expected for systems in the hard state. We searched for X-ray pulsations and imposed an upper limit to their semi-amplitude of 2 per cent (0.001-7 Hz). Finally, we investigated the origin of the low-frequency variability emission present in the XMM-Newton data and ruled out an absorption dip origin. This constraint the orbital inclination of the system to less than or similar to 65 degrees unless the orbital period is longer than 11 h (i.e. the length of the XMM-Newton observation).