Unveiling the nature of INTEGRAL objects through optical spectroscopy -: II.: The nature of four unidentified sources

We present new results from our optical spectrophotometric campaign ongoing at the Astronomical Observatory of Bologna in Loiano (Italy) on hard X-ray sources detected by INTEGRAL. We have observed spectroscopically the putative optical counterparts of four more INTEGRAL sources, IGR J12391- 1610, IGR J18406- 0539, 2E 1853.7+ 1534 and IGR J19473+ 4452. These data have allowed us to determine their nature, finding that IGR J12391- 1610 (= LEDA 170194) and IGR J19473+ 4452 are Seyfert 2 galaxies at redshifts z = 0.036 and z = 0.053, respectively, IGR J18406- 0539 (= SS 406) is a Be massive X-ray binary located at similar to 1.1 kpc from Earth, and 2E 1853.7+ 1534 is a type 1 Seyfert galaxy with z = 0.084. Physical parameters for these objects are also evaluated by collecting and discussing the available multiwavelength information. The determination of the extragalactic nature of a substantial fraction of sources inside the INTEGRAL surveys underlines the importance of hard X-ray observations for the study of background Active Galactic Nuclei located beyond the Zone of Avoidance of the Galactic Plane.