Accurate classification of 75 counterparts of objects detected in the 54-month Palermo Swift/BAT hard X-ray catalogue

Through an optical campaign performed at four telescopes located in the northern and southern hemispheres, we have obtained optical spectroscopy for 75 counterparts of unclassified or poorly studied hard X-ray emitting objects detected with Swift/BAT and listed in the 54-month Palermo BAT catalogue. All these objects also have observations taken with the Swift/XRT, ROSAT, or Chandra satellites, which allowed us to reduce the high-energy error box and pinpoint the most likely optical counterpart(s). We found that 69 sources in our sample are active galactic nuclei (AGNs) of which, 35 are classified as type 1 (with broad and narrow emission lines), 33 are classified as type 2 (with only narrow emission lines), and one is a high-redshift quasi-stellar object; the remaining 6 objects are galactic cataclysmic variables. Of the type 1 AGNs, 32 are objects of intermediate Seyfert type (1.2-1.9) and one is narrow-line Seyfert 1 galaxy; for 29 of the 35 type 1 AGNs, we have been able to estimate the central black hole mass and the Eddington ratio. Of the type 2 AGNs, two display optical features typical of the low-ionization nuclear emission-line region class, three are classified as transition objects, one is a starburst galaxy, and two are X-ray bright, optically normal galaxies. All galaxies classified in this work are relatively nearby objects (0.006-0.213) except for one at redshift 1.137.