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

¹ Istituto di Astrofisica e Planetologia Spaziali (INAF), via Fosso del Cavaliere 100, Roma 00133, Italy
e-mail: pietro.parisi@iaps.inaf.it
² INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, 40129 Bologna, Italy
³ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
⁴ Universidad Nacional Autónoma de México, Apartado Postal 70-264, 04510 México D.F., Mexico
⁵ Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51-216, 72000 Puebla, Mexico
⁶ School of Physics & Astronomy, University of Southampton, Southampton, SO17 1BJ, UK
⁷ Specola Vaticana, 00120 Città del Vaticano, Vatican
⁸ Departamento de Ciencias Físicas, Universidad Andrés Bello, Av. República 220, 83701 Santiago, Chile
⁹ Dipartimento di Fisica ed Astronomia “G.Galilei”, Univeristà di Padova, vicolo dell’Osservatorio 3, 35122 Padova, Italy
¹⁰ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy

Received: 31 July 2013
Accepted: 6 November 2013

Abstract

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.