Unveiling the nature of INTEGRAL objects through optical spectroscopy

II. The nature of four unidentified sources

¹ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, 40129 Bologna, Italy (formerly IASF/CNR, Bologna) e-mail: masetti@bo.iasf.cnr.it
² European Southern Observatory, Casilla 19001, Santiago 19, Chile
³ School of Physics & Astronomy, University of Southampton, Southampton, Hampshire, SO17 1BJ, UK
⁴ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40126 Bologna, Italy
⁵ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Roma, via Fosso del Cavaliere 100, 00133 Rome, Italy (formerly IASF/CNR, Rome)
⁶ INTEGRAL Science Data Centre, Chemin d'Ecogia 16, 1290 Versoix, Switzerland

Received: 22 August 2005
Accepted: 7 November 2005

Abstract

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 ~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.