Letter to the Editor

Unveiling the nature of three INTEGRAL sources through optical spectroscopy^*

Istituto di Astrofisica Spaziale e Fisica Cosmica – Sezione di Bologna, CNR, via Gobetti 101, 40129 Bologna, Italy e-mail: masetti@bo.iasf.cnr.it

Received: 10 August 2004
Accepted: 10 September 2004

Abstract

The results of an optical spectroscopy campaign performed at the Astronomical Observatory of Bologna in Loiano (Italy) on three hard X-ray sources detected by INTEGRAL (IGR J17303-0601, IGR J18027-1455 and IGR J21247+5058) are presented. These data have allowed a determination of the nature for two of them, with IGR J17303-0601 being a low mass X-ray binary in the Galaxy and IGR J18027-1455 a background type 1 Seyfert galaxy at redshift z = 0.035. IGR J21247+5058, instead, has a quite puzzling spectroscopic appearance, with a broad, redshifted H_α complex superimposed onto a “normal” F/G-type Galactic star continuum: these features, together with the spatially coincident extended radio emission, might suggest a chance alignment between a relatively nearby star and a background radio galaxy. These results underline the still non-negligible importance of smaller telescopes in modern astrophysics.