Letter to the Editor

The soft X-ray counterpart of the newly discovered INTEGRAL source IGR J16195–4945

¹ Istituto di Astrofisica Spaziale e Fisica Cosmica – Sezione di Milano “G. Occhialini” – IASF/CNR, via Bassini 15, 20133 Milano, Italy e-mail: sidoli@mi.iasf.cnr.it
² CIFS, Viale Settimio Severo 63, Torino 10133, Italy
³ Istituto di Astrofisica Spaziale e Fisica Cosmica – Sezione di Roma – IASF/CNR, via del Fosso del Cavaliere 100, Roma 00133, Italy
⁴ Dipartimento di Fisica, Università di Tor Vergata, Roma 00133, Italy

Received: 15 October 2004
Accepted: 26 November 2004

Abstract

The INTEGRAL satellite, during its regular scanning observations of the Galactic plane, has discovered several new X-ray sources emitting above 20 keV. The nature of the great majority of them is still unknown. Here we report on the likely low energy counterpart, observed with ASCA in 1994 and 1997, of one of these sources, IGR J16195–4945. The ASCA source is faint ( erg cm^-2 s^-1), highly absorbed ( cm^-2) and has a rather hard spectrum (photon index ~ 0.6). These spectral properties are suggestive of a neutron star in a High Mass X-ray Binary. Our analysis of all the public INTEGRAL data of IGR J16195–4945 shows that this source is variable and was in a high state with a 20–40 keV flux of ~17 mCrab in two occasions in March 2003.