Letter to the Editor

The infrared counterpart of the X-ray burster KS 1731–260 ^*,**

¹ ESO, Karl Schwarzschild Str. 2, 85748 Garching bei München, Germany
² The Open University, Department of Physics and Astronomy Walton Hall, Milton Keynes, MK7 6AA, UK
³ Service d'Astrophysique / CEA, CE-Saclay, 91191 Gif-sur-Yvette, France
⁴ Instituto de Astronomía y Física del Espacio/CONICET. cc5, 1428 Bs As, Argentina
⁵ Istituto di Astrofisica Spaziale e Fisica Cosmica CNR, Sezione di Milano “G.Occhialini”, via Bassini 15, 20133 Milano, Italy

Corresponding author: R. P. Mignani, rmignani@eso.org

Received: 8 March 2002
Accepted: 26 April 2002

Abstract

We present JK' infrared images of the X-ray transient KS 1731–260, obtained in 1997 and in 1998 with IRAC2b at the ESO/MPI 2.2-m telescope at La Silla. Using as a reference the recent Chandra position, we confirm the identification of the X-ray source with the previously proposed counterpart (Wijnands et al. [CITE]), for which we measure and . The source was entering a low X-ray state at the epoch of our observations, and the accretion disk was still dominating the infrared flux. Indeed, when compared with the only published magnitudes in the J-band (Orosz et al. [CITE]), obtained with the source in quiescence, our photometry confirms the fading of the counterpart during the decay of the RXTE/ASM lightcurve.