XMM-Newton detection of Nova Muscae 1991 in quiescence

¹ The Open University, Milton Keynes, UK
² University of Southampton, UK
³ X-ray Astronomy Group, Dept of Physics and Astronomy, University of Leicester, University Rd, Leicester LE1 7RH, UK
⁴ SRON, Utrecht, The Netherlands
⁵ IAC, La Laguna, Tenerife, Spain
⁶ Institute of Astronomy and Astrophysics, National Observatory of Athens, PO Box 20048, Athens 11810, Greece
⁷ Dept. of Astrophysics, Oxford University, UK
⁸ NASA/GSFC, Maryland, USA

Corresponding author: F. K. Sutaria, F.K.Sutaria@open.ac.uk

Received: 19 March 2002
Accepted: 4 June 2002

Abstract

The soft X-ray transient GU Mus has been detected by XMM-Newton in the quiescent state. The source is very faint, with a 0.5–10.0 keV unabsorbed flux of  ergs cm^-2 s^-1. The spectra is well fit by an absorbed powerlaw with a photon index of , close to the value seen when the source was in the low/hard state in Aug. 1991. From our observed luminosity, it seems unlikely that the quiescent state emission is dominated by coronal X-rays from the secondary. The flux also appears to be in agreement with the ADAF model of BH-transients in quiescence.