Letter to the Editor

Discovery of a bright X-ray transient in the Galactic Center with XMM-Newton

¹ Max-Planck-Institut für extraterrestrische Physik, PO Box 1312, Garching bei München 85741, Germany e-mail: dporquet@mpe.mpg.de
² Laboratoire d'Astrophysique de Grenoble, Université Joseph-Fourier, BP 53, 38041 Grenoble Cedex 9, France
³ Department of Astronomy, Odessa National University, T. G. Shevchenko park, 65014 Odessa, Ukraine
⁴ Crimean Astrophysical Observatory, 98409 Nauchny, Ukraine
⁵ Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK

Received: 10 September 2004
Accepted: 2 December 2004

Abstract

We report the discovery of a bright X-ray transient object, XMMU J174554.4–285456, observed in outburst with XMM-Newton on October 3, 2002, and located at 6.3′ from Sgr A*, the supermassive black hole at the Galactic center. This object exhibits a very large X-ray luminosity variability of a factor of about 1300 between two X-ray observations separated by four months. The X-ray spectrum is best fitted by a power-law with a photon index of and absorption column density of cm^-2. This large absorption suggests this source is located at the distance of the Galactic center, i.e., 8 kpc. The 2–10 keV luminosity is about erg s^-1. A pulsation period of about 172 s is hinted by the timing analysis. The X-ray properties strongly suggest a binary system with either a black hole or a neutron star for the compact object.