RX J004717.4-251811: The first eclipsing X-ray binary outside the Local Group^*

Max-Planck-Institut für extraterrestrische Physik, 85741 Garching, Germany

Corresponding author: W. Pietsch, wnp@mpe.mpg.de

Received: 19 December 2002
Accepted: 25 February 2003

Abstract

The X-ray source RX J004717.4-251811 in the nearby starburst galaxy NGC 253 was found to undergo changes from a low to a high state twice, during an XMM-Newton EPIC observation in December 2000 and also during a Chandra observation one year earlier. These transitions are interpreted as egresses from eclipses of a compact object in a high mass X-ray binary system (HMXB). The phase of eclipse egress during the Chandra observation is given by barycenter corrected and the binary period determined to by the time difference between the two egresses and number n of periods in-between. Allowed periods may be further constrained by additional XMM-Newton, Chandra, ROSAT, and Einstein observations resulting in only seven acceptable periods with 1.47024 d and 3.20793 d most promising. No significant regular pulsations of the source in the range 0.3–1000 s were found. Fluctuations on time scales of 1000 s were observed together with extended intervals of low intensity. The energy spectrum during the bright state can best be described by an absorbed flat power law ( = 1.9 cm^-2, ). In the bright state the source luminosity is (0.5–5 keV), just compatible with the Eddington luminosity of a 1.4   neutron star. A possible optical identification is suggested. RX J004717.4-251811 parameters are compared to other eclipsing X-ray binaries (XRBs).