EDP Sciences
Free access
Volume 402, Number 2, May I 2003
Page(s) 457 - 464
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20030274

A&A 402, 457-464 (2003)
DOI: 10.1051/0004-6361:20030274

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

W. Pietsch, F. Haberl and A. Vogler

Max-Planck-Institut für extraterrestrische Physik, 85741 Garching, Germany
(Received 19 December 2002 / Accepted 25 February 2003 )

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 $\rm MJD~51539.276\pm 0.006$ and the binary period determined to $p=(352.870\pm 0.012){\rm d}/n$ 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 $\,\times\,10^{21}$ cm -2, $\Gamma=1.7$). In the bright state the source luminosity is $4\times 10^{38}$ (0.5-5 keV), just compatible with the Eddington luminosity of a 1.4  $M_{\odot}$ neutron star. A possible optical identification is suggested. RX J004717.4-251811 parameters are compared to other eclipsing X-ray binaries (XRBs).

Key words: galaxies: individual: NGC 253 -- X-rays: stars -- stars: binaries: eclipsing

Offprint request: W. Pietsch, wnp@mpe.mpg.de

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© ESO 2003