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Astron. Astrophys. 356, 175-180 (2000)


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Broad-band BeppoSAX observation of the low-mass X-ray binary X 1822-371

A.N. Parmar 1, T. Oosterbroek 1, S. Del Sordo 2, A. Segreto 2, A. Santangelo 2, D. Dal Fiume 3 and M. Orlandini 3

1 Astrophysics Division, Space Science Department of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
2 IFCAI, CNR, Via La Malfa 153, 90146 Palermo, Italy
3 Istituto TESRE, CNR, Via Gobetti 101, 40129 Bologna, Italy

Received 10 November 1999 / Accepted 13 January 2000

Abstract

Results of a 1997 September 9-10 BeppoSAX observation of the 5.57 hr low-mass X-ray binary (LMXRB) X 1822-371 are presented. The 0.3-40 keV spectrum is unusually complex and cannot be fit by any of the standard models applied to other LMXRB. At least two components are required. One component has a shape consistent with that expected from the Comptonization of an input soft (Wien) spectrum while the other, contributing [FORMULA]40% of the 1-10 keV flux, is consistent with being a blackbody. In addition, there is a "dip" in the spectrum which can be modeled by a [FORMULA] keV absorption edge with an optical depth, [FORMULA], of [FORMULA]. If the same model is fit to ASCA Solid-State Imaging Spectrometer spectra obtained in 1993 and 1996, then reasonable fits are also obtained, with a similar absorption feature required. The nature of this feature is highly uncertain; its energy corresponds to the K-edges of highly ionized Ne X and neutral Mg, or to an L-edge of moderately ionized Fe. Surprisingly, no strong ([FORMULA]) Fe-K or ([FORMULA]) O-K edges are visible. The folded lightcurve of X 1822-371 is similar to previous observations, except that no strong softening is seen near the eclipse. An updated orbital ephemeris is provided.

Key words: X-rays: stars – stars: neutron – stars: individual: X 1822-371 – accretion, accretion disks

Send offprint requests to: A.N. Parmar (aparmar@astro.estec. esa.nl)

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000

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