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Astron. Astrophys. 340, L19-L22 (1998)


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Letter to the Editor

The extraordinary X-ray spectrum of XTE J0421+560

A. Orr 1, A.N. Parmar 1, M. Orlandini 2, F. Frontera 2, 3, D. Dal Fiume 2, A. Segreto 4, A. Santangelo 4 and M. Tavani 5, 6

1 Astrophysics Division, Space Science Department of ESA, ESTEC, 2200 AG Noordwijk, The Netherlands
2 Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Via Gobetti 101, I-40129 Bologna, Italy
3 Dipartimento di Fisica, Università di Ferrara, Via Paradiso 11, I-44100 Ferrara, Italy
4 Istituto di Fisica Cosmica ed Applicazioni all'Informatica, CNR, Via U. La Malfa 153, I-90146 Palermo, Italy
5 Columbia Astrophysics Laboratory, Columbia University, 538 West 120th Street, New York, NY 10027, USA
6 Istituto di Fisica Cosmica e Tecnologie Relative, CNR, Via Bassini 15, I-20133 Milano, Italy

Received 2 September 1998 / Accepted 18 October 1999

Abstract

We report results of two BeppoSAX observations of the transient X-ray source XTE J0421+560 during the outburst that started in March 1998. The source exhibits radio jets and coincides with the binary system CI Cam. The 0.1-50 keV spectrum is unlike those of other X-ray transients, and cannot be fit with any simple model. The spectra can be represented by an absorbed two component bremsstrahlung model with narrow Gaussian emission features identified with O, Ne/Fe-L, Si, S, Ca and Fe-K. During the second observation (TOO2) the energies of the O and the Ne/Fe-L features decreased smoothly by [FORMULA]9% over an interval of 30 hrs. No significant energy shift of the other lines is detected with e.g, a 90% confidence upper limit to any Fe-K line shift of 3.5%. No moving lines were detected during the first observation (TOO1) with e.g., an upper limit of [FORMULA]1.4% to any shift of the Fe-K line. The low-energy absorption decreased by a factor [FORMULA]1.8 from [FORMULA][FORMULA] atom cm-2 between TOO1 and TOO2. We propose that the time variable emission lines arise in precessing relativistic jets, while the stationary lines originate in circumstellar material.

Key words: stars: binaries – - stars: emission-line, Be – stars: individual (XTE J0421+560) – stars: novae – X-rays: stars

Send offprint requests to: aparmar@astro.estec.esa.nl

© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998

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