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Astron. Astrophys. 339, L69-L72 (1998)

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Letter to the Editor

Multifrequency observations of XTE J0421+560/CI Cam in outburst

F. Frontera 1, 2, M. Orlandini 1, L. Amati 1, D. Dal Fiume 1, N. Masetti 1, A. Orr 3, A.N. Parmar 3, E. Brocato 4, G. Raimondo 4, A. Piersimoni 4, M. Tavani 5, 6 and R.A. Remillard 7

1 Istituto Tecnologie e Studio Radiazioni Extraterrestri, TeSRE/CNR, Via Gobetti 101, I-40129 Bologna, Italy
2 Dipartimento di Fisica, Università di Ferrara, Via Paradiso 11, I-44100 Ferrara, Italy
3 Astrophysics Division, Space Science Department of ESA, ESTEC, 2200 AG Noordwijk, The Netherlands
4 Osservatorio Astronomico di Teramo, Collurania, I-64100 Teramo, Italy
5 Istituto di Fisica Cosmica e Tecnologie Relative, IFCTR/CNR, Via Bassini 15/A, I-20133 Milano, Italy
6 Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
7 Center for Space Research, MIT, 77 Mass Ave, Cambridge, MA 02139, USA

Received 1 September 1998 / Accepted 5 October 1998

Abstract

We report on two X-ray observations of the transient source XTE J0421+560 performed by BeppoSAX, and on a series of observations performed by the 0.7 m Teramo-Normale Telescope. Outburst peak occurrence time and duration depend on photon energy: the outburst peak is achieved first in the X-ray band, then in the optical and finally in the radio. An exponential decay law fits well the X-ray data except in the TOO2 0.5-1.0 keV band, where erratic time variability is detected. During TOO1 the e-folding time scale decreases with energy up to [FORMULA]20 keV, when it achieves a saturation; during TOO2 it decreases up to [FORMULA]2 keV and then increases. This change is correlated with a spectral change, characterized by the onset of a soft ([FORMULA]2 keV) component in TOO2 (Orr et al. 1998). This component might originate from the relativistic jets, while the hard component is more likely associated to processes occurring in the circumstellar matter and/or near the compact object. Optical observations show that the object appears intrinsically red even during the outburst. The nature of the compact object is discussed.

Key words: stars: binaries: symbiotic – stars: individual (XTE J0421+560) – stars: novae – X-ray: general – X-rays: stars

Send offprint requests to: frontera@tesre.bo.cnr.it

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© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998
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