Astron. Astrophys. 333, L31-L34 (1998)

Letter to the Editor

A deep X-ray low state of AM Herculis

D. , de Martino ¹, B.T. , Gänsicke ², G. , Matt ³, M. , Mouchet ⁴, T. , Belloni ⁵, K. , Beuermann ², J.-M. , Bonnet-Bidaud ⁶, J. , Mattei ⁷, L. , Chiappetti ⁸, C. and Done <sup>9

1</sup> Osservatorio di Capodimonte, Via Moiariello 16, I-80131 Napoli, Italy
² Universitäts-Sternwarte, Geismarlandstrasse 11, D-37083 Göttingen, Germany
³ Dipartimento di Fisisca, Universitá degli studi "Roma Tre", Via della Vasca Navale 84, I-00146 Roma, Italy
⁴ DAEC, Observatoire de Paris, Section de Meudon, F-92195 Meudon Cedex, France
⁵ Astronomical Institute "Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁶ CEA, DSN/DAPNIA/Service d'Astrophysique, CEN Saclay, F-91191 Gif-sur-Yvette Cedex, France
⁷ AAVSO, 25 Birch Street, Cambridge, MA 02138, USA
⁸ Istituto di Fisisca Cosmica CNR, Via Bassini 15, Milano, Italy
⁹ Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK

Received 2 March 1998 / Accepted 12 March 1998

Abstract

We present a BeppoSAX observation of AM Her during a prolonged low state. The source was observed for hrs at a flux level comparable to previous low states, followed by a rapid ( min) drop by a factor of to the deepest X-ray low state ever detected. While the active phase X-ray flux is likely to be accretion induced, coronal emission from the secondary may contribute significantly during the inactive phase. The timescale of this dramatic change in the accretion rate is of the order of the dynamical timescale of the secondary star; no available model can satisfactorily explain the evolution of the X-ray flux detected in these BeppoSAX data.

Key words: accretion binaries: close stars, individual: AM Her X-rays: stars

Send offprint requests to: D. de Martino

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Contents

• 1. Introduction
• 2. Observations
• 3. Analysis and results
  • 3.1. The X-ray light curve
  • 3.2. The X-ray spectrum
• 4. Discussion
  • 4.1. The origin of the X-rays
  • 4.2. Variability of the accretion rate
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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