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Astron. Astrophys. 358, 177-186 (2000)


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BeppoSAX observations of AM Herculis in intermediate and high states

G. Matt 1, D. de Martino 2, B.T. Gänsicke 3, I. Negueruela 4, R. Silvotti 2, J.M. Bonnet-Bidaud 5, M. Mouchet 6,7 and K. Mukai 8

1 Dipartimento di Fisica, Università degli Studi "Roma Tre", Via della Vasca Navale 84, 00146 Roma, Italy
2 Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
3 Universitätssternwarte Göttingen, Geismarlandstrasse 11, 37083 Göttingen, Germany
4 SAX/SDC Nuova Telespazio, Via Corcolle 19, 00131 Roma, Italy
5 CEA, DSN/DAPNIA/Service d'Astrophysique, CEN Saclay, 91191 Gif sur Yvette Cedex, France
6 DAEC, Observatoire de Paris, Section de Meudon, 92195 Meudon Cedex, France
7 Université Denis Diderot, 2 Place Jussieu, 75005 Paris, France
8 NASA/GSFC, Code 668, Greenbelt MD 20771, USA

Received 4 January 2000 / Accepted 24 March 2000

Abstract

Temporal and spectral analyses from BeppoSAX observations of AM Her performed during both an intermediate and a high state are presented and discussed. Optical observations taken a few days after the X-ray ones are also presented.

During the intermediate state observation, the source was in its "normal", one-pole accretion mode. In the high state it switched to an hitherto unobserved atypical "two-pole" accretion mode, with significant soft and hard X-ray emission from both poles. The emission from the second pole is much softer than that from the primary pole, while the soft X-ray excess of the primary pole is fairly modest in this accretion mode. These facts suggest that accretion onto the secondary is mainly due to blobs penetrating deeply in the photosphere, while that on the primary pole is mostly via a more homogeneous column, giving rise to the classical standing shock. A strong X-ray flaring activity is also observed in the soft X-ray band, but not in the hard X-ray and optical emissions indicating that flares are due to inhomogeneous blobby-accretion events.

Key words: stars: binaries: close – stars: novae, cataclysmic variables – X-rays: stars – stars: individual: Am Herculis

Send offprint requests to: G. Matt (matt@fis.uniroma3.it)

© European Southern Observatory (ESO) 2000

Online publication: June 26, 2000

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