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Astron. Astrophys. 329, L41-L44 (1998)


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Letter to the Editor

The broad-band (0.1-200 keV) spectrum
of Her X-1 observed with BeppoSAX

D. Dal Fiume 1, M. Orlandini 1, G. Cusumano 2, S. Del Sordo 2, M. Feroci 3, F. Frontera 1, 4, T. Oosterbroek 5, E. Palazzi 1, A.N. Parmar 5, A. Santangelo 2 and A. Segreto 2

1 Istituto Tecnologie e Studio delle Radiazioni Extraterrestri (TeSRE), C.N.R., via Gobetti 101, I-40129 Bologna, Italy
2 Istituto Fisica Cosmica e Applicazioni all'Informatica (IFCAI), C.N.R., via La Malfa 153, I-90146 Palermo, Italy
3 Istituto di Astrofisica Spaziale (IAS), C.N.R., via Enrico Fermi 21, I-00044 Frascati, Italy
4 Dipartimento di Fisica, Università di Ferrara, via Paradiso 12, I-44100 Ferrara, Italy
5 Astrophysics Division, Space Science Department of ESA, ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands

Received 18 September 1997 / Accepted 7 October 1997

Abstract

The X-ray pulsar Her X-1 was observed for more than two orbital cycles near the maximum of the 35 day X-ray intensity cycle by the Narrow Field Instruments on-board the BeppoSAX satellite. We present the first simultaneous measurement of the 0.1-200 keV spectrum. Three distinct continuum components are evident in the phase averaged spectrum: a low energy excess, modeled as a 0.1 keV blackbody; a power-law and a high energy cut-off. Superposed on this continuum are Fe L and K emission features at 1.0 and 6.5 keV, respectively, and a [FORMULA]  keV cyclotron absorption feature. The cyclotron feature can be clearly seen in raw count spectra. We present the properties of the cyclotron feature with unprecedented precision and discuss the indications given by this measurement on the physical properties of the emitting region.

Key words: X-rays: binaries – individual: Her X-1 – X-rays: cyclotron

Send offprint requests to: D. Dal Fiume
(e-mail: daniele@tesre.bo.cnr.it)

© European Southern Observatory (ESO) 1998

Online publication: December 16, 1997
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