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Astron. Astrophys. 338, L79-L82 (1998)


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Letter to the Editor

Detection of a cyclotron line and its second harmonic in 4U1907+09

G. Cusumano 1, T. Di Salvo 2, L. Burderi 2, M. Orlandini 3, S. Piraino 1, N. Robba 2 and A. Santangelo 1

1 Istituto di Fisica Cosmica ed Applicazioni all'Informatica C.N.R., Via U. La Malfa 153, I-90146, Palermo, Italy
2 Istituto di Fisica dell'Università - Via Archirafi 36, I-90123 Palermo, Italy
3 Istituto Tecnologie a Studio Radiazioni Extraterrestri, C.N.R., Via Gobetti, 101, I-40129 Bologna, Italy

Received 15 June 1998 / Accepted 1 September 1998

Abstract

We report the detection of a cyclotron absorption line and its second harmonic in the average spectrum of the high mass X-ray binary 4U1907+09 observed by the BeppoSAX satellite on 1997 September 27 and 28. The broad band spectral capability of BeppoSAX allowed a good determination of the continuum against which the two absorption features are evident at [FORMULA] 19 and [FORMULA] 39 keV. Correcting for the gravitational redshift of a [FORMULA] [FORMULA] neutron star, the inferred surface magnetic field strength is [FORMULA] G that is typical for this kind of systems. We also detected an iron emission line at [FORMULA] keV, with an equivalent width of [FORMULA] 60 eV.

Key words: binaries: close – star: neutron – pulsars: individual: 4U 1907+09 – X-rays: stars

Send offprint requests to: G. Cusumano, cusumano@ifcai.pa.cnr.it

© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998

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