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

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 <sup>1

1</sup> 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 19 and 39 keV. Correcting for the gravitational redshift of a neutron star, the inferred surface magnetic field strength is G that is typical for this kind of systems. We also detected an iron emission line at keV, with an equivalent width of 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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