HEAD Division Meeting 1999, April 1999
Session 15. X-Ray Binaries
Poster, Tuesday, April 13, 1999, 8:30am-6:02pm, Gold Room

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[15.03] Hunting for Cyclotron Lines with BeppoSAX: OAO1657--415

M. Orlandini, D. Dal Fiume, F. Frontera (TeSRE/CNR), S. Del Sordo, A. Santangelo, A. Segreto (IFCAI/CNR), A.N. Parmar (SSD/ESA)

The 38~s X--ray binary pulsar OAO1657--415 shows one of the hardest spectra among X--ray pulsars, without any evidence of steepening at high (>10 keV) energy. The high energy instruments aboard BeppoSAX, namely HPGSPC and PDS, are the best suited to detect high energy cutoff in hard sources. Indeed, a 30~ksec observation of OAO1657--415 detected for the first time a change of slope in its spectrum, at ~15 keV. The wide band spectrum is well fit by both a cutoff power law, or a power law modified by a high energy cutoff. The two models are equivalent. The inclusion of a cyclotron resonance feature (CRF) at 36 keV significantly improves the \chi2 for the cutoff model (Probability of Chance Improvement (PCI) 1.3\times 10-5), while the PCI for the power law plus high energy cutoff model is moderately high (4.5%). The statistical significance of our data is not sufficient to constrain the CRF width but by fixing its value to a {\em canonical} value of 10 keV, the relation between CRF energy and its FWHM (explained in terms of Doppler broadening of the electrons responsible of the CRF) is fulfilled.


If the author provided an email address or URL for general inquiries, it is as follows:

orlandini@tesre.bo.cnr.it


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