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arXiv · 0812.1149

XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658

A. Papitto·T. Di Salvo·A. D'Aì·R. Iaria·L. Burderi·A. Riggio·M. T. Menna·N. R. Robba
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Abstract

We report on a 63-ks long XMM-Newton observation of the accreting millisecond pulsar SAX J1808.4-3658 during the latest X-ray outburst which started on September 21st 2008. The pn spectrum shows a highly significant emission line in the energy band where the iron K-alpha line is expected, and which we identify as emission from neutral (or mildly ionized) iron. The line profile appears to be quite broad (more than 1 keV FWHM) and asymmetric; the most probable explanation for this profile is Doppler and relativistic broadening from the inner accretion disc. From a fit with a diskline profile we find an inner radius of the disc of 8.7^(+3.7)_(-2.7) R_g, corresponding to 18.0^(+7.6)_(-5.6) km for a 1.4 Msun neutron star. The disc therefore appears truncated inside the corotation radius (31 km for SAX J1808.4-3658) in agreement with the fact that the source was still showing pulsations during the XMM-Newton observation.

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A. Papitto, T. Di Salvo, A. D'Aì, R. Iaria, L. Burderi, A. Riggio, M. T. Menna, N. R. Robba. 2008-12-22. XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658. https://doi.org/10.1051/0004-6361%3A200811401

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