XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658
- Autori: Papitto, A; Di Salvo, T; D'Aì, A; Iaria, R; Burderi, L; Riggio, A; Menna, MT; Robba, N
- Anno di pubblicazione: 2009
- Tipologia: Articolo in rivista (Articolo in rivista)
- Parole Chiave: accretion, accretion disks, line: profiles, stars: pulsars: individual: SAX J1808.4-3658, relativity, X-rays: binaries
- OA Link: http://hdl.handle.net/10447/46429
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-α 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 Mȯ 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.