Issue |
A&A
Volume 493, Number 3, January III 2009
|
|
---|---|---|
Page(s) | L39 - L43 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:200811401 | |
Published online | 11 December 2008 |
Letter to the Editor
XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658
1
Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy e-mail: papitto@oa-roma.inaf.it
2
INAF Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
3
Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy
4
Dipertimento di Fisica, Università degli Studi di Cagliari, SP Monserrato-Sestu, KM 0.7, 09042 Monserrato, Italy
Received:
22
November
2008
Accepted:
3
December
2008
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
, corresponding to
km for a 1.4
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.
Key words: accretion, accretion disks / line: profiles / stars: pulsars: individual: SAX J1808.4-3658 / relativity / X-rays: binaries
© ESO, 2009
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