Broad relativistic iron emission line observed in SAX J1808.4-3658

Abstract

During the September-October 2008 outburst of the accreting millisecond pulsar SAX J1808.4-3658, the source was observed by both Suzaku and XMM-Newton approximately 1 day apart. Spectral analysis reveals a broad relativistic Fe K-alpha emission line which is present in both data-sets, as has recently been reported for other neutron star low-mass X-ray binaries. The properties of the Fe K line observed during each observation are very similar. From modeling the Fe line, we determine the inner accretion disk radius to be 13.2 +/- 2.5 GM/c^2. The inner disk radius measured from the Fe K line suggests that the accretion disk is not very receded in the island state. If the inner disk (as measured by the Fe line) is truncated at the magnetospheric radius this implies a magnetic field strength of ~3E8 G at the magnetic poles, consistent with other independent estimates.

5 pages, 3 figs, 2 tables, accepted to ApJL

References in corpus (4)

• Relativistic X-ray Lines from the Inner Accretion Disks Around Black Holes
• XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658
• Initial Measurements of Black Hole Spin in GX 339-4 from Suzaku Spectroscopy
• Optical Observations of SAX J1808.4-3658 During Quiescence

Cited by in corpus (4)

• Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst
• A decade of timing an accretion-powered millisecond pulsar: The continuing spin down and orbital evolution of SAX J1808.4-3658
• A relativistically smeared spectrum in the neutron star X-ray Binary 4U 1705-44: Looking at the inner accretion disc with X-ray spectroscopy
• SAX J1808.4-3658: high resolution spectroscopy and decrease of pulsed fraction at low energies