A search for iron emission lines in the Chandra X-ray spectra of neutron star low-mass X-ray binaries
Faculty of Science (FNWI)
Anton Pannekoek Institute for Astronomy (API)
While iron emission lines are well studied in black hole systems, both in X-ray binaries and active galactic nuclei, there
has been less of a focus on these lines in neutron star low-mass X-ray binaries (LMXBs). However, recent observations with
Suzaku and XMM-Newton have revealed broad, asymmetric iron line profiles in three neutron star LMXBs, confirming an inner
disk origin for these lines in neutron star systems. Here, we present a search for iron lines in six neutron star LMXBs. For
each object we have simultaneous Chandra and RXTE observations at two separate epochs, allowing for both a high-resolution
spectrum and broadband spectral coverage. Out of the six objects in the survey, we only find significant iron lines in two
of the objects, GX 17+2 and GX 349+2. However, we cannot rule out that there are weak, broad lines present in the other sources.
The equivalent width of the line in GX 17+2 is consistent between the two epochs, while in GX 349+2 the line equivalent width
increases by a factor of ~3 between epochs as the source flux decreases by a factor of 1.3. This suggests that the disk is
highly ionized, and the line is dominated by recombination emission. We find that there appears to be no specific locations
in the long-term hardness-intensity diagrams where iron emission lines are formed, though more sources and further observations
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DOI: 10.1088/0004-637X/690/2/1847; eprintid: arXiv:0809.3171
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