A FURTHER DROP INTO QUIESCENCE BY THE ECLIPSING NEUTRON STAR 4U 2129+47
- Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States)
The low-mass X-ray binary 4U 2129+47 was discovered during a previous X-ray outburst phase and was classified as an accretion disk corona source. A 1% delay between two mid-eclipse epochs measured approx22 days apart was reported from two XMM-Newton observations taken in 2005, providing support to the previous suggestion that 4U 2129+47 might be in a hierarchical triple system. In this work, we present timing and spectral analysis of three recent XMM-Newton observations of 4U 2129+47, carried out between 2007 November and 2008 January. We found that except for the two 2005 XMM-Newton observations, all other observations are consistent with a linear ephemeris with a constant period of 18 857.63 s; however, we confirm the time delay reported for the two 2005 XMM-Newton observations. Compared to a Chandra observation taken in 2000, these new observations also confirm the disappearance of the sinusoidal modulation of the light curve as reported from two 2005 XMM-Newton observations. We further show that, compared to the Chandra observation, all of the XMM-Newton observations have 40% lower 0.5-2 keV absorbed fluxes, and the most recent XMM-Newton observations have a combined 2-6 keV flux that is nearly 80% lower. Taken as a whole, the timing results support the hypothesis that the system is in a hierarchical triple system (with a third body period of at least 175 days). The spectral results raise the question of whether the drop in soft X-ray flux is solely attributable to the loss of the hard X-ray tail (which might be related to the loss of sinusoidal orbital modulation), or is indicative of further cooling of the quiescent neutron star after cessation of residual, low-level accretion.
- OSTI ID:
- 21378120
- Journal Information:
- Astrophysical Journal, Vol. 706, Issue 2; Other Information: DOI: 10.1088/0004-637X/706/2/1069; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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