Other
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009cfdd.confe.145l&link_type=abstract
Chandra's First Decade of Discovery, Proceedings of the conference held 22-25 September, 2009 in Boston, MA. Edited by Scott Wo
Other
Accretion And Outflows
Scientific paper
A Further Drop into Quiescence by the Eclipsing Neutron Star 4U 2129+47 Abstract: 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 due to its broad and partial X-ray eclipses occurring periodically on a 5.24 hr orbit. The source entered a X-ray quiescent state in 1983 wherein its optical modulation disappeared and an F8 IV star--- rather than an expected late K or M star--- was revealed. This suggested that 4U 2129+47 might be in a hierarchical triple system. A 1% delay between two mid-eclipse epochs measured ˜22 days apart was reported from two XMM-Newton observations taken in 2005, providing further support in favor of the triple nature of 4U 2129+47. Compared to a year 2000 Chandra observation, the XMM-Newton observations lacked sinusoidal orbital modulation in the light curve, and only upper limits (roughly consistent with the detection in the Chandra observation) could be placed on the presence of a powerlaw hard tail. In this work we present timing and spectral analysis of three recent XMM-Newton observations of 4U 2129+47, carried out between November 2007 and January 2008. We found that absent the two 2005 XMM-Newton observations, all other observations are consistent with a linear ephemeris with a constant period of 18857.63 s; however, we confirm the time delay reported for the two 2005 XMM-Newton observations. These new observations also confirm the disappearance of the sinusoidal modulation of the lightcurve. We further show that compared to the year 2000 it Chandra observations, all of the XMM-Newton observations have 40% lower 0.5 - 2 keV 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 is likely 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.
Chakrabarty Deepto
Lin Jinrong
Nowak Michael A.
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