Spectral Softening Observed in the Neutron Star LMXB SAX J1750.8-2900
Abstract
We present the analysis of over 30 Swift XRT observations of the neutron star low-mass X-ray binary (LMXB) SAX J1750.8-2900 over the course of 4 years while the system was in and between the outburst and quiescent states. This has been the first Swift XRT study of the long-term behavior of SAX J1750.8-2900. We found evidence of spectral softening with decreasing luminosity from ~1037 to 1034 erg s-1. While softening towards quiescence is regularly detected in black hole LMXBs and is often interpreted as as signature of an advection-dominated accretion flow, the behavior when observed in several neutron star LMXBs requires a much more complicated interpretation due to the interplay of thermal and nonthermal spectral contributions with different physical origins. We discuss the softening and flaring behavior of SAX J1750.8-2900 in the context of changing accretion regimes and the ongoing challenge in discerning the relative thermal and nonthermal components (and their sources) that shape the neutron star LMXB spectrum and its evolution.
- Publication:
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AAS/High Energy Astrophysics Division #14
- Pub Date:
- August 2014
- Bibcode:
- 2014HEAD...1412211A