SPECTRAL SOFTENING BETWEEN OUTBURST AND QUIESCENCE IN THE NEUTRON STAR LOW-MASS X-RAY BINARY SAX J1750.8-2900
Name
Allen-2015-Spectral softening b.pdf
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1.38 MB
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Author(s)
Allen, Jessamyn Leigh
Linares, Manuel Alegret
Homan, Jeroen
Chakrabarty, Deepto
Date Issued
February 2015
Journal
Astrophysical Journal
Publisher
Institute of Physics/American Astronomical Society
Citation
Allen, Jessamyn L., Manuel Linares, Jeroen Homan, and Deepto Chakrabarty. “SPECTRAL SOFTENING BETWEEN OUTBURST AND QUIESCENCE IN THE NEUTRON STAR LOW-MASS X-RAY BINARY SAX J1750.8-2900.” The Astrophysical Journal 801, no. 1 (February 24, 2015): 10. © 2015 American Astronomical Society.
Version
Final published version
Abstract
Tracking the spectral evolution of transiently accreting neutron stars between outburst and quiescence probes relatively poorly understood accretion regimes. Such studies are challenging because they require frequent monitoring of sources with luminosities below the thresholds of current all-sky X-ray monitors. We present the analysis of over 30 observations of the neutron star low-mass X-ray binary SAX J1750.8-2900 taken across four years with the X-ray telescope aboard Swift. We find spectral softening with decreasing luminosity both on long (~1 yr) and short (~days to week) timescales. As the luminosity decreases from 4 × 10[superscript 36] erg s[superscript −1] to $\sim 1\times {{10}^{35}}$ erg s[superscript −1] (0.5–10 keV), the power law photon index increases from 1.4 to 2.9. Although not statistically required, our spectral fits allow an additional soft component that displays a decreasing temperature as the luminosity decreases from 4 × 10[superscript 36] to 6 × 10[superscript 34] erg s[superscript −1]. Spectral softening exhibited by SAX J1750.8-2900 is consistent both with accretion emission whose spectral shape steepens with decreasing luminosity and also with being dominated by a changing soft component, possibly associated with accretion onto the neutron star surface, as the luminosity declines.
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1088/0004-637X/801/1/10
