2016/02/29 by Elena Seifina, Lev Titarchuk, Nikolai Shaposhnikov
Earth and Planetary Sciences · Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Binary number #Black-body radiation #High-pressure geophysics and materials #Optics #Photon #Physics #Pulsars and Gravitational Waves Research #Radiation #Spectral line #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.3847/0004-637x/821/1/23
18 pages, 7 figures, 7 Tables, accepted by the ApJ, on February 29, 2016
arxiv created 2016/02/29 · openalex publication_date 2016/04/05 · arxiv updated 2016/04/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
ABSTRACT We present an X-ray spectral analysis of the high-mass binary 4U 1700-37 during its hard-soft state evolution. We use Beppo SAX, Suzaku , and Rossi X-ray Timing Explorer observations for this investigation. We argue that the X-ray broadband spectra during all of the spectral states can be adequately reproduced by a model consisting of a low-temperature blackbody component, two Comptonized components which are both due to the presence of a Compton cloud (CC) that up-scatters seed photons of T s 1 ≲ 1.4 keV and T s 2 < 1 keV, and an iron-line component. Using this model, we find that the photon power-law index is almost constant, Γ 1 ∼ 2 for all spectral states. However, Γ 2 shows behavior that is dependent on the spectral state. Namely, Γ 2 is quasi-constant at the level of Γ 2 ∼ 2 while the CC plasma temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="italic">kT</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">(</mml:mo> <mml:mn>2</mml:mn> <mml:mo stretchy="true">)</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> is less than 40 keV; on the other hand, Γ 2 is in the range of 1.3 < Γ 2 < 2 when <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="italic">kT</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">(</mml:mo> <mml:mn>2</mml:mn> <mml:mo stretchy="true">)</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> is greater than 40 keV. We explain this quasi-stability of Γ during most of the hard-soft transitions of 4U 1700-37 in the framework of a model in which the resulting spectrum is described by two Comptonized components. We find that these Comptonized spectral components of the high-mass X-ray binaries 4U 1700-37 are similar to those previously found in neutron star (NS) sources. This index dependence versus both the mass accretion rate and kT e revealed in 4U 1700-37 is universal observational evidence for the presence of an NS in 4U 1700-37.