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Title: OPTICAL SPECTROSCOPY OF THE HIGH-MASS γ-RAY BINARY 1FGL J1018.6−5856: A PROBABLE NEUTRON STAR PRIMARY

We present medium-resolution optical spectroscopy with the SOAR telescope of the O star secondary of the high-mass γ-ray binary 1FGL J1018.6–5856 to help determine whether the primary is a neutron star or black hole. We find that the secondary has a low radial velocity semi-amplitude of 11–12 km s{sup −1}, with consistent values obtained for H and He absorption lines. This low value strongly favors a neutron star primary: while a black hole cannot be excluded if the system is close to face on, such inclinations are disallowed by the observed rotation of the secondary. We also find the high-energy (X-ray and γ-ray) flux maxima occur when the star is behind the compact object along our line of sight, inconsistent with a simple model of anisotropic inverse Compton scattering for the γ-ray photons.
Authors:
; ;  [1] ;  [2] ;  [3]
  1. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
  2. Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)
  3. Gemini Observatory, Casilla 603, La Serena (Chile)
Publication Date:
OSTI Identifier:
22518708
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 813; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTROSCOPY; AMPLITUDES; ANISOTROPY; BLACK HOLES; COMPTON EFFECT; COSMIC PHOTONS; COSMIC RAY FLUX; EMISSION SPECTROSCOPY; GAMMA RADIATION; INCLINATION; MASS; NEUTRON STARS; PULSARS; RADIAL VELOCITY; ROTATION; TELESCOPES; X RADIATION