TY - JOUR
T1 - A NICER Viewing Angle on the Accretion Stream of Vela X-1
AU - Rahin, Roi
AU - Behar, Ehud
N1 - Publisher Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.
PY - 2023/6/1
Y1 - 2023/6/1
N2 - Vela X-1 is the archetypal eclipsing high-mass X-ray binary, composed of a neutron star (NS) accreting the B-star wind. It was observed by nearly all X-ray observatories, often multiple times, featuring a rich spectrum of variable emission lines. However, the precise origin of these lines in the binary system remains uncertain. We perform a systematic, orbital-phase-dependent analysis of the reflected Fe Kα fluorescence line at 6.4 keV using over 100 NS Interior Composition Explorer observations. We resolve the line variability into 500 s time bins and find that it is predominantly due to variation in the ionizing flux, with a moderate underlying phase dependence over the 9-day orbital period. Our analysis reveals a significant reflection component that cannot originate from the companion B star alone. We also find that an appreciable portion of the B-star surface is obscured opposite the eclipse, and this obscuration is not symmetric around the midpoint (phase = 0.5). We argue that an accretion stream, from the B star to the NS and distorted by the orbital motion, is responsible both for the additional fluorescence emission component and for obscuring the B star.
AB - Vela X-1 is the archetypal eclipsing high-mass X-ray binary, composed of a neutron star (NS) accreting the B-star wind. It was observed by nearly all X-ray observatories, often multiple times, featuring a rich spectrum of variable emission lines. However, the precise origin of these lines in the binary system remains uncertain. We perform a systematic, orbital-phase-dependent analysis of the reflected Fe Kα fluorescence line at 6.4 keV using over 100 NS Interior Composition Explorer observations. We resolve the line variability into 500 s time bins and find that it is predominantly due to variation in the ionizing flux, with a moderate underlying phase dependence over the 9-day orbital period. Our analysis reveals a significant reflection component that cannot originate from the companion B star alone. We also find that an appreciable portion of the B-star surface is obscured opposite the eclipse, and this obscuration is not symmetric around the midpoint (phase = 0.5). We argue that an accretion stream, from the B star to the NS and distorted by the orbital motion, is responsible both for the additional fluorescence emission component and for obscuring the B star.
UR - http://www.scopus.com/inward/record.url?scp=85163832227&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/acc386
DO - 10.3847/1538-4357/acc386
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AN - SCOPUS:85163832227
SN - 0004-637X
VL - 950
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 170
ER -