2015ApJ...809....9G -
Astrophys. J., 809, 9 (2015/August-8)
The case for a low mass black hole in the low mass X-ray binary V1408 Aquilae (= 4U 1957+115).
GOMEZ S., MASON P.A. and ROBINSON E.L.
Abstract (from CDS):
There are few confirmed black holes with a mass of less ∼4 M☉ and no neutron stars with masses greater than ∼2 M☉, creating a gap in the observed distribution of compact star masses. We present new optical photometry of the Low mass X-ray binary V1408 Aql, which is a persistent X-ray source thought to contain a black hole. The optical light curve of V1408 Aql shows nearly sinusoidal modulations at the orbital period, superimposed on large night-to-night variations. We combined this photometry with previously published photometry to derive a more precise orbital period of P=0.388893(3) days. The orbital light curve agrees with a model in which the modulation is caused by the changing aspect of the heated face of the secondary. The lack of eclipses rules out orbital inclinations 65○. Our best models favor inclinations near 13○ and black hole masses near 3 M☉ with a 90% upper bound of 6.2 M☉, and a lower bound of 2.0 M☉ imposed solely by the maximum mass of neutron stars. We favor a black hole primary over a neutron star based on evidence from the X-ray spectra, the high spin of the compact object, and the lack of any observed type I X-ray bursts. Although uncertainties in the data allow for higher masses, the compact star in V1408 Aql is a candidate for a black hole lying in the mass gap.
Abstract Copyright:
© 2015. The American Astronomical Society. All rights reserved.
Journal keyword(s):
X-rays: binaries - X-rays: individual: 4U 1957+115
Simbad objects:
9
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