Bibcode
Motch, C.; Pakull, M. W.; Soria, R.; Grisé, F.; Pietrzyński, G.
Referencia bibliográfica
Nature, Volume 514, Issue 7521, pp. 198-201 (2014).
Fecha de publicación:
10
2014
Revista
Número de citas
203
Número de citas referidas
186
Descripción
Most ultraluminous X-ray sources have a typical set of properties not
seen in Galactic stellar-mass black holes. They have luminosities of
more than 3 × 1039 ergs per second, unusually soft
X-ray components (with a typical temperature of less than about 0.3
kiloelectronvolts) and a characteristic downturn in their spectra above
about 5 kiloelectronvolts. Such puzzling properties have been
interpreted either as evidence of intermediate-mass black holes or as
emission from stellar-mass black holes accreting above their Eddington
limit, analogous to some Galactic black holes at peak luminosity.
Recently, a very soft X-ray spectrum was observed in a rare and
transient stellar-mass black hole. Here we report that the X-ray source
P13 in the galaxy NGC 7793 is in a binary system with a period of about
64 days and exhibits all three canonical properties of ultraluminous
sources. By modelling the strong optical and ultraviolet modulations
arising from X-ray heating of the B9Ia donor star, we constrain the
black hole mass to be less than 15 solar masses. Our results demonstrate
that in P13, soft thermal emission and spectral curvature are indeed
signatures of supercritical accretion. By analogy, ultraluminous X-ray
sources with similar X-ray spectra and luminosities of up to a few times
1040 ergs per second can be explained by supercritical
accretion onto massive stellar-mass black holes.
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