Bibcode
Waterhouse, A. C.; Degenaar, N.; Wijnands, R.; Brown, E. F.; Miller, J. M.; Altamirano, D.; Linares, M.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 456, Issue 4, p.4001-4014
Fecha de publicación:
3
2016
Número de citas
39
Número de citas referidas
37
Descripción
Aql X-1 is a prolific transient neutron star low-mass X-ray binary that
exhibits an accretion outburst approximately once every year. Whether
the thermal X-rays detected in intervening quiescent episodes are the
result of cooling of the neutron star or due to continued low-level
accretion remains unclear. In this work, we use Swift data obtained
after the long and bright 2011 and 2013 outbursts, as well as the short
and faint 2015 outburst, to investigate the hypothesis that cooling of
the accretion-heated neutron star crust dominates the quiescent thermal
emission in Aql X-1. We demonstrate that the X-ray light curves and
measured neutron star surface temperatures are consistent with the
expectations of the crust cooling paradigm. By using a thermal evolution
code, we find that ≃1.2-3.2 MeV nucleon-1 of shallow
heat release describes the observational data well, depending on the
assumed mass-accretion rate and temperature of the stellar core. We find
no evidence for varying strengths of this shallow heating after
different outbursts, but this could be due to limitations of the data.
We argue that monitoring Aql X-1 for up to ≃1 yr after future
outbursts can be a powerful tool to break model degeneracies and solve
open questions about the magnitude, depth, and origin of shallow heating
in neutron star crusts.