Studying the reflection of X-rays off the inner edge of the accretion disk in
a neutron star low-mass X-ray binary, allows us to investigate the accretion
geometry and to constrain the radius of the neutron star. We report on a NuSTAR
observation of 4U 1608-52 obtained during a faint outburst in 2014 when the
neutron star, which has a known spin frequency of 620 Hz, was accreting at
\~1-2\% of the Eddington limit. The 3-79 keV continuum emission was dominated by
a Gamma\~2 power law, with a \~1-2\% contribution from a kTbb\~0.3-0.6 keV black
body component. The high-quality NuSTAR spectrum reveals the hallmarks of disk
reflection; a broad iron line peaking near 7\~keV and a Compton back-scattering
hump around \~20-30 keV. Modeling the disk reflection spectrum points to a
binary inclination of i\~30-40 degrees and a small `coronal' height of h<8.5
GM/c2. Furthermore, our spectral analysis suggests that the inner disk radius
extended to Rin\~7-10 GM/c2, close to the innermost stable circular obit. This
constrains the neutron star radius to R<21 km and the redshift from the stellar
surface to z>0.12, for a mass of M=1.5 Msun and a spin parameter of a=0.29.
%0 Generic
%1 citeulike:13633438
%A Degenaar, N.
%A Miller, J. M.
%A Chakrabarty, D.
%A Harrison, F.
%A Kara, E.
%A Fabian, A. C.
%D 2015
%K imported
%T A NuSTAR observation of disk reflection from close to the neutron star in 4U 1608-52
%U http://arxiv.org/abs/1505.07112
%X Studying the reflection of X-rays off the inner edge of the accretion disk in
a neutron star low-mass X-ray binary, allows us to investigate the accretion
geometry and to constrain the radius of the neutron star. We report on a NuSTAR
observation of 4U 1608-52 obtained during a faint outburst in 2014 when the
neutron star, which has a known spin frequency of 620 Hz, was accreting at
\~1-2\% of the Eddington limit. The 3-79 keV continuum emission was dominated by
a Gamma\~2 power law, with a \~1-2\% contribution from a kTbb\~0.3-0.6 keV black
body component. The high-quality NuSTAR spectrum reveals the hallmarks of disk
reflection; a broad iron line peaking near 7\~keV and a Compton back-scattering
hump around \~20-30 keV. Modeling the disk reflection spectrum points to a
binary inclination of i\~30-40 degrees and a small `coronal' height of h<8.5
GM/c2. Furthermore, our spectral analysis suggests that the inner disk radius
extended to Rin\~7-10 GM/c2, close to the innermost stable circular obit. This
constrains the neutron star radius to R<21 km and the redshift from the stellar
surface to z>0.12, for a mass of M=1.5 Msun and a spin parameter of a=0.29.
@misc{citeulike:13633438,
abstract = {{Studying the reflection of X-rays off the inner edge of the accretion disk in
a neutron star low-mass X-ray binary, allows us to investigate the accretion
geometry and to constrain the radius of the neutron star. We report on a NuSTAR
observation of 4U 1608-52 obtained during a faint outburst in 2014 when the
neutron star, which has a known spin frequency of 620 Hz, was accreting at
\~{}1-2\% of the Eddington limit. The 3-79 keV continuum emission was dominated by
a Gamma\~{}2 power law, with a \~{}1-2\% contribution from a kTbb\~{}0.3-0.6 keV black
body component. The high-quality NuSTAR spectrum reveals the hallmarks of disk
reflection; a broad iron line peaking near 7\~{}keV and a Compton back-scattering
hump around \~{}20-30 keV. Modeling the disk reflection spectrum points to a
binary inclination of i\~{}30-40 degrees and a small `coronal' height of h\<8.5
GM/c2. Furthermore, our spectral analysis suggests that the inner disk radius
extended to Rin\~{}7-10 GM/c2, close to the innermost stable circular obit. This
constrains the neutron star radius to R\<21 km and the redshift from the stellar
surface to z\>0.12, for a mass of M=1.5 Msun and a spin parameter of a=0.29.}},
added-at = {2019-03-25T08:20:55.000+0100},
archiveprefix = {arXiv},
author = {Degenaar, N. and Miller, J. M. and Chakrabarty, D. and Harrison, F. and Kara, E. and Fabian, A. C.},
biburl = {https://www.bibsonomy.org/bibtex/2d901461f9628dff3e9ff31b6ed64e542/ericblackman},
citeulike-article-id = {13633438},
citeulike-linkout-0 = {http://arxiv.org/abs/1505.07112},
citeulike-linkout-1 = {http://arxiv.org/pdf/1505.07112},
day = 26,
eprint = {1505.07112},
interhash = {ddb451711387c79369ea130116b9281a},
intrahash = {d901461f9628dff3e9ff31b6ed64e542},
keywords = {imported},
month = may,
posted-at = {2015-05-30 23:16:43},
priority = {2},
timestamp = {2019-03-25T08:20:55.000+0100},
title = {{A NuSTAR observation of disk reflection from close to the neutron star in 4U 1608-52}},
url = {http://arxiv.org/abs/1505.07112},
year = 2015
}