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ON THE ORIGIN OF THE NEAR-INFRARED EMISSION FROM THE NEUTRON-STAR LOW-MASS X-RAY BINARY GX 9+1
Ist Teil von
The Astrophysical journal, 2017-01, Vol.834 (1), p.71
Ort / Verlag
Philadelphia: IOP Publishing
Erscheinungsjahr
2017
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
ABSTRACT
We have determined an improved position for the luminous persistent neutron-star low-mass X-ray binary and atoll source GX 9+1 from archival
Chandra X-ray Observatory
data. The new position significantly differs from a previously published
Chandra
position for this source. Based on the revised X-ray position we have identified a new near-infrared (NIR) counterpart to GX 9+1 in
K
s
-band images obtained with the PANIC and FourStar cameras on the
Magellan
Baade Telescope. NIR spectra of this
mag star, taken with the FIRE spectrograph on the Baade Telescope, show a strong Br
γ
emission line, which is a clear signature that we discovered the true NIR counterpart to GX 9+1. The mass donor in GX 9+1 cannot be a late-type giant, as such a star would be brighter than the estimated absolute
K
s
magnitude of the NIR counterpart. The slope of the dereddened NIR spectrum is poorly constrained due to uncertainties in the column density
N
H
and NIR extinction. Considering the source’s distance and X-ray luminosity, we argue that
N
H
likely lies near the high end of the previously suggested range. If this is indeed the case, the NIR spectrum is consistent with thermal emission from a heated accretion disk, possibly with a contribution from the secondary. In this respect, GX 9+1 is similar to other bright atolls and the Z sources, whose NIR spectra do not show the slope that is expected for a dominant contribution from optically thin synchrotron emission from the inner regions of a jet.