3,462 research outputs found
Broad iron lines in neutrons stars: dynamical broadening or wind scattering?
Broad iron emission lines are observed in many accreting systems from black
holes in AGN and X-ray binaries to neutron star low-mass X-ray binaries. The
origin of the line broadening is often interpreted as due to dynamical
broadening and relativistic effects. However, alternative interpretations have
been proposed, included broadening due to Compton scattering in a wind or
accretion disk atmosphere. Here we explore the observational signatures
expected from broadening in a wind, in particular that the iron line width
should increase with an increase in the column density of the absorber (due to
an increase in the number of scatterings). We study the data from three neutron
star low-mass X-ray binaries where both a broad iron emission line and
absorption lines are seen simultaneously, and show that there is no significant
correlation between line width and column density. This favors an inner disk
origin for the line broadening rather than scattering in a wind.Comment: 5 pages, 1 table, 5 figures, accepted for publication in Ap
A detailed study of the 5 Hz quasi-periodic oscillations in the bright X-ray transient and black-hole candidate GRS 1739-278
We present a detailed study of the 5 Hz quasi-periodic oscillation (QPO)
recently discovered in the bright X-ray transient and black-hole candidate GRS
1739-278 (Borozdin & Trudolyubov 2000) during a Rossi X-ray Timing Explorer
observation taken on 1996 March 31. In total 6.6 ksec of on-source data were
obtained, divided in two data sets of 3.4 and 3.2 ksec which were separated by
2.6 ksec. The 5 Hz QPO was only present during the second data set. The QPO
increased in strength from below 2% rms amplitude for photon energies below 4
keV to ~5% rms amplitude for energies above 10 keV. The soft QPO photons (below
5 keV) lagged the hard ones (above 10 keV) by almost 1.5 radian. Besides the
QPO fundamental, its first overtone was detected. The strength of the overtone
increased with photon energy (from <2% rms below 5 keV to ~8% rms above 10
keV). Although the limited statistics did not allow for an accurate
determination of the lags of the first overtone, indications are that also for
this QPO the soft photons lagged the hard ones. When the 5 Hz QPO was not
detected (i.e., during the first part of the observation), a broad noise
component was found for photon energies below 10 keV but it became almost a
true QPO (with a Q value of ~1.9) above that energy, with a frequency of ~3 Hz.
Its hard photons preceded the soft ones in a way reminiscent of the 5 Hz QPO,
strongly suggesting that both features are physically related. We discuss our
finding in the frame work of low-frequency QPOs and their properties in BHCs.Comment: Accepted for publication in MNRAS, 2 August 200
Cooling of the crust in the neutron star low-mass X-ray binary MXB 1659-29
In quasi-persistent neutron star transients, long outbursts cause the neutron
star crust to be heated out of thermal equilibrium with the rest of the star.
During quiescence, the crust then cools back down. Such crustal cooling has
been observed in two quasi-persistent sources: KS 1731-260 and MXB 1659-29.
Here we present an additional Chandra observation of MXB 1659-29 in quiescence,
which extends the baseline of monitoring to 6.6 yr after the end of the
outburst. This new observation strongly suggests that the crust has thermally
relaxed, with the temperature remaining consistent over 1000 days. Fitting the
temperature cooling curve with an exponential plus constant model we determine
an e-folding timescale of 465 +/- 25 days, with the crust cooling to a constant
surface temperature of kT = 54 +/- 2 eV (assuming D=10 kpc). From this, we
infer a core temperature in the range 3.5E7-8.3E7 K (assuming D=10 kpc), with
the uncertainty due to the surface composition. Importantly, we tested two
neutron star atmosphere models as well as a blackbody model, and found that the
thermal relaxation time of the crust is independent of the chosen model and the
assumed distance.Comment: accepted for publication in ApJL, 4 pages, 1 figure
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