3,249 research outputs found
The mass of the neutron star in the low-mass X-ray binary 2A 1822-371
Using phase resolved spectroscopic observations obtained with the Ultraviolet
and Visual Echelle Spectrograph on ESO's Kueyen Very Large Telescope
supplemented by spectroscopic observations obtained with the Boller and Chivens
Spectrograph on the Walter Baade Magellan telescope, we found sinusoidal
radial-velocity variations with a semi-amplitude 327+-17 km/s. From previous
observations and from the fact that the epoch of minimum velocity arrived early
with respect to the epoch calculated from pulse timing we know that the
companion star is suffering from irradiation. Since we most likely observed
primarily the side of the companion star facing the observer at phase ~0.75 the
velocity quoted above is not the true radial velocity semi-amplitude of the
companion star. Assuming a uniform contribution to the line profile from this
hemisphere yields a radial velocity semi-amplitude of 280+-26 km/s for a
systemic velocity of 54+-24 km/s; if the contribution is instead weighted
somewhat more towards the side of the companion facing the X-ray source then
the true semi-amplitude is larger than this value. Together with the well
constrained inclination (81<i<84 degrees) and the mass-function determined from
pulse-timing analysis (2.03+-0.03 x 10^-2 Msun), we derive a lower limit to the
mass of the neutron star and to that of the companion star of 0.97+-0.24 Msun
and 0.33+-0.05 Msun, respectively (1 sigma; including uncertainties in the
inclination). We briefly discuss other aspects of the spectrum and the
implications of our findings.Comment: 6 pages, 2 figures, accepted for publication by MNRA
Constraining the neutron star equation of state using XMM-Newton
We have identified three possible ways in which future XMM-Newton
observations can provide significant constraints on the equation of state of
neutron stars. First, using a long observation of the neutron star X-ray
transient CenX-4 in quiescence one can use the RGS spectrum to constrain the
interstellar extinction to the source. This removes this parameter from the
X-ray spectral fitting of the pn and MOS spectra and allows us to investigate
whether the variability observed in the quiescent X-ray spectrum of this source
is due to variations in the soft thermal spectral component or variations in
the power law spectral component coupled with variations in N_H. This will test
whether the soft thermal spectral component can indeed be due to the hot
thermal glow of the neutron star. Potentially such an observation could also
reveal redshifted spectral lines from the neutron star surface. Second,
XMM-Newton observations of radius expansion type I X-ray bursts might reveal
redshifted absorption lines from the surface of the neutron star. Third,
XMM-Newton observations of eclipsing quiescent low-mass X-ray binaries provide
the eclipse duration. With this the system inclination can be determined
accurately. The inclination determined from the X-ray eclipse duration in
quiescence, the rotational velocity of the companion star and the
semi-amplitude of the radial velocity curve determined through optical
spectroscopy, yield the neutron star mass.Comment: 4 pages, 1 figure, proceedings of the XMM-Newton workshop, June 2007,
accepted for publication in A
Time-resolved X-Shooter spectra and RXTE light curves of the ultra-compact X-ray binary candidate 4U 0614+091
In this paper we present X-Shooter time resolved spectroscopy and RXTE PCA
light curves of the ultra-compact X-ray binary candidate 4U 0614+091. The
X-Shooter data are compared to the GMOS data analyzed previously by Nelemans et
al. (2004). We confirm the presence of C III and O II emission features at ~
4650 {\AA} and ~ 5000 {\AA}. The emission lines do not show evident Doppler
shifts that could be attributed to the motion of the donor star/hot spot around
the center of mass of the binary. We note a weak periodic signal in the
red-wing/blue-wing flux ratio of the emission feature at ~ 4650 {\AA}. The
signal occurs at P = 30.23 +/- 0.03 min in the X-Shooter and at P = 30.468 +/-
0.006 min in the GMOS spectra when the source was in the low/hard state. Due to
aliasing effects the period in the GMOS and X-Shooter data could well be the
same. We deem it likely that the orbital period is thus close to 30 min,
however, as several photometric periods have been reported for this source in
the literature already, further confirmation of the 30 min period is warranted.
We compare the surface area of the donor star and the disc of 4U 0614+091 with
the surface area of the donor star and the disc in typical hydrogen-rich
low-mass X-ray binaries and the class of AM Canum Venaticorum stars and argue
that the optical emission in 4U 0614+091 is likely dominated by the disc
emission. Additionally, we search for periodic signals in all the publicly
available RXTE PCA light curves of 4U 0614+091 which could be associated with
the orbital period of this source. A modulation at the orbital period with an
amplitude of ~ 10% such as those that have been found in other ultra-compact
X-ray binaries (4U 0513-40, 4U 1820-30) is not present in 4U 0614+091.Comment: Accepted for publication in MNRAS, 11 pages, 7 figure
Detection of a 1258 Hz high-amplitude kilohertz quasi-periodic oscillation in the ultra-compact X-ray binary 1A 1246-588
We have observed the ultra-compact low-mass X-ray binary (LMXB) 1A 1246-588
with the Rossi X-ray Timing Explorer (RXTE). In this manuscript we report the
discovery of a kilohertz quasi-periodic oscillation (QPO) in 1A 1246-588. The
kilohertz QPO was only detected when the source was in a soft high-flux state
reminiscent of the lower banana branch in atoll sources. Only one kilohertz QPO
peak is detected at a relatively high frequency of 1258+-2 Hz and at a single
trial significance of more than 7 sigma. Kilohertz QPOs with a higher frequency
have only been found on two occasions in 4U 0614+09. Furthermore, the frequency
is higher than that found for the lower kilohertz QPO in any source, strongly
suggesting that the QPO is the upper of the kilohertz QPO pair often found in
LMXBs. The full-width at half maximum is 25+-4 Hz, making the coherence the
highest found for an upper kilohertz QPO. From a distance estimate of ~6 kpc
from a radius expansion burst we derive that 1A 1246-588 is at a persistent
flux of ~0.2-0.3 per cent of the Eddington flux, hence 1A 1246-588 is one of
the weakest LMXBs for which a kilohertz QPO has been detected. The
root-mean-square (rms) amplitude in the 5-60 keV band is 27+-3 per cent, this
is the highest for any kilohertz QPO source so far, in line with the general
anti-correlation between source luminosity and rms amplitude of the kilohertz
QPO peak identified before. Using the X-ray spectral information we produce a
colour-colour diagram. The source behaviour in this diagram provides further
evidence for the atoll nature of the source.Comment: 4 pages, 3 figures, accepted for publication in MNRA
A fast converging adaptive control scheme for suppression of broadband disturbances on a multi-variable vibration isolation setup
Prison brain? Executive dysfunction in prisoners
A better understanding of the functioning of the brain, particularly executive functions, of the prison population could aid in reducing crime rates through the reduction of recidivism rates. Indeed, reoffending appears to be related to executive dysfunction and it is known that executive functions are crucial for self-regulation. In the current paper, studies to executive functions in regular adult prisoners compared to non-offender controls were reviewed. Seven studies were found. Specific executive functions were found to be impaired in the general prison population, i.e., attention and set-shifting, as well as in separate subgroups of violent (i.e., set-shifting and working memory) and non-violent offenders (i.e., inhibition, working memory and problem solving). We conclude that the limited number of studies is remarkable, considering the high impact of this population on society and elaborate on the implications of these specific impairments that were found. Further empirical research is suggested, measuring executive functioning within subjects over time for a group of detainees as well as a control group
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