9,270 research outputs found
The X-ray spectral properties of very-faint persistent neutron star X-ray binaries
AX J1754.2-2754, 1RXS J171824.2-402934 and 1RXH J173523.7-354013 are three
persistent neutron star low-mass X-ray binaries that display a 2--10 keV
accretion luminosity Lx of only (1-10)x1E34 erg s-1 (i.e., only ~0.005-0.05 %
of the Eddington limit). The phenomenology of accreting neutron stars which
accrete at such low accretion rates is not yet well known and the reason why
they have such low accretion rates is also not clear. Therefore, we have
obtained XMM-Newton data of these three sources and here we report our analysis
of the high-quality X-ray spectra we have obtained for them. We find that AX
J1754.2-2754 has Lx~1E35 erg s-1, while the other two have X-ray luminosities
about an order of magnitude lower. However, all sources have a similar,
relatively soft, spectrum with a photon index of 2.3-2.5, when the spectrum is
fitted with an absorbed power-law model. This model fits the data of AX
J1754.2-2754 adequately, but it cannot fit the data obtained for 1RXS
J171824.2-402934 and 1RXH J173523.7-354013. For those sources a clear soft
thermal component is needed to fit their spectra. This soft component
contributes 40% - 50% to the 0.5-10 keV flux of the sources. When including
this additional spectral component, the power-law photon indices are
significantly lower. It can be excluded that a similar component with similar
contributions to the 2-10 keV X-ray flux is present for AX J1754.2-2754,
indicating that the soft spectrum of this source is mostly due to the fact that
the power-law component itself is not hard. We note that we cannot excluded
that weaker soft component is present in the spectrum of this source which only
contributes up to ~25% to the 0.5-10 keV X-ray flux. We discuss our results in
the context of what is known of accreting neutron stars at very low accretion
rate.Comment: 9 pages, 2 tables, 1 figure. Aceppted for publication in MNRA
XMM-Newton and Swift spectroscopy of the newly discovered very-faint X-ray transient IGR J17494-3030
A growing group of low-mass X-ray binaries are found to be accreting at
very-faint X-ray luminosities of <1E36 erg/s (2-10 keV). Once such system is
the new X-ray transient IGR J17494-3030. We present Swift and XMM-Newton
observations obtained during its 2012 discovery outburst. The Swift
observations trace the peak of the outburst, which reached a luminosity of ~7
E35 (D/8 kpc)^2 erg/s (2-10 keV). The XMM-Newton data were obtained when the
outburst had decayed to an intensity of ~ 8 E34 (D/8 kpc)^2 erg/s. The spectrum
can be described by a power-law with an index of ~1.7 and requires an
additional soft component with a black-body temperature of ~0.37 keV
(contributing ~20% to the total unabsorbed flux in the 0.5-10 keV band). Given
the similarities with high-quality spectra of very-faint neutron star low-mass
X-ray binaries, we suggest that the compact primary in IGR J17494-3030 is a
neutron star. Interestingly, the source intensity decreased rapidly during the
~12 hr XMM-Newton observation, which was accompanied by a decrease in inferred
temperature. We interpret the soft spectral component as arising from the
neutron star surface due to low-level accretion, and propose that the observed
decline in intensity was the result of a decrease in the mass-accretion rate
onto the neutron star.Comment: 3 figures, 2 tables, accepted in MNRAS letter, in pres
Equivariant intersection cohomology of the circle actions
In this paper, we prove that the orbit space B and the Euler class of an
action of the circle S^1 on X determine both the equivariant intersection
cohomology of the pseudomanifold X and its localization. We also construct a
spectral sequence converging to the equivariant intersection cohomology of X
whose third term is described in terms of the intersection cohomology of B.Comment: Final version as accepted in RACSAM. The final publication is
available at springerlink.com; Revista de la Real Academia de Ciencias
Exactas, Fisicas y Naturales. Serie A. Matematicas, 201
The Colombian conflict: a description of a mental health program in the Department of Tolima.
Colombia has been seriously affected by an internal armed conflict for more than 40 years affecting mainly the civilian population, who is forced to displace, suffers kidnapping, extortion, threats and assassinations. Between 2005 and 2008, Médecins Sans Frontières-France provided psychological care and treatment in the region of Tolima, a strategic place in the armed conflict. The mental health program was based on a short-term multi-faceted treatment developed according to the psychological and psychosomatic needs of the population. Here we describe the population attending during 2005-2008, in both urban and rural settings, as well as the psychological treatment provided during this period and its outcomes.We observed differences between the urban and rural settings in the traumatic events reported, the clinical expression of the disorders, the disorders diagnosed, and their severity. Although the duration of the treatment was limited due to security reasons and access difficulties, patient condition at last visit improved in most of the patients. These descriptive results suggest that further studies should be conducted to examine the role of short-term psychotherapy, adapted specifically to the context, can be a useful tool to provide psychological care to population affected by an armed conflict
An X-ray view of the very faint black hole X-ray transient Swift J1357.2-0933 during its 2011 outburst
We report on the X-ray spectral (using XMM-Newton data) and timing behavior
(using XMM-Newton and Rossi X-ray Timing Explorer [RXTE] data) of the very
faint X-ray transient and black hole system Swift J1357.2-0933 during its 2011
outburst. The XMM-Newton X-ray spectrum of this source can be adequately fitted
with a soft thermal component with a temperature of ~0.22 keV (using a disc
model) and a hard, non-thermal component with a photon index of ~1.6 when using
a simple power-law model. In addition, an edge at ~ 0.73 keV is needed likely
due to interstellar absorption. During the first RXTE observation we find a 6
mHz quasi-periodic oscillation (QPO) which is not present during any of the
later RXTE observations or during the XMM-Newton observation which was taken 3
days after the first RXTE observation. The nature of this QPO is not clear but
it could be related to a similar QPO seen in the black hole system H 1743-322
and to the so-called 1 Hz QPO seen in the dipping neutron-star X-ray binaries
(although this later identification is quite speculative). The observed QPO has
similar frequencies as the optical dips seen previously in this source during
its 2011 outburst but we cannot conclusively determine that they are due to the
same underlying physical mechanism. Besides the QPO, we detect strong
band-limited noise in the power-density spectra of the source (as calculated
from both the RXTE and the XMM-Newton data) with characteristic frequencies and
strengths very similar to other black hole X-ray transients when they are at
low X-ray luminosities. We discuss the spectral and timing properties of the
source in the context of the proposed very high inclination of this source. We
conclude that all the phenomena seen from the source cannot, as yet, be
straightforwardly explained neither by an edge-on configuration nor by any
other inclination configuration of the orbit.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in MNRA
Galaxy Peculiar Velocities and Infall onto Groups
We perform statistical analyses to study the infall of galaxies onto groups
and clusters in the nearby Universe. The study is based on the UZC and SSRS2
group catalogs and peculiar velocity samples. We find a clear signature of
infall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc<r<30
h^{-1} Mpc, with an infall amplitude on the order of a few hundred kilometers
per second. We obtain a significant increase in the infall amplitude with group
virial mass (M_{V}) and luminosity of group member galaxies (L_{g}). Groups
with M_{V}<10^{13} M_{\odot} show infall velocities V_{infall} \simeq 150 km
s^{-1} whereas for M_{V}>10^{13} M_{\odot} a larger infall is observed,
V_{infall} \simeq 200 km s^{-1}. Similarly, we find that galaxies surrounding
groups with L_{g}<10^{15} L_{\odot} have V_{infall} \simeq 100 km s^{-1},
whereas for L_{g}>10^{15} L_{\odot} groups, the amplitude of the galaxy infall
can be as large as V_{infall} \simeq 250 km s^{-1}. The observational results
are compared with the results obtained from mock group and galaxy samples
constructed from numerical simulations, which include galaxy formation through
semianalytical models. We obtain a general agreement between the results from
the mock catalogs and the observations. The infall of galaxies onto groups is
suitably reproduced in the simulations and, as in the observations, larger
virial mass and luminosity groups exhibit the largest galaxy infall amplitudes.
We derive estimates of the integrated mass overdensities associated with groups
by applying linear theory to the infall velocities after correcting for the
effects of distance uncertainties obtained using the mock catalogs. The
resulting overdensities are consistent with a power law with \delta \sim 1 at r
\sim 10 h^{-1}Mpc.Comment: 25 pages, 10 figure
Swift J1357.2-0933: the faintest black hole?
Swift J1357.2-0933 is the first confirmed very faint black hole X-ray
transient and has a short estimated orbital period of 2.8 hr. We observed Swift
J1357.2-0933 for ~50 ks with XMM-Newton in 2013 July during its quiescent
state. The source is clearly detected at a 0.5-10 keV unabsorbed flux of
~3x10^-15 erg cm-2 s-1. If the source is located at a distance of 1.5 kpc (as
suggested in the literature), this would imply a luminosity of ~8x10^29 erg
s-1, making it the faintest detected quiescent black hole LMXB. This would also
imply that there is no indication of a reversal in the quiescence X-ray
luminosity versus orbital period diagram down to 2.8 hr, as has been predicted
theoretically and recently supported by the detection of the 2.4 hr orbital
period black hole MAXI J1659-152 at a 0.5-10 keV X-ray luminosity of ~ 1.2 x
10^31 erg s-1. However, there is considerable uncertainty in the distance of
Swift J1357.2-0933 and it may be as distant as 6 kpc. In this case, its
quiescent luminosity would be Lx ~ 1.3 x 10^31 erg s-1, i.e., similar to MAXI
J1659-152 and hence it would support the existence of such a bifurcation
period. We also detected the source in optical at r' ~22.3 mag with the
Liverpool telescope, simultaneously to our X-ray observation. The X-ray/optical
luminosity ratio of Swift J1357.2-0933 agrees with the expected value for a
black hole at this range of quiescent X-ray luminosities.Comment: 5 pages, 3 figures, Accepted for publication in MNRA
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