4,737 research outputs found
INTEGRAL and Swift observations of IGRJ19294+1816 in outburst
IGRJ19294+1816 was discovered by INTEGRAL in 2009 during a bright X-ray
outburst and was classified as a possible Be X-ray binary or supergiant fast
X-ray transient. On 2010 October 28, the source displayed a second X-ray
outburst and a 2 months-long monitoring with Swift was carried out to follow
the evolution of the source X-ray flux during the event. We report on the
INTEGRAL and Swift observations of the second X-ray outburst observed from
IGRJ19294+1816. We detected pulsations in the X-ray emission from the source at
\sim12.5 s up to 50 keV. The source X-ray flux decreased smoothly during the
two months of observation displaying only marginal spectral changes. Due to the
relatively rapid decay of the source X-ray flux, no significant variations of
the source spin period across the event could be measured. This prevented a
firm confirmation of the previously suggested orbital period of the source at
117 d. This periodicity was also searched by using archival Swift /BAT data. We
detected a marginally significant peak in the periodogram and determined the
best period at 116.2\pm0.6 days (estimated chance probability of a spurious
detection 1%). The smooth decline of the source X-ray flux across the two
months of observations after the onset of the second outburst, together with
its relatively low value of the spin period and the absence of remarkable
changes in the spectral parameters (i.e., the absorption column density),
suggests that IGRJ19294+1816 is most likely another member of the Be X-ray
binaries discovered by INTEGRAL and not a supergiant fast X-ray transient.Comment: Accepted for publication in A&A. 7 pages, 10 figure
El razonamiento cualitativo en ingeniería
El razonamiento cualitativo es un campo de investigación reciente en inteligencia artificial. Su objetivo es inferir de forma automática el comportamiento de un diseño preliminar, dada la representación declarativa de las leyes fundamentales del dominio y de la geometría y topología del diseño. Los modelos numéricos tradicionales derivan el comportamiento de un modelo representando parámetros según los números reales y siguiendo un procedimiento preestablecido como por ejemplo la eliminación de Gauss para resolver un sistema de ecuaciones lineales. Tales métodos son de poca utilidad en diseño conceptual pues requieren, generalmente, muchos parámetros que no son conocidos a priori. Además, no es fácil extrapolar resultados a partir de una única solución numérica. En contraposición, el razonamiento cualitativo representa parámetros por intervalos, y un procedimiento tipo búsqueda de soluciones determina un conjunto de soluciones cualitativas.Peer Reviewe
Determination of the forward slope in and elastic scattering up to LHC energy
In the analysis of experimental data on (or ) elastic
differential cross section it is customary to define an average forward slope
in the form , where is the momentum transfer. Taking as
working example the results of experiments at Tevatron and SPS, we will show
with the help of the impact picture approach, that this simplifying assumption
hides interesting information on the complex non-flip scattering amplitude, and
that the slope is not a constant. We investigate the variation of this
slope parameter, including a model-independent way to extract this information
from an accurate measurement of the elastic differential cross section. An
extension of our results to the LHC energy domain is presented in view of
future experiments.Comment: 12 pages, 6 figures, to appear in EPJ
The ephemeris, orbital decay, and masses of 10 eclipsing HMXBs
We take advantage of more than 10 years of monitoring of the eclipsing HMXB
systems LMC X-4, Cen X-3, 4U 1700-377, 4U 1538-522, SMC X-1, IGR J18027-2016,
Vela X-1, IGR J17252-3616, XTE J1855-026, and OAO 1657-415 with the ASM
on-board RXTE and ISGRI on-board INTEGRAL to update their ephemeris. These
results are used to refine previous measurements of the orbital period decay of
all sources (where available) and provide the first accurate values of the
apsidal advance in Vela X-1 and 4U 1538-522. Updated values for the masses of
the neutron stars hosted in the ten HMXBs are also provided, as well as the
long-term lightcurves folded on the sources best determined orbital parameters.
These lightcurves reveal complex eclipse ingresses and egresses, that are
understood mostly as being due to the presence of accretion wakes. The results
reported in this paper constitute a database to be used for population and
evolutionary studies of HMXBs, as well as theoretical modelling of long-term
accretion in wind-fed X-ray binaries.Comment: Accepted for publication on A&
The accretion environment of Supergiant Fast X-ray Transients probed with XMM-Newton
Supergiant fast X-ray transients (SFXTs) are characterized by a remarkable
variability in the X-ray domain, widely ascribed to the accretion from a clumpy
stellar wind. In this paper we performed a systematic and homogeneous analysis
of sufficiently bright X-ray flares from the SFXTs observed with XMM-Newton to
probe spectral variations on timescales as short as a few hundred of seconds.
Our ultimate goal is to investigate if SFXT flares and outbursts are triggered
by the presence of clumps and eventually reveal whether strongly or mildly
dense clumps are required. For all sources, we employ a technique developed by
our group, making use of an adaptive rebinned hardness ratio to optimally
select the time intervals for the spectral extraction. A total of twelve
observations performed in the direction of five SFXTs are reported. We show
that both strongly and mildly dense clumps can trigger these events. In the
former case, the local absorption column density may increase by a factor of
>>3, while in the latter case, the increase is only by a factor of 2-3 (or
lower). Overall, there seems to be no obvious correlation between the dynamic
ranges in the X-ray fluxes and absorption column densities in SFXTs, with an
indication that lower densities are recorded at the highest fluxes. This can be
explained by the presence of accretion inhibition mechanism(s). We propose a
classification of the flares/outbursts from these sources to drive future
observational investigations. We suggest that the difference between the
classes of flares/outbursts is related to the fact that the mechanism(s)
inhibiting accretion can be overcome more easily in some sources compared to
others. We also investigate the possibility that different stellar wind
structures, rather than clumps, could provide the means to temporarily overcome
the inhibition of accretion in SFXTs.Comment: Accepted for publication on A&
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