70 research outputs found
Supergiant Fast X-ray Transients: a review
Supergiant Fast X-ray Transients are a class of Galactic High Mass X-ray
Binaries with supergiant companions. Their extreme transient X-ray flaring
activity was unveiled thanks to INTEGRAL/IBIS observations. The SFXTs dynamic
range, with X-ray luminosities from 1E32 erg/s to 1E37 erg/s, and long time
intervals of low X-ray emission, are puzzling, given that both their donor star
properties and their orbital and spin periodicities seem very similar to those
displayed by massive binaries with persistent X-ray emission. Clumpy supergiant
winds, accretion barriers, orbital geometries and wind anisotropies are often
invoked to explain their behavior, but still several open issues remain. A
review of the main recent observational results will be outlined, together with
a summary of the new scenarios proposed to explain their bright flaring X-ray
activity. The main result of a long Suzaku observation of the SFXT
IGRJ16479-4514 with the shortest orbital period is also briefly summarized. The
observation of the X-ray eclipse in this source allowed us to directly probe
the supergiant wind density at the orbital separation, leading to the
conclusion that it is too large to justify the low X-ray luminosity. A
mechanism reducing the accretion rate onto the compact object is required.Comment: Solicited talk at the 9th INTEGRAL Workshop "An INTEGRAL view of the
high-energy sky (the first 10 years)", held in Paris, France, on 15-19
October 2012; accepted for publication in Proceedings of Scienc
Supergiant Fast X-ray Transients - a short review
I present a brief up-to-date review of the current understanding of
Supergiant Fast X-ray Transients, with an emphasis on the observational point
of view. After more than a decade since their discovery, a remarkable progress
has been made in getting the picture of their phenomenology at X-ray energies.
However, a similar in-depth investigation of the properties of the supergiant
companions is needed, but has started more recently. A multifrequency approach
is the key to fully understand the physical mechanism driving the SFXT
behaviour, still under debate.Comment: 14 pages 4 figures. Accepted for publication in the Proceedings of
the "XII Multifrequency Behaviour of High Energy Cosmic Sources Workshop",
held on 12-17 June 2017, Palermo, Italy (PoS(MULTIF2017)052). The figures
have been modified following the referee repor
An INTEGRAL overview of High Mass X-ray Binaries: classes or transitions?
We analyzed in a systematic way the public INTEGRAL observations spanning
from December 2002 to September 2016, to investigate the hard X-ray properties
of about 60 High Mass X-ray Binaries (HMXBs). We considered both persistent and
transient sources, hosting either a Be star (Be/XRBs) or a blue supergiant
companion (SgHMXBs, including Supergiant Fast X-ray Transients, SFXTs), a
neutron star or a black hole. INTEGRAL X-ray light curves (18-50 keV), sampled
at a bin time of about 2 ks, were extracted for all HMXBs to derive the
cumulative distribution of their hard X-ray luminosity, their duty cycle, the
range of variability of their hard X-ray luminosity. This allowed us to obtain
an overall and quantitative characterization of the long-term hard X-ray
activity of the HMXBs in our sample. Putting the phenomenology observed with
INTEGRAL into context with other known source properties (e.g. orbital
parameters, pulsar spin periods) together with observational constraints coming
from softer X-rays (1-10 keV), enabled the investigation of the way the
different HMXB sub-classes behave (and sometimes overlap). For given source
properties, the different sub-classes of massive binaries seem to cluster in a
suggestive way. However, for what concerns supergiant systems (SgHMXBs versus
SFXTs), several sources with intermediate properties exist, suggesting a smooth
transition between the two sub-classes.Comment: 27 pages, 17 figures, 3 tables; accepted for publication in Monthly
Notices of the Royal Astronomical Society (accepted 2018 August 30. Received
2018 August 22; in original form 2018 May 16
XMM-Newton observation of a spectral state transition in the peculiar radio/X-ray/gamma-ray source LS I +61 303
We report the results of XMM-Newton and BeppoSAX observations of the radio
and X-ray emitting star LS I +61 303, likely associated with the gamma-ray
source 2CG 135+01 and recently detected also at TeV energies. The data include
a long XMM-Newton pointing carried out in January 2005, which provides the
deepest look ever obtained for this object in the 0.3-12 keV range. During this
observation the source flux decreased from a high level of 13E12 erg/cm2/s to
4E12 erg/cm2/s within 2-3 hours.This flux range is the same seen in shorter and
less sensitive observations carried out in the past, but the new data show for
the first time that transitions between the two levels can occur on short time
scales. The flux decrease was accompanied by a significant softening of the
spectrum, which is well described by a power law with photon index changing
from 1.62+/-0.1 to 1.83+/-0.1. A correlation between hardness and intensity is
also found when comparing different short observations spanning almost 10 years
and covering various orbital phases.LS I +61 303 was detected in the 15-70 keV
range with the PDS instrument in one of the BeppoSAX observations, providing
evidence for variability also in the hard X-ray range. The X-ray spectra,
discussed in the context of multiwavelength observations, place some
interesting constraints on the properties and location of the high-energy
emitting region.Comment: Revised version, accepted for publication in A&A. Updated references,
few typos corrected, minor changes following referee's suggestion
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