406 research outputs found
Supergiant fast X-ray transients as an under-luminous class of supergiant X-ray binaries
The usage of cumulative luminosity distributions, constructed thanks to the
long-term observations available through wide field hard X-ray imagers, has
been recently exploited to study the averaged high energy emission (>17 keV)
from Supergiant Fast X-ray Transients (SFXTs) and classical Supergiant High
Mass X-ray Binaries (SgXBs). Here, we take advantage of the long term
monitorings now available with Swift/XRT to construct for the first time the
cumulative luminosity distributions of a number of SFXTs and the classical SgXB
IGR J18027-2016 in the soft X-ray domain with a high sensitivity focusing X-ray
telescope (0.3-10 keV). By complementing previous results obtained in the hard
X-rays, we found that classical SgXBs are characterized by cumulative
distributions with a single knee around 10-10 erg/s, while
SFXTs are found to be systematically sub-luminous and their distributions are
shifted at significantly lower luminosities (a factor of 10-100). As the
luminosity states in which these sources spend most of their time are typically
below the sensitivity limit of large field of view hard X-ray imagers, we
conclude that soft X-ray monitorings carried out with high sensitivity
telescopes are particularly crucial to reconstruct the complete profile of the
SFXT cumulative luminosity distributions. The difference between the cumulative
luminosity distributions of classical SgXBs and SFXTs is interpreted in terms
of accretion from a structured wind in the former sources and the presence of
magnetic/centrifugal gates or a quasi-spherical settling accretion regime in
the latter.Comment: Accepted for publication in Advances in Space Researc
X-ray flashes from the low-mass X-ray binary IGR J17407-2808
IGR J17407-2808 is an enigmatic and poorly studied X-ray binary that was
recently observed quasi-simultaneously with NuSTAR and XMM-Newton. In this
paper we report the results of this observational campaign. During the first 60
ks of observation, the source was caught in a relatively low emission state,
characterised by a modest variability and an average flux of ~8.3E-13
erg/cm^2/s (4-60 keV). Afterwards, IGR J17407-2808 entered a significantly more
active emission state that persisted for the remaining ~40 ks of the NuSTAR
observation. During this state, IGR J17407-2808 displayed several fast X-ray
flares, featuring durations of ~1-100 s and profiles with either single or
multiple peaks. The source flux in the flaring state reached values as high as
2E-9 erg/cm^2/s (4-60 keV), leading to a measured dynamic range during the
NuSTAR and XMM-Newton campaign of >~ 10^3. We also analysed available archival
photometric near-infrared data of IGR J17407-2808 to improve the constraints
available so far on the the nature of the donor star hosted in this system. Our
analysis shows that the donor star can be either a rare K or M-type
sub-subgiant or an K type main sequence star, or sub-giant star. Our findings
support the classification of IGR J17407-2808 as a low-mass X-ray binary. We
discuss the source X-ray behaviour as recorded by NuSTAR and XMM-Newton in view
of this revised classification.Comment: Accepted for publication in Astronomy & Astrophysic
Searching for supergiant fast X-ray transients with Swift
Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs)
hosting a neutron star and an OB supergiant companion. We examine the available
Swift data, as well as other new or archival/serendipitous data, on three
sources: IGR J17407-2808, 2XMM J185114.3-000004, and IGR J18175-2419, whose
X-ray characteristics qualify them as candidate SFXT, in order to explore their
properties and test whether they are consistent with an SFXT nature. As IGR
J17407-2808 and 2XMM J185114.3-000004 triggered the Burst Alert Telescope on
board Swift, the Swift data allow us to provide their first arcsecond
localisations, leading to an unequivocal identification of the source CXOU
J174042.0-280724 as the soft X-ray counterpart of IGR J17407-2808, as well as
their first broadband spectra, which can be fit with models generally
describing accreting neutron stars in HMXBs. While still lacking optical
spectroscopy to assess the spectral type of the companion, we propose 2XMM
J185114.3-000004 as a very strong SFXT candidate. The nature of IGR J17407-2808
remains, instead, more uncertain. Its broad band properties cannot exclude that
the emission originates from either a HMXB (and in that case, a SFXT) or, more
likely, a low mass X-ray binary. Finally, based on the deep non-detection in
our XRT monitoring campaign and a careful reanalysis of the original Integral
data in which the discovery of the source was first reported, we show that IGR
J18175-2419 is likely a spurious detection.Comment: Accepted for publication in Astronomy and Astrophysics. 12 pages, 11
figures, 6 table
Cyclotron line energy in Hercules X-1: stable after the decay
We summarize the results of a dedicated effort made between 2012 and 2019 to follow the evolution of the cyclotron line in Her X-1 through repeated NuSTAR observations. The previously observed nearly 20-year-long decay of the cyclotron line energy has ended in 2012: from then on, the pulse-phase-averaged flux-corrected cyclotron line energy has remained stable and constant at an average value of E_(cyc) = (37.44 ± 0.07) keV (normalized to a flux level of 6.8 RXTE/ASM-cts s⁻¹). The flux dependence of E_(cyc) discovered in 2007 is now measured with high precision, giving a slope of (0.675 ± 0.075) keV/(ASM-cts s⁻¹), corresponding to an increase of 6.5% of E_(cyc) for an increase in flux by a factor of two. We also find that all line parameters as well as the continuum parameters show a correlation with X-ray flux. While a correlation between E_(cyc) and X-ray flux (both positive and negative) is now known for several accreting binaries with various suggestions for the underlying physics, the phenomenon of a long-term decay has so far only been seen in Her X-1 and Vela X-1, with far less convincing explanations
Napromienianie fragmentu piersi z zastosowaniem brachyterapii śródtkankowej HDR: wczesne i późne odczyny popromienne oraz wyniki kosmetyczne
The effect of obesity on electrocardiographic detection of hypertensive left ventricular hypertrophy:Recalibration against cardiac magnetic resonance
Electrocardiograph (ECG) criteria for left ventricular hypertrophy (LVH) are a widely used clinical tool. We recalibrated six ECG criteria for LVH against gold-standard cardiac magnetic resonance (CMR) and assessed the impact of obesity. One hundred and fifty consecutive tertiary hypertension clinic referrals for CMR (1.5 T) were reviewed. Patients with cardiac pathology potentially confounding hypertensive LVH were excluded (n=22). The final sample size was 128 (age: 51.0±15.2 years, 48% male). LVH was defined by CMR. From a 12-lead ECG, Sokolow–Lyon voltage and product, Cornell voltage and product, Gubner–Ungerleidger voltage and Romhilt–Estes score were evaluated, blinded to the CMR. ECG diagnostic performance was calculated. LVH by CMR was present in 37% and obesity in 51%. Obesity significantly reduced ECG sensitivity, because of significant attenuation in mean ECG values for Cornell voltage (22.2±5.7 vs 26.4±9.4 mm, P<0.05), Cornell product (2540±942 vs 3023±1185 mm • ms, P<0.05) and for Gubner–Ungerleider voltage (18.2±7.1 vs 23.3±1.2 mm, P<0.05). Obesity also significantly reduced ECG specificity, because of significantly higher prevalence of LV remodeling (no LVH but increased mass-to-volume ratio) in obese subjects without LVH (36% vs 16%, P<0.05), which correlated with higher mean ECG LVH criteria values. Obesity-specific partition values were generated at fixed 95% specificity; Cornell voltage had highest sensitivity in non-obese (56%) and Sokolow–Lyon product in obese patients (24%). Obesity significantly lowers ECG sensitivity at detecting LVH, by attenuating ECG LVH values, and lowers ECG specificity through changes associated with LV remodeling. Our obesity-specific ECG partition values could improve the diagnostic performance in obese patients with hypertension
Assessment of patients affected by treatment-resistant depression: findings from a real-world study in Italy
Arrhythmogenic right ventricular cardiomyopathy (ARVC) mimics:the knot unravelled by cardiovascular MRI
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