83 research outputs found
Sympatho-Vagal Dysfunction in Patients with End-Stage Lung Disease Awaiting Lung Transplantation
Although the literature demonstrates that cardiac autonomic control (CAC) might be impaired in patients with chronic pulmonary diseases, the interplay between CAC and disease severity in end-stage lung disease has not been studied yet. We investigated the effects of end-stage lung disease on CAC through the analysis of heart rate variability (HRV) among patients awaiting lung transplantation. Forty-nine patients on the waiting list for lung transplantation (LTx; 19 men, age 38 \ub1 15 years) and 49 healthy non-smoking controls (HC; 22 men, age 40 \ub1 16 years) were enrolled in a case-control study at Policlinico Hospital in Milan, Italy. LTx patients were divided into two groups, according to disease severity evaluated by the Lung Allocation Score (LAS). To assess CAC, electrocardiogram (ECG) and respiration were recorded at rest for 10 min in supine position and for 10 min during active standing. Spectral analysis identified low and high frequencies (LF, sympathetic, and HF, vagal). Symbolic analysis identified three patterns, i.e., 0V% (sympathetic) and 2UV% and 2LV% (vagal). Compared to HCs, LTx patients showed higher markers of sympathetic modulation and lower markers of vagal modulation. However, more severely affected LTx patients, compared to less severely affected ones, showed an autonomic profile characterized by loss of sympathetic modulation and predominant vagal modulation. This pattern can be due to a loss of sympathetic rhythmic oscillation and a subsequent prevalent respiratory modulation of heart rate in severely affected patients
Desingularization of vortices for the Euler equation
We study the existence of stationary classical solutions of the
incompressible Euler equation in the plane that approximate singular
stationnary solutions of this equation. The construction is performed by
studying the asymptotics of equation -\eps^2 \Delta
u^\eps=(u^\eps-q-\frac{\kappa}{2\pi} \log \frac{1}{\eps})_+^p with Dirichlet
boundary conditions and a given function. We also study the
desingularization of pairs of vortices by minimal energy nodal solutions and
the desingularization of rotating vortices.Comment: 40 page
Constraining the nature of the 18-min periodic radio transient GLEAM-X J162759.5-523504.3 via multi-wavelength observations and magneto-thermal simulations
We observed the periodic radio transient GLEAM-X J162759.5-523504.3 (GLEAM-X
J1627) using the Chandra X-ray Observatory for about 30-ks on January 22-23,
2022, simultaneously with radio observations from MWA, MeerKAT and ATCA. Its
radio emission and 18-min periodicity led the source to be tentatively
interpreted as an extreme magnetar or a peculiar highly magnetic white dwarf.
The source was not detected in the 0.3-8 keV energy range with a 3-sigma
upper-limit on the count rate of 3x10^{-4} counts/s. No radio emission was
detected during our X-ray observations either. Furthermore, we studied the
field around GLEAM-X J1627 using archival ESO and DECam data, as well as recent
SALT observations. Many sources are present close to the position of GLEAM-X
J1627, but only two within the 2" radio position uncertainty. Depending on the
assumed spectral distribution, the upper limits converted to an X-ray
luminosity of L_{X}<6.5x10^{29} erg/s for a blackbody with temperature kT=0.3
keV, or L_{X}<9x10^{29} erg/s for a power-law with photon index Gamma = 2
(assuming a 1.3 kpc distance). Furthermore, we performed magneto-thermal
simulations for neutron stars considering crust- and core-dominated field
configurations. Based on our multi-band limits, we conclude that: i) in the
magnetar scenario, the X-ray upper limits suggest that GLEAM-X J1627 should be
older than ~1 Myr, unless it has a core-dominated magnetic field or has
experienced fast-cooling; ii) in the white dwarf scenario, we can rule out most
binary systems, a hot sub-dwarf and a hot magnetic isolated white dwarf
(T>10.000 K), while a cold isolated white dwarf is still compatible with our
limits.Comment: 17 pages, 9 figures; ApJ accepte
Timing Analysis of the 2022 Outburst of the Accreting Millisecond X-Ray Pulsar SAX J1808.4-3658: Hints of an Orbital Shrinking
We present a pulse timing analysis of NICER observations of the accreting millisecond X-ray pulsar SAX J1808.4-3658 during the outburst that started on 2022 August 19. Similar to previous outbursts, after decaying from a peak luminosity of â1 Ă 1036 erg s-1 in about a week, the pulsar entered a ~1 month long reflaring stage. Comparison of the average pulsar spin frequency during the outburst with those previously measured confirmed the long-term spin derivative of ÎœËSD=â(1.15±0.06)Ă10â15 Hz s-1, compatible with the spin-down torque of a â1026 G cm3 rotating magnetic dipole. For the first time in the last twenty years, the orbital phase evolution shows evidence for a decrease of the orbital period. The long-term behavior of the orbit is dominated by an ~11 s modulation of the orbital phase epoch consistent with a ~21 yr period. We discuss the observed evolution in terms of a coupling between the orbit and variations in the mass quadrupole of the companion star
A Very Young Radio-loud Magnetar
The magnetar Swift J1818.0â1607 was discovered in 2020 March when Swift detected a 9 ms hard X-ray burst and a long-lived outburst. Prompt X-ray observations revealed a spin period of 1.36 s, soon confirmed by the discovery of radio pulsations. We report here on the analysis of the Swift burst and follow-up X-ray and radio observations. The burst average luminosity was L burst ~ 2 Ă 1039 erg sâ1 (at 4.8 kpc). Simultaneous observations with XMM-Newton and NuSTAR three days after the burst provided a source spectrum well fit by an absorbed blackbody ( = (1.13 ± 0.03) Ă 1023 cmâ2 and kT = 1.16 ± 0.03 keV) plus a power law (Î = 0.0 ± 1.3) in the 1â20 keV band, with a luminosity of ~8 Ă 1034 erg sâ1, dominated by the blackbody emission. From our timing analysis, we derive a dipolar magnetic field B ~ 7 Ă 1014 G, spin-down luminosity erg sâ1, and characteristic age of 240 yr, the shortest currently known. Archival observations led to an upper limit on the quiescent luminosity <5.5 Ă 1033 erg sâ1, lower than the value expected from magnetar cooling models at the source characteristic age. A 1 hr radio observation with the Sardinia Radio Telescope taken about 1 week after the X-ray burst detected a number of strong and short radio pulses at 1.5 GHz, in addition to regular pulsed emission; they were emitted at an average rate 0.9 minâ1 and accounted for ~50% of the total pulsed radio fluence. We conclude that Swift J1818.0â1607 is a peculiar magnetar belonging to the small, diverse group of young neutron stars with properties straddling those of rotationally and magnetically powered pulsars. Future observations will make a better estimation of the age possible by measuring the spin-down rate in quiescence
About curvature, conformal metrics and warped products
We consider the curvature of a family of warped products of two
pseduo-Riemannian manifolds and furnished with metrics of
the form and, in particular, of the type , where are smooth
functions and is a real parameter. We obtain suitable expressions for the
Ricci tensor and scalar curvature of such products that allow us to establish
results about the existence of Einstein or constant scalar curvature structures
in these categories. If is Riemannian, the latter question involves
nonlinear elliptic partial differential equations with concave-convex
nonlinearities and singular partial differential equations of the
Lichnerowicz-York type among others.Comment: 32 pages, 3 figure
Deep X-ray and radio observations of the first outburst of the young magnetar Swift J1818.0-1607
Swift J1818.0-1607 is a radio-loud magnetar with a spin period of 1.36 s and
a dipolar magnetic field strength of B~3E14 G, which is very young compared to
the Galactic pulsar population. We report here on the long-term X-ray
monitoring campaign of this young magnetar using XMM-Newton, NuSTAR, and Swift
from the activation of its first outburst in March 2020 until October 2021, as
well as INTEGRAL upper limits on its hard X-ray emission. The 1-10 keV magnetar
spectrum is well modeled by an absorbed blackbody with a temperature of
kT_BB~1.1 keV, and apparent reduction in the radius of the emitting region from
~0.6 to ~0.2 km. We also confirm the bright diffuse X-ray emission around the
source extending between ~50'' and ~110''. A timing analysis revealed large
torque variability, with an average spin-down rate nudot~-2.3E-11 Hz^2 that
appears to decrease in magnitude over time. We also observed Swift J1818.0-1607
with the Karl G. Jansky Very Large Array (VLA) on 2021 March 22. We detected
the radio counterpart to Swift J1818.0-1607 measuring a flux density of S_v =
4.38+/-0.05 mJy at 3 GHz, and a half ring-like structure of bright diffuse
radio emission located at ~90'' to the west of the magnetar. We tentatively
suggest that the diffuse X-ray emission is due to a dust scattering halo and
that the radio structure may be associated with the supernova remnant of this
young pulsar, based on its morphology.Comment: 19 pages, 8 figures, accepted for publication on Ap
Strongly magnetized pulsars: explosive events and evolution
Well before the radio discovery of pulsars offered the first observational
confirmation for their existence (Hewish et al., 1968), it had been suggested
that neutron stars might be endowed with very strong magnetic fields of
-G (Hoyle et al., 1964; Pacini, 1967). It is because of their
magnetic fields that these otherwise small ed inert, cooling dead stars emit
radio pulses and shine in various part of the electromagnetic spectrum. But the
presence of a strong magnetic field has more subtle and sometimes dramatic
consequences: In the last decades of observations indeed, evidence mounted that
it is likely the magnetic field that makes of an isolated neutron star what it
is among the different observational manifestations in which they come. The
contribution of the magnetic field to the energy budget of the neutron star can
be comparable or even exceed the available kinetic energy. The most magnetised
neutron stars in particular, the magnetars, exhibit an amazing assortment of
explosive events, underlining the importance of their magnetic field in their
lives. In this chapter we review the recent observational and theoretical
achievements, which not only confirmed the importance of the magnetic field in
the evolution of neutron stars, but also provide a promising unification scheme
for the different observational manifestations in which they appear. We focus
on the role of their magnetic field as an energy source behind their persistent
emission, but also its critical role in explosive events.Comment: Review commissioned for publication in the White Book of
"NewCompStar" European COST Action MP1304, 43 pages, 8 figure
The INTEGRAL view of the pulsating hard X-ray sky: from accreting and transitional millisecond pulsars to rotation-powered pulsars and magnetars
In the last 25 years, a new generation of X-ray satellites imparted a significant leap forward in our knowledge of X-ray pulsars. The discovery of accreting and transitional millisecond pulsars proved that disk accretion can spin up a neutron star to a very high rotation speed. The detection of MeV-GeV pulsed emission from a few hundreds of rotation-powered pulsars probed particle acceleration in the outer magnetosphere, or even beyond. Also, a population of two dozens of magnetars has emerged. INTEGRAL played a central role to achieve these results by providing instruments with high temporal resolution up to the hard X-ray/soft gamma-ray band and a large field of view imager with good angular resolution to spot hard X-ray transients. In this article, we review the main contributions by INTEGRAL to our understanding of the pulsating hard X-ray sky, such as the discovery and characterization of several accreting and transitional millisecond pulsars, the generation of the first catalog of hard X-ray/soft gamma-ray rotation-powered pulsars, the detection of polarization in the hard X-ray emission from the Crab pulsar, and the discovery of persistent hard X-ray emission from several magnetars.</p
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