Advanced superconducting magnets investigation

Mathematical models for steady state behavior of composite superconductors and experimental verification using magnet coi

SAX J1808.4-3658, an accreting millisecond pulsar shining in gamma rays?

We report the detection of a possible gamma-ray counterpart of the accreting millisecond pulsar SAX J1808.4-3658. The analysis of ~6 years of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (Fermi-LAT) within a region of 15deg radius around the position of the pulsar reveals a point gamma-ray source detected at a significance of ~6 sigma (Test Statistic TS = 32), with position compatible with that of SAX J1808.4-3658 within 95% Confidence Level. The energy flux in the energy range between 0.6 GeV and 10 GeV amounts to (2.1 +- 0.5) x 10-12 erg cm-2 s-1 and the spectrum is well-represented by a power-law function with photon index 2.1 +- 0.1. We searched for significant variation of the flux at the spin frequency of the pulsar and for orbital modulation, taking into account the trials due to the uncertainties in the position, the orbital motion of the pulsar and the intrinsic evolution of the pulsar spin. No significant deviation from a constant flux at any time scale was found, preventing a firm identification via time variability. Nonetheless, the association of the LAT source as the gamma-ray counterpart of SAX J1808.4-3658 would match the emission expected from the millisecond pulsar, if it switches on as a rotation-powered source during X-ray quiescence.Comment: 8 pages, 4 figures, accepted by MNRA

GRO J1744-28: an intermediate B-field pulsar in a low mass X-ray binary

The bursting pulsar, GRO J1744-28, went again in outburst after $\sim$18 years of quiescence in mid-January 2014. We studied the broad-band, persistent, X-ray spectrum using X-ray data from a XMM-Newton observation, performed almost at the peak of the outburst, and from a close INTEGRAL observation, performed 3 days later, thus covering the 1.3-70.0 keV band. The spectrum shows a complex continuum shape that cannot be modelled with standard high-mass X-ray pulsar models, nor by two-components models. We observe broadband and peaked residuals from 4 to 15 keV, and we propose a self-consistent interpretation of these residuals, assuming they are produced by cyclotron absorption features and by a moderately smeared, highly ionized, reflection component. We identify the cyclotron fundamental at $\sim$ 4.7 keV, with hints for two possible harmonics at 10.4 keV and 15.8 keV. The position of the cyclotron fundamental allows an estimate for the pulsar magnetic field of (5.27 $\pm$ 0.06) $\times$ 10$^{11}$ G, if the feature is produced at its surface. From the dynamical and relativistic smearing of the disk reflected component, we obtain a lower limit estimate for the truncated accretion disk inner radius, ($\gtrsim$ 100 R$_g$), and for the inclination angle (18$^{\circ}$-48$^{\circ}$). We also detect the presence of a softer thermal component, that we associate with the emission from an accretion disk truncated at a distance from the pulsar of 50-115 R$_g$. From these estimates, we derive the magneto-spheric radius for disk accretion to be $\sim$ 0.2 times the classical Alfv\'en radius for radial accretion.Comment: Accepted for publication in MNRA

Examining the nature of the ultraluminous X-ray source Holmberg II X-1

© 2024 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We present a comprehensive spectral analysis of the ultraluminous X-ray source Holmberg II X-1 using broadband and high-resolution X-ray spectra taken with the XMM-Newton satellite over a period of 19 yr, taking advantage of data from a recent campaign. We tested several models for the broadband spectra, including a double thermal component provided a reasonable description for the continuum between 0.3 and 10 keV and enabled us to constrain the properties of the accretion disc. The luminosity–temperature trends of the inner and outer disc components broadly agree with the expectations for a thin disc, although the exact values of the slopes are slightly sensitive to the adopted model. However, all tested models show L − T trends that deviate from a power law above a bolometric luminosity of about 5 × 1039 erg s−1, particularly for the hot thermal component associated with the inner accretion flow. Assuming that such deviations are due to the accretion rate exceeding its Eddington limit or, most likely, the super-critical rate, a compact object with a mass of 16–36 M⊙ was inferred, specifically, a stellar-mass black hole. The time-averaged (2021) high-resolution spectra present narrow emission lines at 1 keV primarily from Ne IX-X and a very strong at 0.5 keV from N VII, which indicate Ne–N-rich gas with non-solar abundances. This favours a nitrogen-rich donor star, such as a blue or red supergiant, which has escaped from its native stellar cluster characterised by a low-metallicity environment.Peer reviewe

Spectral Evolution of Circinus X-1 Along its Orbit

We report on the spectral analysis of Circinus X-1 observed by the ASCA satellite in March 1998 along one orbital period. The luminosity of the source (in the 0.1-100 keV band) ranges from $2.5 \times 10^{38}$ erg s$^{-1}$ at the periastron (orbital phase 0.01) to $1.5 \times 10^{38}$ erg s$^{-1}$ at orbital phase 0.3. From the spectral analysis and the lightcurve we argue that Cir X-1 shows three states along the orbital evolution. The first state is at the orbital phase interval 0.97-0.3: the luminosity becames super-Eddington and a strong flaring activity is present. In this state a shock could form in the inner region of the system due to the super-Eddington accretion rate, producing an outflow of ionized matter whose observational signature could be the prominent absorption edge at $\sim 8.7$ keV observed in the energy spectrum at these phases. In the second state, corresponding to the orbital phase interval between 0.3 and 0.7, the accretion rate is sub-Eddington and we observe a weaker outflow, with smaller hydrogen column: the absorption edge is now at $\sim 8.3$ keV with an optical depth a factor of 2.5 to 6 smaller. The third state corresponds to the orbital phase interval 0.78-0.97. In this state the best fit model to the spectrum requires the presence of a partial covering component, indicating that the emission from the compact object is partially absorbed by neutral matter, probably the atmosphere of the companion star and/or the accreting matter from the companion.Comment: 18 pages, 3 figures. Accepted by Ap

Feasibility and reference values of left atrial longitudinal strain imaging by two-dimensional speckle tracking

<p>Abstract</p> <p>Background</p> <p>The role of speckle tracking in the assessment of left atrial (LA) deformation dynamics is not established. We sought to determine the feasibility and reference ranges of LA longitudinal strain indices measured by speckle tracking in a population of normal subjects.</p> <p>Methods</p> <p>In 60 healthy individuals, peak atrial longitudinal strain (PALS) and time to peak longitudinal strain (TPLS) were measured using a 12-segment model for the left atrium. Values were obtained by averaging all segments (global PALS and TPLS) and by separately averaging segments measured in the two apical views (4- and 2-chamber average PALS and TPLS).</p> <p>Results</p> <p>Adequate tracking quality was achieved in 97% of segments analyzed. Inter and intra-observer variability coefficients of measurements ranged between 2.9% and 5.4%. Global PALS was 42.2 ± 6.1% (5–95° percentile range 32.2–53.2%), and global TPLS was 368 ± 30 ms (5–95° percentile range 323–430 ms). The 2-chamber average PALS was slightly higher than the 4-chamber average PALS (44.3 ± 6.0% vs 40.1 ± 7.9%, p < 0.0001), whereas no differences in TPLS were found (p = 0.93).</p> <p>Conclusion</p> <p>Speckle tracking is a feasible technique for the assessment of longitudinal myocardial LA deformation. Reference ranges of strain indices were reported.</p

Disappearance of Hard X-ray Emission in the Last BeppoSAX Observation of the Z Source GX 349+2

We report on the results from two BeppoSAX observations of the Z source GX 349+2 performed in February 2001 and covering the broad energy range 0.12-200 keV. The light curve obtained from these observations shows a large flaring activity, the count rate varying from ~130 to ~260 counts/s, indicating that the source was in the flaring branch during these observations. The average spectrum is well described by a soft blackbody and a Comptonized component. To well fit the energy spectrum three gaussian lines are needed at 1.2 keV, 2.6 keV, and 6.7 keV with corresponding equivalent widths of 13 eV, 10 eV, and 39 eV, probably associated to L-shell emission of Fe XXIV, Ly-alpha S XVI, and Fe XXV, respectively. These lines may be produced at different distances from the neutron star, which increase when the count rate of the source increases. An absorption edge is also needed at 9 keV with an optical depth of ~3 10^{-2}. From the Color-Color Diagram (CD) we selected five zones from which we extracted the corresponding energy spectra. The temperatures of the blackbody and of the Comptonized component tend to increase when the intensity of the source increases. We discuss our results comparing them to those obtained from a previous BeppoSAX observation, performed in March 2000, during which the source was a similar position of its Z-track. In particular we find that, although the source showed similar spectral states in the 2000 and the 2001 observations, a hard tail, that was significantly detected in March 2000, is not observed in these recent observations.Comment: Accepted for publication on Ap

An Overview of the Cardiorenal Protective Mechanisms of SGLT2 Inhibitors

Sodium-glucose co-transporter 2 (SGLT2) inhibitors block glucose reabsorption in the renal proximal tubule, an insulin-independent mechanism that plays a critical role in glycemic regulation in diabetes. In addition to their glucose-lowering effects, SGLT2 inhibitors prevent both renal damage and the onset of chronic kidney disease and cardiovascular events, in particular heart failure with both reduced and preserved ejection fraction. These unexpected benefits prompted changes in treatment guidelines and scientific interest in the underlying mechanisms. Aside from the target effects of SGLT2 inhibition, a wide spectrum of beneficial actions is described for the kidney and the heart, even though the cardiac tissue does not express SGLT2 channels. Correction of cardiorenal risk factors, metabolic adjustments ameliorating myocardial substrate utilization, and optimization of ventricular loading conditions through effects on diuresis, natriuresis, and vascular function appear to be the main underlying mechanisms for the observed cardiorenal protection. Additional clinical advantages associated with using SGLT2 inhibitors are antifibrotic effects due to correction of inflammation and oxidative stress, modulation of mitochondrial function, and autophagy. Much research is required to understand the numerous and complex pathways involved in SGLT2 inhibition. This review summarizes the current known mechanisms of SGLT2-mediated cardiorenal protection