Engineering topics

Bernardini, F.

Publications and source records attributed to Bernardini, F..

5 records

DOE OSTI2024

Capping Effects on Spin and Charge Excitations in Parent and Superconducting Nd 1-x Sr x⁢ NiO 2

Superconductivity in infinite layer nickelates Nd 1-x⁢ Sr x NiO 2 has so far been achieved only in thin films, raising questions on the role of substrates and interfaces. Given the challenges associated with their synthesis it is imperative to identify their intrinsic properties. We use resonant inelastic x-ray scattering to investigate the influence of the SrTiO 3 capping layer on the excitations of Nd 1-x ⁢Sr x⁢ NiO 2 (x =0 and 0.2). Spin excitations are observed in parent and 20% doped Nd 1-x Sr x ⁢NiO 2 regardless of capping, proving that magnetism is intrinsic to infinite-layer nickelates and appears in a significant fraction of their phase diagram. In parent and superconducting Nd 1-x Sr x ⁢NiO 2 , the spin excitations are slightly hardened in capped samples compared to the noncapped ones. Additionally, a weaker Ni-Nd charge transfer peak at ~0.6 eV suggests that the hybridization between Ni 3⁢d and Nd 5⁢d orbitals is reduced in capped samples. In conclusion, from our data, capping induces only minimal differences in Nd 1-x Sr x NiO 2 and we phenomenologically discuss these differences based on the reconstruction of the SrTiO 3 -NdNiO 2 interface and other mechanisms such as crystalline disorder.

36 MATERIALS SCIENCE↗

NASA NTRS2016

The LOFT Mission Concept - A Status Update

The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, is greater than 8m2 effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission.

Silicon detectors↗

NASA NTRS2014

On the Nature of the Hard X-Ray Sources SWIFT J1907.3-2050, IGR J12123-5802 and IGR J19552+0044

The INTEGRAL and Swift hard X-ray surveys have identified a large number of new sources, among which many are proposed as Cataclysmic Variables (CVs). Here we present the first detailed study of three X-ray selected CVs, Swift J1907.3-2050, IGRJ12123-5802, and IGRJ19552+0044 based on XMM-Newton, Suzaku, Swift observations and ground based optical and archival nIR/IR data. Swift J1907.3-2050 is highly variable from hours to monthsyears at all wavelengths. No coherent X-ray pulses are detected but rather transient features. The X-ray spectrum reveals a multi-temperature optically thin plasma absorbed by complex neutral material and a soft black body component arising from a small area. These characteristics are remarkably similar to those observed in magnetic CVs. A supra-solar abundance of nitrogen could arise from nuclear processed material from the donor star. Swift J1907.3-2050 could be a peculiar magnetic CV with the second longest (20.82 h) binary period. IGRJ12123-5802 is variable in the X-rays on a timescale of approximately or greater than 7.6 h. No coherent pulsations are detected, but its spectral characteristics suggest that it could be a magnetic CV of the Intermediate Polar (IP) type. IGRJ19552+0044 shows two X-ray periods, approximately 1.38 h and approximately 1.69 h and a X-ray spectrum characterized by a multi-temperature plasma with little absorption.We derive a low accretion rate, consistent with a CV below the orbital period gap. Its peculiar nIR/IR spectrum suggests a contribution from cyclotron emission. It could either be a pre-polar or an IP with the lowest degree of asynchronism.

X-ray Sources↗

NASA NTRS2013

On the Nature of the Hard X-ray Sources SWIFT J1907.3-2050, IGR J12123-5802 and IGR J19552+0044

The INTEGRAL and Swift hard X-ray surveys have identified a large number of new sources, among which many are proposed as Cataclysmic Variables (CVs). Here we present the first detailed study of three X-ray selected CVs, Swift J1907.3-2050, IGRJ12123-5802, and IGRJ19552+0044 based on XMM-Newton, Suzaku, Swift observations and ground based optical and archival near-infrared/infrared data. Swift J1907.3-2050 is highly variable from hours to months-years at all wavelengths. No coherent X-ray pulses are detected but rather transient features. The X-ray spectrum reveals a multi-temperature optically thin plasma absorbed by complex neutral material and a soft black body component arising from a small area. These characteristics are remarkably similar to those observed in magnetic CVs. A supra-solar abundance of nitrogen could arise from nuclear processed material from the donor star. Swift J1907.3-2050 could be a peculiar magnetic CV with the second longest (20.82 hours) binary period. IGRJ12123-5802 is variable in the X-rays on a timescale of greater than or approximately 7.6 hours. No coherent pulsations are detected, but its spectral characteristics suggest that it could be a magnetic CV of the Intermediate Polar (IP) type. IGRJ19552+0044 shows two X-ray periods, approximately 1.38 hours and approximately 1.69 hours and a X-ray spectrum characterized by a multi-temperature plasma with little absorption. We derive a low accretion rate, consistent with a CV below the orbital period gap. Its peculiar near-infrared/infrared spectrum suggests a contribution from cyclotron emission. It could either be a pre-polar or an IP with the lowest degree of asynchronism.

individual:↗

NASA NTRS2012

Characterization of New Hard X-ray Cataclysmic Variables

Aims. We aim at characterizing a sample of nine new hard X-ray selected Cataclysmic Variable (CVs), to unambiguously identify them as magnetic systems of the Intermediate Polar (IP) type. Methods. We performed detailed timing and spectral analysis by using X-ray, and simultaneous UV and optical data collected by XMM−Newton, complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse arrival time were used to estimate the orbital periods. The broad band X-ray spectra were fitted using composite models consisting of different absorbing columns and emission components. Results. Strong X-ray pulses at the White Dwarf (WD) spin period are detected and found to decrease with energy. Most sources are spin-dominated systems in the X-rays, though four are beat dominated at optical wavelengths. We estimated the orbital period in all system (except for IGR J16500-3307), providing the first estimate for IGRJ08390-4833, IGRJ18308-1232, and IGR J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX J0636+3535 poses a soft X-ray optically thick component at kT approx. 80 eV. An intense K (sub alpha) Fe line at 6.4 keV is detected in all sources. An absorption edge at 0.76 keV from OVII is detected in IGR J08390-4833. The WD masses and lower limits to the accretion rates are also estimated. Conclusions. We found all sources to be IPs. IGR J08390-4833, V2069 Cyg, and IGR J16500-3307 are pure disc accretors, while IGR J18308-1232, IGR J1509-6649, IGR J17195-4100, and RX J0636+3535 display a disc-overflow accretion mode. All sources show a temperature gradient in the post-shock regions and a highly absorbed emission from material located in the pre-shock flow which is also responsible for the X-ray pulsations. Reflection at the WD surface is likely the origin of the fluorescent iron line. There is an increasing evidence for the presence of a warm absorber in IPs, a feature that needs future exploration. The addition of two systems to the subgroup of soft X-ray IPs confirms a relatively large (∼ 30%) incidence.

hard X-ray↗