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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

A FOCUSED, HARD X-RAY LOOK AT ARP 299 WITH NuSTAR

We report on simultaneous observations of the local starburst system Arp 299 with NuSTAR and Chandra, which provides the first resolved images of this galaxy up to energies of ∼45 keV. Fitting the 3-40 keV spectrum reveals a column density of N {sub H} ∼ 4 × 10{sup 24} cm{sup –2}, characteristic of a Compton-thick active galactic nucleus (AGN), and a 10-30 keV luminosity of 1.2 × 10{sup 43} erg s{sup –1}. The hard X-rays detected by NuSTAR above 10 keV are centered on the western nucleus, Arp 299-B, which previous X-ray observations have shown to be the primary source of neutral Fe-K emission. Other X-ray sources, including Arp 299-A, the eastern nucleus also thought to harbor an AGN, as well as X-ray binaries, contribute ≲ 10% to the 10-20 keV emission from the Arp 299 system. The lack of significant emission above 10 keV other than that attributed to Arp 299-B suggests that: (1) any AGN in Arp 299-A must be heavily obscured (N {sub H} > 10{sup 24} cm{sup –2}) or have a much lower luminosity than Arp 299-B and (2) the extranuclear X-ray binaries have spectra that cut-off above ∼10 keV. Such soft spectra are characteristic of ultraluminous X-ray sources observed to date by NuSTAR.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

CO-spatial white light and hard X-ray flare footpoints seen above the solar limb

We report analysis of three solar flares that occur within 1° of limb passage, with the goal to investigate the source height of chromospheric footpoints in white light (WL) and hard X-rays (HXR). We find the WL and HXR (≥30 keV) centroids to be largely co-spatial and from similar heights for all events, with altitudes around 800 km above the photosphere or 300–450 km above the limb height. Because of the extreme limb location of the events we study, emissions from such low altitudes are influenced by the opacity of the atmosphere and projection effects. STEREO images reveal that for SOL2012-11-20T12:36 the projection effects are smallest, giving upper limits of the absolute source height above the nominal photosphere for both wavelengths of ∼1000 km. To be compatible with the standard thick target model, these rather low altitudes require very low ambient densities within the flare footpoints, in particular if the HXR-producing electrons are only weakly beamed. That the WL and HXR emissions are co-spatial suggests that the observed WL emission mechanism is directly linked to the energy deposition by flare accelerated electrons. If the WL emission is from low-temperature (⩽10{sup 4} K) plasma as currently thought, the energy deposition by HXR-producing electrons above ∼30 keV seems only to heat chromospheric plasma to such low temperatures. This implies that the energy in flare-accelerated electrons above ∼30 keV is not responsible for chromospheric evaporation of hot (>10{sup 6} K) plasma, but that their energy is lost through radiation in the optical range.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

HARD X-RAY EMISSION DURING FLARES AND PHOTOSPHERIC FIELD CHANGES

We study the correlation between abrupt permanent changes of magnetic field during X-class flares observed by the Global Oscillation Network Group and Helioseismic and Magnetic Imager instruments, and the hard X-ray (HXR) emission observed by RHESSI, to relate the photospheric field changes to the coronal restructuring and investigate the origin of the field changes. We find that spatially the early RHESSI emission corresponds well to locations of the strong field changes. The field changes occur predominantly in the regions of strong magnetic field near the polarity inversion line (PIL). The later RHESSI emission does not correspond to significant field changes as the flare footpoints are moving away from the PIL. Most of the field changes start before or around the start time of the detectable HXR signal, and they end at about the same time or later than the detectable HXR flare emission. Some of the field changes propagate with speed close to that of the HXR footpoint at a later phase of the flare. The propagation of the field changes often takes place after the strongest peak in the HXR signal when the footpoints start moving away from the PIL, i.e., the field changes follow the same trajectory as the HXR footpoint, but at an earlier time. Thus, the field changes and HXR emission are spatio-temporally related but not co-spatial nor simultaneous. We also find that in the strongest X-class flares the amplitudes of the field changes peak a few minutes earlier than the peak of the HXR signal. We briefly discuss this observed time delay in terms of the formation of current sheets during eruptions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

OBSERVATION OF THE 2011-02-15 X2.2 FLARE IN THE HARD X-RAY AND MICROWAVE

Previous studies have shown that the energy release mechanism of some solar flares follow the Standard magnetic-reconnection model, but the detailed properties of high-energy electrons produced in the flare are still not well understood. We conducted a unique, multi-wavelength study that discloses the spatial, temporal and energy distributions of the accelerated electrons in the X2.2 solar flare on 2011 February 15. We studied the source locations of seven distinct temporal peaks observed in hard X-ray (HXR) and microwave (MW) light curves using the RHESSI in 50–75 keV channels and Nobeyama Radioheliograph in 34 GHz, respectively. We found that the seven emission peaks did not come from seven spatially distinct sites in HXR and MW, but rather in HXR we observed a sudden change in location only between the second and the third peak, with the same pattern occurring, but evolving more slowly in MW. Comparison between the HXR light curve and the temporal variations in intensity in the two MW source kernels also confirmed that the seven peaks came predominantly from two sources, each with multiple temporal peaks. In addition, we studied the polarization properties of MW sources, and time delay between HXR and MW. We discuss our results in the context of the tether-cutting model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The accreting black hole Swift J1753.5–0127 from radio to hard X-ray

We report on multiwavelength measurements of the accreting black hole Swift J1753.5–0127 in the hard state at low luminosity (L ∼ 2.7 × 10{sup 36} erg s{sup −1} assuming a distance of d = 3 kpc) in 2014 April. The radio emission is optically thick synchrotron, presumably from a compact jet. We take advantage of the low extinction (E(B−V)=0.45 from earlier work) and model the near-IR to UV emission with a multitemperature disk model. Assuming a black hole mass of M{sub BH} = 5 M{sub ⊙} and a system inclination of i = 40°, the fits imply an inner radius for the disk of R{sub in}/R{sub g} > 212d{sub 3}(M{sub BH}/5 M{sub ⊙}){sup −1}, where R{sub g} is the gravitational radius of the black hole and d{sub 3} is the distance to the source in units of 3 kpc. The outer radius is R{sub out}/R{sub g}=90,000 d{sub 3}(M{sub BH}/5 M{sub ⊙}){sup −1}, which corresponds to 6.6 × 10{sup 10} d{sub 3} cm, consistent with the expected size of the disk given previous measurements of the size of the companion's Roche lobe. The 0.5–240 keV energy spectrum measured by Swift/X-ray Telescope (XRT), Suzaku (XIS, PIN, and GSO), and Nuclear Spectroscopic Telescope Array is relatively well characterized by an absorbed power law with a photon index of Γ = 1.722 ± 0.003 (90% confidence error), but a significant improvement is seen when a second continuum component is added. Reflection is a possibility, but no iron line is detected, implying a low iron abundance. We are able to fit the entire (radio to 240 keV) spectral energy distribution (SED) with a multitemperature disk component, a Comptonization component, and a broken power law, representing the emission from the compact jet. The broken power law cannot significantly contribute to the soft X-ray emission, and this may be related to why Swift J1753.5–0127 is an outlier in the radio/X-ray correlation. The broken power law (i.e., the jet) might dominate above 20 keV, which would constrain the break frequency to be between 2.4 × 10{sup 10} and 3.6 × 10{sup 12} Hz. Although the fits to the full SED do not include significant thermal emission in the X-ray band, previous observations have consistently seen such a component, and we find that there is evidence at the 3.1σ level for a disk-blackbody component with a temperature of kT{sub in}=150{sub −20}{sup +30} eV and an inner radius of 5R{sub g}–14R{sub g}. If this component is real, it might imply the presence of an inner optically thick accretion disk in addition to the strongly truncated (R{sub in}> 212R{sub g}) disk. We also perform X-ray timing analysis, and the power spectrum is dominated by a Lorentzian component with ν{sub max} = 0.110 ± 0.003 Hz and ν{sub max} = 0.16 ± 0.04 Hz as measured by XIS and XRT, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Hard X-ray morphological and spectral studies of the galactic center molecular cloud SGR B2: Constraining past SGR A{sup ⋆} flaring activity

In 2013, NuSTAR observed the Sgr B2 region and for the first time resolved its hard X-ray emission on subarcminute scales. Two prominent features are detected above 10 keV: a newly emerging cloud, G0.66−0.13, and the central 90″ radius region containing two compact cores, Sgr B2(M) and Sgr B2(N), surrounded by diffuse emission. It is inconclusive whether the remaining level of Sgr B2 emission is still decreasing or has reached a constant background level. A decreasing X-ray emission can be best explained by the X-ray reflection nebula scenario, where the cloud reprocesses a past giant outburst from Sgr A{sup ⋆}. In the X-ray reflection nebula (XRN) scenario, the 3–79 keV Sgr B2 spectrum allows us to self-consistently test the XRN model using both the Fe Kα line and the continuum emission. The peak luminosity of the past Sgr A{sup ⋆} outburst is constrained to L{sub 3−79keV}∼5×10{sup 38} erg s{sup −1}. A newly discovered cloud feature, G0.66−0.13, shows different timing variability. We suggest that it could be a molecular clump located in the Sgr B2 envelope reflecting the same Sgr A{sup ⋆} outburst. In contrast, if the Sgr B2 X-ray emission has reached a constant background level, it would imply an origin of low-energy cosmic-ray (CR) proton bombardment. In this scenario, from the NuSTAR measurements we infer a CR ion power of dW/dt=(1−4)×10{sup 39} erg s{sup −1} and a CR ionization rate of ζ{sub H}=(6−10)×10{sup −15} H{sup −1} s{sup −1}. These measurements can become powerful tools to constrain the GC CR population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

SEARCHING FOR NEW {gamma}-RAY BLAZAR CANDIDATES IN THE THIRD PALERMO BAT HARD X-RAY CATALOG WITH WISE

We searched for {gamma}-ray blazar candidates among the 382 unidentified hard X-ray sources of the third Palermo BAT Catalog (3PBC) obtained from the analysis of 66 months of Swift Burst Alert Telescope (BAT) survey data and listing 1586 sources. We adopted a recently developed association method based on the peculiar infrared colors that characterize the {gamma}-ray blazars included in the second catalog of active galactic nuclei detected by the Fermi Large Area Telescope. We used this method exploiting the data of the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) to establish correspondences between unidentified 3PBC sources and WISE {gamma}-ray blazar candidates located within the BAT positional uncertainty region at a 99% confidence level. We obtained a preliminary list of candidates for which we analyzed all the available data in the Swift archive to complement the information in the literature and in the radio, infrared, and optical catalogs with the information on their optical-UV and soft X-ray emission. Requiring the presence of radio and soft X-ray counterparts consistent with the infrared positions of the selected WISE sources, as well as a blazar-like radio morphology, we finally obtained a list of 24 {gamma}-ray blazar candidates.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE SWIFT/BAT HARD X-RAY TRANSIENT MONITOR

The Swift/Burst Alert Telescope (BAT) hard X-ray transient monitor provides near real-time coverage of the X-ray sky in the energy range 15-50 keV. The BAT observes 88% of the sky each day with a detection sensitivity of 5.3 mCrab for a full-day observation and a time resolution as fine as 64 s. The three main purposes of the monitor are (1) the discovery of new transient X-ray sources, (2) the detection of outbursts or other changes in the flux of known X-ray sources, and (3) the generation of light curves of more than 900 sources spanning over eight years. The primary interface for the BAT transient monitor is a public Web site. Between 2005 February 12 and 2013 April 30, 245 sources have been detected in the monitor, 146 of them persistent and 99 detected only in outburst. Among these sources, 17 were previously unknown and were discovered in the transient monitor. In this paper, we discuss the methodology and the data processing and filtering for the BAT transient monitor and review its sensitivity and exposure. We provide a summary of the source detections and classify them according to the variability of their light curves. Finally, we review all new BAT monitor discoveries. For the new sources that are previously unpublished, we present basic data analysis and interpretations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Radiation-hardness studies with cerium-doped fused-silica fibers

In this work, we describe our R&D effort to develop potentially radiation-hard scintillating and wavelength shifting fibers by doping fused-silica with cerium. The cerium-doped optical fibers with different core structures and concentrations were exposed to gamma radiation (60Co) at different dose rates up to 100 kGy. We evaluated the radiation-induced degradation in photoluminescence, optical transmission, and recovery phenomena in the wavelength range from 300 to 700 nm. We were able to model the experimental data based on second-order rate equations where the fit parameters that govern the damage profile were utilized to predict recovery. We also measured the influence of radiation on the numerical aperture. Finally, we offer some thoughts on the use of these types of fibers in particle and nuclear physics detectors.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Exploring Secondary Markets to Improve Circularity: A Comparative Case Study of Photovoltaics and Hard-Disk Drives

Each year renewable energy generation increases notably with solar panel installations, but these panels have a limited lifespan and will produce between 2 and 4 million metric tons of waste by 2040. Similarly, there are currently between 20 to 70 million hard-disk drives (HDDs) reaching end-of-life (EOL) annually. The circular economy (CE) strives to recycle and reuse materials that are rare and expensive to obtain, minimizing waste. However, studying the potential circularity of photovoltaics (PV) and HDDs requires various data, for instance, on the maturity of the secondhand markets. In this context, the objective of the present study is to identify the current state of secondhand PV and HDD markets. After conducting a literature review, an automated data collection process was set up for that purpose. The analysis of the literature and collected data assess the maturity of the secondhand PV modules and HDDs markets and highlight differences between them.

agent-based modelling↗
DOE OSTI2012

THE HEIGHT OF A WHITE-LIGHT FLARE AND ITS HARD X-RAY SOURCES

We describe observations of a white-light (WL) flare (SOL2011-02-24T07:35:00, M3.5) close to the limb of the Sun, from which we obtain estimates of the heights of the optical continuum sources and those of the associated hard X-ray (HXR) sources. For this purpose, we use HXR images from the Reuven Ramaty High Energy Spectroscopic Imager and optical images at 6173 A from the Solar Dynamics Observatory. We find that the centroids of the impulsive-phase emissions in WL and HXRs (30-80 keV) match closely in central distance (angular displacement from Sun center), within uncertainties of order 0.''2. This directly implies a common source height for these radiations, strengthening the connection between visible flare continuum formation and the accelerated electrons. We also estimate the absolute heights of these emissions as vertical distances from Sun center. Such a direct estimation has not been done previously, to our knowledge. Using a simultaneous 195 Angstrom-Sign image from the Solar-Terrestrial RElations Observatory spacecraft to identify the heliographic coordinates of the flare footpoints, we determine mean heights above the photosphere (as normally defined; {tau} = 1 at 5000 A) of 305 {+-} 170 km and 195 {+-} 70 km, respectively, for the centroids of the HXR and WL footpoint sources of the flare. These heights are unexpectedly low in the atmosphere, and are consistent with the expected locations of {tau} = 1 for the 6173 Angstrom-Sign and the {approx}40 keV photons observed, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

CORONAL THICK TARGET HARD X-RAY EMISSIONS AND RADIO EMISSIONS

A distinctive class of hard X-ray (HXR) sources located in the corona was recently found, which implies that the collisionally thick target model (CTTM) applies even to the corona. We investigated whether this idea can be independently verified by microwave radiations which have been known as the best companion to HXRs. This study is conducted on the GOES M2.3 class flare which occurred on 2002 September 9 and was observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager and the Owens Valley Solar Array. Interpreting the observed energy-dependent variation of HXR source size under the CTTM, the coronal density should be as high as 5 Multiplication-Sign 10{sup 11} cm{sup -3} over a distance of up to 12''. To explain the cutoff feature of the microwave spectrum at 3 GHz, however, we require a density no higher than 1 Multiplication-Sign 10{sup 11} cm{sup -3}. Additional constraints must be placed on the temperature and magnetic field of the coronal source in order to reproduce the microwave spectrum as a whole. First, a spectral feature called the Razin suppression requires a magnetic field in a range of 250-350 G along with high viewing angles around 75 Degree-Sign . Second, to avoid excess fluxes at high frequencies due to the free-free emission that was not observed, we need a high temperature {>=}2 Multiplication-Sign 10{sup 7} K. These two microwave spectral features, Razin suppression and free-free emissions, become more significant at regions of high thermal plasma density and are essential for validating and determining additional parameters of the coronal HXR sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

SWIFT-BAT HARD X-RAY SKY MONITORING UNVEILS THE ORBITAL PERIOD OF THE HMXB IGR J18219–1347

IGR J18219–1347 is a hard X-ray source discovered by INTEGRAL in 2010. We have analyzed the X-ray emission of this source exploiting the Burst Alert Telescope (BAT) survey data up to 2012 March and the X-Ray Telescope (XRT) data that include also an observing campaign performed in early 2012. The source is detected at a significance level of ∼13 standard deviations in the 88 month BAT survey data, and shows a strong variability along the survey monitoring, going from high intensity to quiescent states. A timing analysis on the BAT data revealed an intensity modulation with a period of P {sub 0} = 72.44 ± 0.3 days. The significance of this modulation is about seven standard deviations in Gaussian statistics. We interpret it as the orbital period of the binary system. The light curve folded at P {sub 0} shows a sharp peak covering ∼30% of the period, superimposed to a flat level roughly consistent with zero. In the soft X-rays the source is detected only in 5 out of 12 XRT observations, with the highest recorded count rate corresponding to a phase close to the BAT folded light-curve peak. The long orbital period and the evidence that the source emits only during a small fraction of the orbit suggests that the IGR J18219–1347 binary system hosts a Be star. The broadband XRT+BAT spectrum is well modeled with a flat absorbed power law with a high-energy exponential cutoff at ∼11 keV.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

SWIFT/BAT DETECTION OF HARD X-RAYS FROM TYCHO'S SUPERNOVA REMNANT: EVIDENCE FOR TITANIUM-44

We report Swift/Burst Alert Telescope survey observations of the Tycho's supernova remnant, performed over a period of 104 months since the mission's launch. The remnant is detected with high significance (>10σ) below 50 keV. We detect significant hard X-ray emission in the 60-85 keV band, above the continuum level predicted by a simple synchrotron model. The location of the observed excess is consistent with line emission from radioactive titanium-44, so far reported only for Type II supernova explosions. We discuss the implications of these results in the context of the galactic supernova rate, and nucleosynthesis in Type Ia supernova.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Hard jet substructure in a multistage approach

We present predictions and postdictions for a wide variety of hard jet-substructure observables using a multistage model within the framework. The details of the multistage model and the various parameter choices are described in []. A novel feature of this model is the presence of two stages of jet modification: a high-virtuality phase [modeled using the modular all twist transverse-scattering elastic-drag and radiation model ()], where modified coherence effects diminish medium-induced radiation, and a lower virtuality phase [modeled using the linear Boltzmann transport model ()], where parton splits are fully resolved by the medium as they endure multiple scattering induced energy loss. Energy-loss calculations are carried out on event-by-event viscous fluid dynamic backgrounds constrained by experimental data. The uniform and consistent descriptions of multiple experimental observables demonstrate the essential role of modified coherence effects and the multistage modeling of jet evolution. Using the best choice of parameters from [], and with no further tuning, we present calculations for the medium modified jet fragmentation function, the groomed jet momentum fraction z g and angular separation r g distributions, as well as the nuclear modification factor of groomed jets. These calculations provide accurate descriptions of published data from experiments at the Large Hadron Collider. Furthermore, we provide predictions from the multistage model for future measurements at the BNL Relativistic Heavy Ion Collider. Published by the American Physical Society 2024

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Photon-in photon-out hard X-ray spectroscopy at the Linac Coherent Light Source

X-ray free-electron lasers (FELs) have opened unprecedented possibilities to study the structure and dynamics of matter at an atomic level and ultra-fast timescale. Many of the techniques routinely used at storage ring facilities are being adapted for experiments conducted at FELs. In order to take full advantage of these new sources several challenges have to be overcome. They are related to the very different source characteristics and its resulting impact on sample delivery, X-ray optics, X-ray detection and data acquisition. Here it is described how photon-in photon-out hard X-ray spectroscopy techniques can be applied to study the electronic structure and its dynamics of transition metal systems with ultra-bright and ultra-short FEL X-ray pulses. In particular, some of the experimental details that are different compared with synchrotron-based setups are discussed and illustrated by recent measurements performed at the Linac Coherent Light Source.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Multimodal hard X-ray nanoprobe techniques for operando investigations of photovoltaic devices

Compared with conventional laboratory-scale X-ray techniques, synchrotron based X-rays with higher brilliance and higher coherence allow for the investigation of various material properties with high spatial resolution. The microscopic behaviours of materials can be examined using the Hard X-ray Nanoprobe beamline (I14) at Diamond Light Source, which provides a 50 nm focused beam and has been successfully employed to identify nanoscale optoelectronic features in energy-harvesting materials such as halide perovskites that exhibit local heterogeneity. We have developed X-ray beam-induced current (XBIC) measurement capability at I14 to address the growing demand for operando analysis in energy-harvesting research. Here, we demonstrate that X-ray fluorescence (XRF)/XBIC multimodal measurements are feasible at I14 and apply these newly implemented techniques to study perovskite solar cells with various additive concentrations to understand the effect of the additive on nanoscale optoelectronic performance. This expanded operando characterization capability offers the possibility of monitoring nanometre-scale compositional variations and corresponding optoelectronic features of actual solar cell configurations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Beta Radiation Hardness of GYGAG(Ce) Transparent Ceramic Scintillators

GYGAG(Ce) transparent ceramic garnet scintillators were irradiated with electrons from 0.5 to 2 MeV with fluences from 10 16 e – /cm 2 to 10 19 e – /cm 2 , corresponding to doses from 0.3 to 310 Gigarad. Absorption spectra were measured before and after irradiations. Light yields from alpha, beta, and gamma excitations were measured before and after irradiation and compared to preirradiation values to gain a deeper understanding of how electron irradiations can affect light yield, as well as defects generated in both the surface and bulk. Within experimental error, no degradation in light yield was observed for the electron-irradiated samples, as measured via beta or gamma excitation, with minimal degradation observed via alpha excitation. A small increase in optical absorption near the wavelength of emission was observed following the largest dose irradiation. These results suggest that GYGAG(Ce) is radiation hard to electron irradiation up to 10 19 e – /cm 2 and doses up to 310 Gigarad. Furthermore, this robustness to irradiation indicates that transparent ceramic garnets may prove useful for applications such as scintillation-based nuclear batteries by allowing for higher energy beta emitters, increased power densities, and enabling long service lifetimes.

36 MATERIALS SCIENCE↗