Bremsstrahlung Research Articles

Importance of Cosmic-Ray Propagation on Sub-GeV Dark Matter Constraints

We study sub-GeV dark matter (DM) particles that may annihilate or decay into Standard Model particles producing an exotic injection component in the Milky Way that leaves an imprint in both photon and cosmic-ray (CR) fluxes. Specifically, the DM particles may annihilate or decay into e + e −, μ + μ −, or π + π − and may radiate photons through their e ± products. The resulting e ± products can be directly observed in probes such as Voyager 1. Alternatively, the e ± products may produce bremsstrahlung radiation and upscatter the low-energy Galactic photon fields via the inverse Compton process, generating a broad emission from X-ray to γ-ray energies observable in experiments such as XMM-Newton. We find that we get a significant improvement in the DM annihilation and decay constraints from XMM-Newton (excluding thermally averaged cross sections of 10−31 cm3 s−1 ≲ 〈σ v〉 ≲ 10−26 cm3 s−1 and decay lifetimes of 1026 s ≲ τ ≲ 1028 s, respectively) by including best-fit CR propagation and diffusion parameters. This yields the strongest astrophysical constraints for this mass range of DM of 1 MeV to a few GeV and even surpasses cosmological bounds across a wide range of masses as well.

Dual Role of Accretion Disk Winds as X-Ray Obscurers and UV Line Absorbers in AGN

X-ray obscuration of active galactic nuclei (AGNs) is considered in the context of ionized winds of stratified structure launched from accretion disks. We argue that a Compton-thick layer of a large-scale disk wind can obscure continuum X-rays and also lead to broad UV absorption, such as in the blue wing of C iv; the former originates from the inner wind and the latter from the outer wind, as a dual role. Motivated by a number of lines of observational evidence showing strong AGN obscuration phenomena in Seyfert 1 AGNs such as NGC 5548, we demonstrate in this work, by utilizing a physically motivated wind model coupled to post-process radiative transfer calculations, that an extended disk wind under certain physical conditions (e.g., morphology and density) could naturally cause a sufficient obscuration qualitatively consistent with UV/X-ray observations. Predicted UV/X-ray correlation is also presented as a consequence of variable spatial size of the wind in this scenario.

Source of the Fe Kalpha emission in T Tauri stars. Radiation induced by relativistic electrons during flares. An application to RY Tau

T Tauri stars (TTSs) are magnetically active stars that accrete matter from the inner border of the surrounding accretion disk; plasma becomes trapped into the large-scale magnetic structures and falls onto the star, heating the surface through the so-called accretion shocks. The X-ray spectra of the TTSs show prominent Fe Kalpha fluorescence emission at 6.4 keV (hereafter, Fe Kalpha emission) that cannot be explained in a pure accretion scenario because its excitation requires significantly more energy than the maximum available through the well-constrained free-fall velocity. Neither can it be produced by the hot coronal plasma. TTSs display all signs of magnetic activity, and magnetic reconnection events are expected to occur frequently. In these events, electrons may become accelerated to relativistic speeds, and their interaction with the environmental matter may result in Fe Kalpha emission. It is the aim of this work to evaluate the expected Fe Kalpha emission in the context of the TTS research and compare it with the actual Fe Kalpha measurements obtained during the flare detected while monitoring RY Tau with the XMM-Newton satellite. The propagation of high-energy electrons in dense gas generates a cascade of secondary particles that results in an electron shower of random nature, whose evolution and radiative throughput was simulated in this work using the Monte Carlo code PENELOPE. A set of conditions representing the environment of the TTSs where these showers may impinge was taken into account to generate a grid of models that can aid the interpretation of the data. The simulations show that the electron beams produce a hot spot at the point of impact; strong Fe Kalpha emission and X-ray continuum radiation are produced by the spot. This emission is compatible with RY Tau observations. The Fe Kalpha emission observed in TTSs could be produced by beams of relativistic electrons accelerated in magnetic reconnection events during flares.

High-speed continuous X-ray imaging method based on SiPM auto-encoding detector

High-speed X-ray imaging can be used to observe the internal evolution of objects in the microsecond range. However, obtaining data and processing images continuously are difficult when the speed of X-ray imaging is more than one million frames per second (fps). The novel method of high-speed X-ray imaging, which is based on a SiPM auto-encoding detector, was proposed. The different response to X-ray is realized by adjusting the bias voltage of different pixels to encode the analog signals. The analog signals from multiple SiPM pixels are simplified into a single signal. In this way, SiPM is constructed as the SiPM auto-encoding detector, which greatly reduces the amount of analog signals to be sampled for each frame of X-ray image, and then the image is reconstructed in the upper computer. The feasibility of the imaging method was verified by coupling the pixelated SiPM and lutetium-ytterbium scintillation crystals to construct a SiPM auto-encoding detector. Six patterns were exposed when pulsed X-rays were performed at frequencies of 100 and 500 kHz. Then, the number of image pixels was compressed from 16 to 4. The peak signal-to-noise ratio of the reconstructed images was above 41, and the structural similarity was above 0.99. Experimental results demonstrated that the speed of continuous X-ray imaging reached 500, 000 fps for six kinds of 4 × 4 pixel patterns. This method can be applied to improve the speed of high-speed continuous X-ray imaging.

Modelling the galaxy radio continuum from star formation and active galactic nuclei in the Shark semi-analytic model

ABSTRACT We present a model of radio continuum emission associated with star formation (SF) and active galactic nuclei (AGNs) implemented in the Shark semi-analytic model of galaxy formation. SF emission includes free-free and synchrotron emission, which depend on the free-electron density and the rate of core-collapse supernovae with a minor contribution from supernova remnants, respectively. AGN emission is modelled based on the jet production rate, which depends on the black hole mass, accretion rate, and spin, and includes synchrotron self-absorption. Shark reproduces radio luminosity functions (RLFs) at $1.4\, \rm GHz$ and $150\, \rm MHz$ for 0 ≤ z ≤ 4, and scaling relations between radio luminosity, star formation rate, and infrared luminosity of galaxies in the local and distant universe in good agreement with observations. The model also reproduces observed number counts of radio sources from 150 MHz to 8.4 GHz to within a factor of 2 on average, though larger discrepancies are seen at the very bright fluxes at higher frequencies. We use this model to understand how the radio continuum emission from radio-quiet AGNs can affect the measured RLFs of galaxies. We find current methods to exclude AGNs from observational samples result in large fractions of radio-quiet AGNs contaminating the ‘star-forming galaxies’ selection and a brighter end to the resulting RLFs.We investigate how this affects the infrared-radio correlation (IRRC) and show that AGN contamination can lead to evolution of the IRRC with redshift. Without this contamination, our model predicts a redshift- and stellar mass-independent IRRC, except at the dwarf-galaxy regime.

Optimization of the N∥ Upshift in the DIII-D high field side lower hybrid current drive experiment

High field side lower hybrid current drive (LHCD) is one potential candidate for efficient non-inductive current drive in tokamak power plants, and the first test of this technology will occur on the DIII-D tokamak during the 2024 campaign. Previous LFS launch experiments operated in the multi-pass regime and relied on scrape-off layer interactions to close the spectral gap. In the DIII-D experiment, single-pass damping is achievable via an upshift in the parallel refractive index N∥ caused by mode converting twice (slow → fast → slow). This mode conversion affects the ray trajectories and can lead to enhanced N∥ upshift depending on where mode conversion occurs. Compared to multi-pass absorption experiments, the optimization of launched N∥ and plasma parameters can be counter-intuitive: increased density may increase efficiency and smaller N∥,launch tend to damp closer to the separatrix. A hard x-ray camera installed to measure the bremsstrahlung (50–250 keV) radiation from LHCD-generated fast electrons is capable of verifying the trends reporting in this paper through comparison to the ray-tracing/Fokker–Planck codes GENRAY/CQL3D.

Cyclotron line formation in the radiative shock of an accreting magnetized neutron star

Context. Magnetic neutron stars (NSs) often exhibit a cyclotron resonant scattering feature (CRSF) in their X-ray spectra. Accretion onto their magnetic poles is responsible for the emergence of X-rays, but the site of the CRSF formation is still a puzzle. A promising candidate for high-luminosity sources has always been the radiative shock in the accretion column. Nevertheless, no quantitative calculations of spectral formation at the radiative shock have been performed so far. Aims. It is well accepted that, in the accretion column of a high-luminosity, accreting magnetic NS, a radiative shock is formed. Here, we aim to explore the scenario where the shock is the site of the cyclotron-line formation. We studied spectral formation at the radiative shock and the emergent spectral shape across a wide range of the parameter space and determined which parameters hold an important role in shaping a prominent CRSF. Methods. We developed a Monte Carlo (MC) code based on the forced first collision numerical scheme to conduct radiation transfer simulations at the radiative shock. The seed photons were due to bremsstrahlung and were emitted in the post-shock region. We properly treated bulk-motion Comptonization in the pre-shock region, thermal Comptonization in the post-shock region, and resonant Compton scattering in both regions. We adopted a fully relativistic scheme for the interaction between radiation and electrons, employing an appropriate polarization-averaged differential cross-section. As a result, we calculated the angle- and energy-dependent emergent X-ray spectrum from the radiative shock, focusing on both the CRSF and the X-ray continuum, under diverse conditions. The accretion column was characterized by cylindrical symmetry, and the radiative shock was treated as a mathematical discontinuity. Results. We find that a power law, hard X-ray continuum, and a CRSF are naturally produced by the first-order Fermi energization as the photons criss-cross the shock. The depth and the width of the CRSF depend mainly on the transverse optical depth and the post-shock temperature. We show that the cyclotron-line energy centroid is shifted by ∼(20 − 30)% to lower energies compared to the classical cyclotron energy; this is due to the Doppler boosting between the shock reference frame and the bulk-motion frame. We demonstrate that a “bump” feature arises in the right wing of the CRSF due to the up-scattering of photons by the accreting plasma and extends to higher energies for larger optical depths and post-shock temperatures. Conclusions. We conclude that resonant Compton scattering of photons by electrons in a radiative shock is efficient in producing a power-law X-ray continuum with a high-energy cutoff accompanied by a prominent CRSF. The implications of the Doppler effect on the centroid of the emergent absorption feature must be considered if an accurate determination of the magnetic field strength is desired.

GalaPy: A highly optimised C++/Python spectral modelling tool for galaxies

Bolstered by upcoming data from new-generation observational campaigns, we are about to enter a new era in the study of how galaxies form and evolve. The unprecedented quantity of data that will be collected from distances that have only marginally been grasped up to now will require analytical tools designed to target the specific physical peculiarities of the observed sources and handle extremely large datasets. One powerful method to investigate the complex astrophysical processes that govern the properties of galaxies is to model their observed spectral energy distributions (SEDs) at different stages of evolution and times throughout the history of the Universe. To address these challenges, we have developed GalaPy, a new library for modelling and fitting SEDs of galaxies from the X-ray to the radio band, as well as the evolution of their components and dust attenuation and reradiation. On the physical side, GalaPy incorporates both empirical and physically motivated star formation histories (SFHs), state-of-the-art single stellar population synthesis libraries, a two-component dust model for attenuation, an age-dependent energy conservation algorithm to compute dust reradiation, and additional sources of stellar continuum such as synchrotron, nebular and free-free emission, as well as X-ray radiation from low-and high-mass binary stars. On the computational side, GalaPy implements a hybrid approach that combines the high performance of compiled C++with the user-friendly flexibility of Python. Also, it exploits an object-oriented design via advanced programming techniques. GalaPy is the fastest SED-generation tool of its kind, with a peak performance of almost 1000 SEDs per second. The models are generated on the fly without relying on templates, thus minimising memory consumption. It exploits a fully Bayesian parameter space sampling, which allows for the inference of parameter posteriors and thereby facilitates the study of the correlations between the free parameters and the other physical quantities that can be derived from modelling. The application programming interface (API) and functions of GalaPy are under continuous development, with planned extensions in the near future. In this first work, we introduce the project and showcase the photometric SED fitting tools already available to users. GalaPy is available on the Python Package Index (PyPI) and comes with extensive online documentation and tutorials.

Non-thermal emission in M31 and M33

Context. Spiral galaxies M31 and M33 are among the γ-ray sources detected by the Fermi Large Area Telescope (LAT). Aims. We aim to model the broadband non-thermal emission of the central region of M31 (a LAT point source) and of the disk of M33 (a LAT extended source), as part of our continued survey of non-thermal properties of local galaxies that includes the Magellanic Clouds. Methods. We analysed the observed emission from the central region of M31 (R < 5.5 kpc) and the disk-sized emission from M33 (R ∼ 9 kpc). For each galaxy, we self-consistently modelled the broadband spectral energy distribution of the diffuse non-thermal emission based on published radio and γ-ray data. All relevant radiative processes involving relativistic and thermal electrons (synchrotron, Compton scattering, bremsstrahlung, and free–free emission and absorption), along with relativistic protons (π0 decay following interaction with thermal protons), were considered, using exact emissivity formulae. We also used the Fermi-LAT-validated γ-ray emissivities for pulsars. Results. Joint spectral analyses of the emission from the central region of M31 and the extended disk of M33 indicate that the radio emission is composed of both primary and secondary electron synchrotron and thermal bremsstrahlung, whereas the γ-ray emission may be explained as a combination of diffuse pionic, pulsar, and nuclear-BH-related emissions in M31 and plain diffuse pionic emission (with an average proton energy density of 0.5 eV cm−3) in M33. Conclusions. The observed γ-ray emission from M33 appears to be mainly hadronic. This situation is similar to other local galaxies, namely, the Magellanic Clouds. In contrast, we have found suggestions of a more complex situation in the central region of M31, whose emission could be an admixture of pulsar emission and hadronic emission, with the latter possibly originating from both the disk and the vicinity of the nuclear black hole. The alternative modelling of the spectra of M31 and M33 is motivated by the different hydrogen distribution in the two galaxies: The hydrogen deficiency in the central region of M31 partially unveils emissions from the nuclear BH and the pulsar population in the bulge and inner disk. If this were to be the case in M33 as well, these emissions would be outshined by diffuse pionic emission originating within the flat central-peak gas distribution in M33.

On the Origin of the X-Ray Emission in Heavily Obscured Compact Radio Sources

X-ray continuum emission of active galactic nuclei (AGNs) may be reflected by circumnuclear dusty tori, producing prominent fluorescence iron lines at X-ray frequencies. Here, we discuss the broadband emission of three radio-loud AGNs belonging to the class of compact symmetric objects (CSOs), with detected narrow Fe Kα lines. CSOs have newly born radio jets, forming compact radio lobes with projected linear sizes of the order of a few to hundreds of parsecs. We model the radio-to-γ-ray spectra of compact lobes in J1407+2827, J1511+0518, and J2022+6137, which are among the nearest and the youngest CSOs known to date, and are characterized by an intrinsic X-ray absorbing column density of N H > 1023 cm−2. In addition to the archival data, we analyze the newly acquired Chandra X-ray Observatory and Submillimeter Array (SMA) observations, and also refine the γ-ray upper limits from Fermi Large Area Telescope monitoring. The new Chandra data exclude the presence of the extended X-ray emission components on scales larger than 1.″5. The SMA data unveil a correlation between the spectral index of the electron distribution in the lobes and N H, which can explain the γ-ray quietness of heavily obscured CSOs. Based on our modeling, we argue that the inverse-Compton emission of compact radio lobes may account for the intrinsic X-ray continuum in all these sources. Furthermore, we propose that the observed iron lines may be produced by a reflection of the lobes’ continuum from the surrounding cold dust.

Quantum calculation of the pressure broadening of H and K lines of Ca+ calcium ion in a gaz of ground-state He helium atoms

In this theoretical study, we have conducted calculations to investigate the pressure broadening of the H ( 4 s 2 S 1 / 2 − 4 p 2 P 1 / 2 ) and the K ( 4 s 2 S 1 / 2 − 4 p 2 P 3 / 2 ) lines of the Ca + calcium ion in a gas of ground-state He helium atoms. The focus of our work is to determine the profiles of the pressure-broadened resonance lines and analyse their behaviour under the influence of binary collisions between Ca + ions and He atoms. To achieve this, we constructed accurate potential energy curves for the ground X 2 Σ 1 / 2 + and the excited D 2 Π 1 / 2 , D 2 Π 3 / 2 and E 2 Σ 1 / 2 + states. Additionally, we constructed the corresponding transition dipole moments based on the data obtained through high-level ab initio methods, including SA-CASSCF, MRCI, and SO coupling, with Davidson and BSSE corrections. The study spans a range of temperatures from 4000 K to 12,000 K and wavelengths from 200 nm to 500 nm . The theoretical profile is characterised by dominant free-free transitions. In the vicinity of the 436 nm wavelength position, there is a satellite peak in the red wing, attributed to the contribution of D 2 Π 1 / 2 ⟵ X 2 Σ 1 / 2 + and D 2 Π 3 / 2 ⟵ X 2 Σ 1 / 2 + transitions. Our findings are in good agreement with previous theoretical results.

NuSTAR detection of a broad absorption line in IGR J06074+2205

BeXRB pulsar IGR J06074+2205 using NuSTAR observations. The temporal and spectral characteristics of the source are investigated. We detect coherent X-ray pulsations of the source and determine the spin period evolution. Using the current spin period data of the source, we show that the source is spinning down at 0.0202(2) sday−1. The pulse profiles are found to evolve with energy and luminosity. Another interesting feature of the source is that the pulse profiles are dual peaked. The dual-peaked pulse profile is characterized by a decreasing secondary peak amplitude with increasing energy. We also observed a proportionate increase in the primary peak amplitude as the energy increases. The pulse fraction exhibits an overall increasing trend with the energy. The X-ray continuum of the source indicates the existence of a characteristic absorption feature with a centroid energy ∼55 keV, which may be interpreted as a cyclotron line. We estimate the corresponding magnetic field strength to be ∼4.74×1012 G. A peculiar ‘10 keV’ absorption feature is observed in the X-ray spectra of the second observation. The luminosity measurements predict that the source may be accreting in the sub-critical regime.

Correlation between accretion rate and free-free emission in protoplanetary disks

Context. The inner regions of protoplanetary disks are believed to be the primary locations of planet formation and the processes that influence the global evolution of the disk, such as magnetohydrodynamic winds and photoevaporation. Transition disks with large inner dust cavities are ideal targets for studying the inner regions (of tens of au) of disks, as this is where the central emission can be fully disentangled from the outer disk emission. Aims. We present a homogeneous multiwavelength analysis of the continuum emission in a sample of 11 transition disks. We investigate the nature of the central emission close to the star, distinguishing between thermal dust and free-free emission. Methods. We combined spatially resolved measurements of continuum emission from the archival Atacama Large Millimeter/Submillimeter Array data with centimeter-wave (cm-wave) observations from the literature to study the spectral indices of the inner and outer disks separately. Results. While the emission from the outer disks is consistent with thermal dust emission, 10 out of 11 of the spectral indices estimated for the central emission close to the star suggest that this emission is free-free emission that is likely associated with an ionized jet or a disk wind. We found no correlation between the free-free luminosity and the accretion luminosity or the X-ray luminosity and this argues against an explanation based on a potential photoevaporative wind. A sub-linear correlation between the ionized mass loss rate and the accretion rate onto the star was observed, suggesting the origin is drawn from the ionized jet. Conclusions. The relative lack of millimeter-dust (mm-dust) grains in the majority of inner disks in transition disks indicates that either such dust grains have drifted quickly towards the central star, that grain growth is less efficient in the inner disk, or that grains rapidly grow to planetesimal sizes in the inner disk. The observed correlation between the ionized mass loss rate and the accretion rate suggests the outflow is strictly connected to stellar accretion and that accretion in these disks is driven by a jet.

One size fits all: Insights into extrinsic thermal absorption based on the similarity of supernova remnant radio-continuum spectra

Typically, integrated radio frequency continuum spectra of supernova remnants (SNRs) exhibit a power-law form due to their synchrotron emission. In numerous cases, these spectra show an exponential turnover, which has long been assumed to be due to thermal free-free absorption in the interstellar medium. We used a compilation of Galactic radio continuum SNR spectra, with and without turnovers, to constrain the distribution of the absorbing ionised gas. We introduce a novel parameterisation of SNR spectra in terms of a characteristic frequency, ν* which depends both on the absorption turnover frequency and the power-law slope. Normalising to v* and to the corresponding flux density, S* we demonstrate that the stacked spectra of our sample reveal a similarity in behavior with low scatter (root mean square, rms, of ~15%), and a unique exponential drop-off that is fully consistent with the predictions of a free-free absorption process. Observed SNRs, whether exhibiting spectral turnovers or not, appear to be spatially well-mixed in the Galaxy without any evident segregation between them. Moreover, their Galactic distribution does not show a correlation with general properties such as heliocentric distance or Galactic longitude, as might have been expected if the absorption were due to a continuous distribution of ionised gas. However, it naturally arises if the absorbers are discretely distributed, as suggested by early low-frequency observations. Modelling based on H II regions tracking Galactic spiral arms successfully reproduces the patchy absorption observed to date. While more extensive statistical datasets should yield more precise spatial models of the absorbing gas distribution, our present conclusion regarding its inhomogeneity will remain robust.

Comparative study of radioprotective effects of endurance training in irradiation-induced nephropathy of rat model.

Considering the antioxidant properties of endurance training, this study aimed to investigate the effects of endurance training on serum levels of oxidative stress and structural changes in the kidney tissue of rats exposed to X-ray irradiation. In this experimental study, 24 rats weighing 220±20 g were randomly divided into four groups (healthy control, healthy with moderate-intensity continuous training, X-ray control, and X-ray with moderate-intensity continuous training). The two groups of rats were irradiated with 4 Gy X-rays. The two training groups also performed moderate-intensity continuous training for 10 weeks. Twenty-four hour after the last training session, the blood serum of rats was collected and kidney tissue was isolated for stereological studies. In this study, X-ray irradiation of the whole body of rats caused a significant increase in kidney volume, cortex volume, interstitial tissue volume, glomerular volume, and serum level of MDA (p≤0.05), but the medulla volume, volume of proximal tubules (total volume, volume of epithelium, and lumen), volume of distal tubules (total volume, volume of epithelium, and lumen), and the length of the proximal and distal tubules had no effect. In addition, TAC and SOD levels were significantly decreased in the radiation control group. Furthermore, performing endurance training in X-ray-irradiated rats significantly reduced kidney volume, cortex volume, glomerular volume, and serum MDA level (p≤0.05). Moderate-intensity continuous training can improve the rate of destruction of kidney tissue in rats exposed to X-rays by reducing oxidative stress and subsequently increasing antioxidant capacity.

On the Galactic radio signal from stimulated decay of axion dark matter

We study the full-sky distribution of the radio emission from the stimulated decay of axions which are assumed to compose the dark matter in the Galaxy. Besides the constant extragalactic and CMB components, the decays are stimulated by a Galactic radio emission with a spatial distribution that we empirically determine from observations. We compare the diffuse emission to the counterimages of the brightest supernovæ remnants, and take into account the effects of free-free absorption. We show that, if the dark matter halo is described by a cuspy NFW profile, the expected signal from the Galactic center is the strongest. Interestingly, the emission from the Galactic anti-center provides competitive constraints that do not depend on assumptions on the uncertain dark matter density in the inner region. Furthermore, the anti-center of the Galaxy is the brightest spot if the Galactic dark matter density follows a cored profile. The expected signal from stimulated decays of axions of mass ma ∼ 10-6 eV is within reach of the Square Kilometer Array for an axion-photon coupling gaγ ≳ (2-3) × 10-11 GeV-1.

Characterisation of Redlen HF-CdZnTe at > 106 ph s-1 mm-2 using HEXITECMHz

In this paper, results are presented from the characterisation of Redlen Technologies high-flux-capable Cadmium Zinc Telluride (HF-CZT) hybridised to the HEXITECMHz ASIC, a novel 1 MHz continuous X-ray imaging system. A 2 mm thick HF-CZT HEXITECMHz detector was characterised on the B16 Test Beamline at the Diamond Light Source and displayed an average FWHM of 850 eV for monochromatic X-rays of energy 20 keV. Measurements revealed a shift in the baseline of irradiated pixels that results in a movement of the entire spectrum to higher ADU values. Datasets taken to analyse the effect's dynamics showed it to be highly localised and flux-dependent, with the excess leakage current generated equivalent to per-pixel shifts of ∼ 543 pA (8.68 nA mm-2) at a flux of 1.26×107 ph s-1 mm-2. Comparison to results from a p-type Si HEXITECMHz device indicate this `excess leakage-current' effect is unique to HF-CZT and it is hypothesised that it originates from trapping at the electrode-CZT interface and a temporary modification of the potential barrier between the CZT and metal electrode.

The Spectral Energy Distributions and Bolometric Luminosities of Local AGN: Study of the Complete 12 μm AGN Sample

We measure the bolometric luminosity of a complete and unbiased 12 μm-selected sample of active galactic nuclei (AGN) in the local Universe. For each galaxy, we used a 10-band radio-to-X-ray spectral energy distribution (SED) to isolate the genuine AGN continuum in each band, including subarcsecond measurements where available, and correcting those contaminated by the host galaxy. We derive the median SED of Seyfert type 1 AGN, Seyferts with hidden broad lines (HBLs), Seyferts of type 2, and LINER nuclei in our sample. The median Seyfert 1 SED shows the characteristic blue bump feature in the UV, but nevertheless, the largest contribution to the bolometric luminosity comes from the IR and X-ray continua. The median SEDs of both HBL and type 2 AGN are affected by starlight contamination in the optical/UV. The median SED of HBL AGN is consistent with that of Seyfert 1s, when an extinction of A V ∼ 1.2 mag is applied. The comprehensive SEDs allowed us to measure accurate bolometric luminosities and derive robust bolometric corrections for the different tracers. The 12 μm and K-band nuclear luminosities have good linear correlations with the bolometric luminosity, similar to those in the X-rays. We derive bolometric corrections for either continuum bands (K band, 12 μm, 2–10 keV, and 14–195 keV) or narrow emission lines (mid-IR high-ionization lines of [O iv] and [Ne v] and optical [O iii] 5007 Å) as well as for combinations of IR continuum and line emission. A combination of continuum plus line emission accurately predicts the bolometric luminosity up to quasar luminosities (∼1046 erg s−1).

Emission of Parasitic X Rays of Vacuum-electron Tubes with Glass Housings: Implications for the Evaluation of Occupational Doses.

Despite the large variety of high-voltage semiconductor components for medium and high voltage switching and pulse-forming applications as well as for high-power high-frequency generation, the use of vacuum electron tubes still prevails to a considerable degree. Due to the common design incorporating a high energy electron beam which finally is dumped into an anode or a resonator cavity, these tubes are also considered as sources of X rays produced as bremsstrahlung and characteristic radiation, which are referred to as parasitic X rays. Here three types of vacuum-electron tubes, diode, tetrode, and thyratron, with glass housings are investigated. They are predominantly operated in the high voltage range below 30 kV and are not subject to licensing laws. The measurements of the dose rate and X-ray-spectra were performed in the laboratory without complex electrical circuitry usually used in making practical measurements for occupational radiation protection. For the diode tube, where a parasitic X-ray emission is observed only in the reverse operation as a blocking diode, a broad distribution of dose rates of electrically equivalent specimens was observed. This is attributed to field emission from the electrodes. For the tetrode and the thyratron tubes, field emission from the electrodes is identified as the dominant mechanism for the generation of parasitic X rays. Thus, technical radiation protection must focus on shielding of the glass tube rather than optimization of the electrical circuitry.

Three-dimensional particle-in-cell simulations of laser-driven multiradiation sources based on double-layer targets.

Double-layer targets (DLTs), made of a low-density foam on top of a solid substrate, can efficiently convert the energy of a high-intensity laser to provide sources of photons and protons. We investigate a 30-fs pulse with a peak intensity of I∼8.7×10^{20}W/cm^{2} and a peak power of ∼120 TW interacting with a DLT using three-dimensional (3D) particle-in-cell simulations. We focus on providing quantitative results in full 3D geometry on the foam thickness dependence; on the competition between two photon-generating processes in DLTs, i.e., nonlinear inverse Compton scattering (NICS) and bremsstrahlung (BS); and on the acceleration of protons via enhanced target-normal sheath acceleration. We discuss conversion efficiency, average energy, and angular distributions of such multiradiation sources. We find that NICS can prevail over BS if the DLT's substrate is thin enough (∼µm) and that the optimal foam thickness that maximizes the conversion efficiency in NICS and BS photons and the proton cutoff energy, among those considered, is the same (15µm). These results show that DLTs constitute an excellent tool for developing relatively compact and optimized laser-driven multicomponent radiation sources.