Hard X-ray Photons Research Articles

A study of jet heating mechanisms with application to the microquasar SS 433

We consider various physical processes that affect the thermal balance of an X-ray jet. We focus on the rapid cooling of dense jets via bremsstrahlung, and all processes are considered from the viewpoint of their contributions to the jet thermal balance. Jet heating by Compton scattering of hard X-ray photons from the hot corona, the effect of shocks in the jet on heating of the jet, and the transformation of jet kinetic energy into heat via Coulomb collisions between protons of the jet and corona are considered. Numerical values have been obtained for the Galactic microquasar SS 433 based on previous results for modeling the X-ray spectrum of this source. Collisions of the jet particles with the ambient gas turns out to be the most important jet heating mechanism for this source.

The optical-UV spectral energy distribution of the unabsorbed AGN population in theXMM-NewtonBright Serendipitous Survey

Active galactic nuclei (AGN) emit radiation over a wide range of wavelengths, with a peak of emission in the far-UV region of the electromagnetic spectrum, a spectral region that is historically difficult to observe. Using optical, GALEX UV and XMM-Newton data we derive the spectral energy distribution (SED) from the optical/UV to X-ray regime of a sizeable sample of AGN. The principal motivation is to investigate the relationship between the optical/UV emission and the X-ray emission and provide bolometric corrections to the hard X-ray (2-10 keV) energy range, kbol, the latter being a fundamental parameter in current physical cosmology. We construct and study the X-ray to optical SED of a sample of 195 X-ray selected Type 1 AGN belonging to the XMM-Newton bright serendipitous survey (XBS). The optical-UV luminosity was computed using data from the Sloan Digital Sky Survey (SDSS), from our own dedicated optical spectroscopy and the satellite Galaxy Evolution Explorer (GALEX), while the X-ray luminosity was computed using XMM-Newton data. Because it covers a wide range of redshift (0.03 < z < 2.2), X-ray luminosities (41.8 < logL[2-10]keV < 45.5 erg/s) and because it is composed of "bright objects", this sample is ideal for this kind of investigation. We find a correlation between kbol and the hard X-ray photon index {\Gamma}(2-10keV) and a tight correlation between the optical-to-X-ray spectral index {\alpha}ox and kbol, so we conclude that both {\Gamma}(2-10keV) and {\alpha}ox can be used as a proxy for kbol.

THERMAL BALANCE OF THE JET IN THE MICROQUASAR SS433

Thermal balance of the jet in the source SS433 is considered accounting for radiative and adiabatic cooling, and different heating mechanisms. We consider jet heating by the Compton effect of coronal hard X-ray photons on jet electrons, the influence of shock wave propagation along the jet, and jet kinetic energy transformation into heat via Coulomb collisions of jet and corona protons. The most important heating mechanism for the source SS433 turns out to be Coulomb collisions of jet particles with the surrounding medium.

THE EMISSION FROM AN INNER DISK AND A CORONA IN THE LOW AND INTERMEDIATE SPECTRAL STATES OF BLACK HOLE X-RAY BINARIES

Recent observations reveal that a cool disk may survive in the innermost stable circular orbit (ISCO) for some black hole X-ray binaries in the canonical low/hard state. The spectrum is characterized by a power law with a photon index $\Gamma \sim 1.5-2.1$ in the range of 2-10 keV and a weak disk component with temperature of $\sim 0.2$ keV. In this work, We revisit the formation of such a cool, optically thick, geometrically thin disk in the most inner region of black hole X-ray binaries at the low/hard state within the context of disk accretion fed by condensation of hot corona. By taking into account the cooling process associated with both Compton and conductive processes in a corona, and the irradiation of the hot corona to the disk, we calculate the structure of the corona. For viscosity parameter $\alpha=0.2$, it's found that the inner disk can exist for accretion rate ranging from $\dot M \sim 0.006-0.03 \dot M_{\rm Edd}$, over which the electron temperatures of the corona are in the range of $1-5\times 10^9\ \rm K$ producing the hard X-ray emission. We calculate the emergent spectra of the inner disk and corona for different mass accretion rates. The effect of viscosity parameter $\alpha$ and albedo $a$ ($a$ is defined as the energy ratio of reflected radiation from the surface of the thin disk to incident radiation upon it from the corona) to the emergent spectra are also presented. Our model is used to explain the recent observations of GX 339-4 and Cyg X-1, in which the thin disk may exist at ISCO region in the low/hard state at luminosity around a few percent of $L_{\rm Edd}$. It's found that the observed maximal effective temperature of the thermal component and the hard X-ray photon index $\Gamma$ can be matched well by our model.

Spatially resolved hard X-ray polarization in solar flares: effects of Compton scattering and bremsstrahlung

This paper aims to study the polarization of hard X-ray (HXR) sources in the solar atmosphere, including Compton backscattering of photons in the photosphere (the albedo effect) and the spatial distribution of polarization across the source. HXR photon polarization and spectra produced via electron-ion bremsstrahlung are calculated from electron distributions typical for solar flares. Compton scattering and photoelectric absorption are then modelled using Monte Carlo simulations of photon transport in the photosphere. Polarization maps across HXR sources (primary and albedo components) for each of the modelled electron distributions are calculated at various source locations from the solar centre to the limb. We show that Compton scattering produces a distinct polarization variation across the albedo patch at peak albedo energies of 20-50 keV for all anisotropies modelled. The results show that there are distinct spatial polarization changes in both the radial and perpendicular to radial directions across the extent of the HXR source at a given disk location. In the radial direction, the polarization magnitude and direction at specific positions along the HXR source will either increase or decrease with increased photon distribution directivity towards the photosphere. We also show how high electron cutoff energies influence the direction of polarization at above ~100 keV. Spatially resolved HXR polarization measurements can provide important information about the directivity and energetics of the electron distribution. Our results indicate the preferred angular resolution of polarization measurements required to distinguish between the scattered and primary components. We also show how spatially resolved polarization measurements could be used to probe the emission pattern of an HXR source, using both the magnitude and the direction of polarization.

Narrow-line Seyfert 1 galaxies at hard X-rays★

Narrow Line Seyfert 1 (NLSy1) galaxies are a peculiar class of type 1 AGN (BLSy1). The X-ray properties of individual objects belonging to this class are often extreme and associated with accretion at high Eddington ratios. Here we present a study on a sample of 14 NLSy1 galaxies selected at hard X-rays (> 20 keV) from the fourth INTEGRAL/IBIS catalogue. The 20-100 keV IBIS spectra show hard X-ray photon indeces flatly distributed (Gamma_{20-100 keV} ranging from ~1.3 to ~3.6) with an average value of <Gamma_{20-100 keV}> = 2.3+/-0.7, compatible with a sample of hard X-ray BLSy1 average slope. Instead, NLSy1 show steeper spectral indeces with respect to BLSy1 when broad-band spectra are considered. Indeed, we combine XMM-Newton and Swift/XRT with INTEGRAL/IBIS data sets to obtain a wide energy spectral coverage (0.3-100 keV). A constraint on the high energy cut-off and on the reflection component is achieved only in one source, Swift J2127.4+5654 (E_{cut-off} ~ 50 keV, R=1.0{+0.5}_{-0.4}). Hard X-ray selected NLSy1 do not display particularly strong soft excess emission, while absorption fully or partially covering the continuum is often measured as well as Fe line emission features. Variability is a common trait in this sample, both at X-ray and at hard X-rays. The fraction of NLSy1 in the hard X-ray sky is likely to be ~15%, in agreement with estimates derived in optically selected NLSy1 samples. We confirm the association of NLSy1 with small black hole masses with a peak at 10^{7} M_{dot} in the distribution, however hard X-ray NLSy1 seem to occupy the lower tail of the Eddington ratios distribution of classical NLSy1.

Measurement of runaway electrons energy by hard X-ray spectroscopy in a small circular cross-section tokamak

In this paper, the measurement of runaway electrons energy was investigated. For this purpose, hard X-ray spectroscopy in IR-T1 tokamak was used. Hard X-ray emissions are produced by collision of the runaway electrons with the plasma particles and limiters. The mean energy was calculated from the slope of the energy spectrum of hard X-ray photons. Here in order to measure the energy of the runaway electrons, hard X-ray energy in every 5 ms intervals was obtained from the beginning to the end of plasma. Results indicate that the mean energy of runaway electrons has its maximum value within the 0–5 ms interval.

Probing bulk electronic structure with hard X-ray angle-resolved photoemission

Traditional ultraviolet/soft X-ray angle-resolved photoemission spectroscopy (ARPES) may in some cases be too strongly influenced by surface effects to be a useful probe of bulk electronic structure. Going to hard X-ray photon energies and thus larger electron inelastic mean-free paths should provide a more accurate picture of bulk electronic structure. We present experimental data for hard X-ray ARPES (HARPES) at energies of 3.2 and 6.0 keV. The systems discussed are W, as a model transition-metal system to illustrate basic principles, and GaAs, as a technologically-relevant material to illustrate the potential broad applicability of this new technique. We have investigated the effects of photon wave vector on wave vector conservation, and assessed methods for the removal of phonon-associated smearing of features and photoelectron diffraction effects. The experimental results are compared to free-electron final-state model calculations and to more precise one-step photoemission theory including matrix element effects.

Self-standing bent silicon crystals for very high efficiency Laue lens

Silicon mono-crystals have been bent thanks to a series of parallel superficial indentations on one of the largest faces of the crystals. This technique relies on irreversible compression of the crystal beneath and beside the indentations. This latter causes deformation with no need for external device, resulting in a uniform self-standing curvature within the crystal. Indented Si crystals have been characterized at European Synchrotron Radiation Facility using a monochromatic beam ranging from 150 to 700 keV. Crystals exhibited very high diffraction efficiency over a broad range of energy, peaking 95% at 150 keV. Measured angular spread of the diffracted beam was always very close to the morphological curvature of the sample under investigation, proving that the energy passband of bent crystals can be controlled by simply imparting a selected curvature to the sample. The method of superficial indentations was found to offer high reproducibility and easy control of diffraction properties of the crystals. Moreover the method is cheap and simple, being based on mass production tools. A Laue lens made of crystals bent by superficial indentations can provide high-efficiency concentration of hard x-ray photons, leading significant improvement in many astrophysical applications.

X-RAY CHARACTERISTICS OF NGC 3516: A VIEW THROUGH THE COMPLEX ABSORBER

We consider new Suzaku data for NGC 3516 taken during 2009, along with other recent X-ray observations of the source. The cumulative characteristics of NGC 3516 cannot be explained without invoking changes in the line-of-sight absorption. Contrary to many other well-studied Seyfert galaxies, NGC 3516 does not show a positive lag of hard X-ray photons relative to soft photons over the timescales sampled. In the context of reverberation models for the X-ray lags, the lack of such a signal in NGC 3516 is consistent with flux variations being dominated by absorption changes. The lack of any reverberation signal in such a highly variable source disfavors intrinsic continuum variability in this case. Instead, the colorless flux variations observed at high flux states for NGC 3516 are suggested to be a consequence of Compton-thick clumps of gas crossing the line-of-sight.

H2 マイクロサテライト用無香料カルマンフィルタに基づくロバストな姿勢決定アルゴリズム(超小型衛星(2))

Technology demonstration satellite Earth Observatory - the TSUBAME has two main mission: Visible Earth observation; Measurement of polarization of hard X-ray photons from gamma-ray bursts (GRB). Attitude Determination System (ADS) of TSUBAME has the following sensors: Magnetometers (TAMs), Solar Sensors, MEMS gyro, Star Trackers, Fiber Optic Gyro (FOG), GPS receiver. To ensure satellite survival during each mission only several types of sensor will be used in order to minimize power consumption. This paper presents a robust algorithm using TAM and MEMS gyro sensors based on Unscented Kalman Filter (UKF) where both the three-axis attitude and gyro sensor biases are estimated. This algorithm will be used during sun pointing mode because of small power consumption of TAMs and MEMS gyro sensors. Numerical simulation example is given to certify the proposed algorithm and its estimation accuracy.

The effect of energetic particle beams on the chromospheric emission of the 2004 July 25 flare

In this paper the role of particle beams in the generation of a close spatial and temporal correlation between hard X-ray (HXR) energy and Hα line emission bursts in the solar flare of 2004 July 25 is discussed. The light curves in the HXR emission and Hα line reveal that the pre-flare and main flare events are correlated with the variations of line-of-sight (LOS) magnetic flux. The HXR emission shows three main bursts during the main flare phase, which are accompanied by Hα intensity increases. The latter appear in 10 locations (kernels) at different times in succession; the kernel locations are associated with strong magnetic sources situated on the opposite side from the magnetic neutral line (MNL). The appearance of Hα kernels in the pre-flare event and those at the start of the main event ia correlated very closely (within a few seconds) with the HXR emission observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) (HXR+Hα kernels), while the appearance of some others, not associated with HXR emission, was delayed by tens of seconds. Electron-beam parameters were derived from the RHESSI spectra in which the observed HXR photon flux was corrected for the self-induced electric field effect. Possible implications of this electric field on the production of transient magnetic fields observed during the flare are discussed. The Hα emission observed during the first burst was simulated in a hydrodynamic atmosphere for 5 levels plus a continuum hydrogen atom with the full non-local thermodynamic equilibrium (non-LTE) approach combining radiative, thermal and non-thermal excitation and ionization by an electron beam with the derived parameters. The simulated temporal profiles of Hα emission produced by non-thermal hydrogen excitation revealed a very good fit to the observed ones in the HXR+Hα kernels and 10–20 s delays in the other kernels. This allows us to speculate that Hα emission is caused mainly by electrons in the HXR+Hα kernels and mainly by protons in the others.

Coulomb explosion imaging of bromobenzene and bromophenol molecules following Br K-shell ionization

We have performed multiple-ion coincidence momentum imaging measurements for bromobenzene and bromophenol molecules irradiated by hard x-ray photons at Br K-shell edge. Dominant fragment ions were singly charged monatomic ions H+, C+, O+ and Br+. This indicates that parent molecules became highly charged through Auger cascade of Br core shell ionization. From an analysis of momentum vectors of ions, we found that the ejection directions of fragment ions strongly reflected the molecular structure of the neutral state. We can reproduce experimental results well by the trajectory analysis of fragment ions based on a Coulomb explosion model. This result shows that hard x-ray radiation enables us to apply Coulomb explosion imaging even for complex molecules such as benzene molecules.

Development of the small satellite “Tsubame”

Tsubame is a university-built small satellite mission to measure polarization of hard X-ray photons (30–200 keV) from gamma-ray bursts (GRB) using azimuthal angle anisotropy of Compton-scattered photons. Polarimetry in the hard X-ray and soft gamma-ray band should play a crucial role in understanding of high energy emission mechanisms, the distribution of magnetic fields and radiation fields of gamma-ray bursts. Tsubame has two instruments: the Wide-field Bust Monitor (WBM) and the Hard X-ray Compton Polarimeter (HXCP). The WBM detects a burst and determines on board the direction of the burst occurrence with an accuracy of 10°. The spacecraft is then slewed to point the GRB within 15 s from the WBM trigger using the Control Moment Gyro (CMG), a high speed attitude control device. HXCP will measure the polarized X-ray photons from the GRB while the spacecraft spins slowly around the bore sight. In this paper, we present an overview of the Tsubame mission, the results of a test experiment for HXCP using a polarized hard X-ray beam, and its comparison with a Monte Carlo simulation.

RELATIVISTIC ACCRETION MEDIATED BY TURBULENT COMPTONIZATION

Black hole and neutron star accretion flows display unusually high levels of hard coronal emission in comparison to all other optically thick, gravitationally bound, turbulent astrophysical systems. Since these flows sit in deep relativistic gravitational potentials, their random bulk motions approach the speed of light, therefore allowing turbulent Comptonization to be an important effect. We show that the inevitable production of hard X-ray photons results from turbulent Comptonization in the limit where the turbulence is trans-sonic and the accretion power approaches the Eddington Limit. In this regime, the turbulent Compton y-parameter approaches unity and the turbulent Compton temperature is a significant fraction of the electron rest mass energy, in agreement with the observed phenomena.

StrongK-edge Magnetic Circular Dichroism Observed in Photon-in–Photon-out Spectroscopy

A large enhancement of the x-ray magnetic circular dichroism is observed at the iron K absorption preedge of magnetite. This is achieved by performing resonant inelastic x-ray scattering (RIXS) experiments with a 2p hole in the final state of the second-order optical process. We measured and calculated the full 1s2p RIXS planes for opposite helicities of the incoming circularly polarized x rays. The crystal field multiplet calculations show that the enhancement arises from 2p-3d Coulomb repulsions and 2p and 3d spin-orbit coupling. The observed magnitude of the RIXS magnetic circular dichroism effect is ∼16%. This opens up new opportunities for a broad range of research fields allowing for truly bulk-sensitive, element-, and site-selective measurements of 3d transition metal magnetic moments and their ordering using hard x-ray photons.

The Spectral Features of Disk and Corona with Mass Evaporation in the Low/Hard State

Abstract We investigate the spectral features of accretion flows composed of an outer cool, optically thick disk and inner hot, optically thin, advection dominated accretion flows (ADAF) within the framework of disk and corona with mass evaporation (Liu et al. 2002a, ApJ, 575, 117). In this work, both the magnetic field and Compton scattering of soft photons from the disk by electrons in the corona are included to calculate the evaporation rates at different distances. The disk is truncated at the distance where the evaporation rate equals to the accretion rate [$\dot m_{\rm evap}$($r_{\rm tr}$) $= \dot m$]. For a series of accretion rates, the corresponding truncation radii are calculated out, with which we are able to calculate the emergent spectra from the inner ADAF $+$ outer disk $+$ corona. At very low accretion rates, the spectra are similar to that of a pure ADAF because the disk is truncated at large distances. The disk component becomes important at high accretion rates since the truncation occurs at small distances. An anti-correlation between the Eddington ratio, $\xi \equiv L_{0.5-25 \ {\rm keV}}/L_{\rm Edd}$, and the hard X-ray photon index, $\Gamma_{3-25 \ {\rm keV}}$, in low/hard states is predicted by the model. Comparing the theoretical results with observations, we find that our model can reproduce the anti-correlation between the Eddington ratio, $\xi$, and the hard X-ray photon index observed for the X-ray binary XTE J1118$+$480.

A bi-prism interferometer for hard X-ray photons

Micro-fabricated bi-prisms have been used to create an interference pattern from an incident hard X-ray beam, and the intensity of the pattern probed with fluorescence from a 30 nm-thick metal film. Maximum fringe visibility exceeded 0.9 owing to the nano-sized probe and the choice of single-crystal prism material. A full near-field analysis is necessary to describe the fringe field intensities, and the transverse coherence lengths were extracted at APS beamline 8-ID-I. It is also shown that the maximum number of fringes is dependent only on the complex refractive index of the prism material.

A COMPARISON OF HARD X-RAY PHOTON INDICES AND IRON Kα EMISSION LINES IN X-RAY LUMINOUS NARROW- AND BROAD-LINE SEYFERT 1 GALAXIES

We use publicly available XMM-Newton data to systematically compare the hard X-ray photon indices, $\Gamma_{\rm 2-10\ keV}$ and the iron K$\alpha$ emission lines of narrow-line (NL) and broad-line Seyfert 1 (BLS1) galaxies. We compile a flux-limited ($f_{\rm 2-10\ keV} \geq 1 \times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$) sample including 114 radio-quiet objects, with the 2-10 keV luminosity ranging from 10$^{41}$ to 10$^{45}$ erg s$^{-1}$. Our main results are: 1) NLS1s and BLS1s show similar luminosity distributions; 2) The weighted mean of $\Gamma_{\rm 2-10\ keV}$ of NLS1s, BLS1s and the total sample is $2.04\pm0.04$, $1.74\pm0.02$, $1.84\pm0.02$, respectively; a significant anti-correlation between \ga and FWHMH$\beta$ suggests that $\Gamma_{\rm 2-10\ keV} > 2.0$ may be taken to indicate X-ray luminous NLS1 type; 3) The 6.4 keV narrow iron K$\alpha$ lines from NLS1s are generally weaker than that from BLS1s; this would indicate a smaller covering factor of the dusty tori in NLS1s, if the line emission originates from the inner boundary region of the dusty torus in an AGN; 4) all the broadened iron K$\alpha$ lines with intrinsic width $\sigma>0.5$ keV correspond to FWHM\hb $\leq 4000 ~\kms$.

Hard X-ray and gamma-ray detector for ASTRO-H based on Si and CdTe imaging sensors

We have been developing a hard X-ray imager and soft gamma-ray detector as on board instruments of the ASTRO-H mission. The Hard X-ray Imager (HXI) is one of the three focal plane detectors of ASTRO-H, which is aimed to realize the focusing imaging of hard X-ray photons in combination with hard X-ray telescopes. By use of the hybrid structure composed of double-sided silicon strip detectors and a cadmium telluride strip detector, it fully covers the energy range up to 80keV with a high quantum efficiency. High spatial resolutions of 250μm pitch and energy resolutions of 1–2keV (FWMH) are at the same time achieved with low noise front-end ASICs. The Soft Gamma-ray Detector (SGD) is a novel and unique detector which is characterized by semiconductor Compton cameras surrounded by narrow field-of-view active shields, and covers a higher energy range (30–600keV) than that of HXI. It consists of four Compton Cameras constructed with many layers of Silicon and CdTe pad detectors. With its multi-layer structure and Compton reconstruction capability, in addition to the BGO active shields read by Avalanche photo-diodes, this detector will achieve an extremely high background rejection efficiency in the orbit. We report the current status of hardware development including the design requirement, expected performance, and technical readinesses of key technologies.