Small Solid Angle Research Articles

Fe-K LINE PROBING OF MATERIAL AROUND THE ACTIVE GALACTIC NUCLEUS CENTRAL ENGINE WITHSUZAKU

We systematically analyzed the high-quality Suzaku data of 88 Seyfert galaxies. We obtained a clear relation between the absorption column density and the equivalent width of the 6.4 keV line above 10$^{23}$ cm$^{-2}$, suggesting a wide-ranging column density of $10^{23-24.5}$ cm$^{-2}$ with a similar solid and a Fe abundance of 0.7--1.3 solar for Seyfert 2 galaxies. The EW of the 6.4 keV line for Seyfert 1 galaxies are typically 40--120 eV, suggesting the existence of Compton-thick matter like the torus with a column density of $>10^{23}$ cm$^{-2}$ and a solid angle of $(0.15-0.4)*4pi$, and no difference of neutral matter is visible between Seyfert 1 and 2 galaxies. An absorber with a lower column density of $10^{21-23}$ cm$^{-2}$ for Compton-thin Seyfert 2 galaxies is suggested to be not a torus but an interstellar medium. These constraints can be understood by the fact that the 6.4 keV line intensity ratio against the 10--50 keV flux is almost identical within a range of 2--3 in many Seyfert galaxies. Interestingly, objects exist with a low EW, 10--30 eV, of the 6.4 keV line, suggesting that those torus subtends only a small solid angle of $<0.2*4pi$. Ionized Fe-K$\alpha$ emission or absorption lines are detected from several percents of AGNs. Considering the ionization state and equivalent width, emitters and absorbers of ionized Fe-K lines can be explained by the same origin, and highly ionized matter is located at the broad line region. The rapid increase in EW of the ionized Fe-K emission lines at $N_{H}>10^{23}$ cm$^{-2}$ is found, like that of the cold material. It is found that these features seem to change for brighter objects with more than several $10^{44}$ erg/s such that the Fe-K line features become weak. We discuss this feature, together with the torus structure.

Understanding reverberation lags in 1H0707-495

The first reverberation lag from the vicinity of a supermassive black hole was recently detected in the NLS1 galaxy 1H0707-495. We interpreted the lag as due to reflection from matter close to the black hole, within a few gravitational radii of the event horizon (an inner reflector). It has since been claimed by Miller et al. that the lag can be produced by more distant matter, at hundreds of gravitational radii (an outer reflector). Here, we critically explore their interpretation of the lag. The detailed energy dependence of the time lags between soft and hard energy bands is well modelled by an inner reflector using our previously published spectral model. A contrary claim by Miller et al. was obtained by not accounting for the blackbody component in the soft band. Soft lags can be produced by a large-scale outer reflector if several, implausible, conditions are met. An additional transfer function is required in the soft band corresponding to a region that is physically close to the continuum source, or lies close to our line of sight and subtends a small solid angle at the source, challenging the production of the observed spectrum. We show that the original inner reflector interpretation of reverberation very close to the black hole provides a self-consistent and robust model which explains the energy spectrum and timing properties, including the time delays, power spectra and the shape of the coherence function. Several of these properties are opposite to the predictions from a simple large-scale outer reflection model.

The deflection angle of a gravitational source with a global monopole in the strong field limit

We investigate the gravitational lensing effect in the strong field background around the Schwarzschild black hole with extremely small mass and solid deficit angle subject to the global monopole by means of the strong field limit issue. We obtain the angular position and magnification of the relativistic images and show that they relate to the global monopole parameter η. We discuss that with the increase of the parameter η, the minimum impact parameter um and angular separation s increase and the relative magnification r decreases. We also find that s grows extremely as the increasing parameter η becomes large enough. The deflection angle will become larger when the parameter η grows. The effect from the solid deficit angle is the dependence of angular position, angular separation, relative magnification and deflection angle on the parameter η, which may offer a way to characterize some possible distinct signatures of the Schwarzschild black hole with a solid deficit angle associated with the global monopole.

WIDE ANGLE X-RAY SKY MONITORING FOR CORROBORATING NON-ELECTROMAGNETIC COSMIC TRANSIENTS

Gravitational waves (GW) can be emitted from coalescing neutron star (NS) and black hole-neutron star (BH-NS) binaries, which are thought to be the sources of short hard gamma ray bursts (SHBs). The gamma ray fireballs seem to be beamed into a small solid angle and therefore only a fraction of detectable GW events is expected to be observationally coincident with SHBs. Similarly ultrahigh energy (UHE) neutrino signals associated with gamma ray bursts (GRBs) could fail to be corroborated by prompt gamma-ray emission if the latter is beamed in a narrower cone than the neutrinos. Alternative ways to corroborate non-electromagnetic signals from coalescing neutron stars are therefore all the more desirable. It is noted here that the extended X-ray tails (XRT) of SHBs are similar to X-ray flashes (XRFs), and that both can be attributed to an off-axis line of sight and thus span a larger solid angle than the hard emission. It is proposed that a higher fraction of detectable GW events may be coincident with XRF/XRT than with hard gamma-rays, thereby enhancing the possibility to detect it as a GW or neutrino source. Scattered gamma-rays, which may subtend a much larger solid angle that the primary gamma ray jet, are also candidates for corroborating non-electromagnetic signals.

Experimental determination of the 233U half-life

The half-life of 233U was determined by a specific activity method, in the frame of an international collaboration project of four metrology institutes. A purified, highly enriched 233U solution was prepared with certified concentration of uranium isotopes. The isotopic composition of the uranium material was determined by thermal ionization mass spectrometry. The ingrowth of daughter nuclides was calculated and confirmed by α-particle and γ-ray spectrometry measurements. Quantitative sources were prepared from aliquots of the 233U solution and their disintegration rate was determined by means of α-particle counting at a defined small solid angle, liquid-scintillation counting and 4π counting in a pressurized proportional counter and in a CsI(Tl) sandwich spectrometer. A half-life value of 1.5867 (14) × 105 a was obtained, in which the relative standard uncertainty amounts to 0.09%. The result is lower than the currently recommended value of 1.592 (2) × 105 a and a new best estimate of T1/2(233U) = 1.5903 (13) × 105 a was calculated from a partially weighted mean of a set of published data.

Theory of Compton scattering in ignited thermonuclear plasmas

Inertially confined, ignited thermonuclear deuterium-tritium plasmas will produce intense blackbody radiation at temperatures of T≳20 keV; it is shown that the injection of GeV electrons into the burning core can efficiently generate high-energy Compton scattering photons, as the high blackbody photon density alleviates the small interaction cross section. Moreover, it is shown that the spectrum scattered in a small solid angle can be remarkably monochromatic, due to kinematic pileup; peak brightness in excess of 1030 photons/(mm2mrad2 s 0.1% bandwidth) are predicted. These results are also discussed within the context of the Schwinger field and the Sunyaev-Zel'dovich effect.

Gamma-ray waveguides

We have developed an approach for gamma-ray optics using layered structures acting as planar waveguides. Experiments demonstrating channeling of 122keV gamma rays in two prototype waveguides validate the feasibility of this technology. Gamma-ray waveguides allow one to control the direction of radiation up to a few MeV. The waveguides are conceptually similar to polycapillary optics, but can function at higher gamma-ray energies. Optics comprised of these waveguides will be able to collect radiation from small solid angles or concentrate radiation into small area detectors. Gamma-ray waveguides may find applications in medical imaging and treatment, astrophysics, and homeland security.

Comment on elimination of polarization dependence from optical excitation functions

The measurement of optical excitation functions excited by electron impact is typically accomplished by recording atomic fluorescence emitted into a small solid angle perpendicular to the incident electron beam. This measured intensity is not proportional to the emission cross section because the fluorescence exhibits an angular distribution and polarization that varies with the energy of the exciting electrons. Typically, a polarizer is set at the “magic angle” (54.7°) with respect to the electron beam axis to remove this polarization dependence. The literature for the derivation of the magic angle value assumes the polarizing element is perfect. An expression for the angle that accounts for the use of a partial polarizer is presented.

Compton Scattering in Ignited Thermonuclear Plasmas

Inertially confined, ignited thermonuclear D-T plasmas will produce intense blackbody radiation at temperatures T greater, similar20 keV; it is shown that the injection of GeV electrons into the burning core can efficiently generate high-energy Compton scattering photons. Moreover, the spectrum scattered in a small solid angle can be remarkably monochromatic, due to kinematic pileup; a peak brightness in excess of 10;{30} photons/(mm(2) mrad(2) s 0.1% bandwidth) is predicted. These results are discussed within the context of the Schwinger field and the Sunyaev-Zel'dovich effect.

The Magnetar 1E 1547.0−5408: Radio Spectrum, Polarimetry, and Timing

We have investigated the radio emission from the anomalous X-ray pulsar 1E 1547.0-5408 (PSR J1550-5418) using the Parkes telescope and the Australia Telescope Compact Array. The flux density of the pulsar is roughly the same between 1.4 and 45 GHz, but shows time variability. The radiation is nearly 100% linearly polarized between frequencies of 45 and 3.2 GHz, but from 2.3 to 1.4 GHz it becomes increasingly more depolarized. The rotation measure of -1860 rad/m^2 is the largest for any known pulsar, and implies an average magnetic field strength along the line of sight of 2.7 microG. The pulse profiles are circularly polarized at all frequencies observed, more so at lower frequencies, at the ~15% level. The observed swing of the position angle of linear polarization as a function of pulse phase suggests that in this neutron star the rotation and magnetic axes are nearly aligned, and that its radio emission is only detectable within a small solid angle. Timing measurements indicate that the period derivative of this 2 s pulsar has increased by nearly 40% in a 6-month period. The flat spectrum and variability in flux density and pulse profiles are reminiscent of the properties of XTE J1810-197, the only other known radio-emitting magnetar, and are anomalous by comparison with those of ordinary radio pulsars.

Neutronic design and measured performance of the Low Energy Neutron Source (LENS) target moderator reflector assembly

The Low Energy Neutron Source (LENS) is an accelerator-based pulsed cold neutron facility under construction at the Indiana University Cyclotron Facility (IUCF). The idea behind LENS is to produce pulsed cold neutron beams starting with ∼ MeV neutrons from (p,n) reactions in Be which are moderated to meV energies and extracted from a small solid angle for use in neutron instruments which can operate efficiently with relatively broad ( ∼ 1 ms ) neutron pulse widths. Although the combination of the features and operating parameters of this source is unique at present, the neutronic design possesses several features similar to those envisioned for future neutron facilities such as long-pulsed spallation sources (LPSS) and very cold neutron (VCN) sources. We describe the underlying ideas and design details of the target/moderator/reflector system (TMR) and compare measurements of its brightness, energy spectrum, and emission time distribution under different moderator configurations with MCNP simulations. Brightness measurements using an ambient temperature water moderator agree with MCNP simulations within the 20% accuracy of the measurement. The measured neutron emission time distribution from a solid methane moderator is in agreement with simulation and the cold neutron flux is sufficient for neutron scattering studies of materials. We describe some possible modifications to the existing design which would increase the cold neutron brightness with negligible effect on the emission time distribution.

Studying High pT Muons in Cosmic-Ray Air Showers

Most cosmic-ray air shower arrays have focused on detecting electromagnetic shower particles and low energy muons. A few groups (most notably MACRO + EASTOP and SPASE + AMANDA) have studied the high energy muon component of showers. However, these experiments had small solid angles, and did not study muons far from the core. The IceTop + IceCube combination, with its 1 km 2 muon detection area can study muons far from the shower core. IceCube can measure their energy loss ( d E / d x ), and hence their energy. With the energy, and the known distribution of production heights, the transverse momentum ( p T ) spectrum of high p T muons can be determined. The production of these muons is calculable in perturbative QCD, so the measured muon spectra can be used to probe the composition of incident cosmic-rays.

A novel time‐of‐flight spectrometer for PAES

AbstractPositron annihilation induced Auger electron spectroscopy (PAES) uses the annihilation of a positron with an electron of the inner shell of atoms whereas X‐rays or high‐energy electrons initiate the ionisation in conventional AES. Advantages of PAES are the extremely high surface sensitivity and the higher signal to noise ratio. In order to benefit from PAES one has to use a low‐energy positron beam of high intensity, which is available at NEPOMUC at the new Munich research reactor FRM‐II. The energy of the Auger electrons is mostly analysed by hemispherical energy analysers. Due to their small solid angle (typically ≥0.1%) and the necessity to scan over certain energy ranges in ≥1eV steps one still needs several hours using an intense positron source like NEPOMUC (at the FRM‐II) or even weeks at the lab‐beam based on a beta‐emitter to obtain an Auger spectrum. For this reason, a novel time‐of‐flight spectrometer (TOF‐PAES) was developed, which efficiently collects the Auger electrons emitted in a solid angle of 2π around the sample, and hence reduces the measurement time to less than one hour. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

An investigation of sensitivity limits in PET scanners

Current systems for positron emission tomography (PET) generally cover a small solid angle which implies low sensitivity and therefore patient studies are relatively lengthy with acquisition comprising multiple bed positions. For cylindrical geometry, the axial field-of-view (FOV) may be increased by incorporating additional rings of block detectors in order to increase the solid angle coverage and hence the overall sensitivity. In this study we have taken that approach to the limit and studied an ultimate configuration with an axial extent up to 1 m or more. We have estimated the point source sensitivity and the absolute sensitivity (NEMA NU-2 2001). These sensitivity values can then be converted into count rates, for a particular phantom. A system comprising three rings of blocks based on the HIREZ block detector (Siemens Molecular Imaging) with 48 blocks/ring is taken as the starting point. Additional rings of blocks are then added. The diameter of the system for this study is 85.5 cm and the axial extent ranged from 16.4 cm, that of the current HIREZ system, up to over 3 m in order to obtain data points with a solid angle close to 4 π. In all calculations, the detectors were assumed to be lutetium oxyorthosilicate (LSO) with a crystal thickness of 2 cm. The calculated count rate values are based on actual experimental data from the Siemens HIREZ scanner and then scaled based on the ratio of the calculated absolute sensitivity to the measured HIREZ absolute sensitivity. The point source sensitivity is given by the solid angle, the square of the crystal sensitivity and the square of the detector packing fraction. The point source sensitivity as a function of the axial extent shows an exponential increase reaching a limiting value as the solid angle approaches 4 π. A system with 100 cm axial extent has a solid angle of ∼75% of 4 π.

Creation of high-energy phonons by four-phonon processes in anisotropic phonon systems of HeII

The problem of the creation of high-energy phonons (h-phonons) by a pulse of low-energy phonons (l-phonons) moving from a heater to a detector in superfluid helium is solved. The rate of h-phonon creation is obtained, and it is shown that the h-phonons created occupy a much smaller solid angle in momentum space than the l-phonons. An analytical expression for the creation rate of h-phonons, along the symmetry axis of a pulse, is derived. It allows us to get useful approximate analytical expressions for the creation rate of h-phonons. The time dependences of the parameters describing the l-phonon pulse are obtained. This shows that half of the initial energy of l-phonon pulse can be transferred into h-phonons. The results of the calculations are compared with experimental data, and we show that this theory explains a number of experimental results. The value of the momentum that separates the l- and h-phonon subsystems is found.

A new design of a bright cascaded arc light source: measurements and simulations

Profiling the arc channel of a cascaded arc into an hourglass-like shape results in an extremely high light output intensity (3.5 × 1012 Wm−2 m−1 sr−1 in the near-infrared) at an input power of 2.2 kW, a good stability (better than 5 × 10−4) and a small solid angle of the emitted light beam (Ω = 0.015 sr). These optical properties are advantageous for spectroscopic applications that require a high light intensity over a broad wavelength range in a small solid angle. The absolute light output is measured and is compared with a fast and flexible modelling scheme. These simulations are used to verify the arc performance and to guide arc design. The calculated emitted radiance at moderate arc input power agrees with the experiments within 30% for moderate input power.

Local Isoperimetric Inequalities for Sectors on Surfaces and Cones

On surfaces we give conditions under which the solution of a restricted local isoperimetric problem for sectors with small solid angle is the circular sector and we characterize these surfaces. Also we study this problem for general spherical cones on hypersurfaces in higher dimensional Riemannian manifolds.

Physical properties of Hickson compact groups and of the loose groups within which they are embedded

Using new data and an enlarged group sample we verify some of our previously published results and present a number of new facts that suggest that compact groups could be casual concentrations in prolate-like looser groups, and thus the nature of compact and ordinary poor groups is probably the same. To this end we used the Sloan Digital Sky Survey (SDSS) redshift catalogue to look for galaxies with accordant redshifts in the nearby environment (up to ∼2 Mpc) of 15 Hickson compact groups (HCG). We also used known member redshifts of looser groups in the environment of 7 other HCGs. From this sample of 22 HCGs we find that: (a) HCG's tend to be aligned with the overall galaxy distribution in their ∼1 Mpc environment; (b) the well-established orientation effect by which the group velocity dispersion σ v correlates with group axial ratio q is present and particularly strong also in the HCG + environment systems; (c) the velocity dispersion σ v of the HCG +environment systems as well as of ordinary poor groups, depends only weakly on the group richness, i.e. on the mass; (d) the mean absolute K-band magnitude of E/S0 galaxies in HCGs is similar to the corresponding one in ordinary poor groups and is brighter than that of isolated E/SO's, indicating that they were formed by the merging of two galaxies of similar luminosity; (e) the fraction of E/S0 galaxies in these HCGs depends, albeit weakly, on the group's richness and on σ v ; (f) the fraction of AGNs is similar in the HCGs and their close environment, while the fraction of starburst galaxies is significantly higher in the HCGs; (g) the fraction of active galaxies (AGNs and starbursts) is anti-correlated with the velocity dispersion of the HCG + environment systems. The combination of all the above facts constitutes a picture in which compact groups are condensations within looser prolate-like, elongated systems, and they appear to be compact when their member galaxies, moving in radial orbits along the group elongation, happen to come close to each other (in which case dynamical interactions among these galaxies become even more probable) or when the group is oriented close to the line of sight, so that many of its members are projected over a small solid angle. The probability of either case is small, so the number of CGs should be much smaller than that of ordinary groups, as observed. Furthermore, the observed fractions of early-type and active galaxies, as well as their correlations with the group velocity dispersion suggests a picture by which nuclear activity and galaxy transformation by merging is instigated by effective gravitational interactions in the low-velocity dispersion groups, which then dynamically evolve via virialization processes to higher velocity dispersion groups, which thus have a higher fraction of early-type galaxies.

Precise study of the final-state continua inLi8andB8decays

We studied \ensuremath{\beta}-delayed singles-\ensuremath{\alpha} spectra from $^{8}\mathrm{Li}$ and $^{8}\mathrm{B}$ decays with special emphasis on a careful calibration of the energy scale. $^{8}\mathrm{Li}$ and $^{8}\mathrm{B}$ activities were produced by $^{7}\mathrm{Li}$($d,p$) and $^{6}\mathrm{Li}$($^{3}\mathrm{He}$,$n$) reactions, respectively, and deposited in thin C foils. Delayed \ensuremath{\alpha}'s were counted in thin, cooled Si detectors with small solid angles to reduce summing with \ensuremath{\beta}'s. The energy scale and detector response were calibrated with spectroscopic grade radioactive sources. We extracted the $^{8}\mathrm{Li}$ and $^{8}\mathrm{B}$ final-state continuum shapes from our spectra by using $R$-matrix analyses that included effects of lepton-recoil broadening and detector response. Our results are in excellent agreement with a recent measurement using $^{8}\mathrm{B}$'s implanted in a Si counter and in good agreement with our reanalysis of the older Wilkinson-Alburger $^{8}\mathrm{Li}$ and $^{8}\mathrm{B}$ data, but disagree with a recent $^{8}\mathrm{B}$ experiment using a coincidence technique.

A cable transducer for measuring angular electron distributions at the output of high-power accelerators

A transducer for measuring angular distributions of pulsed electron beams extracted from high-power accelerators into air is described. The transducer is made of an PK75-9-13 radio-frequency cable and contains a collimator with a small solid angle (∼0.01 sr) and receiving electrode (cable conductor). By using a set of the transducers, the spatial-angular distribution of electrons in beams of ИГУР-3 and ЭМИР-М directaction accelerators at the All-Russia Research Institute of Technical Physics has been measured. The background radiation contribution to the measured signal is taken into account by using separate transducers in the same shot.