Showing papers on "Absorption (logic) published in 2015"

Compton-Thick accretion in the local universe

Abstract: Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes and to play an important role in shaping the observed spectrum of the cosmic X-ray background. Hard X-ray (E > 10 keV) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of the best ways to detect and identify Compton-thick (CT, $\mathrm{log}\;{N}_{{\rm{H}}}\geqslant 24$) active galactic nuclei (AGNs). In this letter we present the first results of the largest broadband (0.3–150 keV) X-ray spectral study of hard X-ray selected AGNs to date, focusing on the properties of heavily obscured sources. Our sample includes the 834 AGNs (728 non-blazar, average redshift z sime 0.055) reported in the 70-month catalog of the all-sky hard X-ray Swift/Burst Alert Monitor survey. We find 55 CT AGNs, which represent ${7.6}_{-2.1}^{+1.1}\%$ of our non-blazar sample. Of these, 26 are reported as candidate CT AGNs for the first time. We correct for selection bias and derive the intrinsic column density distribution of AGNs in the local universe in two different luminosity ranges. We find a significant decrease in the fraction of obscured Compton-thin AGNs for increasing luminosity, from 46 ± 3% (for $\mathrm{log}\;{L}_{14-195}$ = 40–43.7) to 39 ± 3% (for $\mathrm{log}\;{L}_{14-195}$ = 43.7–46). A similar trend is also found for CT AGNs. The intrinsic fraction of CT AGNs with $\mathrm{log}\;{N}_{{\rm{H}}}$ = 24–25 normalized to unity in the $\mathrm{log}\;{N}_{{\rm{H}}}$ = 20–25 range is 27 ± 4%, and is consistent with the observed value obtained for AGNs located within 20 Mpc.

The Identification of Z-dropouts in Pan-STARRS1: Three Quasars at 6.5< z< 6.7

Abstract: Luminous distant quasars are unique probes of the high-redshift intergalactic medium (IGM) and of the growth of massive galaxies and black holes in the early universe. Absorption due to neutral hydrogen in the IGM makes quasars beyond a redshift of $z\simeq 6.5$ very faint in the optical z band, thus locating quasars at higher redshifts requires large surveys that are sensitive above 1 micron. We report the discovery of three new $z\gt 6.5$ quasars, corresponding to an age of the universe of $\lt 850$ Myr, selected as z-band dropouts in the Pan-STARRS1 survey. This increases the number of known $z\gt 6.5$ quasars from four to seven. The quasars have redshifts of z = 6.50, 6.52, and 6.66, and include the brightest z-dropout quasar reported to date, PSO J036.5078 + 03.0498 with ${{M}_{1450}}=-27.4$. We obtained near-infrared spectroscopy for the quasars, and from the Mg ii line, we estimate that the central black holes have masses between 5 × 108 and 4 × 109 ${{M}_{\odot }}$ and are accreting close to the Eddington limit (${{L}_{{\rm Bol}}}/{{L}_{{\rm Edd}}}=0.13-1.2$). We investigate the ionized regions around the quasars and find near-zone radii of ${{R}_{{\rm NZ}}}=1.5-5.2$ proper Mpc, confirming the trend of decreasing near-zone sizes with increasing redshift found for quasars at $5.7\lt z\lt 6.4$. By combining RNZ of the PS1 quasars with those of $5.7\lt z\lt 7.1$ quasars in the literature, we derive a luminosity-corrected redshift evolution of ${{R}_{{\rm NZ},{\rm corrected}}}=(7.2\pm 0.2)-(6.1\pm 0.7)\times (z-6)$ Mpc. However, the large spread in RNZ in the new quasars implies a wide range in quasar ages and/or a large variation in the neutral hydrogen fraction along different lines of sight.

On the possible environmental effect in distributing heavy elements beyond individual gaseous haloes

Abstract: We present a study of extended galaxy halo gas through HI and OVI absorption over two decades in projected distance at $z\approx0.2$. The study is based on a sample of $95$ galaxies from a highly complete ($ > 80\%$) survey of faint galaxies ($L > 0.1L_*$) with archival quasar absorption spectra and $53$ galaxies from the literature. A clear anti-correlation is found between HI (OVI) column density and virial radius normalized projected distance, $d/R_{\rm h}$. Strong HI (OVI) absorption systems with column densities greater than $10^{14.0}$ ($10^{13.5}$) cm$^{-2}$ are found for $48$ of $54$ ($36$ of $42$) galaxies at $d R_{\rm h}$ compared to isolated galaxies ($\kappa_{\rm OVI}\approx0.13$ versus $0.04$) but no excess HI absorption. These findings suggest that environmental effects play a role in distributing heavy elements beyond the enriched gaseous halos of individual galaxies. Finally, we find that differential HI and OVI absorption between early- and late-type galaxies continues from $d < R_{\rm h}$ to $d\approx3\,R_{\rm h}$.

Scaling Relations Between Warm Galactic Outflows and Their Host Galaxies

Abstract: We report on a sample of 51 nearby, star-forming galaxies observed with the Cosmic Origin Spectrograph on the Hubble Space Telescope. We calculate Si II kinematics and densities arising from warm gas entrained in galactic outflows. We use multi-wavelength ancillary data to estimate stellar masses (M$_\ast$), star-formation rates (SFR), and morphologies. We derive significant correlations between outflow velocity and SFR$^{\sim 0.1}$, M$_\ast^{\sim 0.1}$ and v$_\text{circ}^{\sim 1/2}$. Some mergers drive outflows faster than these relations prescribe, launching the outflow faster than the escape velocity. Calculations of the mass outflow rate reveal strong scaling with SFR$^{\sim 1/2}$ and M$_\ast^{\sim 1/2}$. Additionally, mass-loading efficiency factors (mass outflow rate divided by SFR) scale approximately as M$_\ast^{-1/2}$. Both the outflow velocity and mass-loading scaling suggest that these outflows are powered by supernovae, with only 0.7% of the total supernovae energy converted into the kinetic energy of the warm outflow. Galaxies lose some gas if log(M$_\ast$/M$_\odot$) < $9.5$, while more massive galaxies retain all of their gas, unless they undergo a merger. This threshold for gas loss can explain the observed shape of the mass-metallicity relation.

Terahertz carpet cloak based on a ring resonator metasurface

Abstract: In this work we present the concept and design of an ultrathin (\ensuremath{\lambda}/22) terahertz (THz) unidirectional carpet cloak based on the local phase compensation approach enabled by gradient metasurfaces. A triangular surface bump with center height of 4.1 mm (1.1\ensuremath{\lambda}) and tilt angle of 20\ifmmode^\circ\else\textdegree\fi{} is covered with a metasurface composed of an array of suitably designed closed ring resonators with a transverse gradient of surface impedance. The ring resonators provide a wide range of control for the reflection phase with small absorption losses, enabling efficient phase manipulation along the edge of the bump. Our numerical results demonstrate a good performance of the designed cloak in both near field and far field, and the cloaked object mimics a flat ground plane within a broad range of incidence angles, over 35\ifmmode^\circ\else\textdegree\fi{} angular spectrum centered at 45\ifmmode^\circ\else\textdegree\fi{}. The presented cloak design can be applied in radar and antenna systems as a thin, lightweight, and easy to fabricate solution for radio and THz frequencies.

Spatially resolved eastward winds and rotation of HD 189733b

Abstract: We measure wind velocities on opposite sides of the hot Jupiter HD$\,$189733b by modeling sodium absorption in high-resolution HARPS transmission spectra. Our model implicitly accounts for the Rossiter-McLaughlin effect, which we show can explain the high wind velocities suggested by previous studies. Our results reveal a strong eastward motion of the atmosphere of HD$\,$189733b, with a redshift of $2.3^{+1.3}_{-1.5}$$\,$km$\,$s$^{-1}$ on the leading limb of the planet and a blueshift of $5.3^{+1.0}_{-1.4}$$\,$km$\,$s$^{-1}$ on the trailing limb. These velocities can be understood as a combination of tidally locked planetary rotation and an eastward equatorial jet; closely matching the predictions of atmospheric circulation models. Our results show that the sodium absorption of HD$\,$189733b is intrinsically velocity broadened and so previous studies of the average transmission spectrum are likely to have overestimated the role of pressure and thermal broadening.

A High-Resolution Hubble Space Telescope Study of Apparent Lyman Continuum Leakers at $z\sim3$

Abstract: We present $U_{336}V_{606}J_{125}H_{160}$ follow-up $HST$ observations of 16 $z\sim3$ candidate LyC emitters in the HS1549+1919 field. With these data, we obtain high spatial-resolution photometric redshifts of all sub-arcsecond components of the LyC candidates in order to eliminate foreground contamination and identify robust candidates for leaking LyC emission. Of the 16 candidates, we find one object with a robust LyC detection that is not due to foreground contamination. This object (MD5) resolves into two components; we refer to the LyC-emitting component as MD5b. MD5b has an observed 1500\AA\ to 900\AA\ flux-density ratio of $(F_{UV}/F_{LyC})_{obs}=4.0\pm2.0$, compatible with predictions from stellar population synthesis models. Assuming minimal IGM absorption, this ratio corresponds to a relative (absolute) escape fraction of $f_{esc,rel}^{MD5b}=75-100$% ($f_{esc,abs}^{MD5b}=14-19$%). The stellar population fit to MD5b indicates an age of $\lesssim50$Myr, which is in the youngest 10% of the $HST$ sample and the youngest third of typical $z\sim3$ Lyman break galaxies, and may be a contributing factor to its LyC detection. We obtain a revised, contamination-free estimate for the comoving specific ionizing emissivity at $z=2.85$, indicating (with large uncertainties) that star-forming galaxies provide roughly the same contribution as QSOs to the ionizing background at this redshift. Our results show that foreground contamination prevents ground-based LyC studies from obtaining a full understanding of LyC emission from $z\sim3$ star-forming galaxies. Future progress in direct LyC searches is contingent upon the elimination of foreground contaminants through high spatial-resolution observations, and upon acquisition of sufficiently deep LyC imaging to probe ionizing radiation in high-redshift galaxies.

Magnetically-Driven Accretion-Disk Winds and Ultra-Fast Outflows in PG1211+143

Abstract: We present a study of X-ray ionization of magnetohydrodynamic (MHD) accretion-disk winds in an effort to constrain the physics underlying the highly-ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in various sub-classes of Seyfert active galactic nuclei (AGNs). Our primary focus is to show that magnetically-driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of the present X-ray spectroscopic observations. Employing a stratified MHD wind launched across the entire AGN accretion disk, we calculate its X-ray ionization and the ensuing X-ray absorption line spectra. Assuming an appropriate ionizing AGN spectrum, we apply our MHD winds to model the absorption features in an {\it XMM-Newton}/EPIC spectrum of the narrow-line Seyfert, \pg. We find, through identifying the detected features with Fe K$\alpha$ transitions, that the absorber has a characteristic ionization parameter of $\log (\xi_c [erg~cm~s$^{-1}$]) \simeq 5-6$ and a column density on the order of $N_H \simeq 10^{23}$ cm$^{-2}$, outflowing at a characteristic velocity of $v_c/c \simeq 0.1-0.2$ (where $c$ is the speed of light). The best-fit model favors its radial location at $r_c \simeq 200 R_o$ ($R_o$ is the black hole innermost stable circular orbit), with an inner wind truncation radius at $R_{\rm t} \simeq 30 R_o$. The overall K-shell feature in the data is suggested to be dominated by \fexxv\ with very little contribution from \fexxvi\ and weakly-ionized iron, which is in a good agreement with a series of earlier analysis of the UFOs in various AGNs including \pg.

4.7-THz Local Oscillator for the GREAT Heterodyne Spectrometer on SOFIA

Abstract: The design and the performance of a 4.7-THz local oscillator (LO) for the GREAT (German REceiver for Astronomy at Terahertz frequencies) heterodyne spectrometer on SOFIA, the Stratospheric Observatory for Infrared Astronomy, are presented. The LO is based on a quantum-cascade laser, which is mounted in a compact mechanical cryocooler. The LO provides up to ${\hbox{150}}~\mu{\hbox{W}}$ output power into a nearly Gaussian shaped beam. It covers the frequency range from approximately $+{\hbox{2}}$ to $-{\hbox{4}}~{\hbox{GHz}}$ around the fine structure line of neutral atomic oxygen, OI, at 4.7448 THz. The LO has been successfully operated on SOFIA during six observation flights in May 2014 and January 2015.

Electronic structure, local magnetism, and spin-orbit effects of Ir(IV)-, Ir(V)-, and Ir(VI)-based compounds

Abstract: Element- and orbital-selective x-ray absorption and magnetic circular dichroism measurements are carried out to probe the electronic structure and magnetism of Ir $5d$ electronic states in double perovskite ${\mathrm{Sr}}_{2}{M\text{IrO}}_{6}$ ($M=\mathrm{Mg}$, Ca, Sc, Ti, Ni, Fe, Zn, In) and ${\mathrm{La}}_{2}{\mathrm{NiIrO}}_{6}$ compounds. All the studied systems present a significant influence of spin-orbit interactions in the electronic ground state. In addition, we find that the Ir $5d$ local magnetic moment shows different character depending on the oxidation state despite the net magnetization being similar for all the compounds. Ir carries an orbital contribution comparable to the spin contribution for ${\mathrm{Ir}}^{4+} (5{d}^{5})$ and ${\mathrm{Ir}}^{5+} (5{d}^{4})$ oxides, whereas the orbital contribution is quenched for ${\mathrm{Ir}}^{6+} (5{d}^{3})$ samples. Incorporation of a magnetic $3d$ atom allows getting insight into the magnetic coupling between $5d$ and $3d$ transition metals. Together with previous susceptibility and neutron diffraction measurements, the results indicate that Ir carries a significant local magnetic moment even in samples without a $3d$ metal. The size of the (small) net magnetization of these compounds is a result of predominant antiferromagnetic interactions between local moments coupled with structural details of each perovskite structure.

Constraining the radio-loud fraction of quasars at z > 5.5.

Abstract: Radio-loud active galactic nuclei at $z\sim 2-4$ are typically located in dense environments and their host galaxies are among the most massive systems at those redshifts, providing key insights for galaxy evolution. Finding radio-loud quasars at the highest accessible redshifts ($z\sim 6$) is important to the study of their properties and environments at even earlier cosmic time. They could also serve as background sources for radio surveys intended to study the intergalactic medium beyond the epoch of reionization in HI 21 cm absorption. Currently, only five radio-loud ($R={{f}_{ u ,5\,{\rm GHz}}}/{{f}_{ u ,4400\,\overset{\circ}{\rm A} }}\gt 10$) quasars are known at $z\sim 6$. In this paper we search for $5.5\lesssim z\lesssim 7.2$ quasars by cross–matching the optical Panoramic Survey Telescope & Rapid Response System 1 and radio Faint Images of the Radio Sky at Twenty cm surveys. The radio information allows identification of quasars missed by typical color-based selections. While we find no good $6.4\lesssim z\lesssim 7.2$ quasar candidates at the sensitivities of these surveys, we discover two new radio-loud quasars at $z\sim 6$. Furthermore, we identify two additional $z\sim 6$ radio-loud quasars that were not previously known to be radio-loud, nearly doubling the current $z\sim 6$ sample. We show the importance of having infrared photometry for $z\gt 5.5$ quasars to robustly classify them as radio-quiet or radio-loud. Based on this, we reclassify the quasar J0203+0012 (z = 5.72), previously considered radio-loud, to be radio-quiet. Using the available data in the literature, we constrain the radio-loud fraction of quasars at $z\sim 6$, using the Kaplan–Meier estimator, to be $8.1_{-3.2}^{+5.0}\%$. This result is consistent with there being no evolution of the radio-loud fraction with redshift, in contrast to what has been suggested by some studies at lower redshifts.

Effective Limiting Absorption Principles, and Applications

Abstract: The limiting absorption principle asserts that if H is a suitable Schrodinger operator, and f lives in a suitable weighted L2 space (namely \({H^{0, 1/2 + \sigma}}\) for some \({\sigma > 0}\)), then the functions \({R(\lambda + i \varepsilon) f := (H - \lambda - i \varepsilon)^{-1} f}\) converge in another weighted L2 space \({H^{0, -1/2 - \sigma}}\) to the unique solution u of the Helmholtz equation \({(H - \lambda) u = f}\) which obeys the Sommerfeld outgoing radiation condition. In this paper, we investigate more quantitative (or effective) versions of this principle, for the Schrodinger operator on asymptotically conic manifolds with short-range potentials, and in particular consider estimates of the form $$\| R(\lambda + i \varepsilon) f \|_{H^{0, -1/2 - \sigma}} \leq C(\lambda, H) \| f \|_{H^{0, 1/2 + \sigma}}.$$ We are particularly interested in the exact nature of the dependence of the constants \({C(\lambda, H)}\) on both \({\lambda}\) and H. It turns out that the answer to this question is quite subtle, with distinctions being made between low energies \({\lambda \ll 1}\), medium energies \({\lambda \sim 1}\), and large energies \({\lambda \gg 1}\), and there is also a non-trivial distinction between “qualitative” estimates on a single operator H (possibly obeying some spectral condition such as non-resonance, or a geometric condition such as non-trapping), and “quantitative” estimates (which hold uniformly for all operators H in a certain class). Using elementary methods (integration by parts and ODE techniques), we give some sharp answers to these questions. As applications of these estimates, we present a global-in-time local smoothing estimate and pointwise decay estimates for the associated time-dependent Schrodinger equation, as well as an integrated local energy decay estimate and pointwise decay estimates for solutions of the corresponding wave equation, under some additional assumptions on the operator H.

Shadow of a Colossus: A z=2.45 Galaxy Protocluster Detected in 3D Ly-a Forest Tomographic Mapping of the COSMOS Field

Abstract: Using moderate-resolution optical spectra from 58 background Lyman-break galaxies and quasars at $z\sim 2.3-3$ within a $11.5'\times13.5'$ area of the COSMOS field ($\sim 1200\,\mathrm{deg}^2$ projected area density or $\sim 2.4\,h^{-1}\,\mathrm{Mpc}$ mean transverse separation), we reconstruct a 3D tomographic map of the foreground Ly$\alpha$ forest absorption at $2.2

MApping the Most Massive Overdensities Through Hydrogen (MAMMOTH) I: Methodology

Abstract: Modern cosmology predicts that a galaxy overdensity is associated to a large reservoir of the intergalactic gas, which can be traced by the Ly$\alpha$ forest absorption. We have undertaken a systematic study of the relation between Coherently Strong intergalactic Ly$\alpha$ Absorption systems (CoSLAs), which have highest optical depth ($\tau$) in $\tau$ distribution, and mass overdensities on the scales of $\sim$ 10 - 20 $h^{-1}$ comoving Mpc. On such large scales, our cosmological simulations show a strong correlation between the effective optical depth ($\tau_{\rm{eff}}$) of the CoSLAs and the 3-D mass overdensities. In moderate signal-to-noise spectra, however, the profiles of CoSLAs can be confused with high column density absorbers. For $z>2.6$, where the corresponding Ly$\beta$ is redshifted to the optical, we have developed the technique to differentiate between these two alternatives. We have applied this technique to SDSS-III quasar survey at $z = 2.6$ - 3.3, and we present a sample of five CoSLA candidates with $\tau_{\rm{eff}}$ on 15 $h^{-1}$ Mpc greater than $4.5\times$ the mean optical depth. At lower redshifts of $z (1\ h^{-1}$ Gpc)$^3$. In addition, systems traced by CoSLAs will build a uniform sample of the most massive overdensities at $z > 2$ to constrain the models of structure formation, and offer a unique laboratory to study the interactions between galaxy overdensities and the intergalactic medium.

Searching for MeV-scale gauge bosons with IceCube

Abstract: Light gauge bosons can lead to resonant interactions between high-energy astrophysical neutrinos and the cosmic neutrino background. We study this possibility in detail, considering the ability of IceCube to probe such scenarios. We find the most dramatic effects in models with a very light ${Z}^{\ensuremath{'}}$ (${m}_{{Z}^{\ensuremath{'}}}\ensuremath{\lesssim}10\text{ }\text{ }\mathrm{MeV}$), which can induce a significant absorption feature at ${E}_{\ensuremath{ u}}\ensuremath{\sim}5--10\text{ }\text{ }\mathrm{TeV}\ifmmode\times\else\texttimes\fi{}({m}_{{Z}^{\ensuremath{'}}}/\mathrm{MeV}{)}^{2}$. In the case of the inverted hierarchy and a small sum of neutrino masses, such a light ${Z}^{\ensuremath{'}}$ can result in a broad and deep spectral feature at $\ensuremath{\sim}0.1--10\text{ }\text{ }\mathrm{PeV}\ifmmode\times\else\texttimes\fi{}({m}_{{Z}^{\ensuremath{'}}}/\mathrm{MeV}{)}^{2}$. Current IceCube data already excludes this case for a ${Z}^{\ensuremath{'}}$ lighter than a few MeV and couplings greater than $g\ensuremath{\sim}1{0}^{\ensuremath{-}4}$. We emphasize that the ratio of neutrino flavors observed by IceCube can be used to further increase their sensitivity to ${Z}^{\ensuremath{'}}$ models and to other exotic physics scenarios.

Collective excitation interferometry with a toroidal Bose-Einstein condensate

Abstract: The precision of most compact inertial sensing schemes using trapped- and guided-atom interferometers has been limited by uncontrolled phase errors caused by trapping potentials and interactions. Here we propose an acoustic interferometer that uses sound waves in a toroidal Bose-Einstein condensate to measure rotation, and we demonstrate experimentally several key aspects of this type of interferometer. We use spatially patterned light beams to excite counterpropagating sound waves within the condensate and use in situ absorption imaging to characterize their evolution. We present an analysis technique by which we extract separately the oscillation frequencies of the standing-wave acoustic modes, the frequency splitting caused by static imperfections in the trapping potential, and the characteristic precession of the standing-wave pattern due to rotation. Supported by analytic and numerical calculations, we interpret the noise in our measurements, which is dominated by atom shot noise, in terms of rotation noise. While the noise of our acoustic interferometric sensor, at the level of $\ensuremath{\sim}\text{rad}\phantom{\rule{0.16em}{0ex}}{\text{s}}^{\ensuremath{-}1}/\sqrt{\text{Hz}}$, is high owing to rapid acoustic damping and the small radius of the trap, the proof-of-concept device does operate at the high densities and small volumes of trapped Bose-Einstein condensed gases.

Nonrelativistic Dynamics of the Amplitude (Higgs) Mode in Superconductors.

Abstract: Despite the formal analogy with the Higgs particle, the amplitude fluctuations of the order parameter in weakly coupled superconductors do not identify a real mode with a Lorentz-invariant dynamics. Indeed, its resonance occurs at 2Δ_{0}, which coincides with the threshold 2E_{gap} for quasiparticle excitations that spoil any relativistic dynamics. Here we investigate the fate of the Higgs mode in the unconventional case where 2E_{gap} becomes larger than 2Δ_{0}, as due to strong coupling or strong disorder. We show that also in this situation, the amplitude fluctuations never identify a real mode at 2Δ_{0}, since such a "bosonic" limit is always reached via strong mixing with the phase fluctuations, which dominate the low-energy part of the spectrum. Our results have direct implications for the interpretation of the subgap optical absorption in disordered superconductors.

Radio and X-rays From SN 2013df Enlighten Progenitors of Type IIb Supernovae

Abstract: We present radio and X-ray observations of the nearby Type IIb Supernova 2013df in NGC4414 from 10 to 250 days after the explosion. The radio emission showed a peculiar soft-to-hard spectral evolution. We present a model in which inverse Compton cooling of synchrotron emitting electrons can account for the observed spectral and light curve evolution. A significant mass loss rate, $\dot{M} \approx 8 \times 10^{-5}\,\rm M_{\odot}/yr$ for a wind velocity of 10 km/s, is estimated from the detailed modeling of radio and X-ray emission, which are primarily due to synchrotron and bremsstrahlung, respectively. We show that SN 2013df is similar to SN 1993J in various ways. The shock wave speed of SN 2013df was found to be average among the radio supernovae; $v_{sh}/c \sim 0.07$. We did not find any significant deviation from smooth decline in the light curve of SN 2013df. One of the main results of our self-consistent multiband modeling is the significant deviation from energy equipartition between magnetic fields and relativistic electrons behind the shock. We estimate $\epsilon_{e} = 200 \epsilon_{B}$. In general for Type IIb SNe, we find that the presence of bright optical cooling envelope emission is linked with free-free radio absorption and bright thermal X-ray emission. This finding suggests that more extended progenitors, similar to that of SN 2013df, suffer from substantial mass loss in the years before the supernova.

Swift J1357.2−0933: a massive black hole in the Galactic thick disc

Abstract: Swift J1357.2-0933 is one of the shortest orbital period black hole X-ray transients (BHTs). It exhibited deep optical dips together with an extremely broad H$\alpha$ line during outburst. We present 10.4-m GTC time-resolved spectroscopy during quiescence searching for donor star absorption features. The large contribution of the accretion flow to the total luminosity prevents the direct detection of the companion. Nevertheless, we constrain the non-stellar contribution to be larger than $\sim 80\%$ of the total optical light, which sets new lower limits to the distance ($d > 2.29\, \rm{kpc}$) and the height over the Galactic plane ($z>1.75\, \rm{kpc}$). This places the system in the galactic thick disc. We measure a modulation in the centroid of the H$\alpha$ line with a period of $P=0.11\pm0.04\, \rm{d}$ which, combined with the recently presented FWHM-$K_2$ correlation, results in a massive black hole ($M_1>9.3 \, \rm{M_\odot}$) and a $\sim$ M2V companion star ($M_2\sim 0.4\, \rm{M_\odot}$). We also present further evidence supporting a very high orbital inclination ($i\gtrsim 80^\circ$).

The Keck + Magellan Survey for Lyman limit absorption. III. Sample definition and column density measurements.

Abstract: We present an absorption-line survey of optically thick gas clouds—Lyman Limit Systems (LLSs)—observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen ${N}_{{\rm{H}}\;{\rm{I}}}$ and associated metal-line transitions for 157 LLSs at ${z}_{\mathrm{LLS}}=1.76-4.39$ restricted to ${10}^{17.3}\;{\mathrm{cm}}^{-2}\leqslant {N}_{{\rm{H}}\;{\rm{I}}}\lt {10}^{20.3}\;{\mathrm{cm}}^{-2}.$ An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing ${N}_{{\rm{H}}\;{\rm{I}}}$ and that the majority of LLSs are highly ionized, confirming previous expectations. The Si+/H0 ratio spans nearly four orders of magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by $z\sim 3,$ nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (≈5%–10%) that may have super-solar abundances. High Si+/Fe+ ratios suggest an α-enhanced medium, whereas the Si+/C+ ratios do not exhibit the super-solar enhancement inferred previously for the Lyα forest.

First results from the virial survey: The stellar content of UVJ-selected quiescent galaxies at 1.5 < z < 2 from KMOS

Abstract: We investigate the stellar populations of 25 massive galaxies (${\rm log} [{{M}_{*}}/{{M}_{\odot }}]\geqslant 10.9$) at $1.5\lt z\lt 2$ using data obtained with the K-band Multi-Object Spectrograph (KMOS) on the ESO VLT. Targets were selected to be quiescent based on their broadband colors and redshifts using data from the 3D-HST grism survey. The mean redshift of our sample is $\bar{z}=1.75$, where KMOS YJ-band data probe age- and metallicity-sensitive absorption features in the rest-frame optical, including the G-band, Fe i, and high-order Balmer lines. Fitting simple stellar population models to a stack of our KMOS spectra, we derive a mean age of $1.03_{-0.08}^{+0.13}$ Gyr. We confirm previous results suggesting a correlation between color and age for quiescent galaxies, finding mean ages of $1.22_{-0.19}^{+0.56}$ Gyr and $0.85_{-0.05}^{+0.08}$ Gyr for the reddest and bluest galaxies in our sample. Combining our KMOS measurements with those obtained from previous studies at $0.2\lt z\lt 2$ we find evidence for a 2–3 Gyr spread in the formation epoch of massive galaxies. At $z\lt 1$ the measured stellar ages are consistent with passive evolution, while at $1\lt z\lesssim 2$ they appear to saturate at ~1 Gyr, which likely reflects changing demographics of the (mean) progenitor population. By comparing to star formation histories inferred for "normal" star-forming galaxies, we show that the timescales required to form massive galaxies at $z\gtrsim 1.5$ are consistent with the enhanced α-element abundances found in massive local early-type galaxies.

TDLAS-based NH3 mole fraction measurement for exhaust diagnostics during selective catalytic reduction using a fiber-coupled 2.2-µm DFB diode laser

Abstract: A new developed tunable diode laser spectrometer for the measurement of ammonia (NH3) mole fractions in exhaust gas matrices with strong CO2 and H2O background at temperatures up to 800 K is presented. In situ diagnostics in harsh exhaust environments during SCR after treatment are enabled by the use of ammonia transitions in the ν2 + ν3 near-infrared band around 2300 nm. Therefore, three lines have been selected, coinciding near 2200.5 nm (4544.5 cm−1) with rather weak temperature dependency and minimal interference with CO2 and H2O. A fiber-coupled 2.2-μm distributed feedback laser diode was used and attached to the hot gas flow utilizing adjustable gas tight high-temperature fiber ports. The spectrometer spans four coplanar optical channels across the measurement plane and simultaneously detects the direct absorption signal via a fiber-coupled detector unit. An exhaust simulation test rig was used to characterize the spectrometer’s performance in ammonia-doped hot gas environments. We achieved a temporal resolution of 13 Hz and temperature-dependent precisions of NH3 mole fraction ranging from 50 to 70 ppmV. There the spectrometer achieved normalized ammonia detection limits of 7–10 $${\text{ppm}}_{\text{V}}\cdot{\text{m}}$$ and 2–3 $${\text{ppm}}_{\text{V}}\cdot{\text{m}}/\sqrt{\text{Hz}}$$ .

Vortex-assisted mechanism of photon counting in a superconducting nanowire single-photon detector revealed by external magnetic field

Abstract: We use an external magnetic field to probe the detection mechanism of a superconducting nanowire single-photon detector We argue that the hot belt model (which assumes partial suppression of the superconducting order parameter $\mathrm{\ensuremath{\Delta}}$ across the whole width of the superconducting nanowire after absorption of the photon) does not explain observed weak-field dependence of the photon count rate (PCR) for photons with $\ensuremath{\lambda}=450\phantom{\rule{4pt}{0ex}}\mathrm{nm}$ and noticeable decrease of PCR (with increasing the magnetic field) in a range of the currents for photons with wavelengths $\ensuremath{\lambda}=450--1200\phantom{\rule{4pt}{0ex}}\mathrm{nm}$ Found experimental results for all studied wavelengths can be explained by the vortex hot spot model (which assumes partial suppression of $\mathrm{\ensuremath{\Delta}}$ in the area with size smaller than the width of the nanowire) if one takes into account nucleation and entrance of the vortices to the photon induced hot spot and their pinning by the hot spot with relatively large size and strongly suppressed $\mathrm{\ensuremath{\Delta}}$

High-Power Broadly Tunable 3- $\mu\hbox{m}$ Fiber Laser for the Measurement of Optical Fiber Loss

Abstract: We demonstrate a $\hbox{Ho}^{3+}$ , $\hbox{Pr}^{3+} $ co-doped fluoride fiber laser that produces an output power of 7.2 W, a 150-nm tuning range, and a narrow linewidth of $ nm using a power-scalable $\hbox{Yb}^{3+} $ fiber-laser-pumped 1150-nm Raman fiber laser as the excitation source. The maximum output power is achieved at a slope efficiency of 29%, with wavelength tuning between 2825 and 2975 nm that overlaps with the OH absorption region in many mid-infrared transparent glasses. The system is used to provide accurate measurements of the background scattering loss and the degree of water incorporation in the rare-earth-doped core of commercial double-clad fluoride fiber; the high power allows accurate core loss measurements for quite lossy fibers. Furthermore, the spectral location of the OH absorption feature was observed to be dependent on glass composition shifting from 2872 nm in undoped ZBLAN to 2896 nm upon $\hbox{Ho}^{3+}\hbox{Pr}^{3+}$ co-doping, whereas $\hbox{As}_{2}\hbox{S}_{3} $ glass was observed to have an OH peak location of 2911 nm.

Revisiting the measurement of the spin relaxation time in graphene-based devices

Abstract: A long spin relaxation time $({\ensuremath{\tau}}_{\mathrm{sf}})$ is the key for the applications of graphene to spintronics but the experimental values of ${\ensuremath{\tau}}_{\mathrm{sf}}$ have been generally much shorter than expected We show that the usual determination by the Hanle method underestimates ${\ensuremath{\tau}}_{\mathrm{sf}}$ if proper account of the spin absorption by contacts is lacking By revisiting series of experimental results and taking into account the spin absorption, we find that the corrected ${\ensuremath{\tau}}_{\mathrm{sf}}$ are longer and, for series of graphene samples of the same fabrication, less dispersed, which leads to a more unified picture of the ${\ensuremath{\tau}}_{\mathrm{sf}}$

Determining the covering factor of Compton-thick active galactic nuclei with NuSTAR

Abstract: The covering factor of Compton-thick obscuring material associated with the torus in active galactic nuclei (AGN) is at present best understood through the fraction of sources exhibiting Compton-thick absorption along the line of sight ($N_{H}>1.5\times10^{24}$ cm$^{-2}$) in the X-ray band, which reveals the average covering factor. Determining this Compton-thick fraction is difficult however, due to the extreme obscuration. With its spectral coverage at hard X-rays ($>$10 keV), NuSTAR is sensitive to the AGN covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a spectral analysis of 10 AGN observed with NuSTAR where the obscuring medium is optically thick to Compton scattering, so called Compton-thick (CT) AGN. We use the torus models of Brightman & Nandra which predict the X-ray spectrum from reprocessing in a torus and include the torus opening angle as a free parameter and aim to determine the covering factor of the Compton-thick gas in these sources individually. Across the sample we find mild to heavy Compton-thick columns, with $N_{H}$ measured from $10^{24}-10^{26}$ cm$^{-2}$, and a wide range of covering factors, where individual measurements range from 0.2-0.9. We find that the covering factor, $f_{c}$, is a strongly decreasing function of the intrinsic 2-10 keV luminosity, $L_{X}$, where $f_{c}=(-0.41\pm0.13)$log$_{10}$($L_{X}$/erg s$^{-1}$)$+18.31\pm5.33$, across more than two orders of magnitude in $L_{X}$ (10$^{41.5}-10^{44}$ erg s$^{-1}$). The covering factors measured here agree well with the obscured fraction as a function of $L_{X}$ as determined by studies of local AGN with $L_{X}>10^{42.5}$ erg s$^{-1}$.

Synchrotron spectral index and interstellar medium densities of star-forming galaxies

Abstract: The spectral index of synchrotron emission is an important parameter in understanding the properties of cosmic ray electrons (CREs) and the interstellar medium (ISM). We determine the synchrotron spectral index ($\alpha_{\rm nt}$) of four nearby star-forming galaxies, namely NGC 4736, NGC 5055, NGC 5236 and NGC 6946 at sub-kpc linear scales. The $\alpha_{\rm nt}$ was determined between 0.33 and 1.4 GHz for all the galaxies. We find the spectral index to be flatter ($\gtrsim -0.7$) in regions with total neutral (atomic + molecular) gas surface density, $\Sigma_{\rm gas} \gtrsim \rm 50~M_\odot pc^{-2}$, typically in the arms and inner parts of the galaxies. In regions with $\Sigma_{\rm gas} \lesssim \rm 50~M_\odot pc^{-2}$, especially in the interarm and outer regions of the galaxies, the spectral index steepens sharply to $<-1.0$. The flattening of $\alpha_{\rm nt}$ is unlikely to be caused due to thermal free--free absorption at 0.33 GHz. Our result is consistent with the scenario where the CREs emitting at frequencies below $\sim0.3$ GHz are dominated by bremsstrahlung and/or ionization losses. For denser medium ($\Sigma_{\rm gas} \gtrsim \rm 200~M_\odot pc^{-2}$), having strong magnetic fields ($\sim 30~\mu$G), $\alpha_{\rm nt}$ is seen to be flatter than $-0.5$, perhaps caused due to ionization losses. We find that, due to the clumpy nature of the ISM, such dense regions cover only a small fraction of the galaxy ($\lesssim5$ percent). Thus, the galaxy-integrated spectrum may not show indication of such loss mechanisms and remain a power-law over a wide range of radio frequencies (between $\sim 0.1$ to 10 GHz).

Defect complexes in congruentLiNbO3and their optical signatures

Abstract: The structure and stability of defect clusters in ${\mathrm{LiNbO}}_{3}$, as well as their influence on the linear and nonlinear optical susceptibilities, are calculated within density functional theory (DFT) using semilocal and hybrid exchange-correlation functionals. In particular, the complexes modeling the Li shortage during the crystal growth, the Li-vacancy model and the Nb-vacancy model, are examined in detail. It is found that clustering significantly decreases the formation energies of all considered defects with respect to the dilute limit. The Li-vacancy model is energetically preferred with respect to the total formation energy, while the Nb-vacancy model has the lowest formation energy per single point defect. The independent-particle approximation based on the hybrid DFT electronic structure describes the ${\mathrm{LiNbO}}_{3}$ optical response much better than semilocal DFT. A further improvement between the calculated optical absorption and second-harmonic generation spectra with experiment is achieved if the calculations take defect complexes into account. Nb antisite polarons give rise to optical absorption within the band gap.

Thermal noise reduction and absorption optimization via multimaterial coatings

Abstract: Future gravitational wave detectors (GWDs) such as Advanced LIGO upgrades and the Einstein Telescope are planned to operate at cryogenic temperatures using crystalline silicon (cSi) test-mass mirrors at an operation wavelength of 1550 nm. The reduction in temperature in principle provides a direct reduction in coating thermal noise, but the presently used coating stacks which are composed of silica (${\mathrm{SiO}}_{2}$) and tantala (${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$) show cryogenic loss peaks which results in less thermal noise improvement than might be expected. Due to low mechanical loss at low temperature amorphous silicon (aSi) is a very promising candidate material for dielectric mirror coatings and could replace ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$. Unfortunately, such an $\mathrm{aSi}/{\mathrm{SiO}}_{2}$ coating is not suitable for use in GWDs due to high optical absorption in aSi coatings. We explore the use of a three material based coating stack. In this multimaterial design the low absorbing ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$ in the outermost coating layers significantly reduces the incident light power, while aSi is used only in the lower bilayers to maintain low optical absorption. Such a coating design would enable a reduction of Brownian thermal noise by 25%. We show experimentally that an optical absorption of only $(5.3\ifmmode\pm\else\textpm\fi{}0.4)\text{ }\text{ }\mathrm{ppm}$ at 1550 nm should be achievable.

Site-specific magnetism of half-metallic MN 2 Ru x Ga thin films determined by x-ray absorption spectroscopy

Abstract: The site-specific magnetic properties of thin films of the Heusler compound ${\text{Mn}}_{2}{\text{Ru}}_{x}\text{Ga}$, $0.6lxl1.0$, are studied using x-ray absorption and dichroism spectroscopy. There is evidence of half metallicity up to $x=0.7$, and compensation of the Mn $4a$ and $4c$ moments in this range, leading to a zero-moment half metal. We also also discuss the effect of substrate-induced strain on the magnetic properties. By tuning the biaxial strain, simultaneous perfect magnetic compensation and half-metallic character is achievable at, below, or above room temperature.