Viewing Angle Dependence Research Articles

Detectability of kilonovae in optical surveys: post-mortem examination of the LVC O3 run follow-up

ABSTRACT The detection of the binary neutron star (BNS) merger GW170817 and the associated electromagnetic (EM) counterpart, the ‘kilonova’ (kN) AT2017gfo, opened a new era in multimessenger astronomy. However, despite many efforts, it has been proven very difficult to find additional kNe, even though LIGO/Virgo has reported at least one BNS event during their latest run, O3. The focus of this work is the exploration of the sensitivity of the adopted optical surveys searching for kNe during O3. We propose ways to optimize the choices of filters and survey depth to boost the detection efficiency for these faint and fast-evolving transients in the future. In particular, we use kN models to explore the dependence on ejecta mass, geometry, viewing angle, wavelength coverage, and source distance. We find that the kN detection efficiency has a strong viewing-angle dependence, especially for filters blueward of i-band. This loss of sensitivity can be mitigated by early, deep, observations. Efficient gri counterpart searches for kNe at ∼200 Mpc would require reaching a limiting magnitude mlim = 23 mag, to ensure good sensitivity over a wide range of the model phase-space. We conclude that kN searches during O3 were generally too shallow to detect BNS optical counterparts, even under optimistic assumptions.

Effect of Out-of-plane Retardation of Substrate Film on the Viewing-angle Dependence of Transmittance in a Display Device

The effect of the out-of-plane retardation (Rth) of a substrate film on the viewing-angle dependence of transmittance (TR) in a display device was investigated. When the polarization state of input light deviates from the transmission axis of the polarizer, Rth of the substrate film induces inhomogeneous viewing-angle dependence of TR. The inhomogeneity of TR gets worse for greater values of of Rth. The inhomogeneous TR profile can be eliminated by inserting compensation films, which convert the input polarization state to the linear polarization state parallel to the transmission axis of the polarizer.

Printing the light

AbstractThis paper explores the relationship between additive and subtractive mixing for colour printing. Using Spectraval mica pigments (Merck)—marketed as RGB pigments—colour is generated by selective reflection and prints are based on additive colour mixing principles, that when printed onto black paper, create white and a range of colours. Although currently used mostly for decorative effects, they can be the basis of additive 'process' inks, that present new opportunities for and challenges to traditional print markets. The viewing angle dependency of their selective reflection favours applications in security printing similar to the holograms on bank cards for example. Traditional measurement and modelling methods are difficult to apply due to the layering and irregular dispersion of pigments.

Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: global and equatorial dynamics

ABSTRACT Brown dwarfs, planetary-mass objects and directly imaged giant planets exhibit significant observational evidence for active atmospheric circulation, raising critical questions about mechanisms driving the circulation, its fundamental nature and time variability. Our previous work has demonstrated the crucial role of cloud radiative feedback on driving a vigorous atmospheric circulation using local models that assume a Cartesian geometry and constant Coriolis parameters. In this study, we extend the models to a global geometry and explore properties of the global dynamics. We show that, under relatively strong dissipation in the bottom layers of the model, horizontally isotropic vortices are prevalent at mid-to-high latitudes while large-scale zonally propagating waves are dominant at low latitudes near the observable layers. The equatorial waves have both eastward and westward phase speeds, and the eastward components with typical velocities of a few hundred m s−1 usually dominate the equatorial time variability. Lightcurves of the global simulations show variability with amplitudes from 0.5 per cent to a few percent depending on the rotation period and viewing angle. The time evolution of simulated lightcurves is critically affected by the equatorial waves, showing wave beating effects and differences in the lightcurve periodicity to the intrinsic rotation period. The vertical extent of clouds is the largest at the equator and decreases poleward due to the increasing influence of rotation with increasing latitude. Under weaker dissipation in the bottom layers, strong and broad zonal jets develop and modify wave propagation and lightcurve variability. Our modelling results help to qualitatively explain several features of observations of brown dwarfs and directly imaged giant planets, including puzzling time evolution of lightcurves, a slightly shorter period of variability in IR than in radio wavelengths, and the viewing angle dependence of variability amplitude and IR colors.

The effect of jet–ejecta interaction on the viewing angle dependence of kilonova light curves

ABSTRACT The merger of two neutron stars produces an outflow of radioactive heavy nuclei. Within a second of merger, the central remnant is expected to also launch a relativistic jet, which shock-heats and disrupts a portion of the radioactive ejecta. Within a few hours, emission from the radioactive material gives rise to an ultraviolet, optical, and infrared transient (a kilonova). We use the endstates of a suite of 2D relativistic hydrodynamic simulations of jet–ejecta interaction as initial conditions for multidimensional Monte Carlo radiation transport simulations of the resulting viewing angle-dependent light curves and spectra starting at $1.5\, \mathrm{h}$ after merger. We find that on this time-scale, jet shock heating does not affect the kilonova emission for the jet parameters we survey. However, the jet disruption to the density structure of the ejecta does change the light curves. The jet carves a channel into the otherwise spheroidal ejecta, revealing the hot, inner regions. As seen from near (≲30°) the jet axis, the kilonova is brighter by a factor of a few and bluer. The strength of this effect depends on the jet parameters, since the light curves of more heavily disrupted ejecta are more strongly affected. The light curves and spectra are also more heavily modified in the ultraviolet than in the optical.

Chromaticity of structural color in polymer thin film photonic crystals.

A three-dimensional goniometric study of thin-film polymer photonic crystals investigates how the chromaticity of structural color is correlated to structural ordering. Characterization of chromaticity and the angular properties of structural color are presented in terms of CIE 1931 color spaces. We examine the viewing angle dependency of the Bragg scattering cone relative to sample symmetry planes, and our results demonstrate how increased ordering influences angular scattering width and anisotropy. Understanding how the properties of structural color can be quantified and manipulated has significant implications for the manufacture of functional photonic crystals in sensors, smart fabrics, coatings, and other optical device applications.

Improvement of viewing angle dependence of bottom-emitting green organic light-emitting diodes with a strong microcavity effect.

The current efficiency and color purity of organic light-emitting diodes (OLEDs) can be easily improved by means of a microcavity structure, but this improvement is typically accompanied by a deterioration in the characteristics of viewing angle. To minimize the angular dependence of the color characteristics exhibited by these strong microcavity devices, we investigated the changes in the optical properties of the green OLED with a bottom resonant structure. This investigation was based on varying the hole transport layer and semitransparent anode thicknesses. The results of optical simulations revealed that the current efficiency and viewing angle characteristics can be simultaneously improved by adjusting the thickness of the two layers. Furthermore, optical simulations predicted that the angular color dependence could be limited to 0.019 in the International Commission on Illumination (CIE) 1976 coordinate system. This optimum condition yielded a current efficiency of ∼134 cd/A. To further reduce this color shift, a nanosized island array (NIA) was introduced through the dewetting process of cesium chloride. By employing NIAs, the color coordinate shift value was reduced to 0.016 in the CIE 1976 coordinate system, and a current efficiency of 130.7 cd/A was achieved.

P‐229: Late‐News‐Poster: Suppression of Viewing‐Angle Dependence of Top‐Emitting OLEDs by Applying Nanostructured Reflective Anode

To improve the viewing angle dependence of TEOLEDs, we have modified the surface morphology of highly reflective anode by using nano‐island structure. This nano‐island structure is simply fabricated by depositing a specific inorganic material and applying an appropriate environmental condition of a certain temperature and humidity. The resultant TEOLEDs with nano‐structured reflective anode showed stable white angle difference (WAD) with Δ u'v' of 0.005.

An improved air mass factor calculation for nitrogen dioxide measurements from the Global Ozone Monitoring Experiment-2 (GOME-2)

Abstract. An improved tropospheric nitrogen dioxide (NO2) retrieval algorithm from the Global Ozone Monitoring Experiment-2 (GOME-2) instrument based on air mass factor (AMF) calculations performed with more realistic model parameters is presented. The viewing angle dependency of surface albedo is taken into account by improving the GOME-2 Lambertian-equivalent reflectivity (LER) climatology with a directionally dependent LER (DLER) dataset over land and an ocean surface albedo parameterisation over water. A priori NO2 profiles with higher spatial and temporal resolutions are obtained from the IFS (CB05BASCOE) chemistry transport model based on recent emission inventories. A more realistic cloud treatment is provided by a clouds-as-layers (CAL) approach, which treats the clouds as uniform layers of water droplets, instead of the current clouds-as-reflecting-boundaries (CRB) model, which assumes that the clouds are Lambertian reflectors. On average, improvements in the AMF calculation affect the tropospheric NO2 columns by ±15 % in winter and ±5 % in summer over largely polluted regions. In addition, the impact of aerosols on our tropospheric NO2 retrieval is investigated by comparing the concurrent retrievals based on ground-based aerosol measurements (explicit aerosol correction) and the aerosol-induced cloud parameters (implicit aerosol correction). Compared with the implicit aerosol correction utilising the CRB cloud parameters, the use of the CAL approach reduces the AMF errors by more than 10 %. Finally, to evaluate the improved GOME-2 tropospheric NO2 columns, a validation is performed using ground-based multi-axis differential optical absorption spectroscopy (MAXDOAS) measurements at different BIRA-IASB stations. At the suburban Xianghe station, the improved tropospheric NO2 dataset shows better agreement with coincident ground-based measurements with a correlation coefficient of 0.94.

Supernova Ejecta Interacting with a Circumstellar Disk. I. Two-dimensional Radiation-hydrodynamic Simulations

Abstract We perform a series of two-dimensional radiation-hydrodynamic simulations of the collision between supernova ejecta and circumstellar media (CSMs). The hydrodynamic interaction of a fast flow and the surrounding media efficiently dissipates the kinetic energy of the fast flow and is considered as a dominant energy source for a specific class of core-collapse supernovae. Despite some observational evidence for aspherical ejecta and/or CSM structure, multidimensional effects in the ejecta–CSM interaction are relatively unexplored. Our numerical simulations equipped with an adaptive mesh refinement technique successfully reproduce hydrodynamic instabilities developing around the ejecta–CSM interface. We also investigate effects of disklike CSMs on the dynamical evolution of supernova ejecta and bolometric light curves. We find that emission powered by ejecta–disk interaction exhibits significant viewing angle dependence. For a line of sight close to the symmetry axis, the observer directly sees the supernova ejecta, leading to a short brightening timescale. For an observer seeing the emission through the CSM disk, thermal photons diffuse throughout the CSM, and thus the light curve is severely smeared out.

Suppression of viewing angle dependence of TEOLED devices with internal nano-wrinkle structure

Abstract In order to suppress the viewing angle dependence of top emission organic emitting diodes (TEOLEDs) with strong microcavity effect, we introduced randomly distributed nano-wrinkle structure beneath highly reflective anode. By applying such nano-wrinkle pattern, viewing angle dependence and color shift could be improved compared with that without nano-structure [e.g. Δ (u’, v’): 0.077 → 0.025]. However, current efficiency reduced more than half. To compensate this problem, we additionally introduced index matching epoxy filler between encapsulation glass and TEOLED device. By this approach, current efficiency drop of device with nano-wrinkle structure could be improved. For example, the efficiency dropped by 7.7% when we filled the epoxy filler between capping layer and glass lid while, it decreased by 30.8% if we don't use epoxy filler. We found that index matching helps to extract more light confined inside TEOLED, so device performance degradation could be minimized. In addition, when we attached a circular polarizer film to these devices, depolarization was observed in most cases, but we were able to achieve a perfect black state from the devices with nano-wrinkle structure underneath reflective anode.

P‐214: Late‐News Poster: Enhanced Out‐coupling Efficiency of Organic Light‐emitting Diodes Using a Corrugated Microcavity Structure

In this study, organic light‐emitting diodes with enhanced out‐coupling efficiency and suppressed viewing angle dependence were demonstrated by the novel structure of a corrugated microcavity. The corrugated nanopatterned Ag layer were fabricated through a laser interference lithography (LIL) process. The corrugated Ag film increased the EL intensity and suppressed viewing angle dependence.

P‐212: Late‐News Poster: Influence of Index Matching Epoxy Filler at the Encapsulation Part for the Performance of TEOLED with Internal Wrinkle Structure

In this work, we applied random wrinkle structure to top emitting organic light emitting diodes (TEOLEDs) inside. Also, by introducing index matching epoxy filler into the encapsulation part, we could dramatically improve the current efficiency with maintaining the suppression effect of viewing angle dependence as well as color shift.

Terra and Aqua MODIS TEB intercomparison using Himawari-8/AHI as reference

Intercomparison between the two MODIS instruments is very useful for both the instrument calibration and its uncertainty assessment. Terra and Aqua MODIS have almost identical relative spectral response, spatial resolution, and dynamic range for each band, so the site-dependent effect from spectral mismatch for their comparison is negligible. Major challenges in cross-sensor comparison of instruments on different satellites include differences in observation time and view angle over selected pseudoinvariant sites. The simultaneous nadir overpasses (SNO) between the two satellites are mostly applied for comparison and the scene under SNO varies. However, there is a dearth of SNO between the Terra and Aqua. This work focuses on an intercomparison method for MODIS thermal emissive bands using Himawari-8 Advanced Himawari Imager (AHI) as a reference. Eleven thermal emissive bands on MODIS are at least to some degree spectrally matched to the AHI bands. The sites selected for the comparison are an ocean area around the Himawari-8 suborbital point and the Strzelecki Desert located south of the Himawari-8 suborbital point. The time difference between the measurements from AHI and MODIS is <5 min. The comparison is performed using 2017 collection 6.1 L1B data for MODIS. The MODIS–AHI difference is corrected to remove the view angle dependence. The Terra–Aqua MODIS difference for the selected TEB is up to 0.6 K with the exception of band 30. Band 30 has the largest difference, which is site dependent, most likely due to a crosstalk effect. Over the ocean, the band 30 difference between the two MODIS instruments is around 1.75 K, while over the desert; the difference is around 0.68 K. The MODIS precision is also compared from the Gaussian regression of the double difference. Terra bands 27 to 30 have significant extra noise due to crosstalk effects on these bands. These Terra–Aqua comparison results are used for MODIS calibration assessments and are beneficial for future calibration algorithm improvement. The impact of daytime measurements and the scene dependence are also discussed.

The origin of polarization in kilonovae and the case of the gravitational-wave counterpart AT 2017gfo

The Gravitational Wave (GW) event GW 170817 was generated by the coalescence of two neutron stars (NS) and produced an electromagnetic transient, labelled AT 2017gfo, that was target of a massive observational campaign. Polarimetry, a powerful diagnostic tool for probing the geometry and emission processes of unresolved sources, was obtained for this event. The observed linear polarization was consistent with being mostly induced by intervening dust, suggesting that the intrinsic emission was weakly polarized ($P < 0.4-0.5$ %). In this paper, we present and discuss a detailed analysis of the linear polarization expected from a merging NS binary system by means of 3D Monte Carlo radiative transfer simulations assuming a range of possible configurations, wavelengths, epochs and viewing angles. We find that polarization originates from the non-homogeneous opacity distribution within the ejecta and can reach levels of $P\sim1$ % at early times (1$-$2 days after the merger) and in the optical R band. Smaller polarization signals are expected at later epochs and/or different wavelengths. From the viewing-angle dependence of the polarimetric signal, we constrain the observer orientation of AT 2017gfo within $\sim$65$^\circ$ from the polar direction. The detection of non-zero polarization in future events will unambiguously reveal the presence of a lanthanide-free ejecta component and unveil its spatial and angular distribution.

Surface Radioactivity or Interactions? Multiple Origins of Early-excess Type Ia Supernovae and Associated Subclasses

Abstract Early-phase Type Ia supernovae (SNe Ia), especially those with luminosity enhancement within the first few days of explosions (“early-excess SNe Ia”), play an irreplaceable role in addressing the long-standing progenitor and explosion issue of SNe Ia. In this paper, we systematically investigate 11 early-excess SNe Ia from subluminous to luminous subclasses. Eight of them are selected from 23 SNe Ia with extremely early-phase optical light curves (“golden” early-phase SNe Ia), and three of them are selected from 40 SNe Ia (including 14 golden samples) with early-phase UV/NUV light curves. We found that previously discovered early-excess SNe Ia show a clear preference for specific SN Ia subclasses. In particular, the early-excess feature shown in all six luminous (91T- and 99aa-like) SNe Ia is in conflict with the viewing angle dependence predicted by the companion-ejecta interaction scenario. Instead, such a high early-excess fraction is likely related to the explosion physics of luminous SNe Ia; i.e., a more efficient detonation happening in the progenitor of luminous SNe Ia may consequently account for the early-excess feature powered by the radiation from a 56Ni-abundant outer layer. The diversity of early-excess features shown in different SN Ia subclasses suggests multiple origins of the discovered early-excess SNe Ia, challenging their applicability as a robust progenitor indicator. Further understanding of the early-excess diversity relies not only on multiband photometry and prompt-response spectroscopy of individual early-excess SNe Ia but also on investigations of the general early-phase light-curve behavior of each SN Ia subclass, which can be realized through ongoing/forthcoming transient survey projects in the near future.

Electromagnetic Emission from Supermassive Binary Black Holes Approaching Merger

Abstract We present the first relativistic prediction of the electromagnetic emission from the surrounding gas of a supermassive binary black hole system approaching merger. Using a ray-tracing code to post-process data from a general relativistic 3D magnetohydrodynamic simulation, we generate images and spectra, and analyze the viewing angle dependence of the light emitted. When the accretion rate is relatively high, the circumbinary disk, accretion streams, and mini-disks combine to emit light in the UV/extreme-UV bands. We posit a thermal Compton hard X-ray spectrum for coronal emission; at high accretion rates, it is almost entirely produced in the mini-disks, but at lower accretion rates it is the primary radiation mechanism in the mini-disks and accretion streams as well. Due to relativistic beaming and gravitational lensing, the angular distribution of the power radiated is strongly anisotropic, especially near the equatorial plane.

Efficient Outcoupling of Organic Light-Emitting Devices Using a Light-Scattering Dielectric Layer

It has long been a challenge to develop a highly efficient outcoupling method for organic light-emitting diodes that is independent of wavelength and viewing angle, as well as being nonintrusive into the device structure. Here, we demonstrate a transparent, top emitting structure integrated with a high index of refraction waveguide layer and a rough, dielectric diffuse reflector that eliminates plasmonic, waveguide, and substrate modes without introducing wavelength and viewing-angle dependence. The simple outcoupling structure increases the external quantum efficiency from 15 ± 2% to 37 ± 4% compared to an analogous device with a metal mirror, corresponding to a 2.5-fold enhancement without requiring the use of additional outcoupling structures such as microlens arrays or index matching layers to extract substrate modes. The method is potentially suitable for low-cost, solid-state lighting due to its simplicity and high outcoupling efficiency.

Effects of engine acoustic waves on optical environment around turrets in-flight on AAOL-T

Wavefront measurements were performed in-flight for a hemispherical turret on the Airborne Aero-Optics Laboratory-Transonic (AAOL-T). For turret side-looking angles near 90 deg, upstream-propagating optical distortions over the turret aperture were observed. These distortions were contributed to acoustic waves originating from the engine downstream of the turret. The acoustical waves were modeled by combining a potential flow solution for a single-frequency moving acoustic source and a potential flow around a sphere. The model was shown to properly predict the spatial statistics and convective speeds of the experimentally observed wavefronts. The model also correctly explained the viewing-angle dependence of the acoustic-related optical distortions. It was shown that for side-viewing angles between 90 deg and 100 deg, these acoustical distortions can be a significant contributor to the overall aero-optical distortions.

A GRB and Broad-lined Type Ic Supernova from a Single Central Engine

Abstract Unusually high velocities (≳0.1c) and correspondingly high kinetic energies have been observed in a subset of Type Ic supernovae (so-called “broad-lined Ic” supernovae; SNe Ic-BL), prompting a search for a central engine model capable of generating such energetic explosions. A clue to the explosion mechanism may lie in the fact that all supernovae that accompany long-duration gamma-ray bursts (GRBs) belong to the SN Ic-BL class. Using a combination of two-dimensional relativistic hydrodynamics and radiation transport calculations, we demonstrate that the central engine responsible for long GRBs can also trigger an SN Ic-BL. We find that a reasonable GRB engine injected into a stripped Wolf–Rayet progenitor produces a relativistic jet with energy ∼1051 erg, as well as an SN whose synthetic light curves and spectra are fully consistent with observed SNe Ic-BL during the photospheric phase. As a result of the jet’s asymmetric energy injection, the SN spectra and light curves depend on viewing angle. The impact of viewing angle on the spectrum is particularly pronounced at early times, while the viewing-angle dependence for the light curves (∼10% variation in bolometric luminosity) persists throughout the photospheric phase.