Light Travel Research Articles

The NICER “Reverberation Machine”: A Systematic Study of Time Lags in Black Hole X-Ray Binaries

We perform the first systematic search of all NICER archival observations of black hole (and candidate) low-mass X-ray binaries for signatures of reverberation. Reverberation lags result from the light travel time difference between the direct coronal emission and the reflected disk component, and therefore their properties are a useful probe of the disk-corona geometry. We detect new signatures of reverberation lags in eight sources, increasing the total sample from three to 11, and study the evolution of reverberation lag properties as the sources evolve in outbursts. We find that in all of the nine sources with more than one reverberation lag detection, the reverberation lags become longer and dominate at lower Fourier frequencies during the hard-to-soft state transition. This result shows that the evolution in reverberation lags is a global property of the state transitions of black hole low-mass X-ray binaries, which is valuable in constraining models of such state transitions. The reverberation lag evolution suggests that the corona is the base of a jet that vertically expands and/or gets ejected during state transition. We also discover that in the hard state, the reverberation lags get shorter, just as the quasiperiodic oscillations (QPOs) move to higher frequencies, but then in the state transition, while the QPOs continue to higher frequencies, the lags get longer. We discuss the implications of the coronal geometry and physical models of QPOs in light of this new finding.

Polarization-dependent group velocity of light pulses traveling in the optic ray axis directions of a biaxial crystal.

We theoretically prove that the group velocity of a light pulse traveling in an optic ray axis direction of a biaxial crystal depends on the polarization state of the light. Our calculation shows that the group index varies as a sinusoidal function of twice the polarization angle of the light pulse. For monoclinic and triclinic crystals, in general the four directions of the two optic ray axes need to be distinguished. Numerical examples show that in KNbO3 the group velocity varies by 2.7% at 400 nm wavelength, and in Sn2P2S6 it varies by 3.9% at 550 nm wavelength, when the polarization state of the light is changing.

Flares in gamma-ray burst X-ray afterglows as prompt emission from slightly misaligned structured jets

ABSTRACT We develop a model to explain the flaring activity in gamma-ray burst X-ray afterglows within the framework of slightly misaligned observers to structured jets. We suggest that flares could be the manifestation of prompt dissipation within the core of the jet, appearing to a misaligned observer in the X-ray band because of less favourable Doppler boosting. These flares appear during the afterglow phase because of core–observer light travel delays. In this picture, the prompt emission recorded by this observer comes from material along their line of sight, in the lateral structure of the jet, outside the jet’s core. We start by laying down the basic analytical framework to determine the flares characteristics as a function of those of the gamma-ray pulse an aligned observer would see. We show that there is viable parameter space to explain flares with typical observing times and luminosities. We then analytically explore this model, showing that it naturally produces flares with small aspect ratios, as observed. We perform fits of our model to two Swift/XRT flares representing two different types of morphology, to show that our model can capture both. The ejection time of the core jet material responsible of the flare is a critical parameter. While it always remains small compared to the observed time of the flare, confirming that our model does not require very late central engine activity, late ejection times are strongly favoured, sometimes larger than the observed duration of the parent gamma-ray burst’s prompt emission as measured by T90.

Relative Nature of Electric Permittivity and Magnetic Permeability of Electromagnetic Wave

This research is about the special theory of relativity on electric permittivity and magnetic permeability of electromagnetic wave. For this, Four Maxwell’s electromagnetic equations play an important role. James Clerk Maxwell suggested that the light travel as electromagnetic wave which require no material medium for propagation. The speed of light (C) in free space is always constant and is independent of the speed of source or observer or the relative motion of the inertial system and has velocity ‘C’ given by. So velocity of electromagnetic waves depend on obsolute magnetic permeability (μ0) and obsolute electric permittivity (ε0) of free space. These two physical quantities rely on relative motion of inertial system. So μ0 and ε0 are not obsolute quantity but are dependent upon the relative motion between the observer and the phenomenon observed. Electric and magnetic field of a charge rely upon the value of obsolute electric permittivity of medium. Concisely, μ0 and ε0 are variant quantity. Consequently electric and magnetic field get relative for electromagnetic wave. That is electric and magnetic field depend on relative motion of inertial system for electromagnetic waves.

About apparent superluminal drives in generic gravity theories

As is well known, there exists warp drives in GR, such as the Alcubierre bubbles, which achieve an apparent faster than light travel (Alcubierre in Class Quantum Gravity 11:L73, 1994). A result due to Gao and Wald (Class Quantum Gravity 17:4999, 2000) suggests that such a travel is unlikely for GR with matter satisfying both the Null Energy and the Null Generic Conditions. There exists a generalization of this statement due to Galloway, that ensures that the Gao–Wald result is true regardless the underlying gravity model, unless there exists at least one inextendible null geodesic with achronal image in the space time (a null line). The proof of this proposition is based on techniques of causal theories, and has never been released. In the present work an independent proof of this result is presented by use of the Raychaudhuri equation, and avoiding several technical complications described along the text. Some consequences of these affirmations are discussed at last section, in particular their potential use in problems of causality.

Highly Efficient Fiber Optic Thermal Heating Device Based on Turn-Around-Point Long Period Gratings

The use of in-fiber core-to-cladding coupling components for thermal heating purposes has been well assessed in the last decades within the development of fiber optic devices for flow measurements and water thermal conductivity calculation. In these devices, light travelling in the fiber core is transferred into the cladding and absorbed by a metallic layer surrounding the fiber, with the consequent resistive heating generation. Here we demonstrate the use of a Turn-Around-Point (TAP) Long Period Grating (LPG) as resonant core-to-cladding light coupling mechanism for the fabrication of a highly efficient heating device based on metallic coated Fiber Bragg Grating (FBG). A properly designed TAP LPG was fabricated by means of point-to-point UV laser and spliced to a 150 nm thick Au-coated FBG. The heating efficiency characterization of the final device was analyzed, in both air and water, by evaluating the temperature increase in the gold layer surrounding the FBG at incremental values of the injected power. Collected results confirm that the use of LPGs involving the excitation of higher order cladding modes provides an excellent transferring mechanism of the fiber core light into the cladding, which in turn guarantees very high thermal heating efficiency to the final device. Moreover, by comparing such results with the performance of other in-fiber core-to-cladding coupling components already presented in literature, it was found that the TAP LPG-based device exhibits an actuation efficiency 2.5 times greater, thus resulting the most effective and highly performing solution for energy transfer to the metallic overcoat.

Light Curve Analysis and Period Study of Two Eclipsing Binaries UZ Lyr and BR Cyg

Two eclipsing binary systems, UZ Lyr and BR Cyg, are semi-detached types whose secondary component fills its Roche lobe. Although radial velocity and light curves of these systems have already been investigated separately, both their radial velocity and light curves are analyzed simultaneously for the first time in the present study. Also, the orbital period changes of these systems are studied. Our results show that the mass transfers between components have negligible effects on the orbital period changes of these systems, but two light travel time effects are the reasons for the periodic behavior of the O − C curve for UZ Lyr. We could not remark more information about orbital period changes for BR Cyg, but we find a new orbital period for it. By radial velocity and light curve analysis, we find a cold spot on the secondary component of BR Cyg. The new geometrical and physical parameters of both systems are obtained and their positions on the H-R diagram are demonstrated.

CSS J075415.6+191052 and NW Leo: Two Contact Binaries at Different Evolutionary Stages

Multi-color light curves of CSS J075415.6+191052 and NW Leo are presented and the photometric solutions suggest that CSS J075415.6+191052 is an A-subtype contact binary with low mass ratio (q = 0.178) while NW Leo has a high mass ratio (q = 0.707). For CSS J075415.6+191052, the RI light curves show weakening around the left shoulder of the secondary minimum, which indicates that there may be a dark spot on the secondary component. However, the light curves of BV bands are totally symmetric. It is unreasonable if the dark spot is caused by magnetic activity or mass transfer between the two components. Therefore, weakening of the light curves in this contact binary is caused by something else. A possible explanation is mass transferring from the primary component to the common convective envelope through the inner Lagrangian point, and this part of the mass, for some reason, weakens the RI bands of light from the secondary component. O − C analysis of NW Leo reveals a cyclic period change with a modulation period of 4.7 yr, which may be caused by the light travel time effect of a third body. The positions of CSS J075415.6+191052 and NW Leo in the P–J′orb diagram indicate that CSS J075415.6+191052 mainly abides by the angular momentum loss theory while NW Leo is dominated by the thermal relaxation oscillation theory.

Light Refraction and Reflection near a Black Hole

In this paper, we have calculated the angle of refraction that light travels approaching to the strong gravitational field like a black hole by combining the general relativity and the classical Snell’s law, assuming that the gravitational field can act as a non-vacuum filled with medium of some coefficients. We have found that the value of refracted angle exactly coincides with the value from the Einstein’s relativity theory in a weak gravitational field. From this optical interpretation of the traveling of light near a black hole, we have suggested that there might have the reflection phenomenon and investigated that the total reflection occurs at the surface of a black hole. Regardless this might cause controversy, we can explain the recent observation that light reflects from a black hole.

MXene-Coated Wrinkled Fabrics for Stretchable and Multifunctional Electromagnetic Interference Shielding and Electro/Photo-Thermal Conversion Applications.

Stretchability and multifunctional heating abilities are highly desired for wearable electromagnetic interference (EMI) shielding fabrics to tackle the growing electromagnetic pollution for special crowd, such as pregnant women. Herein, we fabricated stretchable MXene-coated thermoplastic polyurethane (TPU) fabrics by simple uniaxial prestretching and spraying methods. The obtained unique wrinkled structure endowed the film with effective strain-invariant electrical conductivity and EMI shielding properties. Specifically, the prepared stretchable film with an extremely low MXene loading (0.417 mg cm-2) exhibited a stable EMI shielding effectiveness of approximately 30 dB under 50% tensile strain and durability during stretching and bending cycles. More importantly, owing to the high electrical conductivity and localized surface plasmon resonance (LSPR) effect of the MXene layer, the stretchable fabrics exhibited excellent Joule heating (up to 104 °C at a voltage of 5 V) and superior photothermal conversion abilities. Moreover, the unique wrinkled MXene-coating layer not only endows the fabrics with stretchable heat abilities but also enhances the photothermal conversion performance by increasing the light absorption area and travel path. We believe that this study offers a novel strategy for the versatile design of stretchable and multifunctional wearable shielding fabrics.

Orbital parameters of the hierarchical triplet system CN Lyn

ABSTRACT CN Lyn is an intriguing triplet system that contains three equal-mass components. However, the orbital parameters of this rare triple system are still unknown. By monitoring the system since 2016 October 19, 13 eclipse times have been obtained. We discover that the observed minus calculated (O − C) diagram of CN Lyn shows a cyclical variation with a period of 15.80 (± 0.40) years and a projected semi-major axis of 0.0074 (± 0.0008) days. The orbital properties of the third body are investigated by analysing the light travel time effect. It is found that the third body is orbiting the central binary in an eccentric orbit (e3 ∼ 0.38 (± 0.18)). The orbital inclination is determined to be i3 = 25°, which reveals that the third body is non-coplanar to the orbit of the central eclipsing binary. This is the reason why investigators did not detect a clear periodicity in the radial velocities of the third body. By analysing one low-dispersion spectrum obtained with the 2.16-m telescope in Xinglong station, stellar atmospheric parameters of CN Lyn were derived. It is shown that the system has a low metallicity that is only about 21.5 per cent of the solar metallicity. The rare composition, eccentric orbit, low metallicity, and low orbital inclination of the triplets all indicate that the CN Lyn system can provide valuable information on the formation of multiple star systems, a matter of active research and debate.

Adaptive polygon rendering for interactive visualization in the Schwarzschild spacetime

Interactive visualization is a valuable tool for introductory or advanced courses in general relativity as well as for public outreach to provide a deeper understanding of the visual implications due to curved spacetime. In particular, the extreme case of a black hole where the curvature becomes so strong that even light cannot escape, benefits from an interactive visualization where students can investigate the distortion effects by moving objects around. However, the most commonly used technique of four-dimensional general-relativistic ray tracing is still too slow for interactive frame rates. Therefore, we propose an efficient and adaptive polygon rendering method that takes light deflection and light travel time into account. An additional advantage of this method is that it provides a natural demonstration of how multiple images occur and how light travel time affects them. Finally, we present our method using three example scenes: a triangle passing behind a black hole, a sphere orbiting a black hole and an accretion disk with different inclination angles.

Charity work of theologian Nurgali Khasanov (1852–1919)

The article is devoted to the charitable work of an authoritative Muslim theologian of the Middle Volga region, Sheikh, Akhun Nurgali Khasanov (1852–1919). This part of his life is revealed on the basis of the pre-revolutionary Tatar newspapers the Koyash, the Yoldyz, the Azad, the Mаglumat magazine, the memoirs of contemporaries, published documents and his work “Al-Gauatyf al-Hamidiya fi ssayakhati nuriya” (Commendable Feelings of Light Travels), dedicated to pilgrimage. The events described cover the period from 1886 to 1917. On the example of charitable activity of this bright personality, it seems possible to perceive the historical processes of that time, to understand what diffi culties Muslim religious fi gures, theologians of the Middle Volga region of the late XIX – early XX centuries encountered in life.

Parameter estimation bias from overlapping binary black hole events in second generation interferometers

Since the initial detection of Gravitational Waves in 2015, 50 candidate events have been reported by the LIGO-Virgo-KAGRA collaboration. As the current generation of detectors move towards their design sensitivity the rate of these detections will increase. The next generation of detectors are likely to have high enough sensitivities that multiple merging binaries will be visible at the same time. In this paper we show that this is likely to happen before the end of the decade, with the move to the LIGO-Voyager detector. We investigate the situation of overlapping Binary-Black-Hole mergers in these detectors. We find that current parameter estimation techniques are capable of distinguishing the louder of two merging BBH events, without significant bias, when their merger times are not less than $\sim0.1$ seconds apart and when the ratio of the signal-to-noise ratios of the systems is uneven. This region of overlapping parameter space is dependent upon the sky locations of the signals and the relation of those locations to the light travel time between detectors. We also find that, if two signals are highly overlapping, then the recovered set of parameters often show strong evidence of precession. Finally we show that bias can occur even when the signal causing the bias is below the detection threshold.

The pseudo-null geometric phase along optical fiber

In this study, a pseudo-null space curve in Minkowski 3-space is used to describe an optical fiber that is injected into monochromatic linear polarized light. The direction of the electric field vector with respect to the Frenet frame of a pseudo-null curve determines the state polarization of a monochromatic linearly polarized light wave traveling along an optical fiber. For the Frenet frame of a pseudo-null curve in Minkowski 3-space, the polarization vector [Formula: see text] is assumed to be perpendicular to the tangent vector [Formula: see text] with respect to anholonomic coordinates. Anholonomic coordinates for the Frenet frame of a pseudo-null curve are used to describe pseudo-null electromagnetic curves in the normal and binormal directions along an optical fiber. For the Frenet frame of the pseudo-null curve, Lorentz force equations in the normal and binormal directions along the optical fiber are presented. Pseudo-normal and binormal Rytov parallel transport laws for electric fields in the normal and binormal directions along with the optical fiber for the Frenet frame of the pseudo-null curve via anholonomic coordinates are presented. For anholonomic coordinates in Minkowski 3-space, rotations of the polarization planes of a light wave traveling in the normal and binormal directions along with the optical fiber with respect to the Frenet frame of the pseudo-null curve are obtained. Finally, a pseudo-null curve’s Maxwellian evolution is determined.

First photometric study of two eclipsing binary star systems: V523 And and V543 And

Detailed photometric analysis of V523 And and V543 And from the Wide Angle Search for Planets survey is presented for the first time. It was found that while V523 And is a detached binary, V543 And is a semi-detached binary star system. The adopted masses and radii for the primary and secondary components are M1=0.77±0.08 M⊙, R1=0.87±0.08 R⊙ and M2=0.50±0.12 M⊙, R2=0.77±0.17 R⊙ for V523 And; and M1=1.59±0.16 M⊙, R1=1.46±0.09 R⊙ and M2=0.58±0.17 M⊙, R2=1.66±0.22 R⊙ for V543 And. Orbital period variations of the systems were analyzed using the O-C method. The O-C change of V523 And is discussed in terms of the magnetic activity cycle of one or both components and light travel time effect (LTTE) due to a third body in the system. Among these mechanisms, LTTE seems to be the most appropriate mechanism to explain the O-C variation of the system since the quadrupole moments of the primary and secondary components (ΔQ) were found to be in the order of 1049 g cm2. The O-C diagram of V543 And shows a downward parabolic trend, which suggests a secular period decrease with a rate of 0.080±0.012 s/year. The parabolic O-C variation of V543 And was interpreted in terms of the non-conservative mass transfer mechanism. According to this scenario, the range of possible values of the mass gain rate (Ṁ1) of the primary component of V543 And as well as the mass-loss rate (Ṁ) of the system were found to be 10−5–10−11 M⊙/year and 10−6–10−8 M⊙/year, respectively.

New light curve analysis and period changes of the HW Vir-type binary system V1828 Aql

The new BVRI photometric observations of the HW Vir-type eclipsing binary system V1828 Aql (P = 0.11037399 days) were presented. From these measurements, 16 new eclipse times have been obtained. The light curves in BVRI colors and the radial curves were simultaneously analyzed by using the Wilson–Devinney method for the system parameters. The system consists of a very hot primary component (T1 = 42000 K) and a cold secondary component (T2 = 3077 ± 250 K). The absolute dimensions were found as follows: (M1 = 0.351 ± 4 0.040 M⊙, M2 = 0.095 ± 0.011 M⊙, R1 = 0.176 ± 0.007 R⊙, R2 = 0.140 ± 0.007 R⊙, L1 =86.91 ± 6.76 L⊙ and L2 = 0.002 ± 0.001 L⊙). The orbital period variation of V1828 Aql was made using all available light minimum times. From the (O - C) diagram, the orbital period shows a variation possibly attributable to the light travel time effect by the presence of the third body. The third body orbital period is P3 = 3317.7−17.2+18.9 days, its minimal mass is M3 = 13.24−0.14+0.13 Mj. The mass value calculated for the third body shows, that this object is right at the border between the planets and the brown dwarfs.

Sensitivity limits of space-based interferometric gravitational wave observatories from the solar wind

Space-based interferometric gravitational wave instruments such as the ESA/NASA Laser Interferometer Space Antenna (LISA) observe gravitational waves by measuring changes in the light travel time between widely-separated spacecraft. One potential noise source for these instruments is interaction with the solar wind, in particular the free electrons in the interplanetary plasma. Variations in the integrated column density of free electrons along the laser links will lead to time-of-flight delays which directly compete with signals produced by gravitational waves. In this paper we present a simplified model of the solar plasma relevant for this problem, anchor key parameters of our model using data from the NASA \emph{Wind}/SWE instrument, and derive estimates for the effect in the LISA measurement. We find that under normal solar conditions, the gravitational-wave sensitivity limit from the free-electron effect is smaller than other noise sources that are expected to limit LISA's sensitivity.

A Bright Fast Radio Burst from FRB 20200120E with Sub-100 Nanosecond Structure

Abstract We have detected a bright radio burst from FRB 20200120E with the NASA Deep Space Network (DSN) 70 m dish (DSS-63) at radio frequencies between 2.2 and 2.3 GHz. This repeating fast radio burst (FRB) is reported to be associated with a globular cluster in the M81 galactic system. With high time resolution recording, low scattering, and large intrinsic brightness of the burst, we find a burst duration of ∼30 μs, comprised of several narrow components with typical separations of 2–3 μs. The narrowest component has a width of ≲100 ns, which corresponds to a light travel time size as small as 30 m. The peak flux density of the narrowest burst component is 270 Jy. We estimate the total spectral luminosity of the narrowest component of the burst to be 4 × 1030 erg s−1 Hz−1, which is a factor of ∼500 above the luminosities of the so-called “nanoshots” associated with giant pulses from the Crab pulsar. This spectral luminosity is also higher than that of the radio bursts detected from the Galactic magnetar SGR 1935 + 2154 during its outburst in April 2020, but it falls on the low-end of the currently measured luminosity distribution of extragalatic FRBs, further indicating the presence of a continuum of FRB luminosities. The temporal separation of the individual components has similarities to the quasiperiodic behavior seen in the microstructure of some pulsars. The known empirical relation between the microstructure quasiperiodicity timescale and the rotation period of pulsars possibly suggests a possible pulsar as the source of this FRB, with a rotation period of a few milliseconds.

Optical Fiber Waveguiding Soft Photoactuators Exhibiting Giant Reversible Shape Change

AbstractSoft actuators, an emerging field in robotics, have great potential for wide‐ranging applications in biology, medicine, engineering, and oceanography. Photoactuators that are stimulated by light to produce reversible mechanical deformation have attracted significant interest in recent years owing to their advantages of high resolution, fast switching, flexible controllability, and electromagnetic interference immunity. Conventional photoactuators rely on free‐space illumination, which limits the control in light‐obstructed surroundings. A low loss optical fiber waveguide‐based soft photoactuator composed of photothermally responsive material hinges and high‐transparency elastomer fiber arms is proposed. When light travels in the elastomer fiber arms, the hinges exhibit a very large shape change so that the arms bend by themselves, with a maximum repeatable bending angle of approximately 145°. The angle is determined by the injected optical power. A fiber photoactuator with dual hinges is designed that is capable of reversible complex deformation. Moreover, in a narrow silicone tube, the fiber photoactuator can still be stimulated with considerable deformation by the light injected along the fiber. A fiber photoactuator‐constructed microhook is demonstrated for grabbing object in water.