Einstein Cross Research Articles

DESI-253.2534+26.8843: A New Einstein Cross Spectroscopically Confirmed with Very Large Telescope/MUSE and Modeled with GIGA-Lens

Gravitational lensing provides unique insights into astrophysics and cosmology, including the determination of galaxy mass profiles and constraining cosmological parameters. We present spectroscopic confirmation and lens modeling of the strong lensing system DESI-253.2534+26.8843, discovered in the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys data. This system consists of a massive elliptical galaxy surrounded by four blue images forming an Einstein Cross pattern. We obtained spectroscopic observations of this system using the Multi Unit Spectroscopic Explorer on ESO’s Very Large Telescope and confirmed its lensing nature. The main lens, which is the elliptical galaxy, has a redshift of z L1 = 0.636 ± 0.001, while the spectra of the background source images are typical of a starburst galaxy and have a redshift of z s = 2.597 ± 0.001. Additionally, we identified a faint galaxy foreground of one of the lensed images, with a redshift of z L2 = 0.386. We employed the GIGA-Lens modeling code to characterize this system and determined the Einstein radius of the main lens to be , which corresponds to a velocity dispersion of σ = 379 ± 2 km s−1. Our study contributes to a growing catalog of this rare kind of strong lensing system and demonstrates the effectiveness of spectroscopic integral field unit observations and advanced modeling techniques in understanding the properties of these systems.

Unscrambling the Lensed Galaxies in JWST Images behind SMACS 0723

The first deep field images from the James Webb Space Telescope (JWST) of the galaxy cluster SMACS J0723.3-7327 reveal a wealth of new lensed images at uncharted infrared wavelengths, with unprecedented depth and resolution. Here we securely identify 14 new sets of multiply imaged galaxies totaling 42 images, adding to the five sets of bright and multiply imaged galaxies already known from Hubble Space Telescope data. We find examples of arcs crossing critical curves, allowing detailed community follow-up, such as JWST spectroscopy for precise redshift determinations, and measurements of the chemical abundances and of the detailed internal gas dynamics of very distant, young galaxies. One such arc contains a pair of compact knots that are magnified by a factor of hundreds, and features a microlensed transient. We also detect an Einstein cross candidate only visible thanks to JWST’s superb resolution. Our parametric lens model is available through the following link (https://www.dropbox.com/sh/gwup2lvks0jsqe5/AAC2RRSKce0aX-lIFCc9vhBXa?dl=0) and will be regularly updated using additional spectroscopic redshifts. The model is constrained by 16 of these sets of multiply imaged galaxies, three of which have spectroscopic redshifts, and reproduces the multiple images to better than an rms of 0.″5, allowing for accurate magnification estimates of high-redshift galaxies. The intracluster light extends beyond the cluster members, exhibiting large-scale features that suggest a significant past dynamical disturbance. This work represents a first taste of the enhanced power JWST will have for lensing-related science.

Wave-optical study of the Einstein cross formed by a quadrupole gravitational lens

We study imaging of point sources with a quadrupole gravitational lens while focusing on the formation and evolution of the Einstein cross formed on the image sensor of an imaging telescope. We use a new type of a diffraction integral that we developed to study generic, opaque, weakly aspherical gravitational lenses. To evaluate this integral, we use the method of stationary phase that yields a quartic equation with respect to a Cartesian projection of the observer's position vector with respect to the vector of the impact parameter. The resulting quartic equation can be solved analytically using the method first published by Cardano in 1545. We find that the resulting solution provides a good approximation of the electromagnetic (EM) field almost everywhere in the image plane, yielding the well-known astroid caustic of the quadrupole lens. The sole exception is the immediate vicinity of the caustic boundary, where a numerical treatment of the diffraction integral yields better results. We also convolve the quartic solution for the EM field on the image plane with the point-spread function of a thin lens imaging telescope. By doing so, we are able to explore the direct relationship between the algebraic properties of the quartic solution for the EM field, the geometry of the astroid caustic, and the geometry and shape of the resulting Einstein-cross that appear on the image plane of the thin lens telescope. The new quartic solution leads to significant improvements in numerical modeling as evaluation of this solution is computationally far less expensive than a direct numerical treatment of the new diffraction integral. In the case of the solar gravitational lens (SGL), the new results drastically improve the speed of numerical simulations related to sensitivity analysis performed in the context of high-resolution imaging of exoplanets.

Lessons from the First Multiply Imaged Supernova: Revised Strong-lensing Models for the Galaxy Cluster MACS J1149.5+2223

Abstract We present two grid-based lens models for the galaxy cluster MACS J1149.5+2223, concentrating on the properties of the first multiply imaged supernova Refsdal, which first appeared in this cluster as an Einstein cross (images S1–S4) around a cluster galaxy in late 2014, and about a year later as an additional image (SX) in a different image of the supernova (SN) host galaxy. One model is our updated light-traces-mass (LTM) strong-lensing model for this cluster, and the second is a parametric model (dPIEeNFW), generated using the same pipeline but with a different parameterization. Together these two models probe different possible solutions in a relatively self-consistent manner and can be used to examine systematic uncertainties and relevant differences between the two parameterizations. We obtain reasonably similar (agreeing to within ≃1σ–3σ, in most cases) time delays and magnification ratios, with respect to S1, from the two different methods, although the LTM predictions seem to be systematically shorter/smaller for some of the images. Most notably, the time delay [and 95% CI] between the Einstein cross (in particular, image S1), and SX, differs substantially between the parametric method (326 [300–359] days) and the LTM method (224 [198–306] days), which seems to underestimate the true reappearance time. The cause for this systematic difference is unclear at present. We speculate on its possible origin and note that a refined measurement of SN Refsdal’s properties should help to more strongly discriminate between the two solutions, and thus between the two descriptions for the intrinsic shape of the underlying matter distribution. We also discuss the implications of our results for the Hubble constant.

Imaging point sources with the gravitational lens of an extended sun

We study the optical properties of the solar gravitational lens (SGL) while treating the Sun as an extended, axisymmetric and rotating body. The gravitational field of the Sun is represented using a set of zonal harmonics. We develop an analytical description of the intensity of light that is observed in the image plane in the strong interference region of a realistic SGL. This formalism makes it possible to model not only the point-spread function of point sources, but also actual observables, images that form in the focal plane of an imaging telescope positioned in the image plane. Perturbations of the monopole gravitational field of the Sun are dominated by the solar quadrupole moment, which results in forming an astroid caustic on the image plane. Consequently, an imaging telescope placed inside the astroid caustic observes four bright spots, forming the well-known pattern of an Einstein cross. The relative intensities and positions of these spots change as the telescope is moved in the image plane, with spots merging into bright arcs when the telescope approaches the caustic boundary. Outside the astroid caustic, only two spots remain and the observed pattern eventually becomes indistinguishable from the imaging pattern of a monopole lens at greater distances from the optical axis. We present results from extensive numerical simulations, forming the basis of our ongoing study of prospective exoplanet imaging with the SGL. These results are also applicable to describe a large class of gravitational lensing scenarios involving axisymmetric lenses that can be represented using zonal harmonics.

Gravitational lensing by an extended mass distribution

We continue our investigation of the optical properties of the solar gravitational lens (SGL). We treat the Sun as an extended axisymmetric body and model its gravitational field using zonal harmonics. We consider a point source that is positioned at a large but finite distance from the Sun and, using our new angular eikonal method, we established the electromagnetic field on the image plane in the focal region behind the SGL and derive the SGL impulse response in the form of its point-spread function (PSF). The expression that we derive describes the extended Sun in all regions of interest, including the regions of strong and weak interference and the region of geometric optics. The result is in the form of a single integral with respect to the azimuthal angle of the impact parameter, covering all lensing regimes of the SGL. The same expression can be used to describe gravitational lensing by a compact axisymmetric mass distribution, characterized by small deviations from spherical symmetry. It is valid in all lensing regimes. We also derive results that describe the intensity of light observed by an imaging telescope in the focal region. We present results of numerical simulations showing the view by a telescope that moves in the image plane toward the optical axis. We consider imaging of both point and extended sources. We show that while point sources yield a number of distinct images consistent with the caustics due to zonal harmonics of a particular order (e.g., Einstein cross), extended sources always result in the formation of an Einstein ring. These results represent the most comprehensive wave-theoretical treatment of gravitational lensing in the weak gravitational field of a compact axisymmetric gravitating object.

X-raying winds in distant quasars: The first high-redshift wind duty cycle

Aims. Theoretical models of wind-driven feedback from active galactic nuclei (AGN) often identify ultra-fast outflows as being the main agent in the generation of galaxy-sized outflows, which are possibly the main actors in establishing so-called AGN-galaxy co-evolution. Ultra-fast outflows are well characterized in local AGN but much less is known in quasars at the cosmic time when star formation and AGN activity peaked (z ≃ 1–3). It is therefore necessary to search for evidence of ultra-fast outflows in high-z sources to test wind-driven AGN feedback models. Methods. Here we present a study of Q2237+030, the Einstein Cross, a quadruply-imaged radio-quiet lensed quasar located at z = 1.695. We performed a systematic and comprehensive temporally and spatially resolved X-ray spectral analysis of all the available Chandra and XMM-Newton data (as of September 2019). Results. We find clear evidence for spectral variability, possibly due to absorption column density (or covering fraction) variability intrinsic to the source. For the first time in this quasar, we detect a fast X-ray wind outflowing at vout ≃ 0.1c that would be powerful enough (Ėkin ≃ 0.1 Lbol) to significantly affect the evolution of the host galaxy. We report also on the possible presence of an even faster component of the wind (vout ∼ 0.5c). For the first time in a high-z quasar, given the large sample and long time interval spanned by the analyzed X-ray data, we are able to roughly estimate the wind duty cycle as ≃0.46 (0.31) at 90% (95%) confidence level. Finally, we also confirm the presence of a Fe Kα emission line with variable energy, which we discuss in the light of microlensing effects as well as considering our findings on the source.

Liverpool-Maidanak monitoring of the Einstein Cross in 2006–2019

Quasar microlensing offers a unique opportunity to resolve tiny sources in distant active galactic nuclei and study compact object populations in lensing galaxies. We therefore searched for microlensing-induced variability of the gravitationally lensed quasar QSO 2237+0305 (Einstein Cross) using 4374 optical frames taken with the 2.0 m Liverpool Telescope and the 1.5 m Maidanak Telescope. These gVrRI frames over the 2006–2019 period were homogeneously processed to generate accurate long-term multi-band light curves of the four quasar images A–D. Through difference light curves, we found strong microlensing signatures. We then focused on the analytical modelling of two putative caustic-crossing events in image C, finding compelling evidence that this image experienced a double caustic crossing. Additionally, our overall results indicate that a standard accretion disc accounts reasonably well for the brightness profile of UV continuum emission sources and for the growth in source radius when the emission wavelength increases: Rλ ∝ λα, α = 1.33 ± 0.09. However, we caution that numerical microlensing simulations are required before firm conclusions can be reached on the UV emission scenario because the VRI-band monitoring during the first caustic crossing and one of our two α indicators lead to a few good solutions with α ≈ 1.

Decadal Variability Survey in MACSJ1149

Abstract We present a long temporal baseline variability survey in the Frontier Field MACSJ1149. In this study, we identify active galactic nuclei (AGNs) and other transient sources via their variability using over a decade of Hubble Space Telescope (HST) images for thousands of galaxies in the cluster region and detect significant variability in galaxies extending down to an apparent nuclear magnitude of m i < 26.5. Our analysis utilizes HST images obtained in six different wavelengths from 435 nm to 1.6 microns and covers timescales 12 hr to 12 yr apart. We find that ∼2% of galaxies in these images are variable, with 49 AGN candidates and 4 new supernovae candidates detected. Half of the variables are in the cluster and these are primarily elliptical galaxies displaying variability only in the near-infrared bands. About 20% of the AGN candidates have morphologies and colors consistent with quasars, though most of the variables appear to be dominated by the host galaxy light. The structure function for these sources shows a greater amplitude of variability at shorter wavelengths, with slopes shallower than typical quasars. We also report a previously unknown Einstein cross identified in this field.

Gravitational lensing by a magnetized compact object in the presence of plasma

In the weak field approximation, we study the gravitational lensing by spherical symmetric compact object immersed in magnetic field in the presence of magnetized plasma. The external magnetic field causes the split of the deflection angle of the photon, Einstein ring and Einstein cross as the counterpart of the Zeeman effect. In particular, the magnetic field affects the magnification of images, creating additional components. We also study the time delay of an electromagnetic signal due to the geometry and the gravitational field around the lensing source. We show that the time delay of the electromagnetic signal strongly depends on the plasma parameters, and it slightly decreases in the plasma in comparison with that in vacuum.

A New Einstein Cross Gravitational Lens of a Lyman-break Galaxy

Abstract We report the study of an “Einstein Cross” configuration first identified in a set of HST images by Cerny et al. Deep spectroscopic observations obtained at the Spanish 10.4 m Gran Telescopio Canarias telescope, allowed us to demonstrate the lens nature of the system, that consists of a Lyman-break galaxy (LBG), not a quasi-stellar object as is usually the case, at z = 3.03 lensed by a galaxy at z = 0.556. Combining the new spectroscopy with the archival HST data, it turns out that the lens is an elliptical galaxy with M V = −21.0, effective radius 2.8 kpc, and stellar velocity dispersion σ = 208 ± 39 km s−1. The source is an LBG with Lyα luminosity ∼L* at that redshift. From the modeling of the system, performed by assuming a singular isothermal ellipsoid (SIE) with external shear, we estimate that the flux source is magnified about 4.5 times, and the velocity dispersion of the lens is km s−1, in good agreement with the value derived spectroscopically. This is the second case known of an Einstein cross of an LBG.

Optical properties of magnetized black hole in plasma

We study in the weak field limit the gravitational lensing by spherically symmetric compact object immersed in an asymptotically uniform magnetic field in the presence of plasma and our approach is based on the medium modified Hamiltonian one. We show that the magnetized plasma in the environment of compact object may lead to split of the Einstein cross, creating additional lensed components. Finally we calculate magnification and time delay related to the individual images.

Synchronized Oscillations of Arterial Oxygen Saturation, Cerebral Tissue Oxygenation and Heart Rate in Preterm Neonates: Investigation of Long-Term Measurements with Multiple Einstein's Cross Wavelet Analysis.

In preterm neonates, the cardiovascular and cerebral vascular control is immature, making the brain vulnerable to an increased incidence of hypoxic and hyperoxic episodes. The aim of the study was to apply the recently developed multiple Einstein's cross wavelet analysis (MECWA) to quantify the coupling of fluctuations of peripherally measured arterial oxygen saturation (SpO2), cerebral tissue oxygen saturation (StO2) and heart rate (HR). Two long-term measurements on preterm neonates with a gestational age at birth of 26.4 and 26.8weeks and a postnatal age of 2.1 and 3.9weeks were analyzed. MECWA was applied to SpO2, StO2 and HR. MECWA showed that the fluctuations of SpO2, StO2 and HR were synchronized in the low-frequency range with periods of ~1h and ~0.5h. The amplitudes of the synchronization frequencies were dependent on the individual neonate. MECWA is a useful novel tool to assess the coupling of physiological signals. The parameters determined by MECWA seem to be related to the chronobiological processes, as well as constant regulations of the cardiovascular and cerebral perfusion state. MECWA was able to identify long-term synchronization of the cardiovascular and cerebral perfusion state in preterm neonates with periods of ~1h and ~0.5h.

Detection of the rapid variability in the Q2237+0305 quasar

Rapid intrinsic variability has been detected for the first time in the Einstein Cross QSO 2237+0305, a radio quiet flat spectrum quasar at z=1.7 that is quadruply lensed by a foreground galaxy at z=0.04. The observed short-period event at the time scale of several days and with amplitudes of about 0.1-0.2 mag can be traced in the light curves of the 2004 observing season for all macroimages and in all the three filters (V, R and I). The accuracy of the existing estimates of the time delays in Q2237+0305 is insufficient to either confirm or disprove the estimations of time delays based on the lens models of this system, especially taking into account the presence of strong microlensing events. The detected short-period variations in the Q2237+0305 light curves have made possible to obtain new estimates of the time delays, which are more accurate as compared to the earlier determinations by other authors.

SN REFSDAL: CLASSIFICATION AS A LUMINOUS AND BLUE SN 1987A-LIKE TYPE II SUPERNOVA

ABSTRACT We have acquired Hubble Space Telescope (HST) and Very Large Telescope near-infrared spectra and images of supernova (SN) Refsdal after its discovery as an Einstein cross in fall 2014. The HST light curve of SN Refsdal has a shape consistent with the distinctive, slowly rising light curves of SN 1987A-like SNe, and we find strong evidence for a broad Hα P-Cygni profile and Na I D absorption in the HST grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn, largely powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong Hα and Na I D absorption. From the grism spectrum, we measure an Hα expansion velocity consistent with those of SN 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the Hα emission of the WFC3 and X-shooter spectra, separated by ∼2.5 months in the rest frame, provide additional evidence that supports the SN 1987A-like classification. In comparison with other examples of SN 1987A-like SNe, photometry of SN Refsdal favors bluer B − V and V − R colors and one of the largest luminosities for the assumed range of potential magnifications. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material. Using MOSFIRE and X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3 ± 0.1 dex and <8.4 dex, respectively) near the explosion site.

The different origins of high- and low-ionization broad emission lines revealed by gravitational microlensing in the Einstein cross

We investigate the kinematics and ionization structure of the broad emission line region of the gravitationally lensed quasar QSO2237+0305 (the Einstein cross) using differential microlensing in the high- and low-ionization broad emission lines. We combine visible and near-infrared spectra of the four images of the lensed quasar and detect a large-amplitude microlensing effect distorting the high-ionization CIV and low-ionization H$\alpha$ line profiles in image A. While microlensing only magnifies the red wing of the Balmer line, it symmetrically magnifies the wings of the CIV emission line. Given that the same microlensing pattern magnifies both the high- and low-ionization broad emission line regions, these dissimilar distortions of the line profiles suggest that the high- and low-ionization regions are governed by different kinematics. Since this quasar is likely viewed at intermediate inclination, we argue that the differential magnification of the blue and red wings of H$\alpha$ favors a flattened, virialized, low-ionization region whereas the symmetric microlensing effect measured in CIV can be reproduced by an emission line formed in a polar wind, without the need of fine-tuned caustic configurations.

The Multiply Imaged Strongly Lensed Supernova Refsdal

AbstractIn 1964, Sjur Refsdal first considered the possibility that the light from a background supernova could traverse multiple paths around a strong gravitational lens towards us. He showed that the arrival times of the supernova's light would depend on the cosmic expansion rate, as well as the distribution of matter in the lens. I discussed the discovery of the first such multiply imaged supernova, which exploded behind the MACS J1149.6+2223 galaxy cluster. We have obtained Hubble Space Telescope grism and ground-based spectra of the four images of the supernova, which form an Einstein Cross configuration around an elliptical cluster member. These spectra as well as rest-frame optical light curves have allowed us to learn about the properties of the peculiar core-collapse supernova explosion, which occurred 4.3 Gyr after the Bang Bang, and contain information about the lenses matter distribution as well as their stellar populations. A delayed image of the supernova is expected close to the galaxy cluster center as early as this Fall, and will serve as an unprecedented probe of the potential of a massive galaxy cluster.

Einstein cross in supernovae

Einstein cross in supernovae

Predicted properties of multiple images of the strongly lensed supernova SN Refsdal

Abstract We construct a mass model of the cluster MACS J1149.6+2223 to study the expected properties of multiple images of SN Refsdal, the first example of a gravitationally lensed supernova with resolved multiple images recently reported by Kelly et al. We find that the best-fitting model predicts six supernova images in total, i.e. two extra images in addition to the observed four Einstein cross supernova images S1–S4. One extra image is predicted to have appeared about 17 years ago, whereas the other extra image is predicted to appear in about one year from the appearance of S1–S4, which is a testable prediction with near-future observations. The predicted magnification factors of individual supernova images range from ∼18 for the brightest image to ∼4 for the faint extra images. Confronting these predictions with future observations should provide an unprecedented opportunity to improve our understanding of cluster mass distributions.

The spinning heart of the Einstein Cross

Black Holes![Figure][1] PHOTO: NASA/ESA/STSCI Supermassive black holes power entire galaxies from their cores, but how they grew so large is uncertain. When astronomers describe a black hole, they rely on two features: its mass and how fast it spins. The spin rate provides information about how the black hole grew, but it is tricky to measure. Reynolds et al. have determined the spin for the most distant quasar yet, a source called the Einstein Cross. This source got its name because the quasar's light is bent around a massive galaxy and reimaged four times. The high spin rate suggests that several dramatic accretion events produced the black hole rather than many small ones. Astrophys. J. Lett. 10.1088/2041-8205/792/1/L19 (2014). [1]: pending:yes