Electromagnetic Observations Research Articles

Prospects for Multimessenger Observations of Thorne–Żytkow Objects

Abstract Thorne–Żytkow objects (TŻOs) are a class of stellar object comprised of a neutron star core surrounded by a large and diffuse envelope. Their exterior appearance is identical to red supergiants; the distinctive electromagnetic signature of a TŻO is a suite of unusual chemical abundance patterns, including excesses of Li, Rb, Mo, and Ca. However, electromagnetic observations cannot unambiguously identify the presence of a neutron star core. Detection of continuous gravitational wave emission from a rotating neutron star core would provide strong supporting evidence for the existence of TŻOs. We present a model for gravitational wave detector confirmation of TŻOs and demonstrate that these objects should be detectable with Advanced LIGO. We also investigate possible targets for joint optical and gravitational searches, and comment on prospects for detectability in both current and future gravitational wave detector networks.

High-energy Neutrinos from Choked Gamma-Ray Bursts in Active Galactic Nucleus Accretion Disks

Abstract Both long-duration gamma-ray bursts (LGRBs) from the core collapse of massive stars and short-duration GRBs (SGRBs) from mergers of a binary neutron star or a neutron star–black hole are expected to occur in the accretion disk of active galactic nuclei (AGNs). We show that GRB jets embedded in the migration traps of AGN disks are promised to be choked by the dense disk material. Efficient shock acceleration of cosmic rays at the reverse shock is expected, and high-energy neutrinos would be produced. We find that these sources can effectively produce detectable TeV–PeV neutrinos through pγ interactions. From a choked LGRB jet with isotropic equivalent energy of 1053 erg at 100 Mpc, one expects ∼2(7) neutrino events detectable by IceCube (IceCube-Gen2). The contribution from choked LGRBs to the observed diffuse neutrino background depends on the unknown local event rate density of these GRBs in AGN disks. For example, if the local event rate density of choked LGRBs in an AGN disk is ∼5% that of low-luminosity GRBs (∼10 Gpc−3 yr−1), the neutrinos from these events would contribute to ∼10% of the observed diffuse neutrino background. Choked SGRBs in AGN disks are potential sources for future joint electromagnetic, neutrino, and gravitational wave multimessenger observations.

Estimates of the Early Electromagnetic Emission from Compact Binary Mergers

Abstract Compact binary mergers that involve at least one neutron star, either binary neutron star or black hole–neutron star coalescences, are thought to be the potential sources of electromagnetic emission due to the material ejected during the merger or those left outside the central object after the merger. Since the intensity of these electromagnetic transients decays rapidly with time, one should pay more attention to early emissions from such events, which are useful in revealing the nature of these mergers. In this work, we study the early emission of kilonovae, short gamma-ray bursts (GRBs), and cocoons that could be produced in those mergers. We estimate their luminosities and timescales as functions of the chirp mass, which is the most readily constrained parameter from the gravitational wave detections of these events. We focus on the range of chirp mass as 1.3–2.7 M ⊙, which is compatible with one of the merging components being a so-called “mass gap” black hole. We show that the electromagnetic observation of these transients could be used to distinguish the types of the mergers when the detected chirp mass falls in the range of 1.5–1.7 M ⊙. Applying our analysis to the subthreshold GRB GBM-190816, we found that for this particular event the effective spin should be larger than 0.6 and the mass of the heavier object might be larger than 5.5 M ⊙ for the phenomenological Steiner–Fischer–Hempel equation of state.

Testing F(R) Gravity with the Simulated Data of Gravitational Waves from the Einstein Telescope

Abstract In this paper we analyze the implications of gravitational waves (GWs) as standard sirens on the modified gravity models by using the third-generation GW detector, i.e., the Einstein Telescope. Two viable models in f(R) theories within the Palatini formalism are considered in our analysis ( and ), with the combination of simulated GW data and the latest electromagnetic (EM) observational data (including the recently released Pantheon type Ia supernovae sample, the cosmic chronometer data, and baryon acoustic oscillation distance measurements). Our analysis reveals that the standard siren GWs, which provide an independent and complementary alternative to current experiments, could effectively eliminate the degeneracies among parameters in the two modified gravity models. In addition, we thoroughly investigate the nature of geometrical dark energy in the modified gravity theories with the assistance of Om(z) and statefinder diagnostic analysis. The present analysis makes it clear-cut that the simplest cosmological constant model is still the most preferred by the current data. However, the combination of future naturally improved GW data and the most recent EM observations will reveal the consistency or acknowledge the tension between the ΛCDM model and modified gravity theories.

Geoelectrical inhomogeneities of the Crimean region as the seismicity and oil-gas potential zones

The three-dimensional geoelectrical model of the Earth’s crust and upper mantle of the Crimean region and adjacent territories has been built for the first time. It is based on the results of the Earth’s low-frequency electromagnetic field experimental observations, conducted in 2008—2013 by the Institutes of the National Academy of Sciences of Ukraine. The subvertical conductive zones or contacts of the different resistivity mainly in the near-surface layers coincide with the fault structures, most of which are confined to the boundaries between the different tectonic elements, such as the Scythian Plate and Mountain Crimea, North and South Kerch Zones and the other faults: Chongarskiy, Melitopol-Novotsarytsynskiy, Korsarsko-Feodosiyskiy, Gornostaevskiy and Kerch-Chkalivskiy. The Mykolayiv and West Crimean fault systems occur as large separate submeridional conductive zone. Deeper in the Earth’s crust and upper mantle, geoelectrical inhomogeneities are transformed into the subhorizontal structures (layers) and manifest themselves in regional anomalies. This fact may indicate the high permeability for deep fluids of contact zones during their formation. The deep sublatitudinal structure in the Earth’s crust is confidently traced, in the west it confirms and details the well-known Tarkhankut anomaly, and continues through the central Crimea to the northwestern part of the Kerch Peninsula. It is assumed that there is the strong sublatitudinal anomaly in the interior of the northwestern shelf of the Black Sea and in the northeastern part of the Kerch-Taman Depression at the crust — upper mantle boundary, it is contouring the Crimean Peninsula. The ultradeep fluid manifestation zones obtained according to seismotomography, the conductivity anomalies in the Earth’s crust and the upper mantle, increased heat flow and the spread of the earthquake hypocenters confirm the relationship between the Crimea seismicity and collision processes. It is shown the spatial coincidences of the hydrocarbon manifestations and the isolated conductivity anomalies, which are characterized by subvertical channels galvanically connected to sediments, or subvertical contact zones of different resistivity, which are observed not only in the Earth’s crust but also in the upper mantle layers (60—90, 110—140 km) and may cause the superdeep fluid inflow.

Time‐Domain Modeling of Three‐Dimensional Earth's and Planetary Electromagnetic Induction Effect in Ground and Satellite Observations

AbstractElectric currents induced in conductive planetary interiors by time‐varying magnetospheric and ionospheric current systems have a significant effect on electromagnetic (EM) field observations. Complete characterization of EM induction effects is difficult owing to nonlinear interactions between the three‐dimensional electrical structure of a planet and spatial complexity of inducing current systems. We present, a general framework for time‐domain modeling of three‐dimensional EM induction effects in heterogeneous conducting planets. Our approach does not assume that the magnetic field is potential, allows for an arbitrary distribution of electrical conductivity within a planet, and can deal with spatially complex time‐varying current systems. The method is applicable to both data measured at stationary observation sites and satellite platforms, and enables the calculation of three‐dimensional EM induction effects in near real‐time settings.

Follow-up of Astrophysical Transients in Real Time with the IceCube Neutrino Observatory

Abstract In multi-messenger astronomy, rapid investigation of interesting transients is imperative. As an observatory with a 4π steradian field of view, and ∼99% uptime, the IceCube Neutrino Observatory is a unique facility to follow up transients, as well as to provide valuable insights for other observatories and inform their observational decisions. Since 2016, IceCube has been using low-latency data to rapidly respond to interesting astrophysical events reported by the multi-messenger observational community. Here, we describe the pipeline used to perform these followup analyses, and provide a summary of the 58 analyses performed as of July 2020. We find no significant signal in the first 58 analyses performed. The pipeline has helped inform various electromagnetic observation strategies, and has constrained neutrino emission from potential hadronic cosmic accelerators.

Where Binary Neutron Stars Merge: Predictions from IllustrisTNG

Abstract The rate and location of binary neutron star (BNS) mergers are determined by a combination of the star formation history and the delay-time distribution (DTD) function. In this paper, we couple the star formation rate histories from the IllustrisTNG model to a series of varied assumptions for the BNS DTD to make predictions for the BNS merger host galaxy mass function. These predictions offer two outcomes: (i) in the near term they influence the BNS merger event follow-up strategy by scrutinizing where most BNS merger events are expected to occur, and (ii) in the long term they constrain the DTD for BNS merger events once the host galaxy mass function is observationally well determined. From our fiducial model analysis, we predict that 50% of BNS mergers will occur in host galaxies with stellar mass between 1010 and 1011 M ⊙, 68% between 4 × 109 and 3 × 1011 M ⊙, and 95% between 4 × 108 and 2 × 1012 M ⊙. We find that the details of the DTD employed do not have a strong effect on the peak of the host mass function. However, varying the DTD provides enough spread that the true DTD can be determined from enough electromagnetic observations of BNS mergers. Knowing the true DTD can help us determine the prevalence of BNS systems formed through highly eccentric and short-separation fast-merging channels and can constrain the dominant source of r-process material.

A new borehole electromagnetic receiver developed for controlled-source electromagnetic methods

Abstract. Conventional surface electromagnetic methods have limitations of a shallow detection depth and low resolution. To increase the detection depth and resolution, borehole–surface electromagnetic methods for electromagnetic three-dimensional observations of the ground, tunnels, and boreholes have been developed. Current borehole receivers only measure a single parameter of the magnetic field component, which does not meet the special requirements of controlled-source electromagnetic (CSEM) methods. This study proposes a borehole electromagnetic receiver that realizes synchronous acquisition of the vertical electric field component in the borehole and the three-axis orthogonal magnetic field components. This receiver uses Ti electrodes and fluxgate magnetometers (fluxgates) as sensors to acquire electric and magnetic field components. Multi-component comprehensive observation methods that add the electric field component can effectively support the CSEM method, improve detection accuracy, and exhibit a strong potential for detecting deep ore bodies. We conducted laboratory and field experiments to verify the performance of our new borehole electromagnetic receiver. The receiver achieved a magnetic field noise of less than 6 pTHz-1/2 at 1 kHz, and the electric field noise floor was approximately 20 nVm-1Hz-1/2 at 1 kHz. The −3 dB electric field bandwidth can reach DC −10 kHz. The results of our experiments prove that high-quality CSEM signals can be obtained using this new borehole electromagnetic receiver and that the electric field component exhibits sufficient advantages for measuring the vertical component of the electric field.

Black Holes and Other Clues to the Quantum Structure of Gravity

Bringing gravity into a quantum-mechanical framework is likely the most profound remaining problem in fundamental physics. The “unitarity crisis” for black hole evolution appears to be a key facet of this problem, whose resolution will provide important clues. Investigating this raises the important structural question of how to think about subsystems and localization of information in quantum gravity. Paralleling field theory, the answer to this is expected to be an important ingredient in the mathematical structure of the theory. Perturbative gravity results indicate a structure different from that of quantum field theory, but suggest an avenue to defining subsystems. If black holes do behave similarly to familiar subsystems, unitarity demands new interactions that transfer entanglement from them. Such interactions can be parameterized in an effective approach, without directly addressing the question of the fundamental dynamics, whether that is associated with quantum spacetime, wormholes, or something else. Since such interactions need to extend outside the horizon, that raises the question of whether they can be constrained, or might be observed, by new electromagnetic or gravitational wave observations of strong gravity regions. This note overviews and provides connections between these developments.

A tidal disruption event coincident with a high-energy neutrino

Cosmic neutrinos provide a unique window into the otherwise-hidden mechanism of particle acceleration in astrophysical objects. A flux of high-energy neutrinos was discovered in 2013, and the IceCube Collaboration recently reported the likely association of one high-energy neutrino with a flare from the relativistic jet of an active galaxy pointed towards the Earth. However a combined analysis of many similar active galaxies revealed no excess from the broader population, leaving the vast majority of the cosmic neutrino flux unexplained. Here we present the likely association of a radio-emitting tidal disruption event, AT2019dsg, with a second high-energy neutrino. AT2019dsg was identified as part of our systematic search for optical counterparts to high-energy neutrinos with the Zwicky Transient Facility. The probability of finding any coincident radio-emitting tidal disruption event by chance is 0.5%, while the probability of finding one as bright in bolometric energy flux as AT2019dsg is 0.2%. Our electromagnetic observations can be explained through a multi-zone model, with radio analysis revealing a central engine, embedded in a UV photosphere, that powers an extended synchrotron-emitting outflow. This provides an ideal site for PeV neutrino production. Assuming that the association is genuine, our observations suggest that tidal disruption events with mildly-relativistic outflows contribute to the cosmic neutrino flux.

Combining Electromagnetic and Gravitational-Wave Constraints on Neutron-Star Masses and Radii.

We perform a joint Bayesian inference of neutron-star mass and radius constraints based on GW170817, observations of quiescent low-mass x-ray binaries (QLMXBs), photospheric radius expansion x-ray bursting sources, and x-ray timing observations of J0030+0451. With this dataset, the form of the prior distribution still has an impact on the posterior mass-radius curves and equation of state (EOS), but this impact is smaller than recently obtained when considering QLMXBs alone. We analyze the consistency of the electromagnetic data by including an "intrinsic scattering" contribution to the uncertainties, and find only a slight broadening of the posteriors. This suggests that the gravitational-wave and electromagnetic observations of neutron-star structure are providing a consistent picture of the neutron-star mass-radius curve and the EOS.

Constraining extra dimensions on cosmological scales with LISA future gravitational wave siren data

The Universe is undergoing a late time acceleration. We investigate the idea that this acceleration could be the consequence of gravitational leakage into extra dimensions on cosmological scales rather than the result of a non-zero cosmological constant, and consider the ability of future gravitational-wave (GW) siren observations to probe this phenomenon and constrain the parameters of phenomenological models of this gravitational leakage. A gravitational space interferometer such as LISA will observe massive black hole binary (MBHB) merger events at cosmological distances, and will also provide sky localization information that may permit optical and other electromagnetic (EM) surveys to identify an EM counterpart of these events. In theories that include additional non-compact spacetime dimensions, the gravitational leakage intro extra dimensions leads to a reduction in the amplitude of observed gravitational waves and thereby a systematic discrepancy between the distance inferred to such sources from GW and EM observations. We investigate the capability of LISA to probe this modified gravity on large scales, specifically in the Dvali, Gabadadze and Porrati (DGP) model. Additionally, we include a Supernova Ia sample at lower redshift in order to explore the efficacy of this cosmological probe across a range of redshifts. We then use previously published simulated catalogues of cosmologically distant MBHB merger events detectable by LISA, and which are likely to produce an observable EM counterpart. We find that the extent to which LISA will be able to place limits on the number of spacetime dimensions and other cosmological parameters characterising modified gravity will strongly depend on the actual number and redshift distribution of sources, together with the uncertainty on the GW distance measurements. A relatively small number of sources (∼ 1) and high measurement uncertainties would strongly restrict the ability of LISA to place meaningful constraints on the parameters in cosmological scenarios where gravity is only five-dimensional and modified at scales larger than about ∼ 4 times the Hubble radius. Conversely, if the number of sources observed amounts to a four-year average of ∼ 27, then in the most favourable cosmological scenarios LISA has the potential to place meaningful constraints on the cosmological parameters—with a precision of ∼ 1% on the number of dimensions and ∼ 7.5% on the scale beyond which gravity is modified, thereby probing the late expansion of the universe up to a redshift of ∼ 8, i.e. on scales not yet tested by present EM observations.

Search for Radio Remnants of Nearby Off-axis Gamma-Ray Bursts in a Sample of Swift/BAT Events

Abstract The multi-messenger discovery of gravitational waves (GWs) and light from the binary neutron star (NS) merger GW170817, associated with gamma-ray burst (GRB) 170817A and kilonova AT2017gfo, has marked the start of a new era in astrophysics. GW170817 has confirmed that binary NS mergers are progenitors of at least some short GRBs. The peculiar properties of the GRB 170817A radio afterglow, characterized by a delayed onset related to the off-axis geometry, have also demonstrated how some nearby short GRBs may not be identified as such with standard short-timescale electromagnetic follow-up observations. Building upon this new information, we performed late-time radio observations of a sample of four short GRBs with unknown redshift and no previously detected afterglow in the Swift/BAT sample in order to identify nearby ( Mpc) off-axis GRB candidates via their potential late-time radio signatures. We find a previously uncatalogued radio source within the error region of GRB 130626 with a flux density consistent with an NS radio flare at a distance of ∼100 Mpc. An origin related to a persistent radio source unrelated to the GRB cannot be excluded nor confirmed given the high chance of false positives in error regions as large as those considered here, and the limited time baseline of our observations. Further radio (and X-ray) follow-up observations are needed to better understand the origin of this source.

Application of airborne electromagnetic method in the exploration of Qingchengzi mine in Liaoning Province, China

Qingchengzi area of Liaoning Province is an important concentration of polymetallic minerals in China. But with the long-term mining, Qingchengzi mining area has become a crisis mine, and the prospecting and prediction in the mining area has become a key work. The resistivity data is closely related to the existence of minerals. We carried out the VTEM airborne electromagnetic observation in this area. The primary processing results show that the inversion result is very consistent with the existing geological information. The processing results of airborne electromagnetic data will provide an important guarantee for the electrical structure, fault distribution and structural framework in the ore concentration area, as well as the delineation of the mineral target area.

Weighing Milky Way satellites with LISA

ABSTRACT White dwarf stars are a well-established tool for studying Galactic stellar populations. Two white dwarfs in a tight binary system offer us an additional messenger – gravitational waves – for exploring the Milky Way and its immediate surroundings. Gravitational waves produced by double white dwarf (DWD) binaries can be detected by the future Laser Interferometer Space Antenna (LISA). Numerous and widespread DWDs have the potential to probe shapes, masses, and formation histories of the stellar populations in the Galactic neighbourhood. In this work we outline a method for estimating the total stellar mass of Milky Way satellite galaxies based on the number of DWDs detected by LISA. To constrain the mass we perform a Bayesian inference using binary population synthesis models and considering the number of detected DWDs associated with the satellite and the measured distance to the satellite as the only inputs. Based on a fiducial binary population synthesis model we find that for large satellites the stellar masses can be recovered to within (1) a factor 2 if the star formation history (SFH) is known and (2) an order of magnitude when marginalizing over different SFH models. For smaller satellites we can place upper limits on their stellar mass. Gravitational wave observations can provide mass measurements for large satellites that are comparable, and in some cases more precise, than standard electromagnetic observations.

Testing the general theory of relativity using gravitational wave propagation from dark standard sirens

ABSTRACT Alternative theories of gravity predict modifications in the propagation of gravitational waves (GW) through space–time. One of the smoking-gun predictions of such theories is the change in the GW luminosity distance to GW sources as a function of redshift relative to the electromagnetic (EM) luminosity distance expected from EM probes. We propose a multimessenger test of the theory of general relativity from the propagation of GWs by combining EM and GW observations to resolve these issues from GW sources without EM counterparts (which are also referred to as dark standard sirens). By using the relation between the geometric distances accessible from baryon acoustic oscillation measurements, and luminosity distance measurements from the GW sources, we can measure any deviation from the general theory of relativity via the GW sources of unknown redshift that will be detectable by networks of GW detectors such as LIGO, Virgo, and KAGRA. Using this technique, the fiducial value of the frictional term can be measured to a precision $\Xi _0=0.98^{+0.04}_{-0.23}$ after marginalizing over redshift dependence, cosmological parameters, and GW bias parameters with ∼3500 dark standard sirens of masses $30\, \rm M_\odot$ each distributed up to redshift z = 0.5. For a fixed redshift dependence, a value of $\Xi _0=0.99^{+0.02}_{-0.02}$ can be measured with a similar number of dark sirens. Application of our methodology to the far more numerous dark standard sirens detectable with next-generation GW detectors, such as LISA, Einstein Telescope and Cosmic Explorer, will allow achievement of higher accuracy than possible from use of bright standard sirens.

ІНТЕРПРЕТАЦІЯ 3D ГЕОЕЛЕКТРИЧНОЇ МОДЕЛІ НАДР СТЕПОВОГО КРИМУ. ЄВПАТОРІЙСЬКИЙ ТА САКСЬКИЙ ПРОФІЛІ

The interpretation of the segment of the deep three-dimensional Crimean region geoelectrical model within the Saki and Yevpatoria profiles, built on the basis of the Earth's low-frequency electromagnetic field experimental observations, was obtained in 2012 by the INSTITUTE OF GEOPHYSICS named after S.I.Subbotin. The main result of the analysis is the identification of vertical and horizontal alternation of high and low resistivity, both in the earth's crust and in the upper mantle. It is shown that the geoelectrical sections along all the profile sections of the model are characterized by a dip to the north of the consolidated basement surface depth and, accordingly, an increase of the near-surface layer conductivity. The conductivity anomaly in the consolidated earth's crust was revealed in the depth interval of 5-10 km with resistivity (ρ) of 5 Ohmꞏm, galvanically connected with the sedimentary cover. Deeper than 10 km, homogeneous and inhomogeneous layers in ρ alternate: 10-60 km with ρ = 1000 Ohmꞏm; 60-90 km with ρ = 100 and 1000 Ohmꞏm; 90-110 km with ρ = 1000 Ohmꞏm; 110-140 km with ρ = 40 and 1000 Ohmꞏm, the contact corresponds to the different ρ of normal geoelectrical sections of different-aged structures of the Scythian plate and the East European platform; also horizontally layered normal section. It has been analyzed that earthquake sources of the Steppe Crimea seismic region are concentrated in geoelectrically inhomogeneous zones and tend to contact structures with ρ differ - above the upper margin, outside and between the conductivity anomalies in the consolidated rocks of the earth's crust. The considered material confidently indicates the confinement of hydrocarbon manifestations to the high electrical conductivity anomalies identified according to the data of geoelectromagnetical sounding and three-dimensional modeling, which are characterized by subvertical channels galvanically connected with sedimentary deposits, and layering in the earth's crust and upper mantle. Geoelectrical inhomogeneities, which reflect the current state of the earth's crust and upper mantle and are probably due to the influence of modern mantle fluids, correspond to manifestations of seismicity and hydrocarbon content.

Constraining scalar-tensor modified gravity with gravitational waves and large scale structure surveys

The first multi-messenger gravitational wave event has had a transformative effect on the space of modified gravity models. In this paper we study the enhanced tests of gravity that are possible with a future set of gravitational wave standard siren events. We perform MCMC constraint forecasts for parameters in Horndeski scalar-tensor theories. In particular, we focus on the complementarity of gravitational waves with electromagnetic large-scale structure data from galaxy surveys. We find that the addition of fifty low redshift (z ≲ 0.2) standard sirens from the advanced LIGO network offers only a modest improvement (a factor 1.1–1.3, where 1.0 is no improvement) over existing constraints from electromagnetic observations of large-scale structures. In contrast, high redshift (up to z ∼ 10) standard sirens from the future LISA satellite will improve constraints on the time evolution of the Planck mass in Horndeski theories by a factor ∼ 5. By simulating different scenarios, we find this improvement to be robust to marginalisation over unknown merger inclination angles and to variation between three plausible models for the merger source population.

First Observations of Elves and Their Causative Very Strong Lightning Discharges in an Unusual Small‐Scale Continental Spring‐Time Thunderstorm

AbstractWe show for the first time that elves can be produced by an unusual small‐scale continental spring‐time thunderstorm. The storm occurred in Central Europe, covered a very small area of ∼50 × ∼30 km and lasted only for ∼4 h on April 2, 2017. The fraction of intense positive cloud‐to‐ground lightning strokes was unusually high, reaching 55%, with a mean peak current of 64 kA. The peak currents of return strokes (RS) associated with elves exceeded ∼300 kA. Elves and their causative RS have been observed with different optical and electromagnetic recordings. Signatures of ionospheric disturbances indicating the presence of elves were found in measurements of displacement currents, ionospheric reflections of sferics and man‐made narrow‐band transmissions. All these electromagnetic observations coincide with four optical detections of elves and strongly suggest the occurrence of two more elves later in the decaying phase of the storm. Surprisingly, the same electromagnetic measurements indicate that other strong strokes did not produce any elves. Our simulation results show that the formation of an elve is not only determined by the high‐peak current of their causative strokes but that it is also controlled by the conductivity of the lightning channels and velocity of the current wavefront. We hypothesize that because of a lower conductivity of RS lightning channels and/or slower current waves only very strong strokes with peak currents above ∼300 kA might have been capable to produce observable elves during this thunderstorm.