arXiv subjects

J. Harms

Publications and source records attributed to J. Harms.

At least 19 recordsLinked to original sources

arXiv2026

A new era for Dual AGN science with SHARP

The search for and the characterization of ultra-compact dual active galactic nuclei (AGN) are among the hottest topics of current extragalactic astrophysics. These systems involve two accreting massive black holes (MBHs) embedded within the same host galaxy, with relative projected separations from a few hundred pc down to a few pc. They are central to understanding hierarchical galaxy formation, black hole growth and demographics, and accretion-feedback coupling in the most extreme interaction phases. Even more compellingly, such tight pairs are the most direct precursors of gravitationally bound binary MBHs (sub-pc scale separation), which are among the loudest emitters of gravitational waves (GWs) in the low-frequency ranges. SHARP will deliver the first statistical census and physical characterization of ultra-compact dual AGN up to cosmic distances, finally bridging the observational gap between kpc-scale pairs and sub-pc GW-emitting binaries, and enabling a breakthrough understanding of MBH growth, feedback and co-evolution across cosmic time.

astro-ph.GA↗

arXiv2025

Expanding Horizons - Transforming Astronomy in the 2040s Time-Domain Multi-Messenger Astronomy in the 2040s: EM Follow-up of LGWA Sources

The coming decades will see gravitational-wave (GW) astronomy expand decisively into the mHz-Hz frequency range, opening access to a population of compact binaries that are currently invisible or only detectable moments before merger. The Lunar Gravitational Wave Antenna (LGWA) concept is designed to probe this gap, enabling continuous observation of compact binaries over months to years prior to coalescence, and detecting sources inaccessible to both space-based mHz detectors and current ground-based >10 Hz facilities. This new GW window fundamentally alters the landscape of time-domain multi-messenger astronomy. Rather than reacting to mergers after the fact, LGWA enables predictive, scheduled electromagnetic (EM) follow-up, transforming how compact-object mergers, their environments, and their astrophysical channels are studied. However, fully exploiting LGWA discoveries requires EM capabilities that do not exist today and are unlikely to be available by the 2030s, particularly for wide-area, rapid, spectroscopically rich follow-up at optical and near-infrared wavelengths. This White Paper identifies the key science cases enabled by LGWA that motivate new ground-based capabilities in the 2040s.

astro-ph.IM↗

arXiv2024

Prospects for optical detections from binary neutron star mergers with the next-generation multi-messenger observatories

Next-generation gravitational wave (GW) observatories, such as the Einstein Telescope (ET) and Cosmic Explorer, will observe binary neutron star (BNS) mergers across cosmic history, providing precise parameter estimates for the closest ones. Innovative wide-field observatories, such as the Vera Rubin Observatory, will quickly cover large portions of the sky with unprecedented sensitivity to detect faint transients. This study aims to assess the prospects for detecting optical emissions from BNS mergers with next-generation detectors, considering how uncertainties in neutron star (NS) population properties and microphysics may affect detection rates. Starting from BNS merger populations exploiting different NS mass distributions and equations of state (EOSs), we model the GW and kilonova (KN) signals based on source properties. We model KN ejecta through numerical-relativity informed fits, considering the effect of prompt collapse of the remnant to black hole and new fitting formulas appropriate for more massive BNS systems, like GW190425. We include optical afterglow emission from relativistic jets consistent with observed short gamma-ray bursts. We evaluate the detected mergers and the source parameter estimations for different geometries of ET, operating alone or in a network of current or next-generation GW detectors. Finally, we estimate the number of detected optical signals simulating realistic observational strategies by the Rubin Observatory. ET as a single observatory will enable the detection of about ten to a hundred KNe per year by the Rubin Observatory. This improves by a factor of about 10 already when operating in the network with current GW detectors. Detection rate uncertainties are dominated by the poorly constrained local BNS merger rate, and depend to a lesser extent on the NS mass distribution and EOS.

astro-ph.HE↗

arXiv2021

Synergies of THESEUS with the large facilities of the 2030s and guest observer opportunities

The proposed THESEUS mission will vastly expand the capabilities to monitor the high-energy sky, and will exploit large samples of gamma-ray bursts to probe the early Universe back to the first generation of stars, and to advance multi-messenger astrophysics by detecting and localizing the counterparts of gravitational waves and cosmic neutrino sources. The combination and coordination of these activities with multi-wavelength, multi-messenger facilities expected to be operating in the thirties will open new avenues of exploration in many areas of astrophysics, cosmology and fundamental physics, thus adding considerable strength to the overall scientific impact of THESEUS and these facilities. We discuss here a number of these powerful synergies.

astro-ph.IM↗

arXiv2020

Technologies for the ELGAR large scale atom interferometer array

We proposed the European Laboratory for Gravitation and Atom-interferometric Research (ELGAR), an array of atom gradiometers aimed at studying space-time and gravitation with the primary goal of observing gravitational waves (GWs) in the infrasound band with a peak strain sensitivity of $3.3 \times 10^{-22}/\sqrt{\text{Hz}}$ at 1.7 Hz. In this paper we detail the main technological bricks of this large scale detector and emphasis the research pathways to be conducted for its realization. We discuss the site options, atom optics, and source requirements needed to reach the target sensitivity. We then discuss required seismic isolation techniques, Gravity Gradient Noise reduction strategies, and the metrology of various noise couplings to the detector.

physics.atom-ph↗

arXiv2019

Seismic array measurements at Virgo's West End Building for the configuration of a Newtonian-noise cancellation system

Terrestrial gravity fluctuations produce so-called Newtonian noise (NN) which is expected to limit the low frequency sensitivity of existing gravitational-waves (GW) detectors LIGO and Virgo, when they will reach their full potential, and of next-generation detectors like the Einstein Telescope. In this paper, we present a detailed characterization of the seismic field at Virgo's West End Building as part of the development of a Newtonian noise cancellation system. The cancellation system will use optimally filtered data from a seismometer array to produce an estimate of the Newtonian-noise generated by the seismic field, and to subtract this estimate from the gravitational-wave channel of the detector. By using an array of 38 seismic sensors, we show that, despite the influence of the complexity of Virgo's infrastructure on the correlation across the array, Wiener filtering can still be very efficient in reconstructing the seismic field around the test-mass location. Taking into account the division of the building's foundations into separate concrete slabs, and the different properties of the seismic field across them, we conclude that the arrays to be used for the Newtonian-noise cancellation at Virgo will require a relatively large number of seismometers per test mass, i.e. significantly more than 10. Moreover, observed variations of the absolute noise residuals over time, related to the daily evolution of anthropogenic noise, suggest that the Wiener filter will need to be updated regularly, probably more often than every hour, to achieve stationarity of the background level after subtraction.

astro-ph.IM↗

arXiv2019

Coherence-based approaches for estimating the composition of the seismic wavefield

As new techniques exploiting the Earth's ambient seismic noise field are developed and applied, such as for the observation of temporal changes in seismic velocity structure, it is crucial to quantify the precision with which wave-type measurements can be made. This work uses array data at the Homestake mine in Lead, South Dakota and an array at Sweetwater, Texas to consider two aspects that control this precision: the types of seismic wave contributing to the ambient noise field at microseism frequencies and the effect of array geometry. Both are quantified using measurements of wavefield coherence between stations in combination with Wiener filters. We find a strong seasonal change between body-wave and surface-wave content. Regarding the inclusion of underground stations, we quantify the lower limit to which the ambient noise field can be characterized and reproduced; the applications of the Wiener filters are about 4 times more successful in reproducing ambient noise waveforms when underground stations are included in the array, resulting in predictions of seismic timeseries with less than a 1\% residual, and are ultimately limited by the geometry and aperture of the array, as well as by temporal variations in the seismic field. We discuss the implications of these results for the geophysics community performing ambient seismic noise studies, as well as for the cancellation of seismic Newtonian gravity noise in ground-based, sub-Hz, gravitational-wave detectors.

gr-qc↗

arXiv2019

ELGAR -- a European Laboratory for Gravitation and Atom-interferometric Research

Gravitational Waves (GWs) were observed for the first time in 2015, one century after Einstein predicted their existence. There is now growing interest to extend the detection bandwidth to low frequency. The scientific potential of multi-frequency GW astronomy is enormous as it would enable to obtain a more complete picture of cosmic events and mechanisms. This is a unique and entirely new opportunity for the future of astronomy, the success of which depends upon the decisions being made on existing and new infrastructures. The prospect of combining observations from the future space-based instrument LISA together with third generation ground based detectors will open the way towards multi-band GW astronomy, but will leave the infrasound (0.1 Hz to 10 Hz) band uncovered. GW detectors based on matter wave interferometry promise to fill such a sensitivity gap. We propose the European Laboratory for Gravitation and Atom-interferometric Research (ELGAR), an underground infrastructure based on the latest progress in atomic physics, to study space-time and gravitation with the primary goal of detecting GWs in the infrasound band. ELGAR will directly inherit from large research facilities now being built in Europe for the study of large scale atom interferometry and will drive new pan-European synergies from top research centers developing quantum sensors. ELGAR will measure GW radiation in the infrasound band with a peak strain sensitivity of $4.1 \times 10^{-22}/\sqrt{\text{Hz}}$ at 1.7 Hz. The antenna will have an impact on diverse fundamental and applied research fields beyond GW astronomy, including gravitation, general relativity, and geology.

physics.atom-ph↗

arXiv2018

Implications of dedicated seismometer measurements on Newtonian-noise cancellation for Advanced LIGO

Newtonian gravitational noise from seismic fields will become a limiting noise source at low frequency for second-generation, gravitational-wave detectors. It is planned to use seismic sensors surrounding the detectors' test masses to coherently subtract Newtonian noise using Wiener filters derived from the correlations between the sensors and detector data. In this work, we use data from a seismometer array deployed at the corner station of the LIGO Hanford detector combined with a tiltmeter for a detailed characterization of the seismic field and to predict achievable Newtonian-noise subtraction levels. As was shown previously, cancellation of the tiltmeter signal using seismometer data serves as the best available proxy of Newtonian-noise cancellation. According to our results, a relatively small number of seismometers is likely sufficient to perform the noise cancellation due to an almost ideal two-point spatial correlation of seismic surface displacement at the corner station, or alternatively, a tiltmeter deployed under each of the two test masses of the corner station at Hanford will be able to efficiently cancel Newtonian noise. Furthermore, we show that the ground tilt to differential arm-length coupling observed during LIGO's second science run is consistent with gravitational coupling.

astro-ph.IM↗

arXiv2017

Control strategy to limit duty cycle impact of earthquakes on the LIGO gravitational-wave detectors

Advanced gravitational-wave detectors such as the Laser Interferometer Gravitational-Wave Observatories (LIGO) require an unprecedented level of isolation from the ground. When in operation, they are expected to observe changes in the space-time continuum of less than one thousandth of the diameter of a proton. Strong teleseismic events like earthquakes disrupt the proper functioning of the detectors, and result in a loss of data until the detectors can be returned to their operating states. An earthquake early-warning system, as well as a prediction model have been developed to help understand the impact of earthquakes on LIGO. This paper describes a control strategy to use this early-warning system to reduce the LIGO downtime by 30%. It also presents a plan to implement this new earthquake configuration in the LIGO automation system.

physics.ins-det↗

arXiv2016

MIGA: Combining laser and matter wave interferometry for mass distribution monitoring and advanced geodesy

The Matter-Wave laser Interferometer Gravitation Antenna, MIGA, will be a hybrid instrument composed of a network of atom interferometers horizontally aligned and interrogated by the resonant field of an optical cavity. This detector will provide measurements of sub Hertz variations of the gravitational strain tensor. MIGA will bring new methods for geophysics for the characterization of spatial and temporal variations of the local gravity field and will also be a demonstrator for future low frequency Gravitational Wave (GW) detections. MIGA will enable a better understanding of the coupling at low frequency between these different signals. The detector will be installed underground in Rustrel (FR), at the "Laboratoire Souterrain Bas Bruit" (LSBB), a facility with exceptionally low environmental noise and located far away from major sources of anthropogenic disturbances. We give in this paper an overview of the operating mode and status of the instrument before detailing simulations of the gravitational background noise at the MIGA installation site.

physics.atom-ph↗

arXiv2013

Realistic Filter Cavities for Advanced Gravitational Wave Detectors

The ongoing global effort to detect gravitational waves continues to push the limits of precision measurement while aiming to provide a new tool for understanding both astrophysics and fundamental physics. Squeezed states of light offer a proven means of increasing the sensitivity of gravitational wave detectors, potentially increasing the rate at which astrophysical sources are detected by more than an order of magnitude. Since radiation pressure noise plays an important role in advanced detectors, frequency dependent squeezing will be required. In this paper we propose a practical approach to producing frequency dependent squeezing for Advanced LIGO and similar interferometric gravitational wave detectors.

physics.optics↗

arXiv2012

Scientific Potential of Einstein Telescope

Einstein gravitational-wave Telescope (ET) is a design study funded by the European Commission to explore the technological challenges of and scientific benefits from building a third generation gravitational wave detector. The three-year study, which concluded earlier this year, has formulated the conceptual design of an observatory that can support the implementation of new technology for the next two to three decades. The goal of this talk is to introduce the audience to the overall aims and objectives of the project and to enumerate ET's potential to influence our understanding of fundamental physics, astrophysics and cosmology.

gr-qc↗

arXiv2012

Scientific Objectives of Einstein Telescope

The advanced interferometer network will herald a new era in observational astronomy. There is a very strong science case to go beyond the advanced detector network and build detectors that operate in a frequency range from 1 Hz-10 kHz, with sensitivity a factor ten better in amplitude. Such detectors will be able to probe a range of topics in nuclear physics, astronomy, cosmology and fundamental physics, providing insights into many unsolved problems in these areas.

gr-qc↗

arXiv2010

Sensitivity Studies for Third-Generation Gravitational Wave Observatories

Advanced gravitational wave detectors, currently under construction, are expected to directly observe gravitational wave signals of astrophysical origin. The Einstein Telescope, a third-generation gravitational wave detector, has been proposed in order to fully open up the emerging field of gravitational wave astronomy. In this article we describe sensitivity models for the Einstein Telescope and investigate potential limits imposed by fundamental noise sources. A special focus is set on evaluating the frequency band below 10Hz where a complex mixture of seismic, gravity gradient, suspension thermal and radiation pressure noise dominates. We develop the most accurate sensitivity model, referred to as ET-D, for a third-generation detector so far, including the most relevant fundamental noise contributions.

gr-qc↗

arXiv2007

Quantum-Noise Power Spectrum of Fields with Discrete Classical Components

We present an algorithmic approach to calculate the quantum-noise spectral density of photocurrents generated by optical fields with arbitrary discrete classical spectrum in coherent or squeezed states. The measurement scheme may include an arbitrary number of demodulations of the photocurrent. Thereby, our method is applicable to the general heterodyne detection scheme which is implemented in many experiments. For some of these experiments, e.g. in laser-interferometric gravitational-wave detectors, a reliable prediction of the quantum noise of fields in coherent and squeezed states plays a decisive role in the design phase and detector characterization. Still, our investigation is limited in two ways. First, we only consider coherent and squeezed states of the field and second, we demand that the photocurrent depends linearly on the field's vacuum amplitudes which means that at least one of the classical components is comparatively strong.

quant-ph↗

arXiv2006

BBO and the Neutron-Star-Binary Subtraction Problem

The Big Bang Observer (BBO) is a proposed space-based gravitational-wave (GW) mission designed primarily to search for an inflation-generated GW background in the frequency range 0.1-1 Hz. The major astrophysical foreground in this range is gravitational radiation from inspiraling compact binaries. This foreground is expected to be much larger than the inflation-generated background, so to accomplish its main goal, BBO must be sensitive enough to identify and subtract out practically all such binaries in the observable universe. It is somewhat subtle to decide whether BBO's current baseline design is sufficiently sensitive for this task, since, at least initially, the dominant noise source impeding identification of any one binary is confusion noise from all the others. Here we present a self-consistent scheme for deciding whether BBO's baseline design is indeed adequate for subtracting out the binary foreground. We conclude that the current baseline should be sufficient. However if BBO's instrumental sensitivity were degraded by a factor 2-4, it could no longer perform its main mission. It is impossible to perfectly subtract out each of the binary inspiral waveforms, so an important question is how to deal with the "residual" errors in the post-subtraction data stream. We sketch a strategy of "projecting out" these residual errors, at the cost of some effective bandwidth. We also provide estimates of the sizes of various post-Newtonian effects in the inspiral waveforms that must be accounted for in the BBO analysis.

gr-qc↗

arXiv2004

The finite mass beamsplitter in high power interferometers

The beamplitter in high-power interferometers is subject to significant radiation-pressure fluctuations. As a consequence, the phase relations which appear in the beamsplitter coupling equations oscillate and phase modulation fields are generated which add to the reflected fields. In this paper, the transfer function of the various input fields impinging on the beamsplitter from all four ports onto the output field is presented including radiation-pressure effects. We apply the general solution of the coupling equations to evaluate the input-output relations of the dual-recycled laser-interferometer topology of the gravitational-wave detector GEO600 and the power-recycling, signal-extraction topology of advanced LIGO. We show that the input-output relation exhibits a bright-port dark-port coupling. This mechanism is responsible for bright-port contributions to the noise density of the output field and technical laser noise is expected to decrease the interferometer's sensitivity at low frequencies. It is shown quantitatively that the issue of technical laser noise is unimportant in this context if the interferometer contains arm cavities.

gr-qc↗