A crucial component to maximizing the science gain from the multi-messenger follow-up of gravitational-wave (GW) signals from compact binary mergers is the prompt discovery of the electromagnetic counterpart. Ideally, the GW detection and localization must be reported early enough to allow for telescopes to slew to the location of the GW-event before the onset of the counterpart. However, the time available for early warning is limited by the short duration spent by the dominant ($\ell = m = 2$) mode within the detector's frequency band. Nevertheless, we show that, including higher modes - which enter the detector's sensitivity band well before the dominant mode - in GW searches, can enable us to significantly improve the early warning ability for compact binaries with asymmetric masses (such as neutron-star-black-hole binaries). We investigate the reduction in the localization sky-area when the $\ell = m = 3$ and $\ell = m = 4$ modes are included in addition to the dominant mode, considering typical slew-times of electromagnetic telescopes ($30-60$ sec). We find that, in LIGO's projected "O5" ("Voyager") network with five GW detectors, some of the neutron-star-black-hole mergers, located at a distance of $40$ Mpc, can be localized to a few hundred sq. deg. $\sim 45$ sec prior to the merger, corresponding to a reduction-factor of $3-4$ ($5-6$) in sky-area. For a third-generation network, we get gains of up to 1.5 minutes in early warning times for a localization area of $100$ sq. deg., even when the source is placed at $100$ Mpc.
Since gravitational and electromagnetic waves from a compact binary coalescence carry independent information about the source, the joint observation is important for understanding the physical mechanisms of the emissions. Rapid detection and source localization of a gravitational wave signal are crucial for the joint observation to be successful. For a signal with a high signal-to-noise ratio, it is even possible to detect it before the merger, which is called early warning. In this letter, we estimate the performances of the early warning for neutron-star black-hole binaries, considering the…
We investigate the prospects of electromagnetic follow-up observations for binary neutron star (BNS) mergers, with the help of early warnings from decihertz gravitational-wave (GW) observatories, B-DECIGO and DO-Optimal. Extending the previous work, we not only give quick assessments of joint short $γ$-ray burst (sGRB) detection rates for different $γ$-ray satellites and BNS population models, but also elaborate on the analyses and results on multi-band kilonova detections for survey telescopes with different limiting magnitudes. During an assumed 4-year mission time for decihertz GW observato…
Binary neutron stars (BNSs) will spend $\simeq 10$ -- 15 minutes in the band of Advanced LIGO and Virgo detectors at design sensitivity. Matched-filtering of gravitational-wave (GW) data could in principle accumulate enough signal-to-noise ratio (SNR) to identify a forthcoming event tens of seconds before the companions collide and merge. Here we report on the design and testing of an early warning gravitational-wave detection pipeline. Early warning alerts can be produced for sources that are at low enough redshift so that a large enough SNR accumulates $\sim 10 - 60\,\rm s$ before merger. We…
We describe realistic observing scenarios for early warning detection of binary neutron star mergers with the current generation of ground-based gravitational-wave detectors as these approach design sensitivity. Using Fisher analysis, we estimate that Advanced LIGO and Advanced Virgo will detect one signal before merger in their fourth observing run provided they maintain a 70\% duty cycle. 60\% of all observations and 8\% of those detectable 20 seconds before merger will be localized to $\lesssim 100 \thinspace \mathrm{deg}^2$. If KAGRA is able to achieve a 25 Mpc horizon, these prospects inc…
The pre-merger (early-warning) gravitational-wave (GW) detection and localization of a compact binary merger would enable astronomers to capture potential electromagnetic (EM) emissions around the time of the merger, thus shedding light on the complex physics of the merger. While early detection and sky localization are of primary importance to the multimessenger follow-up of the event, improved estimates of luminosity distance and orbital inclination could also provide insights on the observability of the EM emission. In this work, we demonstrate that the inclusion of higher modes of gravitat…
A gravitational-wave (GW) early-warning of a compact-binary coalescence event, with a sufficiently tight localisation skymap, would allow telescopes to point in the direction of the potential electromagnetic counterpart before its onset. This will enable astronomers to extract valuable information of the complex astrophysical phenomena triggered around the time of the merger. Use of higher-modes of gravitational radiation, in addition to the dominant mode typically used in templated real-time searches, was recently shown to produce significant improvements in early-warning times and skyarea lo…
We present the prospects for the early (pre-merger) detection and localization of compact-binary coalescences using gravitational waves over the next 10 years. Early warning can enable the direct observation of the prompt and early electromagnetic emission of a neutron star merger. We examine the capabilities of the ground based detectors at their "Design" sensitivity (2021-2022), the planned "A+" upgrade (2024-2026), and the envisioned "Voyager" concept (late 2020's). We find that for a fiducial rate of binary neutron star mergers of $1000 ~\mathrm{Gpc}^{-3} \mathrm{yr}^{-1}$, the Design, A+,…
The detections of gravitational waves (GWs) from binary neutron star (BNS) systems and neutron star--black hole (NSBH) systems provide new insights into dense matter properties in extreme conditions and associated high-energy astrophysical processes. However, currently information about NS equation of state (EoS) is extracted with very limited precision. Meanwhile, the fruitful results from the serendipitous discovery of the $γ$-ray burst alongside GW170817 show the necessity of early warning alerts. Accurate measurements of the matter effects and sky location could be achieved by joint GW det…
Pre-merger gravitational-wave (GW) sky-localisation of binary neutron star (BNS) and neutron star black hole (NSBH) coalescence events, would enable telescopes to capture precursors and electromagnetic (EM) emissions around the time of the merger. We propose a novel astrophysical scenario that could provide early-warning times of hours to days before coalescence with sub-arcsecond localisation, provided that these events are gravitationally lensed. The key idea is that if the BNS/NSBH is lensed, then so must the host galaxy identified via the EM counterpart. From the angular separation of the …
We investigated the detection rates and early warning parameters of binary neutron star (BNS) populations with decihertz gravitational-wave observatories in a realistic detecting strategy. Assuming 4 years' operation of B-DECIGO, we based on parameter precision to classify the detectable BNSs into three categories: (a) sources that merge within 1 year, which could be localized with an uncertainty of $ΔΩ\sim 10^{0}$ deg$^2$; (b) sources that merge in 1-4 years, which take up three quarters of the total events and yield the most precise angular resolution with $ΔΩ\sim 10^{-2}$ deg$^2$ and time-o…
Gravitational-wave observations became commonplace in Advanced LIGO-Virgo's recently concluded third observing run. 56 non-retracted candidates were identified and publicly announced in near real time. Gravitational waves from binary neutron star mergers, however, remain of special interest since they can be precursors to high-energy astrophysical phenomena like $γ$-ray bursts and kilonovae. While late-time electromagnetic emissions provide important information about the astrophysical processes within, the prompt emission along with gravitational waves uniquely reveals the extreme matter and …
For third generation gravitational wave detectors, such as the Einstein Telescope, gravitational wave signals from binary neutron stars can last up to a few days before the neutron stars merge. To estimate the measurement uncertainties of key signal parameters, we develop a Fisher matrix approach which accounts for effects on such long duration signals of the time-dependent detector response and the earths rotation. We use this approach to characterize the sky localization uncertainty for gravitational waves from binary neutron stars at 40, 200, 400, 800 and 1600Mpc, for the Einstein Telescope…
Detection, sky localization and early warning for binary neutron star mergers by detectors located in China of different configurations in third generation detector network
本文评估了在中国部署不同构型第三代探测器对 ET-CE 网络探测双中子星并合的提升，发现中国探测器可提高探测率、显著改善天区定位并增强预警能力，其中 20 km 高频探测器在远距离探测上贡献突出。
Early Warning From Eccentric Compact Binaries: Template Initialization And Sub-dominant Mode Effects
International Centre for Theoretical Sciences, Tata Institute of Fundamental Research（国际理论科学中心，塔塔基础研究所）；Gravity Exploration Institute, School of Physics and Astronomy, Cardiff University（引力探索研究所，卡迪夫大学物理与天文学院）；Department of Physics, Indian Institute of Technology Madras（印度马德拉斯理工学院物理系）；Centre for Strings, Gravitation and Cosmology, Department of Physics, Indian Institute of Technology Madras（印度马德拉斯理工学院物理系弦、引力和宇宙学中心）
The success of the multi-messenger astronomy relies on gravitational-wave observatories like LIGO and Virgo to provide prompt warning of merger events involving neutron stars (including both binary neutron stars and neutron-star-black-holes), which further depends critically on the low-frequency sensitivity of LIGO as a typical binary neutron star stays in this band for minutes. However, the current sub-60 Hz sensitivity of LIGO has not yet reached its design target and the excess noise can be more than an order of magnitude below 20 Hz. It is limited by nonlinearly coupled noises from auxilia…
We explore the intriguing possibility of employing future ground-based gravitational-wave interferometers to detect the inspiral of binary neutron stars sufficiently early to alert electromagnetic observatories so that a gamma-ray burst (GRB) can be observed in its entirety from its very beginning. We quantify the ability to predict a GRB by computing the time a binary neutron star (BNS) system takes to inspiral from its moment of detection to its final merger. We define the moment of detection to be the instant at which the interferometer network accumulates a signal-to-noise ratio of 15. For…
The discovery of gravitational waves from merging compact objects has opened up a new window to the Universe. Planned third-generation gravitational-wave detectors such as Einstein Telescope will potentially deliver hundreds of such events at redshifts below $z\sim0.1$. Finding electromagnetic counterparts to these events will be a major observational challenge. We demonstrate how Einstein Telescope will provide advance warning of such events on a timescale of hours, based on the low frequency emission from the pre-merger system. In addition, we suggest how this early warning enables prompt id…
PyCBC Live Search for Compact Binary Mergers in Advanced LIGO and Virgo's Fourth Observing Run
University of Maryland, College Park（马里兰大学帕克分校）；Institute for Cosmology and Gravitation, University of Portsmouth（朴茨茅斯宇宙学与引力研究所，朴茨茅斯大学）；Université Paris-Saclay, CNRS/IN2P3, IJCLab（巴黎-萨克雷大学，法国国家科学研究中心/欧洲核子研究学院，IJCLab）；Instituto Galego de Física de Altas Enerxías, Universidade de Santiago de Compostela（加利西亚高能物理研究所，圣地亚哥-德孔波斯特拉大学）
本文改进了 PyCBC Live 低延迟搜索管道，用于 LIGO-Virgo-KAGRA 第四次观测运行（O4），通过增强排名统计量、优化信噪比恢复和实现预警搜索，将灵敏度提高 1.7-2.3 倍，并实现 2.5-3.5 秒延迟的并合前预警。
Pre-merger alert to detect the very-high-energy prompt emission from binary neutron-star mergers: Einstein Telescope and Cherenkov Telescope Array synergy
The barycenter of a massive black hole binary will lie outside the event horizon of the primary black hole for modest values of mass ratio and binary separation. Analagous to radial velocity shifts in stellar emission lines caused by the tug of planets, the radial velocity of the primary black hole around the barycenter can leave a tell-tale oscillation in the broad component of Fe K$α$ emission from accreting gas. Near-future X-ray telescopes such as Astro-H and Athena will have the energy resolution ($δE/E \lesssim 10^{-3}$) to search nearby active galactic nuclei (AGN) for the presence of b…
We present the astrophysical science case for a space-based, decihertz gravitational-wave (GW) detector. We particularly highlight an ability to infer a source's sky location, both when combined with a network of ground-based detectors to form a long triangulation baseline, and by itself for the early warning of merger events. Such an accurate location measurement is the key for using GW signals as standard sirens for constraining the Hubble constant. This kind of detector also opens up the possibility to test type Ia supernovae progenitor hypotheses by constraining the merger rates of white d…
Massive black hole binaries (MBHBs) of $10^5 \, \rm M_\odot - 3 \times 10^7 \, \rm M_\odot $ merging in low redshift galaxies ($z\le4$) are sufficiently loud to be detected weeks before coalescence with the Laser Interferometer Space Antenna (LISA). This allows us to perform the parameter estimation $on$ $the$ $fly$, i.e. as a function of the time to coalescence during the inspiral phase, relevant for early warning of the planned LISA protected periods and for searches of electromagnetic signals. In this work, we study the evolution of the sky position, luminosity distance, chirp mass and mass…
We investigate the prospects of detecting gravitational waves from coalescing massive black hole binaries in the Universe with the TianQin observatory, a space-based gravitational wave interferometer proposed to be launched in the 2030s. To frame the scientific scope of the mission, in this paper, we carry out a preliminary estimation of the signal-to-noise ratio, detection rate and parameter estimation precision of massive black hole binaries detectable by TianQin. In order to make our results as robust as possible, we consider several models of the growth history of massive black holes, expl…
Neutron stars in astrophysical binary systems represent exciting sources for multi-messenger astrophysics. A potential source of electromagnetic transients from compact binary systems is the neutron star ocean, the external fluid layer encasing a neutron star. We present a groundwork study into tidal waves in neutron star oceans and their consequences. Specifically, we investigate how oscillation modes in neutron star oceans can be tidally excited during compact binary inspirals and parabolic encounters. We find that neutron star oceans can sustain tidal waves with frequencies between $0.01-20…
Since 2015 the gravitational-wave observations of LIGO and Virgo have transformed our understanding of compact-object binaries. In the years to come, ground-based gravitational-wave observatories such as LIGO, Virgo, and their successors will increase in sensitivity, discovering thousands of stellar-mass binaries. In the 2030s, the space-based LISA will provide gravitational-wave observations of massive black holes binaries. Between the $\sim 10$-$10^3~\mathrm{Hz}$ band of ground-based observatories and the $\sim10^{-4}$-$10^{-1}~\mathrm{Hz}$ band of LISA lies the uncharted decihertz gravitati…
The gravitational-wave astronomical revolution began in 2015 with LIGO's observation of the coalescence of two stellar-mass black holes. Over the coming decades, ground-based detectors like LIGO will extend their reach, discovering thousands of stellar-mass binaries. In the 2030s, the space-based LISA will enable gravitational-wave observations of the massive black holes in galactic centres. Between LISA and ground-based observatories lies the unexplored decihertz gravitational-wave frequency band. Here, we propose a Decihertz Observatory to cover this band, and complement observations made by…
