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Recent detection of nHz stochastic gravitational wave background (SGWB) by multiple pulsar timing arrays (PTAs) has stimulated intensive discussions about its physical origin. In principle, either supermassive black hole binaries (SMBHBs)…

Cosmology and Nongalactic Astrophysics · Physics 2025-02-10 Xiao Xue , Zhen Pan , Liang Dai

Accurately estimating the parameters of the nanohertz gravitational-wave background is essential for understanding its origin. The background is typically modeled with a power-law spectrum, parametrized with an amplitude $A$, which…

General Relativity and Quantum Cosmology · Physics 2026-03-25 Valentina Di Marco , Andrew Zic , Ryan M. Shannon , Eric Thrane , Atharva D. Kulkarni

The stochastic gravitational wave background (SGWB) consists of an incoherent collection of waves from both astrophysical and cosmological sources. To distinguish the SGWB from noise, it is essential to verify its quadrupolar nature,…

General Relativity and Quantum Cosmology · Physics 2025-08-22 Yifan Chen , Yuxiang Liu , Jing Shu , Bin Xu , Xiao Xue , Yanjie Zeng

The collection of individually resolvable gravitational wave (GW) events makes up a tiny fraction of all GW signals which reach our detectors, while most lie below the confusion limit and go undetected. Like voices in a crowded room, the…

General Relativity and Quantum Cosmology · Physics 2022-03-02 Arianna I. Renzini , Boris Goncharov , Alexander C. Jenkins , Pat M. Meyers

Gravity theories that modify General Relativity in the slow-motion regime can introduce nonperturbative corrections to the stochastic gravitational-wave background~(SGWB) from supermassive black-hole binaries in the nano-Hertz band, while…

General Relativity and Quantum Cosmology · Physics 2024-05-08 Enrico Cannizzaro , Gabriele Franciolini , Paolo Pani

Supermassive black hole binaries are promising sources of low-frequency gravitational waves (GWs) and bright electromagnetic emission. Pulsar timing array searches for resolved binaries are complex and computationally expensive and so far…

General Relativity and Quantum Cosmology · Physics 2023-04-11 Maria Charisi , Stephen R. Taylor , Caitlin A. Witt , Jessie Runnoe

Finding and characterizing gravitational waves from individual supermassive black hole binaries is a central goal of pulsar timing array experiments, which will require analysis methods that can be efficient on our rapidly growing datasets.…

General Relativity and Quantum Cosmology · Physics 2024-10-28 Bence Bécsy

Revealing the nature of the nanoHz gravitational wave (GW) signal recently reported by Pulsar Timing Arrays (PTAs) collaborations around the world is the next goal of low-frequency GW astronomy. The signal likely originates from the…

A new model independent method is presented for the analysis of pulsar timing data and the estimation of the spectral properties of an isotropic gravitational wave background (GWB). We show that by rephrasing the likelihood we are able to…

Instrumentation and Methods for Astrophysics · Physics 2013-06-26 Lindley Lentati , Paul Alexander , Michael P. Hobson , Stephen Taylor , Jonathon Gair , Sreekumar T. Balan , Rutger van Haasteren

Pulsar timing arrays have found evidence for a low-frequency gravitational wave background (GWB). Assuming the GWB is produced by supermassive black hole binaries (SMBHBs), the next gravitational wave (GW) signals astronomers anticipate are…

High Energy Astrophysical Phenomena · Physics 2024-04-24 Emiko C. Gardiner , Luke Zoltan Kelley , Anna-Malin Lemke , Andrea Mitridate

We present the results of a search for gravitational waves (GWs) from individual sources using high-cadence observations of PSR J1909\(-\)3744 obtained during an intensive observing campaign with the International Pulsar Timing Array second…

High Energy Astrophysical Phenomena · Physics 2026-03-13 Jing Zou , Jingbo Wang Jianping Yuan , De Zhao , Yirong Wen , Wei Li , Na Wang , Yong Xia

Pulsar Timing Array projects have found evidence of a stochastic background of gravitational waves (GWB) using data from an ensemble of pulsars. In the literature, minimal assumptions are made about the signal and noise processes that…

Instrumentation and Methods for Astrophysics · Physics 2024-11-28 Rutger van Haasteren

We develop a unified framework for testing gravity beyond General Relativity (GR) with continuous gravitational waves (CWs) from individual supermassive black hole binaries (SMBHBs). These long-lived, nearly monochromatic nanohertz signals…

General Relativity and Quantum Cosmology · Physics 2026-05-08 Qinyuan Zheng , Bjorn Larsen , Ellis Eisenberg , Chiara M. F. Mingarelli

Highly energetic astrophysical phenomena like supermassive black hole binary (SMBHB) mergers are predicted to emit prodigious amounts of gravitational waves (GWs). An anticipated component of the gravitational waveform known as "memory" is…

High Energy Astrophysical Phenomena · Physics 2015-06-19 D. R. Madison , J. M. Cordes , S. Chatterjee

Gravitational waves (GWs) are powerful probes of new physics in the early Universe. In particular, GWs induced by primordial isocurvature perturbations encode information of novel dynamics beyond the standard $\Lambda$CDM model. Existing…

Cosmology and Nongalactic Astrophysics · Physics 2026-05-08 Yi-Fu Cai , Peizhi Du , Jiahang Zhong

Gravitational waves are predicted by Einstein's theory of general relativity as well as other theories of gravity. The rotational stability of the fastest pulsars means that timing of an array of these objects can be used to detect and…

Solar and Stellar Astrophysics · Physics 2015-05-28 J. Ellis , M. A. McLaughlin , J. P. W. Verbiest

Gravitational waves provide a new probe of the Universe which can reveal a number of cosmological and astrophysical phenomena that cannot be observed by electromagnetic waves. Different frequencies of gravitational waves are detected by…

General Relativity and Quantum Cosmology · Physics 2021-11-08 Jun'ichi Yokoyama

The most conservative interpretation of the nHz stochastic gravitational wave background (SGWB) discovered by NANOGrav and other Pulsar Timing Array (PTA) Collaborations is astrophysical, namely that it originates from supermassive black…

By monitoring the times of arrival of radio pulses from millisecond pulsars, Pulsar Timing Arrays (PTAs) serve as unique gravitational wave (GW) laboratories in the nanohertz band. To date, the primary astrophysical sources of GWs targeted…

High Energy Astrophysical Phenomena · Physics 2026-04-24 Hippolyte Quelquejay Leclere

The nanohertz gravitational wave background (GWB) is expected to be an aggregate signal of an ensemble of gravitational waves emitted predominantly by a large population of coalescing supermassive black hole binaries in the centres of…