Showing 1–50 of 161 results for author: Zhao, Z

Evidence of young magnetars in massive binary embedded in a supernova remnant as sources of active fast radio bursts

Authors: F. Y. Wang, H. T. Lan, Z. Y. Zhao, Q. Wu, Y. Feng, S. X. Yi, Z. G. Dai, K. S. Cheng

Abstract: Fast radio bursts (FRBs) are intense pulses with unknown origins. A subclass of repeating FRBs show some common features, such as associated compact persistent radio sources (PRSs), high burst rates, and large host-galaxy dispersion measures (DMs). Meanwhile, they show diverse DM and rotation measure (RM) variations, which cannot be explained by current models. A unified model urgently needs to be… ▽ More Fast radio bursts (FRBs) are intense pulses with unknown origins. A subclass of repeating FRBs show some common features, such as associated compact persistent radio sources (PRSs), high burst rates, and large host-galaxy dispersion measures (DMs). Meanwhile, they show diverse DM and rotation measure (RM) variations, which cannot be explained by current models. A unified model urgently needs to be established. Here we show the first evidence for a supernova remnant surrounding the FRB 20190520B source. We then demonstrate that the five active repeating FRB sources associated with PRSs can be understood within a single model in which central objects are young magnetars in massive binary systems embedded in supernova remnants. This model naturally predicts distinct variations of DM and RM for repeating FRBs. Crucially, young magnetar wind nebulae can generate bright PRSs. As a magnetar becomes older, the luminosity of a PRS will fade, which can naturally explain less-luminous PRSs for some active FRBs. Our results support a unified population of active FRBs in dynamic magnetized environments. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Comments: 15 pages, 6 figures, 1 table, submitted

Collapse of Axion Domain Wall Induced by Helical Primordial Magnetic Fields

Authors: Zizhuo Zhao, Yuefeng Di, Ligong Bian, Jing Shu

Abstract: Stable domain wall (DW) must decay to avoid overclose the Universe. A commonly used solution is to slightly break the PQ symmetry by introducing a bias term in the potential. In this work, we propose an alternative, symmetry-preserving mechanism: coupling the axion field to a helical primordial magnetic field (PMF) via the Chern-Simons term. Using three-dimensional lattice simulations, we evolve t… ▽ More Stable domain wall (DW) must decay to avoid overclose the Universe. A commonly used solution is to slightly break the PQ symmetry by introducing a bias term in the potential. In this work, we propose an alternative, symmetry-preserving mechanism: coupling the axion field to a helical primordial magnetic field (PMF) via the Chern-Simons term. Using three-dimensional lattice simulations, we evolve the DW network and demonstrate that it can successfully drive DW decay. Our quantitative results further show that the correlation length of the PMF plays a crucial role in determining the decay rate of the DW network and the resulting axion and gravitational wave radiation. △ Less

Submitted 28 November, 2025; originally announced November 2025.

Comments: 7 pages + 9 pages, 14 figures, comments welcome

Search for planetary-mass ultra-compact binaries using data from the first part of the LIGO--Virgo--KAGRA fourth observing run

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1743 additional authors not shown)

Abstract: We present a search for gravitational waves from inspiraling, planetary-mass ultra-compact binaries using data from the first part of the fourth observing run of LIGO, Virgo and KAGRA. Finding no evidence of such systems, we determine the maximum distance reach for such objects and their merger rate densities, independently of how they could have formed. Then, we identify classes of primordial bla… ▽ More We present a search for gravitational waves from inspiraling, planetary-mass ultra-compact binaries using data from the first part of the fourth observing run of LIGO, Virgo and KAGRA. Finding no evidence of such systems, we determine the maximum distance reach for such objects and their merger rate densities, independently of how they could have formed. Then, we identify classes of primordial black-hole mass distributions for which these rate limits can be translated into relevant constraints on the mass distribution of primordial black holes, assuming that they compose all of dark matter, in the mass range $[10^{-6},10^{-3}]M_\odot$. Our constraints are consistent with existing microlensing results in the planetary-mass range, and provide a complementary probe to sub-solar mass objects. △ Less

Submitted 5 December, 2025; v1 submitted 24 November, 2025; originally announced November 2025.

Comments: 6 pages (main) + 7 pages (appendix) + refs; 8 figures

Report number: P2500248

Probing the Penrose Process: Images of Split Hotspots and Their Observational Signatures

Authors: Zhixing Zhao, Zhong-Ying Fan, Xiaobao Wang, Minyong Guo, Bin Chen

Abstract: While theoretically established for decades, the Penrose process - energy extraction from rotating black holes - still lacks clear observational evidence. A promising theoretical framework posits magnetic reconnection in the ergosphere as a trigger, causing a plasmoid to separate into an escaping positive-energy fragment and an infalling negative-energy one. In this work, we investigate the observ… ▽ More While theoretically established for decades, the Penrose process - energy extraction from rotating black holes - still lacks clear observational evidence. A promising theoretical framework posits magnetic reconnection in the ergosphere as a trigger, causing a plasmoid to separate into an escaping positive-energy fragment and an infalling negative-energy one. In this work, we investigate the observational imprints of this scenario. We treat the energized plasmoid as a hotspot and calculate its light curves for a realistic plasma magnetization. In particular, we further compare with the scenario in which the plasmoid, after fragmentation, falls into the black hole with positive energy, while all other conditions remain unchanged. Our results reveal that the process of fragmentation generates distinct flares, whose characteristics depend heavily on whether the infalling fragment carries negative or positive energy. We propose that these differences serve as identifiable signatures of the Penrose process. △ Less

Submitted 31 October, 2025; originally announced October 2025.

Direct multi-model dark-matter search with gravitational-wave interferometers using data from the first part of the fourth LIGO-Virgo-KAGRA observing run

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1745 additional authors not shown)

Abstract: Gravitational-wave detectors can probe the existence of dark matter with exquisite sensitivity. Here, we perform a search for three kinds of dark matter -- dilatons (spin-0), dark photons (spin-1) and tensor bosons (spin-2) -- using three independent methods on the first part of the most recent data from the fourth observing run of LIGO--Virgo--KAGRA. Each form of dark matter could have interacted… ▽ More Gravitational-wave detectors can probe the existence of dark matter with exquisite sensitivity. Here, we perform a search for three kinds of dark matter -- dilatons (spin-0), dark photons (spin-1) and tensor bosons (spin-2) -- using three independent methods on the first part of the most recent data from the fourth observing run of LIGO--Virgo--KAGRA. Each form of dark matter could have interacted with different standard-model particles in the instruments, causing unique differential strains on the interferometers. While we do not find any evidence for a signal, we place the most stringent upper limits to-date on each of these models. For scalars with masses between $[4\times 10^{-14},1.5\times 10^{-13}]$ eV that couple to photons or electrons, our constraints improve upon those from the third observing run by one order of magnitude, with the tightest limit of $\sim 10^{-20}\,\text{GeV}^{-1}$ at a mass of $\sim2\times 10^{-13}\text{ eV}$. For vectors with masses between $[7\times 10^{-13},8.47\times 10^{-12}]$ eV that couple to baryons, our constraints supersede those from MICROSCOPE and Eöt-Wash by one to two orders of magnitude, reaching a minimum of $\sim 5\times 10^{-24}$ at a mass of $\sim 10^{-12}$ eV. For tensors with masses of $[4\times 10^{-14},8.47\times 10^{-12}]$ eV (the full mass range analyzed) that couple via a Yukawa interaction, our constraints surpass those from fifth-force experiments by four to five orders of magnitude, achieving a limit as low as $\sim 8\times 10^{-9}$ at $\sim2\times 10^{-13}$ eV. Our results show that gravitational-wave interferometers have become frontiers for new physics and laboratories for direct multi-model dark-matter detection. △ Less

Submitted 11 December, 2025; v1 submitted 30 October, 2025; originally announced October 2025.

Comments: 9 pages, 1 figure (+1 figure in appendix)

Report number: P2500252

GW241011 and GW241110: Exploring Binary Formation and Fundamental Physics with Asymmetric, High-Spin Black Hole Coalescence

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1761 additional authors not shown)

Abstract: We report the observation of gravitational waves from two binary black hole coalescences during the fourth observing run of the LIGO--Virgo--KAGRA detector network, GW241011 and GW241110. The sources of these two signals are characterized by rapid and precisely measured primary spins, non-negligible spin--orbit misalignment, and unequal mass ratios between their constituent black holes. These prop… ▽ More We report the observation of gravitational waves from two binary black hole coalescences during the fourth observing run of the LIGO--Virgo--KAGRA detector network, GW241011 and GW241110. The sources of these two signals are characterized by rapid and precisely measured primary spins, non-negligible spin--orbit misalignment, and unequal mass ratios between their constituent black holes. These properties are characteristic of binaries in which the more massive object was itself formed from a previous binary black hole merger, and suggest that the sources of GW241011 and GW241110 may have formed in dense stellar environments in which repeated mergers can take place. As the third loudest gravitational-wave event published to date, with a median network signal-to-noise ratio of $36.0$, GW241011 furthermore yields stringent constraints on the Kerr nature of black holes, the multipolar structure of gravitational-wave generation, and the existence of ultralight bosons within the mass range $10^{-13}$--$10^{-12}$ eV. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: Data available from Zenodo (https://zenodo.org/records/17343574) or the Gravitational-Wave Open Science Center (https://gwosc.org)

Report number: LIGO-P2500402

Journal ref: Astrophys. J. Letters, 993, L21 (2025)

Cosmological and High Energy Physics implications from gravitational-wave background searches in LIGO-Virgo-KAGRA's O1-O4a runs

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1747 additional authors not shown)

Abstract: We search for gravitational-wave background signals produced by various early Universe processes in the Advanced LIGO O4a dataset, combined with the data from the earlier O1, O2, and O3 (LIGO-Virgo) runs. The absence of detectable signals enables powerful constraints on fundamental physics. We derive gravitational-wave background energy density upper limits from the O1-O4a data to constrain parame… ▽ More We search for gravitational-wave background signals produced by various early Universe processes in the Advanced LIGO O4a dataset, combined with the data from the earlier O1, O2, and O3 (LIGO-Virgo) runs. The absence of detectable signals enables powerful constraints on fundamental physics. We derive gravitational-wave background energy density upper limits from the O1-O4a data to constrain parameters associated with various possible processes in the early Universe: first-order phase transitions, cosmic strings, domain walls, stiff equation of state, axion inflation, second-order scalar perturbations, primordial black hole binaries, and parity violation. In our analyses, the presence of an astrophysical background produced by compact (black hole and neutron star) binary coalescences throughout the Universe is also considered. We address the implications for various cosmological and high energy physics models based on the obtained parameter constraints. We conclude that LIGO-Virgo data already yield significant constraints on numerous early Universe scenarios. △ Less

Submitted 7 November, 2025; v1 submitted 30 October, 2025; originally announced October 2025.

Comments: Main paper: 45 pages, 20 figures

Report number: LIGO-PP2500150

Evidence of cosmic-ray acceleration up to sub-PeV energies in the supernova remnant IC 443

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen , et al. (291 additional authors not shown)

Abstract: Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy $γ$-ray emission from the SN… ▽ More Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy $γ$-ray emission from the SNR IC 443 using the Large High Altitude Air Shower Observatory (LHAASO). The morphological analysis reveals a pointlike source whose location and spectrum are consistent with those of the Fermi-LAT-detected compact source with $π^0$-decay signature, and a more extended source which is consistent with a newly discovered source, previously unrecognized by Fermi-LAT. The spectrum of the point source can be described by a power-law function with an index of $\sim3.0$, extending beyond $\sim 30$ TeV without apparent cutoff. Assuming a hadronic origin of the $γ$-ray emission, the $95\%$ lower limit of accelerated protons reaches about 300 TeV. The extended source might be coincident with IC 443, SNR G189.6+3.3 or the putative pulsar wind nebula CXOU J061705.3+222127, and can be explained by either a hadronic or leptonic model. The LHAASO results provide compelling evidence that CR protons up to sub-PeV energies can be accelerated by the SNR. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Directional Search for Persistent Gravitational Waves: Results from the First Part of LIGO-Virgo-KAGRA's Fourth Observing Run

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1743 additional authors not shown)

Abstract: The angular distribution of gravitational-wave power from persistent sources may exhibit anisotropies arising from the large-scale structure of the Universe. This motivates directional searches for astrophysical and cosmological gravitational-wave backgrounds, as well as continuous-wave emitters. We present results of such a search using data from the first observing run through the first portion… ▽ More The angular distribution of gravitational-wave power from persistent sources may exhibit anisotropies arising from the large-scale structure of the Universe. This motivates directional searches for astrophysical and cosmological gravitational-wave backgrounds, as well as continuous-wave emitters. We present results of such a search using data from the first observing run through the first portion of the fourth observing run of the LIGO-Virgo-KAGRA Collaborations. We apply gravitational-wave radiometer techniques to generate skymaps and search for both narrowband and broadband persistent gravitational-wave sources. Additionally, we use spherical harmonic decomposition to probe spatially extended sources. No evidence of persistent gravitational-wave signals is found, and we set the most stringent constraints to date on such emissions. For narrowband point sources, our sensitivity estimate to effective strain amplitude lies in the range $(0.03 - 8.4) \times 10^{-24}$ across all sky and frequency range $(20 - 160)$ Hz. For targeted sources -- Scorpius X-1, SN 1987A, the Galactic Center, Terzan 5, and NGC 6397 -- we constrain the strain amplitude with best limits ranging from $\sim 1.1 \times 10^{-25}$ to $6.5 \times 10^{-24}$. For persistent broadband sources, we constrain the gravitational-wave flux $F_{α, \hat{n}}^{95\%, \mathrm{UL}}(25\, \mathrm{Hz}) < (0.008 - 5.5) \times 10^{-8}\, \mathrm{erg\, cm^{-2}\, s^{-1}\, Hz^{-1}}$, depending on the sky direction $\hat{n}$ and spectral index $α=0,\,2/3,\,3$. Finally, for extended sources, we place upper limits on the strain angular power spectrum $C_\ell^{1/2} < (0.63 - 17) \times 10^{-10} \,\mathrm{sr}^{-1}$. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: Main paper: 11 pages and 4 figures; Total with appendices: 39 pages and 12 figures

Report number: LIGO-P250038

A Giant Peanut-shaped Ultra-High-Energy Gamma-Ray Emitter Off the Galactic Plane

Authors: Zhen Cao, Felix Aharonian, Yunxiang Bai, Yiwei Bao, Denis Bastieri, Xiaojun Bi, YuJiang Bi, Mr Bian WenYi, A. Butkevich, Chengmiao Cai, Wenyu Cao, Zhe Cao, Jin Chang, Jinfan Chang, Mr Aming Chen, Ensheng Chen, Mr Guo-Hai Chen, Mr Huaxi Chen, Liang Chen, Long Chen, Mingjun Chen, Mali Chen, Qihui Chen, Shi Chen, Suhong Chen , et al. (291 additional authors not shown)

Abstract: Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts), γ-rays manifests extreme particle acceleration in astrophysical sources. Recent observations by γ-ray telescopes, particularly by the Large High Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE sources, indicating numerous Galactic sources capable of accelerating particles to PeV (10^15 electronvolts) energi… ▽ More Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts), γ-rays manifests extreme particle acceleration in astrophysical sources. Recent observations by γ-ray telescopes, particularly by the Large High Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE sources, indicating numerous Galactic sources capable of accelerating particles to PeV (10^15 electronvolts) energies. However, discerning the dominant acceleration mechanisms (leptonic versus hadronic), the relative contributions of specific source classes, and the role of particle transport in shaping their observed emission are central goals of modern UHE astrophysics. Here we report the discovery of a giant UHE γ-ray emitter at -17.5° off the Galactic plane - a region where UHE γ-ray sources are rarely found. The emitter exhibits a distinctive asymmetric shape, resembling a giant "Peanut" spanning 0.45° \times 4.6°, indicative of anisotropic particle distribution over a large area. A highly aged millisecond pulsar (MSP) J0218+4232 is the sole candidate accelerator positionally coincident with the Peanut region. Its association with UHE γ-rays extending to 0.7 PeV, if confirmed, would provide the first evidence of a millisecond pulsar powering PeV particles. Such a finding challenges prevailing models, which posit that millisecond pulsars cannot sustain acceleration to PeV energies. The detection reveals fundamental gaps in understanding particle acceleration, cosmic-ray transport, and interstellar magnetic field effects, potentially revealing new PeV accelerator (PeVatron) classes. △ Less

Submitted 25 October, 2025; v1 submitted 8 October, 2025; originally announced October 2025.

Testing black hole metrics with binary black hole inspirals

Authors: Zhe Zhao, Swarnim Shashank, Debtroy Das, Cosimo Bambi

Abstract: Gravitational wave astronomy has opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime. In this study, we examine a series of well-motivated deviations from the classical Kerr solution of General Relativity and employ gravitational wave data to place constraints on possible deviations from the Kerr geometry. The method involves calculating the phas… ▽ More Gravitational wave astronomy has opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime. In this study, we examine a series of well-motivated deviations from the classical Kerr solution of General Relativity and employ gravitational wave data to place constraints on possible deviations from the Kerr geometry. The method involves calculating the phase of gravitational waves using the effective one-body formalism and then applying the parameterized post-Einsteinian framework to constrain the parameters appearing in these scenarios beyond General Relativity. The effective one-body method, known for its capability to model complex gravitational waveforms, is used to compute the wave phase, and the post-Einsteinian framework allows for a flexible, model-independent approach to parameter estimation. We demonstrate that gravitational wave data provide evidence supporting the Kerr nature of black holes, showing no significant deviations from General Relativity, thereby affirming its validity within the current observational limits. This work bridges theoretical waveform modeling with observational constraints, providing a pathway to test the no-hair theorem and probe the astrophysical viability of modified black holes. △ Less

Submitted 6 October, 2025; originally announced October 2025.

Comments: 25 pages, 12 figures

GW250114: testing Hawking's area law and the Kerr nature of black holes

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1763 additional authors not shown)

Abstract: The gravitational-wave signal GW250114 was observed by the two LIGO detectors with a network matched-filter signal-to-noise ratio of 80. The signal was emitted by the coalescence of two black holes with near-equal masses $m_1 = 33.6^{+1.2}_{-0.8}\,M_\odot$ and $m_2 = 32.2^{+0.8}_{-1.3}\,M_\odot$, and small spins $χ_{1,2} \leq 0.26$ (90% credibility) and negligible eccentricity $e \leq 0.03$. Post-… ▽ More The gravitational-wave signal GW250114 was observed by the two LIGO detectors with a network matched-filter signal-to-noise ratio of 80. The signal was emitted by the coalescence of two black holes with near-equal masses $m_1 = 33.6^{+1.2}_{-0.8}\,M_\odot$ and $m_2 = 32.2^{+0.8}_{-1.3}\,M_\odot$, and small spins $χ_{1,2} \leq 0.26$ (90% credibility) and negligible eccentricity $e \leq 0.03$. Post-merger data excluding the peak region are consistent with the dominant quadrupolar $(\ell = |m| = 2)$ mode of a Kerr black hole and its first overtone. We constrain the modes' frequencies to $\pm 30\%$ of the Kerr spectrum, providing a test of the remnant's Kerr nature. We also examine Hawking's area law, also known as the second law of black hole mechanics, which states that the total area of the black hole event horizons cannot decrease with time. A range of analyses that exclude up to 5 of the strongest merger cycles confirm that the remnant area is larger than the sum of the initial areas to high credibility. △ Less

Submitted 9 September, 2025; originally announced September 2025.

Comments: 6 pages, 5 figures (plus supplement)

Report number: LIGO-P2500421

Directed searches for gravitational waves from ultralight vector boson clouds around merger remnant and galactic black holes during the first part of the fourth LIGO-Virgo-KAGRA observing run

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1747 additional authors not shown)

Abstract: We present the first directed searches for long-transient and continuous gravitational waves from ultralight vector boson clouds around known black holes (BHs). We use LIGO data from the first part of the fourth LIGO-Virgo-KAGRA observing run. The searches target two distinct types of BHs and use two new semicoherent methods: hidden Markov model (HMM) tracking for the remnant BHs of the mergers GW… ▽ More We present the first directed searches for long-transient and continuous gravitational waves from ultralight vector boson clouds around known black holes (BHs). We use LIGO data from the first part of the fourth LIGO-Virgo-KAGRA observing run. The searches target two distinct types of BHs and use two new semicoherent methods: hidden Markov model (HMM) tracking for the remnant BHs of the mergers GW230814_230901 and GW231123_135430 (referred to as GW230814 and GW231123 in this study), and a dedicated method using the Band Sampled Data (BSD) framework for the galactic BH in the Cygnus X-1 binary system. Without finding evidence of a signal from vector bosons in the data, we estimate the mass range that can be constrained. For the HMM searches targeting the remnants from GW231123 and GW230814, we disfavor vector boson masses in the ranges $[0.94, 1.08]$ and $[2.75, 3.28] \times 10^{-13}$ eV, respectively, at 30% confidence, assuming a 1% false alarm probability. Although these searches are only marginally sensitive to signals from merger remnants at relatively large distances, future observations are expected to yield more stringent constraints with high confidence. For the BSD search targeting the BH in Cygnus X-1, we exclude vector boson masses in the range $[0.85, 1.59] \times 10^{-13}$ eV at 95% confidence, assuming an initial BH spin larger than 0.5. △ Less

Submitted 14 September, 2025; v1 submitted 8 September, 2025; originally announced September 2025.

Comments: 33 pages, 4 figures

Report number: LIGO-P2500256

GWTC-4.0: Constraints on the Cosmic Expansion Rate and Modified Gravitational-wave Propagation

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1750 additional authors not shown)

Abstract: We analyze data from 142 of the 218 gravitational-wave (GW) sources in the fourth LIGO-Virgo-KAGRA Collaboration (LVK) Gravitational-Wave Transient Catalog (GWTC-4.0) to estimate the Hubble constant $H_0$ jointly with the population properties of merging compact binaries. We measure the luminosity distance and redshifted masses of GW sources directly; in contrast, we infer GW source redshifts stat… ▽ More We analyze data from 142 of the 218 gravitational-wave (GW) sources in the fourth LIGO-Virgo-KAGRA Collaboration (LVK) Gravitational-Wave Transient Catalog (GWTC-4.0) to estimate the Hubble constant $H_0$ jointly with the population properties of merging compact binaries. We measure the luminosity distance and redshifted masses of GW sources directly; in contrast, we infer GW source redshifts statistically through i) location of features in the compact object mass spectrum and merger rate evolution, and ii) identifying potential host galaxies in the GW localization volume. Probing the relationship between source luminosity distances and redshifts obtained in this way yields constraints on cosmological parameters. We also constrain parameterized deviations from general relativity which affect GW propagation, specifically those modifying the dependence of a GW signal on the source luminosity distance. Assuming our fiducial model for the source-frame mass distribution and using GW candidates detected up to the end of the fourth observing run (O4a), together with the GLADE+ all-sky galaxy catalog, we estimate $H_0 = 76.6^{+13.0}_{-9.5} (76.6^{+25.2}_{-14.0})$ km s$^{-1}$ Mpc$^{-1}$. This value is reported as a median with 68.3% (90%) symmetric credible interval, and includes combination with the $H_0$ measurement from GW170817 and its electromagnetic counterpart. Using a parametrization of modified GW propagation in terms of the magnitude parameter $Ξ_0$, we estimate $Ξ_0 = 1.2^{+0.8}_{-0.4} (1.2^{+2.4}_{-0.5})$, where $Ξ_0 = 1$ recovers the behavior of general relativity. △ Less

Submitted 7 October, 2025; v1 submitted 4 September, 2025; originally announced September 2025.

Comments: As part of the Astrophysical Journal Letters Focus Issue on the Gravitational Wave Transient Catalog

Report number: LIGO-P2400152

Upper Limits on the Isotropic Gravitational-Wave Background from the first part of LIGO, Virgo, and KAGRA's fourth Observing Run

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1751 additional authors not shown)

Abstract: We present results from the search for an isotropic gravitational-wave background using Advanced LIGO and Advanced Virgo data from O1 through O4a, the first part of the fourth observing run. This background is the accumulated signal from unresolved sources throughout cosmic history and encodes information about the merger history of compact binaries throughout the Universe, as well as exotic physi… ▽ More We present results from the search for an isotropic gravitational-wave background using Advanced LIGO and Advanced Virgo data from O1 through O4a, the first part of the fourth observing run. This background is the accumulated signal from unresolved sources throughout cosmic history and encodes information about the merger history of compact binaries throughout the Universe, as well as exotic physics and potentially primordial processes from the early cosmos. Our cross-correlation analysis reveals no statistically significant background signal, enabling us to constrain several theoretical scenarios. For compact binary coalescences which approximately follow a 2/3 power-law spectrum, we constrain the fractional energy density to $Ω_{\rm GW}(25{\rm Hz})\leq 2.0\times 10^{-9}$ (95% cred.), a factor of 1.7 improvement over previous results. Scale-invariant backgrounds are constrained to $Ω_{\rm GW}(25{\rm Hz})\leq 2.8\times 10^{-9}$, representing a 2.1x sensitivity gain. We also place new limits on gravity theories predicting non-standard polarization modes and confirm that terrestrial magnetic noise sources remain below detection threshold. Combining these spectral limits with population models for GWTC-4, the latest gravitational-wave event catalog, we find our constraints remain above predicted merger backgrounds but are approaching detectability. The joint analysis combining the background limits shown here with the GWTC-4 catalog enables improved inference of the binary black hole merger rate evolution across cosmic time. Employing GWTC-4 inference results and standard modeling choices, we estimate that the total background arising from compact binary coalescences is $Ω_{\rm CBC}(25{\rm Hz})={0.9^{+1.1}_{-0.5}\times 10^{-9}}$ at 90% confidence, where the largest contribution is due to binary black holes only, $Ω_{\rm BBH}(25{\rm Hz})=0.8^{+1.1}_{-0.5}\times 10^{-9}$. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Comments: 31 pages, 7 figures

Report number: LIGO-P2500349

GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO-Virgo-KAGRA Observing Run

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1748 additional authors not shown)

Abstract: Version 4.0 of the Gravitational-Wave Transient Catalog (GWTC-4.0) adds new candidates detected by the LIGO, Virgo, and KAGRA observatories through the first part of the fourth observing run (O4a: 2023 May 24 15:00:00 to 2024 January 16 16:00:00 UTC) and a preceding engineering run. In this new data, we find 128 new compact binary coalescence candidates that are identified by at least one of our s… ▽ More Version 4.0 of the Gravitational-Wave Transient Catalog (GWTC-4.0) adds new candidates detected by the LIGO, Virgo, and KAGRA observatories through the first part of the fourth observing run (O4a: 2023 May 24 15:00:00 to 2024 January 16 16:00:00 UTC) and a preceding engineering run. In this new data, we find 128 new compact binary coalescence candidates that are identified by at least one of our search algorithms with a probability of astrophysical origin $p_{\rm astro} \geq 0.5$ and that are not vetoed during event validation. We also provide detailed source property measurements for 86 of these that have a false alarm rate $< 1 \rm{yr}^{-1}$. Based on the inferred component masses, these new candidates are consistent with signals from binary black holes and neutron star-black hole binaries (GW230518_125908 and GW230529_181500). Median inferred component masses of binary black holes in the catalog now range from $5.79\,M_\odot$ (GW230627_015337) to $137\,M_\odot$ (GW231123_135430), while GW231123_135430 was probably produced by the most massive binary observed in the catalog. For the first time we have discovered binary black hole signals with network signal-to-noise ratio exceeding 30, GW230814_230901 and GW231226_01520, enabling high-fidelity studies of the waveforms and astrophysical properties of these systems. Combined with the 90 candidates included in GWTC-3.0, the catalog now contains 218 candidates with $p_{\rm astro} \geq 0.5$ and not otherwise vetoed, doubling the size of the catalog and further opening our view of the gravitational-wave Universe. △ Less

Submitted 8 September, 2025; v1 submitted 25 August, 2025; originally announced August 2025.

Comments: As part of the Astrophysical Journal Letters Focus Issue on the Gravitational Wave Transient Catalog

Report number: LIGO-P2400386

Open Data from LIGO, Virgo, and KAGRA through the First Part of the Fourth Observing Run

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1746 additional authors not shown)

Abstract: LIGO, Virgo, and KAGRA form a network of gravitational-wave observatories. Data and analysis results from this network are made publicly available through the Gravitational Wave Open Science Center. This paper describes open data from this network, including the addition of data from the first part of the fourth observing run (O4a) and selected periods from the preceding engineering run, collected… ▽ More LIGO, Virgo, and KAGRA form a network of gravitational-wave observatories. Data and analysis results from this network are made publicly available through the Gravitational Wave Open Science Center. This paper describes open data from this network, including the addition of data from the first part of the fourth observing run (O4a) and selected periods from the preceding engineering run, collected from May 2023 to January 2024. The public data set includes calibrated strain time series for each instrument, data from additional channels used for noise subtraction and detector characterization, and analysis data products from version 4.0 of the Gravitational-Wave Transient Catalog. △ Less

Submitted 4 November, 2025; v1 submitted 25 August, 2025; originally announced August 2025.

Comments: 26 pages. The version updates Table 3, updates the author list, removes one figure, and updates some text for clarity and grammar

Report number: LIGO-P2500167

Decadal upgrade strategy for KAGRA toward post-O5 gravitational-wave astronomy

Authors: KAGRA Collaboration, T. Akutsu, M. Ando, M. Aoumi, A. Araya, Y. Aso, L. Baiotti, R. Bajpai, K. Cannon, A. H. -Y. Chen, D. Chen, H. Chen, A. Chiba, C. Chou, M. Eisenmann, K. Endo, T. Fujimori, S. Garg, D. Haba, S. Haino, R. Harada, H. Hayakawa, K. Hayama, S. Fujii, Y. Himemoto , et al. (129 additional authors not shown)

Abstract: The KAGRA Collaboration has investigated a ten-year upgrade strategy for the KAGRA gravitational wave detector, considering a total of 14 upgrade options that vary in mirror mass, quantum noise reduction techniques, and the quality of cryogenic suspensions. We evaluated the scientific potential of these configurations with a focus on key targets such as parameter estimation of compact binary coale… ▽ More The KAGRA Collaboration has investigated a ten-year upgrade strategy for the KAGRA gravitational wave detector, considering a total of 14 upgrade options that vary in mirror mass, quantum noise reduction techniques, and the quality of cryogenic suspensions. We evaluated the scientific potential of these configurations with a focus on key targets such as parameter estimation of compact binary coalescences, binary neutron star post-merger signals, and continuous gravitational waves. Rather than aiming to improve all science cases uniformly, we prioritized those most sensitive to the detector configuration. Technical feasibility was assessed based on required hardware developments, associated R\&D efforts, cost, and risk. Our study finds that a high-frequency upgrade plan that enhances sensitivity over a broad frequency range above ~200 Hz offers the best balance between scientific return and technical feasibility. Such an upgrade would enable sky localization of binary neutron star mergers at 100 Mpc to better than 0.5 deg$^2$ in a LIGO-Virgo-KAGRA network, and improve the measurement precision of tidal deformability parameter by approximately 10% at median, compared to a network without KAGRA. △ Less

Submitted 5 August, 2025; originally announced August 2025.

Report number: JGW-P2516701

SN 2024gy: Multi-epoch Spectroscopic Features Suggestive of Delayed Detonation in a Type Ia Supernova

Authors: Liping Li, Zhenyu Wang, Jialian Liu, Yu Pan, Alexei V. Filippenko, Jujia Zhang, Xiaofeng Wang, Brajesh Kumar, Yi Yang, Thomas G. Brink, WeiKang Zheng, Xiangcun Meng, Lingzhi Wang, Zeyi Zhao, Qian Zhai, Yongzhi Cai, Giuliano Pignata, Xinlei Chen, Xingzhu Zou, Jiewei Zhao, Xiangkun Liu, Xiaowei Liu, Xinzhong Er, A. Reguitti, R. Michael Rich , et al. (6 additional authors not shown)

Abstract: We present photometric and spectroscopic observations of SN 2024gy, a Type Ia supernova (SN Ia) exhibiting high-velocity features (HVFs) in its early-time spectra. This SN reaches a peak $B$-band magnitude of $-19.25 \pm 0.29$ mag and subsequently declines by $Δm_{15}(B) \approx 1.12$ mag, consistent with the luminosity-width relation characteristic of normal SNe Ia. Based on the peak thermal lumi… ▽ More We present photometric and spectroscopic observations of SN 2024gy, a Type Ia supernova (SN Ia) exhibiting high-velocity features (HVFs) in its early-time spectra. This SN reaches a peak $B$-band magnitude of $-19.25 \pm 0.29$ mag and subsequently declines by $Δm_{15}(B) \approx 1.12$ mag, consistent with the luminosity-width relation characteristic of normal SNe Ia. Based on the peak thermal luminosity of $(1.2 \pm 0.3) \times 10^{43}$ erg s$^{-1}$, we estimate that $0.57 \pm 0.14~\rm M_{\odot}$ of $^{56}$Ni was synthesized during the explosion. Our dense early spectral monitoring revealed significant velocity disparities within the ejecta. Notably, absorption features from the Ca II near-infrared triplet were observed at velocities exceeding 25,000 km s$^{-1}$, while the Si II $λ$6355 line velocity at the same epoch was significantly lower at $\sim$ 16,000 km s$^{-1}$. This velocity disparity likely reflects distinct ionization states of intermediate-mass elements in the outermost layers. The prominent Ca II HVFs may originate from ionization suppression within the highest-velocity ejecta, potentially indicative of minimal hydrogen mixing in a delayed-detonation explosion scenario. Additionally, the Ni/Fe ratio derived from the nebular spectrum of SN 2024gy provides further support for this model. △ Less

Submitted 30 October, 2025; v1 submitted 2 August, 2025; originally announced August 2025.

Comments: 23 pages, 11 figures, accepted for publication in ApJ

Metalens-coupled terahertz NbN hot electron bolometer mixer

Authors: D. Ren, J. R. G. Silva, S. Cremasco, Z. Zhao, W. Ji, J. de Graaff, A. J. L. Adam, J. R. Gao

Abstract: Enabled by planarized phase engineering, metalenses based on metasurfaces offer compact and scalable solutions for applications such as sensing, imaging, and virtual reality. They are particularly attractive for multi-pixel, large-scale heterodyne focal plane arrays in space observatories, where a flat metalens array on a silicon wafer can replace individual lenses, greatly simplifying system inte… ▽ More Enabled by planarized phase engineering, metalenses based on metasurfaces offer compact and scalable solutions for applications such as sensing, imaging, and virtual reality. They are particularly attractive for multi-pixel, large-scale heterodyne focal plane arrays in space observatories, where a flat metalens array on a silicon wafer can replace individual lenses, greatly simplifying system integration and beam alignment. In this work, we demonstrate, for the first time, a superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixer coupled with a silicon-based metalens operating at terahertz frequencies. The metalens phase profile was derived from a finite-size Gaussian beam source using the Rayleigh-Sommerfeld diffraction integral, and its focusing behavior was validated through 2D simulation. Experimentally, the metalens-coupled NbN HEB receiver exhibited a noise temperature of 1800 K at 1.63 THz. The power coupling efficiency from free space to the mixer via the metalens was measured to be 25 %. Measured far-field beam profiles are Gaussian-like with sidelobes below -14 dB. These results demonstrate the feasibility of integrating metalenses with HEB mixers for THz detection, offering a scalable path for compact focal plane arrays in space-based THz instrumentation. △ Less

Submitted 22 July, 2025; originally announced July 2025.

Decadal evolution of a repeating fast radio burst source

Authors: P. Wang, J. S. Zhang, Y. P. Yang, D. K. Zhou, Y. K. Zhang, Y. Feng, Z. Y. Zhao, J. H. Fang, D. Li, W. W. Zhu, B. Zhang, F. Y. Wang, Y. F. Huang, R. Luo, J. L. Han, K. J. Lee, C. W. Tsai, Z. G. Dai, H. Gao, X. P. Zheng, J. H. Cao, X. L. Chen, E. Gugercinoglu, J. C. Jiang, W. C. Jing , et al. (26 additional authors not shown)

Abstract: The origin of fast radio bursts (FRBs), the brightest cosmic radio explosions, is still unknown. Bearing critical clues to FRBs' origin, the long-term evolution of FRBs has yet to be confirmed, since the field is still young and most FRBs were seen only once. Here we report clear evidence of decadal evolution of FRB~20121102A, the first precisely localized repeater. In conjunction with archival da… ▽ More The origin of fast radio bursts (FRBs), the brightest cosmic radio explosions, is still unknown. Bearing critical clues to FRBs' origin, the long-term evolution of FRBs has yet to be confirmed, since the field is still young and most FRBs were seen only once. Here we report clear evidence of decadal evolution of FRB~20121102A, the first precisely localized repeater. In conjunction with archival data, our FAST and GBT monitoring campaign since 2020 reveals a significant 7% decline of local dispersion measure (DM). The rotation measure (RM) of 30,755$\pm$16 $\mathrm{rad\,m^{-2}}$ detected in the last epoch represents a 70% decrease compared to that from December 2016. The $σ_{RM}$ parameter, which describes the complexity of the magneto-ionic environment surrounding the source, was shown to have decreased by 13%. These general trends reveal an evolving FRB environment, which could originate from an early-phase supernova associated with an enhanced pair wind from the FRB central engine. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: 85 pages, 14 figures, under review of Nature Astronomy

GW231123: a Binary Black Hole Merger with Total Mass 190-265 $M_{\odot}$

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu , et al. (1749 additional authors not shown)

Abstract: On 2023 November 23 the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes with masses $137^{+23}_{-18}\, M_\odot$ and $101^{+22}_{-50}\, M_\odot$ (90\% credible intervals), at luminosity distance 0.7-4.1 Gpc and redshift of $0.40^{+0.27}_{-0.25}$, and a network signal-to-noise ratio of $\sim$20.7. Both black holes exhibit high… ▽ More On 2023 November 23 the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes with masses $137^{+23}_{-18}\, M_\odot$ and $101^{+22}_{-50}\, M_\odot$ (90\% credible intervals), at luminosity distance 0.7-4.1 Gpc and redshift of $0.40^{+0.27}_{-0.25}$, and a network signal-to-noise ratio of $\sim$20.7. Both black holes exhibit high spins, $0.9^{+0.10}_{-0.19}$ and $0.80^{+0.20}_{-0.52}$ respectively. A massive black hole remnant is supported by an independent ringdown analysis. Some properties of GW231123 are subject to large systematic uncertainties, as indicated by differences in inferred parameters between signal models. The primary black hole lies within or above the theorized mass gap where black holes between 60-130 $M_\odot$ should be rare due to pair instability mechanisms, while the secondary spans the gap. The observation of GW231123 therefore suggests the formation of black holes from channels beyond standard stellar collapse, and that intermediate-mass black holes of mass $\sim$200 $M_\odot$ form through gravitational-wave driven mergers. △ Less

Submitted 10 November, 2025; v1 submitted 10 July, 2025; originally announced July 2025.

Comments: 27 pages, 10 figures

Report number: DCC: P2500026-v8

Journal ref: ApJL 993 L25 (2025)

Imaging-spectroscopy diagnosis of the giant sloshing spiral in the Virgo cluster with the Einstein Probe Follow-up X-ray Telescope

Authors: X. Zheng, S. Jia, C. Li, Y. Chen, H. Yu, H. Feng, D. Xu, A. Liu, L. Song, C. Liu, F. Lu, S. Zhang, W. Yuan, J. Sanders, J. Wang, T. Chen, C. Cui, W. Cui, W. Feng, N. Gao, J. Guan, D. Han, D. Hou, H. Hu, M. Huang , et al. (26 additional authors not shown)

Abstract: We performed deep X-ray observations of the Virgo cluster using the Einstein Probe Follow-up X-ray Telescope (EP-FXT) with a total exposure of 295 ks. Leveraging the large field of view (FoV) and low particle background of EP-FXT, the image reveals a giant spiral feature connecting the cold fronts in the northwest and southeast, forming a coherent structure consistent with earlier results from XMM… ▽ More We performed deep X-ray observations of the Virgo cluster using the Einstein Probe Follow-up X-ray Telescope (EP-FXT) with a total exposure of 295 ks. Leveraging the large field of view (FoV) and low particle background of EP-FXT, the image reveals a giant spiral feature connecting the cold fronts in the northwest and southeast, forming a coherent structure consistent with earlier results from XMM-Newton and Suzaku. We also present two-dimensional maps of temperature, metallicity, and entropy across the Virgo Cluster, covering a FoV of approximately 28.5 arcmin. These maps clearly show a spiral structure with high density, low temperature, high metallicity, and low entropy. The results support a scenario where the spiral morphology arises from gas sloshing driven by a minor merger. Additionally, EP-FXT temperature measurements agree well with XMM-Newton data within uncertainties. △ Less

Submitted 23 July, 2025; v1 submitted 10 July, 2025; originally announced July 2025.

Comments: 10 pages, 16 figures. Accepted for publication in A&A

Journal ref: A&A 700, A248 (2025)

New constraints on cosmological gravitational waves from CMB and BAO in light of dynamical dark energy

Authors: Sai Wang, Zhi-Chao Zhao

Abstract: In this work, we derive upper limits on the physical energy-density fraction today of cosmological gravitational waves, denoted by $Ω_{\rm{gw}}h^{2}$, via analyzing \emph{Planck} \& ACT \& SPT CMB and DESI BAO data combination. In the standard cosmological model, we establish 95\% CL upper limits of $Ω_{\rm{gw}}h^{2} < 1.0 \times 10^{-6}$ for adiabatic initial conditions and… ▽ More In this work, we derive upper limits on the physical energy-density fraction today of cosmological gravitational waves, denoted by $Ω_{\rm{gw}}h^{2}$, via analyzing \emph{Planck} \& ACT \& SPT CMB and DESI BAO data combination. In the standard cosmological model, we establish 95\% CL upper limits of $Ω_{\rm{gw}}h^{2} < 1.0 \times 10^{-6}$ for adiabatic initial conditions and $Ω_{\rm{gw}}h^{2} < 2.7 \times 10^{-7}$ for homogeneous initial conditions, assuming a uniform prior for $Ω_{\rm gw}h^{2}$. In light of dynamical dark energy, we get $Ω_{\rm{gw}}h^{2} < 7.2 \times 10^{-7}$ (adiabatic) and $Ω_{\rm{gw}}h^{2} < 2.4 \times 10^{-7}$ (homogeneous). In contrast, if a log-uniform prior was assumed for $Ω_{\rm gw}h^{2}$, these constraints can become tighter by a factor of $\sim4$, suggesting the results to be prior-sensitive. Furthermore, we project the sensitivity achievable with LiteBIRD \& CMB Stage-IV measurements of CMB and CSST observations of BAO, forecasting 68\% CL uncertainties of $σ= 2.5 \times 10^{-7}$ (adiabatic) and $σ= 1.0 \times 10^{-7}$ (homogeneous) for ${Ω_{\rm{gw}}h^{2}}$. The constraints we obtained in this work provide critical benchmarks for exploring the cosmological origins of gravitational waves within the frequency band $f \gtrsim 10^{-15}$\,Hz and potentially enable joint analysis with direct gravitational-wave detection sensitive to this regime. △ Less

Submitted 21 October, 2025; v1 submitted 9 July, 2025; originally announced July 2025.

Comments: 12 pages, one column, 4 figures, 3 tables, to appear in the Chinese Physics C

Cosmic baryon census with fast radio bursts and gravitational waves

Authors: Ji-Guo Zhang, Ji-Yu Song, Ze-Wei Zhao, Wan-Peng Sun, Jing-Fei Zhang, Xin Zhang

Abstract: The cosmic baryon density fraction ($Ω_{\rm b}$) is intrinsically correlated with the Hubble constant ($H_0$) through the critical density of the Universe. In the context of the decade-long $H_0$ tension, the significant discrepancy between early- and late-Universe measurements of $H_0$ implies that fixing its value or imposing an external prior could bias the baryon census. To address this concer… ▽ More The cosmic baryon density fraction ($Ω_{\rm b}$) is intrinsically correlated with the Hubble constant ($H_0$) through the critical density of the Universe. In the context of the decade-long $H_0$ tension, the significant discrepancy between early- and late-Universe measurements of $H_0$ implies that fixing its value or imposing an external prior could bias the baryon census. To address this concern, we construct a late-Universe probe framework that unifies fast radio bursts (FRBs) and gravitational-wave (GW) standard sirens, which can respectively resolve the missing baryon problem and the $H_0$ tension through their dispersion measures and absolute luminosity distances. By combining $104$ localized FRBs with $47$ GW events, we obtain an $H_0$-free measurement of $Ω_{\rm b}=0.0488\pm0.0064$ ($1σ$), in concordance with early-Universe observations of CMB + BBN. Although the current precision ($\sim 13\%$) is limited by sample size, the growing detections of both FRBs and GWs will make their synergy a powerful probe of low-redshift cosmology. △ Less

Submitted 2 December, 2025; v1 submitted 9 July, 2025; originally announced July 2025.

Comments: 14 pages, 4 figures

Testing Nambu-Goto approximation of cosmic string by lattice field simulations

Authors: Zizhuo Zhao, Ligong Bian, Jing Shu

Abstract: The precise calculation of gravitational wave (GW) and particle emissions from cosmic string networks is of significant theoretical and experimental interest. In this Letter, we perform numerical simulations of near-global and local string networks, comparing the GW spectra predictions from both lattice field simulation and the Nambu-Goto (NG) approximation methods. We find the discrepancy between… ▽ More The precise calculation of gravitational wave (GW) and particle emissions from cosmic string networks is of significant theoretical and experimental interest. In this Letter, we perform numerical simulations of near-global and local string networks, comparing the GW spectra predictions from both lattice field simulation and the Nambu-Goto (NG) approximation methods. We find the discrepancy between the GW spectra computed via the NG approximation and the lattice field simulation is negligible for near-global string and grow with increasing gauge coupling. Additionally, we confirm that particle emission significantly dominates energy emission, with the ratio of GW energy to particle energy approximately $10^{-3}$ to $10^{-2}$ for both near-global and local string scenarios. △ Less

Submitted 1 July, 2025; originally announced July 2025.

Comments: 6 pages + 5 pages, 13 figures, comments welcome

Identification of Noise-Associated Glitches in KAGRA O3GK with Hveto

Authors: T. Akutsu, M. Ando, M. Aoumi, A. Araya, Y. Aso, L. Baiotti, R. Bajpai, K. Cannon, A. H. -Y. Chen, D. Chen, H. Chen, A. Chiba, C. Chou, M. Eisenmann, K. Endo, T. Fujimori, S. Garg, D. Haba, S. Haino, R. Harada, H. Hayakawa, K. Hayama, S. Fujii, Y. Himemoto, N. Hirata , et al. (127 additional authors not shown)

Abstract: Transient noise ("glitches") in gravitational wave detectors can mimic or obscure true signals, significantly reducing detection sensitivity. Identifying and excluding glitch-contaminated data segments is therefore crucial for enhancing the performance of gravitational-wave searches. We perform a noise analysis of the KAGRA data obtained during the O3GK observation. Our analysis is performed with… ▽ More Transient noise ("glitches") in gravitational wave detectors can mimic or obscure true signals, significantly reducing detection sensitivity. Identifying and excluding glitch-contaminated data segments is therefore crucial for enhancing the performance of gravitational-wave searches. We perform a noise analysis of the KAGRA data obtained during the O3GK observation. Our analysis is performed with hierarchical veto (Hveto) which identifies noises based on the statistical time correlation between the main channel and the auxiliary channels. A total of 2,531 noises were vetoed by 28 auxiliary channels with the configuration (i.e., signal-to-noise threshold set to 8) that we chose for Hveto. We identify vetoed events as glitches on the spectrogram via visual examination after plotting them with Q-transformation. By referring to the Gravity Spy project, we categorize 2,354 glitches into six types: blip, helix, scratchy, and scattered light, which correspond to those listed in Gravity Spy, and dot and line, which are not found in the Gravity Spy classification and are thus named based on their spectrogram morphology in KAGRA data. The remaining 177 glitches are determined not to belong to any of these six types. We show how the KAGRA glitch types are related to each subsystem of KAGRA. To investigate the possible correlation between the main channel and the round winner - an auxiliary channel statistically associated with the main channel for vetoing purposes - we visually examine the similarity or difference in the glitch pattern on the spectrogram. We compare the qualitative correlation found through visual examination with coherence, which is known to provide quantitative measurement for the correlation between the main channel and each auxiliary channel. Our comprehensive noise analysis will help improve the data quality of KAGRA by applying it to future KAGRA observation data. △ Less

Submitted 26 June, 2025; originally announced June 2025.

Comments: To appear in Progress of Theoretical and Experimental Physics (PTEP), accepted June 2025

Journal ref: Prog Theor Exp Phys (2025)

Phase transitions in a holographic superfluid model with non-linear terms beyond the probe limit

Authors: Zi-Qiang Zhao, Zhang-Yu Nie, Jing-Fei Zhang, Xin Zhang

Abstract: We study the holographic s-wave superfluid model with 4th and 6th power self-interaction terms $λ|ψ|^4$ and $τ|ψ|^6$ with considering the full back-reaction of the matter fields on the metric in the 3+1 dimensional bulk. The self-interaction terms are good at controlling the condensate to realize various phase transitions, such as the zeroth-order, first-order, and second-order phase transitions w… ▽ More We study the holographic s-wave superfluid model with 4th and 6th power self-interaction terms $λ|ψ|^4$ and $τ|ψ|^6$ with considering the full back-reaction of the matter fields on the metric in the 3+1 dimensional bulk. The self-interaction terms are good at controlling the condensate to realize various phase transitions, such as the zeroth-order, first-order, and second-order phase transitions within the single condensate s-wave superfluid model. Therefore, in this work, we are able to investigate the influence of the back-reaction strength on the various phase transitions, including the zeroth and first order phase transitions. In addition, we confirm that the influence of the 4th and 6th power terms on the superfluid phase transition in the case of finite back-reaction are qualitative the same as in the probe limit, thus present universality. We also plot the special value $λ_s$ of the parameter $λ$ at different back-reaction strength, below which the condensate grows to an opposite direction and is important in controlling the order of the superfluid phase transitions. Comparing the influence of the back-reaction parameter and that of the higher-order nonlinear coefficients, we see that the back-reaction strength brings in both the effective couplings similar to the 4th power and 6th power terms. △ Less

Submitted 3 October, 2025; v1 submitted 12 June, 2025; originally announced June 2025.

Comments: 9 pages, 10 figures; published in EPJC

Journal ref: Eur. Phys. J. C 85 (2025) 9, 1064

Prospects for Time-Domain and Multi-Messenger Science with eXTP

Authors: Shu-Xu Yi, Wen Zhao, Ren-Xin Xu, Xue-Feng Wu, Giulia Stratta, Simone Dall'Osso, Yan-Jun Xu, Andrea Santangelo, Silvia Zane, Shuang-Nan Zhang, Hua Feng, Huan Yang, Junjie Mao, Junqiang Ge, Lijing Shao, Mi-Xiang Lan, He Gao, Lin Lin, Ning Jiang, Qingwen Wu, Tong Liu, Yun-Wei Yu, Xiang-Yu Wang, Jin Zhang, Dafne Guetta , et al. (53 additional authors not shown)

Abstract: In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including a… ▽ More In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including advanced polarimetry, high sensitivity & large effective area, and wide energy range coverage, which make it a groundbreaking project in high-energy astrophysics. In this article, we briefly introduce the potential time-domain and multi-messenger targets for eXTP, including gravitational-wave (GW) counterparts, gamma-ray bursts (GRBs), magnetars and fast radio bursts (FRBs), tidal disruption events (TDEs), supernovae, high energy neutrinos and TeV active galactic nucleus (AGNs), and so on. We discuss the advantages of future eXTP observations for detecting these sources, their detection capabilities, the abilities to distinguish theoretical models, and their applications in gravity and cosmology. △ Less

Submitted 8 September, 2025; v1 submitted 9 June, 2025; originally announced June 2025.

Comments: accepted for publication in the SCIENCE CHINA Physics, Mechanics & Astronomy

Observatory Science with eXTP

Authors: Ping Zhou, Jirong Mao, Liang Zhang, Alessandro Patruno, Enrico Bozzo, Yanjun Xu, Andrea Santangelo, Silvia Zane, Shuang-Nan Zhang, Hua Feng, Yuri Cavecchi, Barbara De Marco, Junhui Fan, Xian Hou, Pengfei Jiang, Patrizia Romano, Gloria Sala, Lian Tao, Alexandra Veledina, Jacco Vink, Song Wang, Junxian Wang, Yidi Wang, Shanshan Weng, Qingwen Wu , et al. (75 additional authors not shown)

Abstract: Scheduled for launch in 2030, the enhanced X-ray Timing and Polarization (eXTP) telescope is a Chinese space-based mission aimed at studying extreme conditions and phenomena in astrophysics. eXTP will feature three main payloads: Spectroscopy Focusing Arrays (SFAs), Polarimetry Focusing Arrays (PFAs), and a Wide-field Camera (W2C). This white paper outlines observatory science, incorporating key s… ▽ More Scheduled for launch in 2030, the enhanced X-ray Timing and Polarization (eXTP) telescope is a Chinese space-based mission aimed at studying extreme conditions and phenomena in astrophysics. eXTP will feature three main payloads: Spectroscopy Focusing Arrays (SFAs), Polarimetry Focusing Arrays (PFAs), and a Wide-field Camera (W2C). This white paper outlines observatory science, incorporating key scientific advances and instrumental changes since the publication of the previous white paper [1]. We will discuss perspectives of eXTP on the research domains of flare stars, supernova remnants, pulsar wind nebulae, cataclysmic variables, X-ray binaries, ultraluminous X-ray sources, AGN, and pulsar-based positioning and timekeeping. △ Less

Submitted 8 September, 2025; v1 submitted 9 June, 2025; originally announced June 2025.

Comments: accepted for publication in the SCIENCE CHINA Physics, Mechanics & Astronomy

The enhanced X-ray Timing and Polarimetry mission -- eXTP for launch in 2030

Authors: Shuang-Nan Zhang, Andrea Santangelo, Yupeng Xu, Hua Feng, Fangjun Lu, Yong Chen, Mingyu Ge, Kirpal Nandra, Xin Wu, Marco Feroci, Margarita Hernanz, Congzhan Liu, Huilin He, Yusa Wang, Weichun Jiang, Weiwei Cui, Yanji Yang, Juan Wang, Wei Li, Xiaohua Liu, Bin Meng, Xiangyang Wen, Aimei Zhang, Jia Ma, Maoshun Li , et al. (136 additional authors not shown)

Abstract: In this paper we present the current status of the enhanced X-ray Timing and Polarimetry mission, which has been fully approved for launch in 2030. eXTP is a space science mission designed to study fundamental physics under extreme conditions of matter density, gravity, and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring the effects of… ▽ More In this paper we present the current status of the enhanced X-ray Timing and Polarimetry mission, which has been fully approved for launch in 2030. eXTP is a space science mission designed to study fundamental physics under extreme conditions of matter density, gravity, and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring the effects of quantum electro-dynamics, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, the eXTP mission is poised to become a leading observatory for time-domain and multi-messenger astronomy in the 2030's, as well as providing observations of unprecedented quality on a variety of galactic and extragalactic objects. After briefly introducing the history and a summary of the scientific objectives of the eXTP mission, this paper presents a comprehensive overview of: 1) the cutting-edge technology, technical specifications, and anticipated performance of the mission's scientific instruments; 2) the full mission profile, encompassing spacecraft design, operational capabilities, and ground segment infrastructure. △ Less

Submitted 8 September, 2025; v1 submitted 9 June, 2025; originally announced June 2025.

Comments: accepted for publication in the SCIENCE CHINA Physics, Mechanics & Astronomy

Design and Validation of the Digital Receiver System for the next-generation radio interferometer

Authors: Donghao Qu, Jiajun Zhang, Yajun Wu, Zhang Zhao, Yanbin Yang, Zixuan Liu

Abstract: This paper presents the design and validation of a digital receiver system developed for the next-generation radio interferometer projects. The receiver supports 8 analog inputs with 12-bit, 4GHz sampling and performs real-time signal processing using FPGA-based channelization. Field experiments were conducted to observe the Sun, a satellite beacon, and Cassiopeia A. Interference fringes were anal… ▽ More This paper presents the design and validation of a digital receiver system developed for the next-generation radio interferometer projects. The receiver supports 8 analog inputs with 12-bit, 4GHz sampling and performs real-time signal processing using FPGA-based channelization. Field experiments were conducted to observe the Sun, a satellite beacon, and Cassiopeia A. Interference fringes were analyzed and modeled. Time delay compensation was implemented in two ways: theoretical calculation and Gaussian Process Regression (GPR) fitting. Results show sub-nanosecond consistency between the two methods. The field experiments demonstrate the receiver's suitability for future radio telescopes such as the BINGO-ABDUS project. △ Less

Submitted 31 May, 2025; originally announced June 2025.

Comments: 18 pages, 12 figures

All-sky search for individual Primordial Black Hole bursts with LHAASO

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen , et al. (293 additional authors not shown)

Abstract: Primordial Black Holes~(PBHs) are hypothetical black holes with a wide range of masses that formed in the early universe. As a result, they may play an important cosmological role and provide a unique probe of the early universe. A PBH with an initial mass of approximately $10^{15}$~g is expected to explode today in a final burst of Hawking radiation. In this work, we conduct an all-sky search for… ▽ More Primordial Black Holes~(PBHs) are hypothetical black holes with a wide range of masses that formed in the early universe. As a result, they may play an important cosmological role and provide a unique probe of the early universe. A PBH with an initial mass of approximately $10^{15}$~g is expected to explode today in a final burst of Hawking radiation. In this work, we conduct an all-sky search for individual PBH burst events using the data collected from March 2021 to July 2024 by the Water Cherenkov Detector Array of the Large High Altitude Air Shower Observatory (LHAASO). Three PBH burst durations, 10~s, 20~s, and 100~s, are searched, with no significant PBH bursts observed. The upper limit on the local PBH burst rate density is set to be as low as 181~pc$^{-3}$~yr$^{-1}$ at 99$\%$ confidence level, representing the most stringent limit achieved to date. △ Less

Submitted 2 November, 2025; v1 submitted 30 May, 2025; originally announced May 2025.

Comments: 8 pages, 2 figures

Ground Calibration Result of the Wide-field X-ray Telescope (WXT) onboard the Einstein Probe

Authors: Huaqing Cheng, Chen Zhang, Zhixing Ling, Xiaojin Sun, Shengli Sun, Yuan Liu, Yanfeng Dai, Zhenqing Jia, Haiwu Pan, Wenxin Wang, Donghua Zhao, Yifan Chen, Zhiwei Cheng, Wei Fu, Yixiao Han, Junfei Li, Zhengda Li, Xiaohao Ma, Yulong Xue, Ailiang Yan, Qiang Zhang, Yusa Wang, Xiongtao Yang, Zijian Zhao, Longhui Li , et al. (2 additional authors not shown)

Abstract: We report on results of the on-ground X-ray calibration of the Wide-field X-ray Telescope (WXT) built from novel lobster-eye micro-pore optics, onboard the Einstein Probe (EP) satellite. To fully characterize the instrumental performance and properties, a series of tests and calibrations have been carried out at different levels of devices, assemblies and the complete module before the launch of E… ▽ More We report on results of the on-ground X-ray calibration of the Wide-field X-ray Telescope (WXT) built from novel lobster-eye micro-pore optics, onboard the Einstein Probe (EP) satellite. To fully characterize the instrumental performance and properties, a series of tests and calibrations have been carried out at different levels of devices, assemblies and the complete module before the launch of EP. In this paper, we present the calibration results of three flight model modules (FM1, FM5 and FM11) obtained during their end-to-end module calibration experiments carried out at the 100-m X-ray Test Facility (100XF) of IHEP, CAS. Measurements of the Point Spread Function (PSF), effective area, and energy response were performed for multiple incident directions and several characteristic X-ray emission line energies. Specifically, the distributions of the PSF and effective areas are found to be roughly uniform across the FoV, in large agreement with the prediction of lobster-eye optics. Their energy dependence behavior aligns well with theoretical predictions and Monte Carlo simulations. At 1.25 keV, the full width at half maximum (FWHM) of the focal spot is in range of 3-7 arcmin (a median of 4.2) and the effective area in range of 2-3 $cm^2$. Noticeably, the flight model instruments demonstrate a $\sim1.5$ arcmin spatial resolution improvement over the previously launched Lobster Eye Imager for Astronomy. The properties of the complementary metal-oxide semiconductor (CMOS) sensors were also calibrated. The gain coefficients are in range of 6.4-6.9 eV/DN. The energy resolutions are in range of 120-140 eV at 1.25 keV, meeting design requirements. These calibration results have been ingested into the first version of calibration database (CALDB) and applied to the analysis of the scientific data acquired by WXT after the launch of EP. △ Less

Submitted 24 May, 2025; originally announced May 2025.

Comments: 28 pages, 18 figures, 2 tables. submitted to Experimental Astronomy

Two Periodic Activity Epochs in FRB 20201124A: Coincident with Critical RM Evolution Epochs and Its Implications

Authors: Wen-Long Zhang, Chen-Ran Hu, Chen Du, Wen-Jun Tan, Zhen-Yin Zhao, Shao-Lin Xiong, Shuang-Xi Yi, Fa-Yin Wang, Li-Ming Song, Cheng-Kui Li, Shuang-Nan Zhang, Chen-Wei Wang, Sheng-Lun Xie, Xiao-Fei Dong, Yong-Feng Huang

Abstract: Recent observations of the repeating fast radio burst FRB 20201124A by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) revealed a second-scale periodic modulation ($\sim$1.7\,s) in burst activity during two distinct observational windows. We find that these two periodic activity epochs temporally coincide with the transitional states of the source's Faraday rotation measure (RM),… ▽ More Recent observations of the repeating fast radio burst FRB 20201124A by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) revealed a second-scale periodic modulation ($\sim$1.7\,s) in burst activity during two distinct observational windows. We find that these two periodic activity epochs temporally coincide with the transitional states of the source's Faraday rotation measure (RM), and the chance coincidence is only about 0.07$\%$. This correlation is can be understood within the magnetar/Be-star binary system framework. Considering that only the polar cap region can remain stable for such an extended period, we apply a coherent linear periodic evolution model to jointly constrain the initial burst period \( P_0 \) and the period derivative \( \dot{P} \) across both observation windows (MJD 59310 and MJD 59347). We obtain spin parameters consistent with blind search results: an initial spin period $P_0 = 1.7060155$\,s at the reference time and spin period derivative $\dot{P} = 6.1393 \times 10^{-10}$\,s\,s$^{-1}$. We conclude that during these two observational windows, the magnetar was just crossing the disk of the Be star. The disk-magnetar interaction at these two geometric positions may surpress the multi-polar magnetic fields at low latitudes of the magnetar, which enhances the dominance of the polar cap region emissions and makes the periodic activity detectable. △ Less

Submitted 26 May, 2025; v1 submitted 23 May, 2025; originally announced May 2025.

Comments: 5 pages, 4 figures, submitted to ApJL

Isotropy, anisotropies and non-Gaussianity in the scalar-induced gravitational-wave background: diagrammatic approach for primordial non-Gaussianity up to arbitrary order

Authors: Jun-Peng Li, Sai Wang, Zhi-Chao Zhao, Kazunori Kohri

Abstract: Produced nonlinearly by the enhanced linear cosmological curvature perturbations, the scalar-induced gravitational waves (SIGWs) can serve as a potentially powerful probe of primordial non-Gaussianity (PNG) in the early Universe. In this work, we comprehensively investigate the imprints of local-type PNG on the SIGW background beyond the widely used quadratic and cubic approximations. We develop a… ▽ More Produced nonlinearly by the enhanced linear cosmological curvature perturbations, the scalar-induced gravitational waves (SIGWs) can serve as a potentially powerful probe of primordial non-Gaussianity (PNG) in the early Universe. In this work, we comprehensively investigate the imprints of local-type PNG on the SIGW background beyond the widely used quadratic and cubic approximations. We develop a diagrammatic approach capable of analyzing SIGWs for PNG up to arbitrary order. Following this approach, we derive semi-analytic formulas for the energy-density fraction spectrum, the angular power spectrum, and the angular bispectrum and trispectrum to describe the isotropic component, anisotropies, and non-Gaussianity of the SIGW background, respectively. Particularly, focusing on PNG up to quartic approximation (parameterized by $f_\mathrm{NL}$, $g_\mathrm{NL}$, and $h_\mathrm{NL}$), we numerically compute all contributions to these SIGW spectra. We find that PNG can significantly alter the magnitude of the SIGW energy-density spectrum, and can generate substantial anisotropies through the initial inhomogeneities in the SIGW distribution. Furthermore, we observe that the SIGW angular bispectrum and trispectrum always vanish when the primordial curvature perturbations are Gaussian; otherwise, they do not, indicating their potential utility as probes of PNG. Therefore, we anticipate that the SIGW background will provide essential information about the early Universe. △ Less

Submitted 10 September, 2025; v1 submitted 22 May, 2025; originally announced May 2025.

Comments: 107 pages, 36 figures. Version 2: Added discussions on the infrared scaling of the SIGW energy-density spectra in Section 6 and the Appendix. Corrected the calculation of PBH abundance in Section 6. Corrected some typos and included several new references

Report number: KEK-TH-2724, KEK-Cosmo-0381

First Identification and Precise Spectral Measurement of the Proton Component in the Cosmic-Ray `Knee'

Authors: The LHAASO Collaboration, Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen , et al. (292 additional authors not shown)

Abstract: We report the first high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and syst… ▽ More We report the first high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and systematic accuracy comparable to satellite data at lower energies. The proton spectrum shows significant hardening relative to low-energy extrapolations, culminating at 3 PeV, followed by sharp softening. This distinct spectral structure - closely aligned with the knee in the all-particle spectrum - points to the emergence of a new CR component at PeV energies, likely linked to the dozens of PeVatrons recently discovered by LHAASO, and offers crucial clues to the origin of Galactic cosmic rays. △ Less

Submitted 20 May, 2025; originally announced May 2025.

Probabilistic Zeeman-Doppler imaging of stellar magnetic fields: I. Analysis of tau Scorpii in the weak-field limit

Authors: Jennifer Rosina Andersson, Oleg Kochukhov, Zheng Zhao, Jens Sjölund

Abstract: Zeeman-Doppler imaging (ZDI) is used to study the surface magnetic field topology of stars, based on high-resolution spectropolarimetric time series observations. Multiple ZDI inversions have been conducted for the early B-type star tau Sco, which has been found to exhibit a weak but complex non-dipolar surface magnetic field. The classical ZDI framework suffers from a significant limitation in th… ▽ More Zeeman-Doppler imaging (ZDI) is used to study the surface magnetic field topology of stars, based on high-resolution spectropolarimetric time series observations. Multiple ZDI inversions have been conducted for the early B-type star tau Sco, which has been found to exhibit a weak but complex non-dipolar surface magnetic field. The classical ZDI framework suffers from a significant limitation in that it provides little to no reliable uncertainty quantification for the reconstructed magnetic field maps, with essentially all published results being confined to point estimates. To fill this gap, we propose a Bayesian framework for probabilistic ZDI. Here, the proposed framework is demonstrated on tau Sco in the weak-field limit. We propose three distinct statistical models, and use archival ESPaDOnS high-resolution Stokes V observations to carry out the probabilistic magnetic inversion in closed form. The surface magnetic field is parameterised by a high-dimensional spherical-harmonic expansion. By comparing three different prior distributions over the latent variables in the spherical-harmonic decomposition, our results showcase the ZDI sensitivity to various hyperparameters. The mean magnetic field maps are qualitatively similar to previously published point estimates, but analysis of the magnetic energy distribution indicates high uncertainty and higher energy content at low angular degrees l. Our results effectively demonstrate that, for stars in the weak-field regime, reliable uncertainty quantification of recovered magnetic field maps can be obtained in closed form with natural assumptions on the statistical model. Future work will explore extending this framework beyond the weak-field approximation and incorporating prior uncertainty over multiple stellar parameters in more complex magnetic inversion problems. △ Less

Submitted 7 May, 2025; originally announced May 2025.

Comments: Accepted for publication in A&A

Journal ref: A&A 699, A63 (2025)

Fermi-LAT and FAST observation of the gamma-ray binary HESS J0632+057

Authors: Yanlv Yang, Dengke Zhou, Zihao Zhao, Jian Li, Diego F. Torres, Pei Wang

Abstract: Using 15 years of data from the Fermi Large Area Telescope (Fermi-LAT), we performed a comprehensive analysis on the gamma-ray binary HESS J0632+057. Its spectrum in 0.1-300 GeV band is well described by a power law model with an index of $2.40\pm0.16$, leading to an energy flux of (5.5$\pm$1.6$)\times$ 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$. The GeV Spectral Energy Distribution (SED) of HESS J0632+057… ▽ More Using 15 years of data from the Fermi Large Area Telescope (Fermi-LAT), we performed a comprehensive analysis on the gamma-ray binary HESS J0632+057. Its spectrum in 0.1-300 GeV band is well described by a power law model with an index of $2.40\pm0.16$, leading to an energy flux of (5.5$\pm$1.6$)\times$ 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$. The GeV Spectral Energy Distribution (SED) of HESS J0632+057 hints for a spectral turn-over between $\sim$10-100 GeV. Orbital analysis reveals a flux enhancement during the phase range of 0.2-0.4, consistent with the X-ray and TeV light curves, indicating an origin of a common particle population. We carried out six deep radio observations on HESS J0632+057 with the Five-hundred-meter Aperture Spherical Telescope (FAST), evenly distributed across its orbit, reaching a detection sensitivity of 2$μ$Jy. However, no radio pulsation was detected within these observations. The absence of radio pulsation may be attributed to the dense stellar wind environment of HESS J0632+057. △ Less

Submitted 23 April, 2025; originally announced April 2025.

Constraints on the lepton asymmetry from DESI DR2 BAO data

Authors: Zhi-Chao Zhao, Dong-Mei Xia, Sai Wang

Abstract: It is important to explore the potential existence of lepton asymmetry in the neutrino sector. Conducting a joint analysis of DESI DR2 BAO data and \emph{Planck} 2018 CMB data, we obtain the upper limits on the neutrino degeneracy parameter, i.e., $ξ<0.56$ for the normal mass hierarchy while $ξ<0.62$ for the inverted mass hierarchy, at 95\% confidence level. Considering the influence of the dynami… ▽ More It is important to explore the potential existence of lepton asymmetry in the neutrino sector. Conducting a joint analysis of DESI DR2 BAO data and \emph{Planck} 2018 CMB data, we obtain the upper limits on the neutrino degeneracy parameter, i.e., $ξ<0.56$ for the normal mass hierarchy while $ξ<0.62$ for the inverted mass hierarchy, at 95\% confidence level. Considering the influence of the dynamical dark energy, we find that these upper limits remain to be robust. This work may provide helpful implications for model buildings of the matter-antimatter asymmetry in the universe. △ Less

Submitted 24 November, 2025; v1 submitted 13 April, 2025; originally announced April 2025.

Comments: 11 pages, 3 figures, 2 tables, to appear in the Physical Review D

Characterized behaviors of black hole thermodynamics in the supercritical region

Authors: Zi-Qiang Zhao, Zhang-Yu Nie, Jing-Fei Zhang, Xin Zhang

Abstract: The comprehension of universal thermodynamic behaviors in the supercritical region is crucial for examining the characteristics of black hole systems under high temperature and pressure. This study is devoted to the analysis of characteristic lines and crossover behaviors within the supercritical region. By making use of the free energy, we introduce three key thermodynamic quantities: scaled vari… ▽ More The comprehension of universal thermodynamic behaviors in the supercritical region is crucial for examining the characteristics of black hole systems under high temperature and pressure. This study is devoted to the analysis of characteristic lines and crossover behaviors within the supercritical region. By making use of the free energy, we introduce three key thermodynamic quantities: scaled variance, skewness, and kurtosis. Our results demonstrate that the Widom line, associated with the maximal scaled variance, can effectively differentiate between small and large black hole-like subphases, each displaying distinct thermodynamic behaviors within the supercritical region. Furthermore, by utilizing quasinormal modes, we identify the Frenkel line, offering a dynamic perspective to distinguish between small and large black hole-like subphases. These contribute to a deeper comprehension of black hole subphases in the supercritical region, thus illuminating new facets of black hole thermodynamics. △ Less

Submitted 14 October, 2025; v1 submitted 7 April, 2025; originally announced April 2025.

Comments: 5 pages, 3 figures

Journal ref: Chinese Physics Letters 42, 101102 (2025)

Upper limits on the gamma-ray emission from the microquasar V4641 Sgr

Authors: Zihao Zhao, Jian Li, Diego F. Torres

Abstract: Following a recent detection of TeV radiation by the Large High Altitude Air Shower Observatory (LHAASO) and the High-Altitude Water Cherenkov Observatory (HAWC), coincident with the direction of the microquasar V4641 Sgr, we search for possible GeV emission from this source. We explored the morphology and temporal features of the source as well as two nearby unassociated point sources which could… ▽ More Following a recent detection of TeV radiation by the Large High Altitude Air Shower Observatory (LHAASO) and the High-Altitude Water Cherenkov Observatory (HAWC), coincident with the direction of the microquasar V4641 Sgr, we search for possible GeV emission from this source. We explored the morphology and temporal features of the source as well as two nearby unassociated point sources which could be a part of extended structure of V4641 Sgr, and compared results with corresponding X-ray and TeV emissions. The 95% confidence level upper limits for the flux from the source, assuming both point and extended source models were 5.38$\times$ 10$^{-13}$ erg cm$^{-2}$ s$^{-1}$ and 1.12$\times$ 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$, respectively. Additionally, no correlation between gamma-ray light curve and X-ray outbursts was observed. △ Less

Submitted 21 March, 2025; originally announced March 2025.

Comments: 10 pages, 6 figures, accepted by ApJ

Numerical simulations of density perturbation and gravitational wave production from cosmological first-order phase transition

Authors: Jintao Zou, Zhiqing Zhu, Zizhuo Zhao, Ligong Bian

Abstract: We conducted three-dimensional lattice simulations to study the density perturbation and gravitational waves (GWs) during first-order phase transition (FOPT). We find that for phase transition strength $α> 1$, the forward motion of bubble walls becomes the primary source, whereas for $α< 1$, the dominant contribution to the density perturbation comes from the delay of vacuum decay. Additionally, t… ▽ More We conducted three-dimensional lattice simulations to study the density perturbation and gravitational waves (GWs) during first-order phase transition (FOPT). We find that for phase transition strength $α> 1$, the forward motion of bubble walls becomes the primary source, whereas for $α< 1$, the dominant contribution to the density perturbation comes from the delay of vacuum decay. Additionally, the power spectrum of density perturbations generated by the phase transition exhibits a slope of $k^3$ at small wavenumbers and $k^{-1.5}$ at large wavenumbers. Furthermore, we calculated the GW power spectra, which exhibit the slope of $k^3$ at small wavenumbers and $k^{-2}$ at large wavenumbers. Our numerical simulations confirm that slow PTs can produce PBHs and provide predictions for the GW power spectrum, offering theoretical support for GW detection. △ Less

Submitted 18 December, 2025; v1 submitted 27 February, 2025; originally announced February 2025.

Comments: 23 pages, 12 figures

Ultra-high-energy $γ$-ray emission associated with the tail of a bow-shock pulsar wind nebula

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen , et al. (274 additional authors not shown)

Abstract: In this study, we present a comprehensive analysis of an unidentified point-like ultra-high-energy (UHE) $γ$-ray source, designated as 1LHAASO J1740+0948u, situated in the vicinity of the middle-aged pulsar PSR J1740+1000. The detection significance reached 17.1$σ$ (9.4$σ$) above 25$\,$TeV (100$\,$TeV). The source energy spectrum extended up to 300$\,$TeV, which was well fitted by a log-parabola f… ▽ More In this study, we present a comprehensive analysis of an unidentified point-like ultra-high-energy (UHE) $γ$-ray source, designated as 1LHAASO J1740+0948u, situated in the vicinity of the middle-aged pulsar PSR J1740+1000. The detection significance reached 17.1$σ$ (9.4$σ$) above 25$\,$TeV (100$\,$TeV). The source energy spectrum extended up to 300$\,$TeV, which was well fitted by a log-parabola function with $N0 = (1.93\pm0.23) \times 10^{-16} \rm{TeV^{-1}\,cm^{-2}\,s^{-2}}$, $α= 2.14\pm0.27$, and $β= 1.20\pm0.41$ at E0 = 30$\,$TeV. The associated pulsar, PSR J1740+1000, resides at a high galactic latitude and powers a bow-shock pulsar wind nebula (BSPWN) with an extended X-ray tail. The best-fit position of the gamma-ray source appeared to be shifted by $0.2^{\circ}$ with respect to the pulsar position. As the (i) currently identified pulsar halos do not demonstrate such offsets, and (ii) centroid of the gamma-ray emission is approximately located at the extension of the X-ray tail, we speculate that the UHE $γ$-ray emission may originate from re-accelerated electron/positron pairs that are advected away in the bow-shock tail. △ Less

Submitted 24 February, 2025; v1 submitted 21 February, 2025; originally announced February 2025.

Comments: Corrected spelling errors in several author names

Journal ref: The Innovation (2025), 100802

Broadband $γ$-ray spectrum of supernova remnant Cassiopeia A

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen , et al. (293 additional authors not shown)

Abstract: The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $γ$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telesc… ▽ More The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $γ$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telescopes (IACTs) and its flux near $\sim 1$ TeV is about two times higher. In combination with analyses of more than 16 years of \textit{Fermi}-LAT data covering $0.1 \, \mathrm{GeV} - 1 \, \mathrm{TeV}$, we find that the spectrum above 30 GeV deviates significantly from a single power-law, and is best described by a smoothly broken power-law with a spectral index of $1.90 \pm 0.15_\mathrm{stat}$ ($3.41 \pm 0.19_\mathrm{stat}$) below (above) a break energy of $0.63 \pm 0.21_\mathrm{stat} \, \mathrm{TeV}$. Given differences in the angular resolution of LHAASO-WCDA and IACTs, TeV $γ$-ray emission detected with LHAASO may have a significant contribution from regions surrounding the SNR illuminated by particles accelerated earlier, which, however, are treated as background by IACTs. Detailed modelling can be used to constrain acceleration processes of TeV particles in the early stage of SNR evolution. △ Less

Submitted 7 February, 2025; originally announced February 2025.

Flaring Activities of Fast Rotating Stars have Solar-like Latitudinal Distribution

Authors: Huiqin Yang, Xin Cheng, Jifeng Liu, Shuai Liu, Zhanhao Zhao, Guiping Zhou, Yijun Hou, Changliang Gao, Zexi Niu

Abstract: The dynamo theory has always been one of the biggest mysteries in stellar physics. One key reason for its uncertainty is poor knowledge of the dynamo process on stars except the Sun. The most important observation feature of solar dynamo is that active regions only appear at low latitudes, which provides a crucial constraint to the dynamo theory, while Doppler imaging, the current technique to spa… ▽ More The dynamo theory has always been one of the biggest mysteries in stellar physics. One key reason for its uncertainty is poor knowledge of the dynamo process on stars except the Sun. The most important observation feature of solar dynamo is that active regions only appear at low latitudes, which provides a crucial constraint to the dynamo theory, while Doppler imaging, the current technique to spatially resolve stellar hemisphere, is difficult to distinguish the equatorial region . Hence, the latitudinal distribution of active regions (LDAR) of stars is ambiguous and controversial, mainly due to the limit of the current technique for spatially resolving the stellar surface. Fast rotating stars, which are young and active, are thought to operate with a different dynamo process than the Sun. We study their LDAR and compare them with the Sun to reveal the underlying dynamo process. Flares are drastic and observational activity events, which occur in active regions. Here, we propose a new method to study how the apparent flaring activity varies with respect to the inclination to determine the LDAR of fast rotating stars.We find that the LDAR of fast rotating stars is consistent with that of the Sun, contrary to expectations. Our results provide a crucial constraint to stellar dynamo, indicating that the solar-like dynamo also applies to fast rotating stars, even spanning different stages of their evolution. △ Less

Submitted 7 February, 2025; v1 submitted 27 January, 2025; originally announced January 2025.

Comments: 12 pages,10 figures, accepted by A&A

Journal ref: A&A 695, A21 (2025)

Identification of 4876 Bent-Tail Radio Galaxies in the FIRST Survey Using Deep Learning Combined with Visual Inspection

Authors: Baoqiang Lao, Heinz Andernach, Xiaolong Yang, Xiang Zhang, Rushuang Zhao, Zhen Zhao, Yun Yu, Xiaohui Sun, Sheng-Li Qin

Abstract: Bent-tail radio galaxies (BTRGs) are characterized by bent radio lobes. This unique shape is mainly caused by the movement of the galaxy within a cluster, during which the radio jets are deflected by the intra-cluster medium. A combined method, which involves a deep learning-based radio source finder along with visual inspection, has been utilized to search for BTRGs from the Faint Images of the R… ▽ More Bent-tail radio galaxies (BTRGs) are characterized by bent radio lobes. This unique shape is mainly caused by the movement of the galaxy within a cluster, during which the radio jets are deflected by the intra-cluster medium. A combined method, which involves a deep learning-based radio source finder along with visual inspection, has been utilized to search for BTRGs from the Faint Images of the Radio Sky at Twenty-centimeters survey images. Consequently, a catalog of 4876 BTRGs has been constructed, among which 3871 are newly discovered. Based on the classification scheme of the opening angle between the two jets of the galaxy, BTRGs are typically classified as either wide-angle-tail (WAT) sources or narrow-angle-tail (NAT) sources. Our catalog comprises 4424 WATs and 652 NATs. Among these, optical counterparts are identified for 4193 BTRGs. This catalog covers luminosities in the range of $1.91\times10^{20} \leq L_{\rm 1.4\,GHz} \leq 1.45\times10^{28}$ ${\rm W\,Hz^{-1}}$ and redshifts from $z = 0.0023$ to $z = 3.43$. Various physical properties of these BTRGs and their statistics are presented. Particularly, by the nearest neighbor method, we found that 1825 BTRGs in this catalog belong to galaxy clusters reported in literature. △ Less

Submitted 16 January, 2025; originally announced January 2025.

Comments: 25 pages, 11 figures, 3 tables, accepted for publication in ApJS

Journal ref: ApJS 276, 46 (2025)

An Intermediate-mass Black Hole Lurking in A Galactic Halo Caught Alive during Outburst

Authors: C. -C. Jin, D. -Y. Li, N. Jiang, L. -X. Dai, H. -Q. Cheng, J. -Z. Zhu, C. -W. Yang, A. Rau, P. Baldini, T. -G. Wang, H. -Y. Zhou, W. Yuan, C. Zhang, X. -W. Shu, R. -F. Shen, Y. -L. Wang, S. -X. Wen, Q. -Y. Wu, Y. -B. Wang, L. L. Thomsen, Z. -J. Zhang, W. -J. Zhang, A. Coleiro, R. Eyles-Ferris, X. Fang , et al. (116 additional authors not shown)

Abstract: Stellar-mass and supermassive black holes abound in the Universe, whereas intermediate-mass black holes (IMBHs) of ~10^2-10^5 solar masses in between are largely missing observationally, with few cases found only. Here we report the real-time discovery of a long-duration X-ray transient, EP240222a, accompanied by an optical flare with prominent H and He emission lines revealed by prompt follow-up… ▽ More Stellar-mass and supermassive black holes abound in the Universe, whereas intermediate-mass black holes (IMBHs) of ~10^2-10^5 solar masses in between are largely missing observationally, with few cases found only. Here we report the real-time discovery of a long-duration X-ray transient, EP240222a, accompanied by an optical flare with prominent H and He emission lines revealed by prompt follow-up observations. Its observed properties evidence an IMBH located unambiguously in the halo of a nearby galaxy and flaring by tidally disrupting a star -- the only confirmed off-nucleus IMBH-tidal disruption event so far. This work demonstrates the potential of sensitive time-domain X-ray surveys, complemented by timely multi-wavelength follow-ups, in probing IMBHs, their environments, demographics, origins and connections to stellar-mass and supermassive black holes. △ Less

Submitted 16 January, 2025; originally announced January 2025.

Comments: 64 pages, 15 figures, submitted

A universal break in energy functions of three hyperactive repeating fast radio bursts

Authors: Q. Wu, F. Y. Wang, Z. Y. Zhao, P. Wang, H. Xu, Y. K. Zhang, D. J. Zhou, J. R. Niu, W. Y. Wang, S. X. Yi, Z. Q. Hua, S. B. Zhang, J. L. Han, W. W. Zhu, K. J. Lee, D. Li, X. F. Wu, Z. G. Dai, B. Zhang

Abstract: Fast radio bursts (FRBs) are millisecond-duration pulses occurring at cosmological distances with a mysterious origin. Observations show that at least some FRBs are produced by magnetars. All magnetar-powered FRB models require some triggering mechanisms, among which the most popular is the crust cracking of a neutron star, which is called starquake. However, so far there has been no decisive evid… ▽ More Fast radio bursts (FRBs) are millisecond-duration pulses occurring at cosmological distances with a mysterious origin. Observations show that at least some FRBs are produced by magnetars. All magnetar-powered FRB models require some triggering mechanisms, among which the most popular is the crust cracking of a neutron star, which is called starquake. However, so far there has been no decisive evidence for this speculation. Here we report the energy functions of the three most active repeating FRBs, which show a universal break around $10^{38}$ erg. Such a break is similar to that of the frequency-magnitude relationship of earthquakes. The break and change of the power-law indices below and above it can be well understood within the framework of FRBs triggered by starquakes in the magnetar models. The seed of weak FRBs can grow both on the magnetar surface and in the deeper crust. In contrast, the triggering of strong FRBs is confined by the crustal thickness and the seed of strong FRBs can only grow on the surface. This difference in dimensionality causes a break in the scaling properties from weak to strong FRBs, occurring at a point where the penetration depth of starquakes equals the crustal thickness. Our result, together with the earthquake-like temporal properties of these FRBs, strongly supports that FRBs are triggered by starquakes, providing a new opportunity to study the physical properties of the neutron star crust. △ Less

Submitted 15 January, 2025; originally announced January 2025.

Comments: 16 pages, 6 figures. Accepted for publication in The Astrophysical Journal Letters

Study of primordial non-Gaussianity $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ with the cross-correlations between the scalar-induced gravitational waves and the cosmic microwave background

Authors: Zhi-Chao Zhao, Sai Wang, Jun-Peng Li, Kazunori Kohri

Abstract: The stochastic gravitational-wave background originating from cosmic sources contains vital information about the early universe. In this work, we comprehensively study the cross-correlations between the energy-density anisotropies in scalar-induced gravitational waves (SIGWs) and the temperature anisotropies and polarization in the cosmic microwave background (CMB). In our analysis of the angular… ▽ More The stochastic gravitational-wave background originating from cosmic sources contains vital information about the early universe. In this work, we comprehensively study the cross-correlations between the energy-density anisotropies in scalar-induced gravitational waves (SIGWs) and the temperature anisotropies and polarization in the cosmic microwave background (CMB). In our analysis of the angular power spectra for these cross-correlations, we consider all contributions of the local-type primordial non-Gaussianity $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ that can lead to large anisotropies. We show that the angular power spectra are highly sensitive to primordial non-Gaussianity. Furthermore, we project the sensitivity of future gravitational-wave detectors to detect such signals and, consequently, measure the primordial non-Gaussianity. △ Less

Submitted 24 November, 2025; v1 submitted 3 December, 2024; originally announced December 2024.

Comments: 18 pages, 5 figures, one column, version accepted by EPJC. The code is available on GitHub at https://github.com/Zhi-ChaoZhao/sigw_class

Report number: KEK-Cosmo-0364, KEK-TH-2670, KEK-QUP-2024-0025

Journal ref: Eur.Phys.J.C 85 (2025) 12, 1406