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Physics Astrophysics High Energy Astrophysical Phenomena

astro-ph.HE Watch High Energy Astrophysical Phenomena

Sunday 9 August

High Energy Astrophysical Phenomena

Simulation-based inference for AGN jet population modelling: Towards more robust comparisons of black hole jet speeds

Clara Lilje, James H. Matthews and Rob Fender

We present the most complete modelling of the MOJAVE 1.5 Jansky Quarter Century active galactic nuclei (AGN) jet population, using likelihood-free simulation-based inference. Due to the complex impact of a flux-limit on observed AGN data sets, careful modelling of the parent population is required. In particular, when observing and fitting to multiple data distributions likelihoods become non-intuitive. Parameter degeneracies further complicate the problem and make it suitable for likelihood-free, simulation-based inference. This method relies on a normalising flow learning the likelihood surface or posteriors directly. We extensively validate the flow to show that previous parameter estimates for the AGN jet speed distributions underestimated parameter errors significantly and do not capture the non-gaussianity of the parameter posteriors. The new results enable a better statistical comparison to other AGN population studies, but also a more accurate comparison of supermassive black hole jets with their lower mass counterparts, X-ray binaries (XRB). We find that the AGN follow a Lorentz factor distribution of the shape $N(\Gamma) \propto \Gamma^b$ with $b= -1.32_{-0.19}^{+0.20}$. This slope is consistent with the XRB Lorentz factor distribution at $2\sigma$. Simulation-based inference as a method is generally well-suited to many astrophysical problems, and this paper shows the convenient applicability of this methodology to parent population studies of jetted AGN with multiple observables specifically.
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High Energy Astrophysical Phenomena

Slow Cosmic-Ray Diffusion in Supersonic and Super-Alfvénic Turbulence

Yue Hu

Extended TeV-PeV gamma-ray halo observations imply cosmic-ray (CR) diffusion that is both substantially slower than the Galactic mean and only weakly anisotropic, despite the presence of a large-scale Galactic magnetic field. We investigate whether such transport can arise in partially ionized source environments, where ion-neutral damping removes the small-scale fluctuations responsible for gyroresonant scattering. Using two-fluid magnetohydrodynamic turbulence simulations with relativistic test-particle tracking, we find that damping increases the parallel diffusion coefficient by approximately two orders of magnitude in trans-sonic turbulence, thereby strongly enhancing field-aligned transport. In supersonic turbulence, shock-associated magnetic fluctuations survive the damping and sustain non-resonant pitch-angle scattering, limiting the increase in parallel diffusion to a factor of a few to ten. At high Alfvénic Mach numbers, $M_A\gtrsim5$, the magnetic-field direction decorrelates over the Alfvén scale, driving parallel diffusion coefficient $D_\parallel$ and perpendicular diffusion coefficient $D_\perp$ toward equality. For $M_s\simeq10$, $M_A\simeq5$-$10$, and representative parameters for hundred-TeV gamma-ray source environments, we obtain comparable $D_\parallel$ and $D_\perp$, within the observationally inferred range of $\sim10^{27}$-$10^{28}\,\mathrm{cm^2\,s^{-1}}$. These results show that strongly supersonic, highly super-Alfvénic turbulence in source environments can sustain slow, nearly isotropic CR transport even when the ion-neutral damping effect is important.
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High Energy Astrophysical Phenomena

Plasmoid-Mediated 2D Magnetic Reconnection in Partially Ionized Plasmas

Yue Hu, Siyao Xu, Grzegorz Kowal et al. (+3 more)

Magnetic reconnection in partially ionized plasmas is an important channel for energy release. While the plasmoid instability is well characterized in 2D fully ionized plasmas, its behavior in the presence of neutral-dominated plasma remains poorly understood in the nonlinear, high-Lundquist-number ($S = 10^5$) regime. We present high-resolution ($16384 \times 4096$ cells) two-dimensional two-fluid (ion $+$ neutral) simulations of Harris-sheet reconnection with upstream plasma beta $\beta = 2$, comparing fully ionized and partially ionized (ionization fraction $\xi = 10^{-1}$ and $10^{-2}$) regimes. Neutral-ion decoupling accelerates the linear tearing stage and alters the plasmoid hierarchy: the large-scale “monster” plasmoid that dominates the fully ionized case is suppressed, and the sheet instead fragments into a dense chain of sub-scale plasmoids. Below the neutral-ion decoupling scale $\ell_{\rm dec}$, ions concentrate into the plasmoids, reaching peak overdensities $\rho_i/\rho_{i,0} \approx 10$ ($\xi = 10^{-1}$) and $3-5\times10^{3}$ ($\xi = 10^{-2}$), while the neutrals remain comparatively smooth. This local pile-up raises the ionization fraction and recouples the two fluids within the plasmoids. Measured from the out-of-plane electric field at the reconnection sites, the reconnection rate in the $\xi = 10^{-2}$ case achieves $R_{\rm rec}\approx0.01$, whereas the $\xi = 10^{-1}$ case rises to a rate $\approx0.02$ and further $0.035$ when apparent coalescence occurs. In the $\xi = 10^{-2}$ case, the ambipolar drift drives a rapid ion inflow $\sim0.5\,v_{A,0}$ into the layer at the same reconnection sites, far above the neutral inflow velocity $\sim0.1\,v_{A,0}$. Here, $v_{A,0}$ is the upstream total Alfvén speed.
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All authors Yue Hu, Siyao Xu, Grzegorz Kowal, James M. Stone, Alex Lazarian, Hui Li

High Energy Astrophysical Phenomena

Three-Dimensional Expansion of Iron Ejecta in Cassiopeia A with Chandra and XRISM

Aya Bamba, Tomoki Kadoya, Kouichi Hagino et al. (+4 more)

Measurement of the expansion structure of ejecta in supernova remnants (SNRs) provides important information about their explosion mechanism. We combine Chandra proper-motion measurements with XRISM Doppler measurements to derive an approximate, region-averaged three-dimensional velocity map of the Fe-K-emitting ejecta in Cassiopeia A (Cas A), one of the youngest Galactic core-collapse SNRs. Proper motions were measured using the optical flow method. We find that the Fe-K-emitting ejecta expand predominantly outward, except in the western region, with projected velocities of up to ~4580 km/s. The southeastern ejecta exhibit the highest three-dimensional velocity, reaching 5160+-320 km/s, based on the combined proper-motion and Doppler measurements. This velocity exceeds those measured for intermediate-mass elements (IMEs) such as Si and S, and the corresponding ejecta exhibit a relatively small line-of-sight velocity dispersion. These results are broadly consistent with the previously suggested inversion between the Fe-rich and IME-rich ejecta layers. The apparent inward motion or emergence of a new Fe-K emission component in the western region may reflect interaction with dense surrounding material, although the present data do not allow us to distinguish uniquely between these possibilities or to determine their physical origin.
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All authors Aya Bamba, Tomoki Kadoya, Kouichi Hagino, Jacco Vink, Manan Agarwal, Masahiro Ichihashi, Paul Plucinsky

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

The ALMA carbon monoxide supernova (ACOS) survey II. Turbulent giant molecular clouds at the positions of core-collapse supernovae

M. Solar, M. J. Michałowski, J. Nadolny et al. (+11 more)

Context. Study of cold molecular hydrogen gas (hereafter molecular gas) provides crucial insights into its interplay with star-forming regions. However, the connection between molecular gas turbulence and the sites of massive star ($> 8~\rm{M}_{\odot}$) explosions as core-collapse supernovae (CCSNe) remains unexplored. Aims. We measure for the first time the turbulence of molecular gas in environments of CCSNe, with the aim to constrain the nature of their progenitors. Methods. In order to reach spatial resolutions of giant molecular cloud (GMC) sizes ($\sim 100~\rm{pc}$), we collected ALMA carbon monoxide $J = 2 \rightarrow 1$ spectral line ($\sim 230.54~\rm{GHz}$) observations (as a tracer of molecular gas) at the locations of 33 nearby CCSNe ($< 100~\rm{Mpc}$). Results. We found that CCSNe prefer molecular gas regions with high velocity dispersion compared to the average of their host galaxies. Conclusions. For CCSN progenitors, this observational evidence supports their increased formation in regions of high densities and/or their binary nature.
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All authors M. Solar, M. J. Michałowski, J. Nadolny, J. Sollerman, E. Zapartas, A. Oliva, L. Galbany, J. Hjorth, B. Ayala, M. Koprowski, A. Leśniewska, P. Nowaczyk, O. Ryzhov, B. Šlaus

Saturday 8 August

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR

From Light to Sound: Spectroscopic Evolution & Sonification of the flaring Nova V612 Scuti

Pragati Acharya, Elias Aydi, Kirill V. Sokolovsky et al. (+17 more)

We present photometric and spectroscopic observations of the 2017 Galactic nova V612 Sct, whose optical evolution was marked by multiple unusually large maxima. The eruption included two prominent flares lasting around a month each and reaching amplitudes of about 2.5 mag, followed by a series of smaller flares. Extensive spectroscopic monitoring reveals a striking pattern: with each flare, new absorption systems emerge at progressively higher velocities. This behavior, also seen in other flaring novae, provides evidence for repeated episodes of mass ejection or outflow at increasing velocities. V612 Sct also alternated between Fe II and He/N spectral phases during different stages of the eruption, establishing a clear connection between the photometric flares and major spectral transitions. We present two-dimensional dynamic spectra that directly trace the appearance of new absorption features contemporaneous with the light-curve flares. We also introduce a sonification of the spectroscopic sequence, offering an alternative representation of the temporal evolution of the eruption. These results support a picture in which repeated ejection episodes and shock formation play a central role in powering the multiple maxima observed in flaring novae.
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All authors Pragati Acharya, Elias Aydi, Kirill V. Sokolovsky, Brian D. Metzger, Laura Chomiuk, Peter Craig, Luca Izzo, Justin D. Linford, Shazrene Mohamed, Isabella Molina, Koji Mukai, Ken J. Shen, Jennifer L. Sokoloski, Paul Luckas, Terry Bohlsen, Olivier Garde, Joan G. Flo, Paolo Bellavista, Umberto Sollecchia, Forrest Sims

High Energy Astrophysical Phenomena

On the Physical Origins of Long Period Radio Transients

Yuanhong Qu and Bing Zhang

Long-period radio transients (LPRTs) are a rapidly growing class of coherent radio sources with periods ranging from minutes to hours, whose central engines and emission mechanisms remain unclear. Motivated by the detection of red dwarf (RD) companions in several LPRTs and by generic period constraints from the Roche limit and the mass transfer limit, we argue that LPRTs naturally separate into two broad classes: shorter-period sources that are likely isolated compact objects and longer-period sources that are compact objects in binary systems that are likely detached. For isolated objects, we find that isolated white dwarfs (WDs) generally have difficulty sustaining pair production and coherent radio emission unless the surface temperature is extremely high, while slow rotating neutron stars (NSs) can remain marginally active through inverse-Compton-driven pair cascades. For binary systems, asynchronous WD / NS + RD systems can power coherent radio emission through unipolar induction when the WD / NS magnetic field dominates the companion surface field, with relativistic electron cyclotron maser emission as the radiation mechanism, while at larger separations the system enters the magnetospheric interaction regime, possibly powered by magnetic reconnection. Bright X-ray counterparts favor magnetar-related systems and undetected X-ray emission is expected from WD-related channels. We propose a diagnostic flow chart that uses observational criteria to classify LPRTs and identify their central engines. These criteria lead to a physically motivated classification framework for LPRTs.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Probing Memory-Burdened Primordial Black Holes with High-Energy Neutrinos

Arian Moradi Asl, Sandhya Choubey and Andreas Lund

The memory-burden effect can suppress the late-time evaporation of primordial black holes (PBHs), allowing those that would otherwise have evaporated via Hawking radiation to survive until the present epoch. These lighter PBHs emit high-energy and ultra-high-energy neutrinos, opening the tentalizing possibility of discovery via neutrino telescopes. We study the constraints on memory-burdened PBHs from current IceCube HESE, MESE, and EHE data; and forecast the sensitivity reach of IceCube-Gen2 radio and GRAND200k. In particular, we study how this signal depends on whether the initial PBH population is described by a log-normal mass function or by a monochromatic one. We find that log-normally distributed populations can be more strongly constrained than monochromatic populations with the same median mass primarily because their low-mass tails enhance the high-energy neutrino flux. We show that current IceCube data provide the leading limits for a lower memory burden parameter $k$, whereas the projected radio detectors become substantially more sensitive for higher values of $k$. We also study a scenario where future experiments would see a positive signal coming from PBHs. We consider a representative 30-event signal in IceCube-Gen2 radio and GRAND200k and study how well one could distinguish the two mass-function hypotheses. We find that it is easier to disfavor the monochromatic distribution when the log-normal distribution is assumed to be true. Finally, we study how well the parameters of the memory-burdened PBHs can be estimated in these future experiments.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

Diagnosing the Fe line complex of the intracluster medium by XRISM high-resolution spectroscopy

K. Fukushima, L. Hirata, N. Y. Yamasaki et al. (+17 more)

We aim to test the validity of the CIE framework in the ICM by performing line diagnostics based mainly on resolved Fe-K emission lines. Methods. We analyse Resolve full-array spectra of 17 galaxy clusters. Prominent Fe-K line components (the Fe xxv w, x, y, z, and Fe xxvi Ly{\alpha}1,2 lines) are removed from plasma emission models and instead fitted with Gaussian profiles, enabling direct measurements of line fluxes without relying on synthetic spectral models. Some cool-core systems show w/z ratios lower than predicted by about 20 per cent, and a broader w than z, consistent with resonant scattering effects. The y/x ratios exhibit marginal deviations from model predictions for some objects, suggesting possible origins of cascade process due to electron recombination and contribution from low-ionised Fe. The Fe Ly{\alpha}2/Ly{\alpha}1 ratios are globally close to the expected value of about 0.5, and the samples with good photon statistics prefer 0.55. This subtle excess is consistent with an unresolved contribution to Ly{\alpha}2 from the magnetic-dipole (M1) transition, which is absent from one of the atomic codes considered here. More interestingly, systems at around 7 keV preferentially exhibit Ly{\alpha}2/Ly{\alpha}1 ratios above 0.55. Although the statistical significance of this trend is limited, it suggests that resolved Fe Ly{\alpha} spectroscopy may provide a sensitive probe of additional atomic processes to collisional excitation, including dielectronic and radiative recombination and polarisation effects.
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All authors K. Fukushima, L. Hirata, N. Y. Yamasaki, P. Chakraborty, S. Dupourqué, Y. Fujita, L. Gu, C. Kilbourne, K. Matsushita, F. Mernier, E. D. Miller, K. Nakazawa, Y. Omiya, N. Ota, A. Sarkar, K. Sato, M. Sun, Y. Uchida, I. Zhuravleva, H. Yamaguchi

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Gravitational radiation from binary systems with time varying masses

Teodora M. Matei, Cristian A. Croitoru and Tiberiu Harko

We consider the properties of the gravitational radiation emitted by massive stars in binary systems with time varying mass, orbiting around each other in Keplerian orbits under the influence of the gravitational force. When this effect is combined to the quadrupole expression of the gravitational radiation, some supplementary terms in the standard formulae describing radiative effects do appear. By using the generalized quadrupole formalism, with time dependent masses, we obtain the expressions describing the time variation of the angular momentum, semimajor axis, eccentricity and periastron shift of the binary system. As a simple application of the developed formalism we consider in detail two cases of the mass variation, by assuming a linear and an exponential time dependence, respectively. The gravitational radiation characteristics corresponding to these models are fully investigated numerically with the help of a dedicated software package \href{https://github.com/croi900/GRAV-T}{GRAV-T}, specifically developed for the study of the gravitational radiation of the mass varying systems. The impact of the gravitational wave emission on the merger of two magnetars losing mass due to neutrino heated winds is also investigated in detail. The obtained results could be important for the understanding of general relativistic effects in the case of the variation of the gravitational mass with time, which sensitively influences the properties of the gravitational radiation emission.
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High Energy Astrophysical Phenomena

Anisotropic Particle Transport from a Pulsar Wind Nebula Revealed by Einstein Probe and LHAASO

Zhen Cao, F. Aharonian, Y.X. Bai et al. (+342 more)

Pulsar wind nebulae (PWNe) are major cosmic ray accelerators, yet the mechanisms transporting high-energy particles into the interstellar medium remain elusive. Building on the LHAASO discovery of an ultra-high-energy (UHE) $\gamma$-ray source near the bow-shock PWN powered by the pulsar PSR J1740+1000, we present a joint Einstein Probe (EP) and LHAASO study of this system. EP observations reveal an extended X-ray tail far exceeding the structure previously seen by XMM-Newton. Updated LHAASO observations show that the $\gamma$-ray emission is elongated, with its major axis aligned with the extended X-ray tail revealed by EP. This is the first detection of an X-ray pulsar tail associated with a spatially coincident extended UHE $\gamma$-ray emission. The X-ray and $\gamma$-ray spectrum can be well explained with a single population of relativistic electrons via synchrotron and inverse Compton radiation, respectively, removing the need for particle re-acceleration during propagation. The results unambiguously show that electrons/positrons above 100 TeV are escaping from the PWN. Instead of the immediate, isotropic diffusion into ambient interstellar medium that is typically assumed, these particles are transported anisotropically over at least $\sim$10 pc, either guided by the background magnetic field or carried by an advective outflow.
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All authors Zhen Cao, F. Aharonian, Y.X. Bai, Y.W. Bao, D. Bastieri, X.J. Bi, Y.J. Bi, W. Bian, J. Blunier, A.V. Bukevich, C.M. Cai, W.Y. Cao, Zhe Cao, J. Chang, J.F. Chang, E.S. Chen, G.H. Chen, H.K. Chen, L.F. Chen, Liang Chen, Long Chen, M.J. Chen, M.L. Chen, Q.H. Chen, S. Chen, S.H. Chen, S.Z. Chen, T.L. Chen, X.B. Chen, X.J. Chen, X.P. Chen, Yang Chen, Yong Chen, N. Cheng, Q.Y. Cheng, Y.D. Cheng, Y.H. Chi, M.Y. Cui, S.W. Cui, X.H. Cui, Y.D. Cui, B.Z. Dai, H.L. Dai, L.X. Dai, Z.G. Dai, Danzengluobu, Y.X. Diao, A.J. Dong, X.D. Duan, J.H. Fan, Y.Z. Fan, J. Fang, J.H. Fang, K. Fang, C.F. Feng, H. Feng, L. Feng, S.H. Feng, X.T. Feng, Y. Feng, Y.L. Feng, S. Gabici, B. Gao, Q. Gao, W. Gao, C. Ge, M.M. Ge, T.T. Ge, L.S. Geng, G. Giacinti, G.H. Gong, Q.B. Gou, M.H. Gu, W.M. Gu, F.L. Guo, J. Guo, K.J. Guo, X.L. Guo, Y.Q. Guo, R.P. Han, O.A. Hannuksela, M. Hasan, H.H. He, H.N. He, J.Y. He, X.Y. He, Y. He, S. Hernández-Cadena, C. Hou, X. Hou, H.B. Hu, S.C. Hu, D.H. Huang, F. Huang, J.J. Huang, X.L. Huang, X.T. Huang, X.Y. Huang, Y. Huang, Z.J. Huang, A. Inventar, X.L. Ji, H.Y. Jia, K. Jia, S.M. Jia, H.B. Jiang, K. Jiang, X.W. Jiang, Z.J. Jiang, C.C. Jin, M. Jin, S. Kaci, M.M. Kang, I. Karpikov, D. Khangulyan, D. Kuleshov, K. Kurinov, W.H. Lei, Cheng Li, C.K. Li, Cong Li, D. Li, F. Li, H.B. Li, H.C. Li, Jian Li, Jie Li, K. Li, L. Li, R.L. Li, T.Y. Li, W.L. Li, X.R. Li, X.Y. Li, Y. Li, Zhe Li, Zhuo Li, E.W. Liang, Y.F. Liang, S.J. Lin, B. Liu, C. Liu, D. Liu, D.B. Liu, H. Liu, J. Liu, J.L. Liu, J.R. Liu, M.Y. Liu, Q. Liu, R.Y. Liu, S.M. Liu, T. Liu, W. Liu, Y. Liu, Y. Liu, Yuan Liu, Y.N. Liu, Y.Q. Lou, Q. Luo, Y. Luo, H.K. Lv, B.Q. Ma, L.L. Ma, X.H. Ma, I.O. Maliy, J.R. Mao, Z. Min, W. Mitthumsiri, Y. Mizuno, G.B. Mou, A. Neronov, C.-Y. Ng, K.C.Y. Ng, M.Y. Ni, L. Nie, L.J. Ou, Z.W. Ou, H.W. Pan, P. Pattarakijwanich, Z.Y. Pei, D.Y. Peng, J.C. Qi, M.Y. Qi, J.J. Qin, H. Qu, A. Raza, C.Y. Ren, M.Q. Ruan, D. Ruffolo, A. Sáiz, D. Savchenko, D. Semikoz, L. Shao, O. Shchegolev, Y.Z. Shen, X.D. Sheng, F.W. Shu, H.C. Song, Yu.V. Stenkin, Y. Su, C.Y. Sun, D.X. Sun, H. Sun, J.X. Sun, M. Sun, Q.N. Sun, X.N. Sun, Z.B. Sun, N.H. Tabasam, J. Takata, P.H.T. Tam, H.B. Tan, Q.W. Tang, R. Tang, Z.B. Tang, L. Tao, W.W. Tian, C.N. Tong, L.H. Wan, C. Wang, D.H. Wang, G.W. Wang, H.G. Wang, J.C. Wang, J.F. Wang, J.S. Wang, K. Wang, Kai Wang, Kai Wang, L.P. Wang, L.Y. Wang, W. Wang, X.G. Wang, X.J. Wang, X.Y. Wang, Y. Wang, Y.D. Wang, Z.H. Wang, Z.X. Wang, Zheng Wang, D.M. Wei, J.J. Wei, Y.J. Wei, T. Wen, S.S. Weng, C.Y. Wu, H.R. Wu, Q.W. Wu, S. Wu, X.F. Wu, Y.S. Wu, S.Q. Xi, J. Xia, G.M. Xiang, D.X. Xiao, G. Xiao, Y.F. Xiao, B.H. Xie, F. Xie, Y.L. Xin, H.D. Xing, Y. Xing, D.R. Xiong, B.N. Xu, C.Y. Xu, D.L. Xu, R.X. Xu, S.S. Xu, L. Xue, D.H. Yan, T. Yan, C. Yang, C.Y. Yang, F.F. Yang, L.L. Yang, M.J. Yang, R.Z. Yang, W.X. Yang, Z.H. Yang, Z.G. Yao, X.A. Ye, L.Q. Yin, N. Yin, X.H. You, Z.Y. You, Y.H. Yu, Q. Yuan, W.M. Yuan, H. Yue, H.D. Zeng, T.X. Zeng, W. Zeng, X.T. Zeng, M. Zha, B. Zhang, B.B. Zhang, B.T. Zhang, C. Zhang, H. Zhang, H.M. Zhang, H.Y. Zhang, J. Zhang, J.L. Zhang, J.Y. Zhang, L.Y. Zhang, Li Zhang, P.F. Zhang, R. Zhang, R.Y. Zhang, S.R. Zhang, S.S. Zhang, S.Y. Zhang, W. Zhang, X. Zhang, X.L. Zhang, X.P. Zhang, Yi Zhang, Yong Zhang, Z.P. Zhang, H.S. Zhao, J. Zhao, L. Zhao, L.Z. Zhao, X.H. Zhao, F. Zheng, T.C. Zheng, B. Zhou, H. Zhou, J.N. Zhou, L. Zhou, M. Zhou, P. Zhou, R. Zhou, X.X. Zhou, X.X. Zhou, B.Y. Zhu, C.G. Zhu, F.R. Zhu, H. Zhu, K.J. Zhu, Y.F. Zhu, Z.F. Zhu, Y.C. Zou, X. Zuo

Friday 7 August

High Energy Astrophysical Phenomena

Insights into the Pulsar Timing Array hypothesis space

El Mehdi Zahraoui, Patricio Maturana-Russel, Willem van Straten et al. (+2 more)

We present novel insights into the pulsar-noise model space in pulsar timing array (PTA) experiments. Through a comparative analysis of the same Parkes PTA second data release observations processed with the 2020 and 2023 pipelines, we show that data processing materially changes the distribution of posterior support across competing noise hypotheses and increases sensitivity to weak contributions such as the solar wind. A solar-wind component appears in the highest-posterior hypothesis for ten pulsars under the 2023 pipeline, against four under the 2020 pipeline, while the corresponding mean electron density estimates are consistent with PPTA DR3 results. Furthermore, hypothesis-space analysis exposes model competition and degeneracies that are hidden by single-model summaries. Approximately 75% of the pulsars retain substantial posterior support for alternative noise descriptions. Therefore, understanding the nature of the pulsar noise hypothesis space is crucial for robust inference and nanohertz gravitational-wave background searches.
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All authors El Mehdi Zahraoui, Patricio Maturana-Russel, Willem van Straten, Renate Meyer, Sergei Gulyaev

High Energy Astrophysical Phenomena

A Systematic Study of Type Ia Supernova Remnants: Using Nucleosynthesis to Probe their Supernova Progenitors

Cole Treyturik, Samar Safi-Harb and Gilles Ferrand

We present the first systematic, spatially resolved X-ray spectroscopic study of a largely thermonuclear (Type Ia) sample of supernova remnants (SNRs), aimed at probing the explosion properties and progenitors through a comparison to a suite of nucleosynthesis models available in the literature. Our sample focuses on Galactic and LMC ejecta-dominated SNRs believed to be, or otherwise assumed to be, of thermonuclear origin. Using archival XMM-Newton observations (and Chandra for G1.9+0.3), we extract spectra from adaptively binned regions across each remnant and model the emission to constrain the plasma temperature, ionization timescale, and ejecta abundances. We then compare abundance ratios (relative to Si) to a library of 335 individual models spanning 11 commonly-used supernova nucleosynthesis simulation sets from the literature including seven thermonuclear and four core-collapse sets. Across the sample, we find that individual remnants can be well matched by subsets of models, but no single model reproduces all measured elemental ratios at once. As a result, the best fit model for a given object is typically set by a selection of well-fitted abundance ratios, highlighting both the strength and limitations in yield-based model determination. For some SNRs, the abundance comparisons show better agreement with particular families of Type Ia SN explosions, including near-Chandrasekhar-mass delayed detonations, sub-Chandrasekhar-mass explosions, and dynamically driven double detonations, although these interpretations are not unique. Finally, we outline the need for model improvements, including refined nuclear reaction rates, higher dimensional treatment of mixing and turbulence, expanded metallicity coverage, and the exploration of non-standard supernova explosion energies.
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High Energy Astrophysical Phenomena

Neutrino quantum kinetics for fast flavor conversion in a time-dependent environment

Zewei Xiong and Meng-Ru Wu

Fast flavor conversions (FFCs) of neutrinos, driven by the fast flavor instability (FFI), can reshape the neutrino flavor content in dense astrophysical environments such as core-collapse supernovae and neutron star mergers. Most studies of FFCs adopt a two-step approach, in which a flavor-unstable state containing deep electron-minus-heavy-flavor lepton number (E-XLN) angular crossings is first constructed and subsequently evolved. Because realistic crossings should instead develop gradually through neutrino transport, the validity of such setups has been called into question. We investigate this issue by solving the neutrino quantum kinetic equations with self-consistent collisional rates in a spherically symmetric supernova background whose electron fraction evolves in time through a sequence of stages, starting from a configuration free of E-XLN crossings. We find that the evolution proceeds through three characteristic episodes. In the shallow-crossing episode, FFCs develop from marginally unstable, shallow crossings, carrying small-scale structures consistent with linear stability analysis. In the near-crossing-elimination episode, the balance between collisions and FFCs keeps the system in a near-quasistationary state in which the emerging crossings are continuously eliminated, so that the strongly unstable regime is never reached. In the swapping episodes, the E-XLN reverses sign and a dynamically propagating flavor-swap E-XLN zero surface forms. We find that the evolved flavor content at the end of different time stages broadly agrees with the quasistationary solutions obtained in the corresponding two-step models adopting fixed matter backgrounds. In addition, we investigate the robustness of the effective classical transport (ECT) framework that adopts subgrid flavor redistribution using different parametrized prescriptions. Notably, except during the swapping [abridged]
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High Energy Astrophysical Phenomena

Do Accretion Disks Get Bent Out of Shape? Investigating the Origin of Rapid Fluctuations in the Tails of Long Thermonuclear X-ray Bursts

D.R. Ballantyne and N. Degenaar

Thermonuclear X-ray bursts from the surfaces of neutron stars affect the surrounding accretion flow, revealing details of the underlying physical processes influencing accretion physics. In this context, we perform a spectral analysis of 5 long X-ray bursts that exhibit temporary rapid flux variations during the tails of their light curves. In all cases, spectra extracted from before, during and after the time of fluctuations show evidence for relativistic, ionized reflection with the blackbody from the neutron star often hidden from view. Both the properties of the reflecting region and the observed fraction of the blackbody vary as the fluctuations start and stop. These results are compared to a sample of 5 similar bursts without fluctuations in their light curves, and we find that spectra from 4 of the bursts in the control sample are best described by a simple absorbed blackbody. The bursts with fluctuations are longer and more energetic than those without fluctuations, in agreement with the prediction that radiatively-driven warps are impacting the accretion disks of the bursts with fluctuations. This result would also imply that these accretion disks must have large viscosity parameters. The lack of reflection in bursts from the control sample may result from lower accretion rates, as these disks would have smaller surface densities and would expand and become Compton-thin due to heating from the burst. High-throughput, time-resolved spectral analysis of X-ray bursts that undergo warping would give insight into the strength of accretion disk viscosity.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

Mapping Gas Accretion and Stellar Kinematics to Sub-kiloparsec Scales in NGC 4696 with JWST/NIRSpec

Mathieu Marquis, Julie Hlavacek-Larrondo, Olivia Pereira et al. (+35 more)

We present JWST/NIRSpec IFU spectroscopy of the central $618\times618$ pc$^2$ ($\sim3''\times3''$) of NGC 4696, the BCG in the Centaurus cluster. Leveraging the $\sim0.1''$ ($20.6$ pc) pixel size of JWST, we resolve a compact circumnuclear rotating disk (radius of $\sim120$ pc) traced by Pa$\alpha$ and H$_2$ 1$-$0 S(1) emission, which allows a reassessment of the AGN position based on the kinematic centre of this disk. A central Pa$\alpha$ velocity dispersion reaching $\sigma\sim449$ km s$^{-1}$ implies a SMBH mass of $\sim10^9$ M$_\odot$, corresponding to a sphere of influence of $r_\mathrm{inf}\sim60$ pc, resolved by our observations. Position-velocity diagrams reveal an increase from $\sim-200$ to $\sim600$ km s$^{-1}$ on scales of $\sim150$ pc (a gradient of $4.7$ km s$^{-1}$ pc$^{-1}$) and an accretion rate of $\sim18$ M$_\odot$ yr$^{-1}$ feeding the CND. The Pa$\alpha$ emission shows a double-component in the core, with a high-dispersion redshifted component reaching $\sigma\sim600$ km s$^{-1}$. In contrast, MUSE H$\alpha$ observations covering the $\sim10$ kpc-scale filamentary structure recover only weak velocity gradients ($\lesssim150$ km s$^{-1}$) within $\sim300\times300$ pc$^2$ and do not resolve the disk due to larger PSFs and pixel sizes. ALMA CO(2-1) data reveal only compact molecular clumps within a $\sim410\times410$ pc$^2$ region, with no extended counterpart to the structures traced by Pa$\alpha$ and H$_2$ 1$-$0 S(1). Stellar kinematics show a smooth velocity field and broad dispersion profile, clearly decoupled from both the multiphase gas and the hot ICM probed by XRISM. These results provide a direct, spatially resolved view of gas dynamics within the inner few hundred parsecs, demonstrating the power of JWST/NIRSpec to probe SMBH feeding.
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All authors Mathieu Marquis, Julie Hlavacek-Larrondo, Olivia Pereira, Michael Reefe, Hyunseop Choi, Jorge Barrera-Ballesteros, Benjamin Vigneron, Ming Sun, Rebecca E. A. Canning, Gregory Taylor, Loïc Albert, Francesco D'Eugenio, Megan Donahue, Andrew C. Fabian, Gary J. Ferland, John S. Gallagher, Marie-Lou Gendron-Marsolais, Pierre Guillard, Minghao Guo, Nina Hatch, Ralf Kotulla, Yuan Li, Roberto Maiolino, Allison Man, Michael A. McDonald, Brian R. McNamara, Valeria Olivares, Marine Prunier, Christopher S. Reynolds, Carter Rhea, Annabelle Richard-Laferrière, Helen R. Russell, Philippe Salomé, Prathamesh Tamhane, Auriane Thilloy, Grant R. Tremblay, G. Mark Voit, Stephen A. Walker

High Energy Astrophysical Phenomena

Capture Driven Evolution of Asymmetric Dark Matter in Non-rotating Neutron Stars

Peiran Liu and Wenrong Sun

We develop a self-consistent framework that connects dark matter capture to the long term accumulation and structural evolution of neutron stars, allowing us to quantify the impact of capture driven asymmetric dark matter on gravitational wave observables over astrophysical timescales. We model cold, non-rotating neutron stars using a three layer polytropic EoS coupled to a dark matter component through the two fluid Tolman Oppenheimer Volkoff equations, and reconstruct the long term evolution using a time dependent dark matter capture formalism. By exploring a wide range of astrophysical conditions, including extreme environments designed to maximize the capture efficiency, we derive conservative upper bounds on the effects of dark matter accumulation over a Hubble time. Even under these deliberately optimistic assumptions, the accumulated dark matter component remains subdominant and induces limited structural modifications. In particular, dark matter accumulation increases the stellar compactness while suppressing the Love number and tidal deformability. Significant evolution occurs only in extreme Galactic center like environments over Hubble time scales, whereas for realistic Galactic or cluster dark matter densities the corresponding deviations remain negligible. We therefore conclude that capture driven dark matter accumulation is unlikely to produce detectable signatures in current or near future gravitational wave observations of neutron stars.
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High Energy Astrophysical Phenomena

Fast and Accurate Prediction of Neutron Star Structure with Deep Neural Networks

Kaushikk V N, Bhaskar Biswas and Stephan Rosswog

Solving the Tolman–Oppenheimer–Volkoff (TOV) equations, together with the tidal perturbation equations, for large numbers of equation-of-state (EOS) samples is a major computational bottleneck in Bayesian inference of the dense-matter EOS, and this will become increasingly limiting as next-generation observatories deliver far larger and more precise datasets. We develop neural-network surrogates for the forward TOV mapping that predict neutron star mass, radius, and tidal deformability simultaneously and directly from the EOS parameters and central density. We train and compare two architectures: a conventional feedforward network and a residual network, the latter of which, to our knowledge, has not previously been explored for TOV surrogate modeling. Trained on a piecewise polytropic EOS parameter space, both networks reproduce the numerical solutions to high accuracy, with the coefficient of determination exceeding 0.999 for all three observables, while accelerating the evaluation of stellar observables by roughly two orders of magnitude relative to direct numerical integration. We find that both architectures achieve excellent predictive accuracy at the network sizes considered here, with the residual network providing a modest improvement in accuracy over the feedforward network at the expense of slightly longer inference times. The overall performance differences remain small, indicating that a feedforward network already has sufficient capacity for this mapping while residual connections offer only incremental gains. Nevertheless, the residual architecture provides a robust baseline for future extensions to richer EOS parameterizations or higher-dimensional regression tasks. The resulting surrogates are well-suited to large-scale Bayesian EOS inference and population studies, where repeated TOV evaluations would otherwise dominate the computational cost.
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High Energy Astrophysical Phenomena

X-Ray Observation of Type II Supernova 2024ggi

Elisa J. Gao and Vikram V. Dwarkadas

We investigate the Chandra and XMM-Newton X-ray emission from the core-collapse SN 2024ggi. Spectral fitting is carried out using the vapec model. We find X-ray temperatures between 5-7 keV, lower than the value assumed by previous authors by about a factor of 4-6. However the unabsorbed flux is consistent with published values within the error bars. The X-ray luminosity evolution is somewhat steeper than expected for a steady wind, although it could be consistent with a steady wind within the error bars.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

The large-scale ordered magnetic field in the Galactic halo and the Local Bubble

Elena Orlando

All-sky synchrotron polarization observations are the primary probe of the Galactic large-scale ordered magnetic field, which includes both coherent and ordered random components. However, magnetic-field strength estimates from synchrotron observations depend on the assumed cosmic-ray electron model, which itself depends on the magnetic-field configuration and strength throughout the Galaxy. We aim to constrain the strength of the large-scale ordered magnetic field in the Galactic halo through a self-consistent treatment of cosmic-ray electrons with the latest coherent magnetic-field configuration inferred by Xu & Han from rotation measures corrected for local contamination. We compare the Planck 30 GHz synchrotron polarization maps with our large-scale synchrotron models that jointly treat cosmic rays and magnetic fields and are constrained by direct cosmic-ray measurements and multifrequency data. Since the inferred field strength depends on the halo size, we explore different cosmic-ray propagation halo sizes. We observe a significant large-scale synchrotron excess relative to model predictions, which requires an ordered toroidal magnetic-field component in the halo with a peak strength of 3.2-4.3 microG, depending on the assumed halo size. We also find that the cosmic-ray propagation model with a 4 kpc halo size is preferred by the Planck synchrotron polarization maps. This result shows that the ordered magnetic field is 4-6 times stronger than the coherent field inferred from rotation measures by Xu & Han, establishing the presence of an ordered random field in the Galactic halo that is not traced by rotation measures. Attributing the synchrotron excess entirely to the Local Bubble would require non-standard Local Bubble properties, disfavoring this interpretation.
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High Energy Astrophysical Phenomena

Wild behaviour near the finish line: the Type Ibn SN 2020able and its stratified environment

L. Tartaglia, E. Cappellaro, G. Valerin et al. (+29 more)

We present spectrophotometric observations of the Type Ibn supernova SN~2020able, along with a comprehensive analysis and modelling of its evolution. The transient occurred in SDSS J092602.93+243115.1, a faint host galaxy characterised by significantly sub-solar metallicity ($12+\log(\rm{O/H})\simeq8.28\,\rm{dex}$). The early photometric evolution and high peak luminosity ($L_{peak}\simeq4.4\times10^{43}\,\rm{erg}\,\rm{s^{-1}}$) indicate an efficient conversion of ejecta kinetic energy into radiation via interaction with the circumstellar medium. Light-curve modelling suggests that this interaction involves ejecta with a mass of $M_{\rm{ej}}\simeq1.3\,M_{\odot}$ impacting a shell of $M_{\rm{CSM}}\simeq0.6\,M_{\odot}$. However, interaction is found to be geometrically and temporally confined within a few days after explosion, with the later evolution of the transient being dominated by the free expansion of the ejecta. Spectroscopic analysis reveals a complex, stratified circumstellar environment. In addition to the innermost shocked region, we identify two additional He-rich shells: a dense inner one ($n_{\rm{e}}\simeq1.4\times10^{9}\,\rm{cm^{-3}}$) located at $R\gtrsim9.3\times10^{14}\,\rm{cm}$, and a more extended outer component reaching $R_{out}\simeq3.3\times10^{15}\,\rm{cm}$ and expanding at approximately $1.2\times10^3\,\rm{km}\,\rm{s^{-1}}$. The physical parameters of the former suggest it was produced by a discrete pre-supernova eruptive event similar to that of SN~2006jc, which expelled approximately $1.8\times10^{-2}\,M_{\odot}$ of material. Conversely, the expansion velocity of the outermost shell is consistent with the escape velocity of WR stars, pointing towards a late WN to WC-type progenitor as the most viable candidate for SN~2020able.
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All authors L. Tartaglia, E. Cappellaro, G. Valerin, A. Pastorello, S. Benetti, A. Reguitti, L. Tomasella, P. Lundqvist, K. Misra, A. Gangopadhyay, R. Dastidar, B. Ailawadhi, Dimple, B. Kumar, V. K. Jha, M. Singh, N. Elias-Rosa, C. P. Gutiérrez, D. A. Howell, D. Hiramatsu, C. Pellegrino, J. Andrews, D. J. Sand, N. Smith, J. Pearson, S. Wyatt, P. Ochner, Y.-Z. Cai, J. Burke, C. McCully, M. Newsome, E. Padilla Gonzalez

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Celephais: efficient spectral initial data code for precessing compact binaries

Hao-Jui Kuan

Large numerical-relativity surveys require compact-binary initial data that are both spectrally accurate and inexpensive to construct, including for systems with unequal masses and misaligned spins. We present \celephais, a compact-object initial-data code built on the Kadath spectral library, that constructs binary-neutron-star and black-hole–neutron-star initial data without imposing equatorial symmetry. The method exploits the sparse structure of the globally coupled multi-domain Jacobian and the approximate parity separation of fields. The assembled matrix is factored with MUMPS and reused as a refreshed right preconditioner in a Jacobian-free Newton–Krylov iteration, thereby avoiding dense storage. An adaptive $hp$–refinement scheme then concentrates resolution where the spectral tails are not yet resolved. For a mass-ratio-$20$ black-hole–neutron-star benchmark, the adaptive schemes recover the uniform-grid constraint accuracy with about three times fewer unknowns. We also extend the post-Newtonian force-balance estimate to arbitrary spin orientations and use it to initialise eccentricity reduction. Validation comprises binding-energy comparisons with post-Newtonian sequences, a precessing binary-neutron-star eccentricity-reduction test, and a full evolution whose waveform-reconstructed precession axis follows a post-Newtonian simple-precession model. These results establish an efficient route to spectrally resolved binary-neutron-star and black-hole–neutron-star initial data with arbitrary spin orientations.
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High Energy Astrophysical Phenomena

Constraints on magnetic monopoles from X-ray observations of neutron stars

Mainak Mukhopadhyay, Daniele Perri and Edward W. Kolb

Magnetic monopoles are captured efficiently by neutron stars, and if they catalyze nucleon decay, the decay products would thermalize and generate observable X-ray surface emission. We use archival Chandra, XMM-Newton, and Swift-XRT data for old isolated millisecond pulsars to place conservative limits on the Galactic monopole flux ($F_M$). For a benchmark cross-section of $\sigma_{\Delta \rm B} \sim 10^{-27}\ {\rm cm^2}$, our constraint as a function of monopole mass $m_M$ is given by $F_{\rm M}(m_M) \lesssim 6 \times 10^{-19}~\mathrm{cm^{-2}s^{-1}sr^{-1}} \times \max \big(4 \times 10^{-6}, \min (2 \times 10^{11}~\mathrm{(GeV/c^2)}/m_{\rm M} , 1 ) \big)$. These limits improve previous neutron-star bounds, provide the strongest constraints to date on $F_M$ for $m_M$ between $10^{11} - 10^{13}\ {\rm GeV/c^2}$, and are competitive to existing constraints for this scenario. We also derive complementary constraints from the measured thermal emission of the Magnificent Seven. Our results demonstrate that neutron star X-ray observations provide a powerful probe of magnetic monopoles and motivate dedicated X-ray searches for old neutron stars as a means to test monopole-induced heating.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

A clear detection of proper motion confirms that the claimed $\mathbf{z\simeq32}$ galaxy candidate, "Capotauro”, is a Y-type brown dwarf

F.-Y. F. Liu, D. J. McLeod, B. J. Sutlieff et al. (+13 more)

The compact red source “Capotauro”, discovered in deep JWST imaging in 2025, has been suggested as a possible galaxy candidate at redshift $z\simeq32$ on account of its extreme NIRCam colours. However, given the lack of evidence that this source is spatially resolved, a very cool brown dwarf, at a distance consistent with the scale-height of the Milky Way stellar disc ($\simeq 500$ pc), provides an alternative explanation of the observed photometry. Here we exploit new medium-band NIRCam imaging obtained $\simeq 3.5$ years after the discovery data to test this hypothesis. Using filter-dependent point-spread-function fitting, a robust local relative astrometric frame defined by 68 compact reference sources, and a joint four-image injection-recovery analysis, we show that Capotauro has moved by $132 \pm 20$ mas over the 3.5-yr interval span of the observations, ruling out the possibility that it is an extragalactic source (galaxy, AGN, or supernova) at $> 6 \sigma$. The observed apparent proper motion is $(\mu_\xi,\mu_\eta)=(+9.4^{+6.4}_{-4.8},-35.6^{+5.1}_{-5.9})$ mas yr$^{-1}$, or $37.6^{+5.5}_{-5.6}$ mas yr$^{-1}$ in total. Through comparison of its photometric spectral energy distribution with empirical templates, we find that Capotauro is best described as a brown dwarf of spectral type Y$1.0\pm0.5$ ($T_{\rm eff}\approx350$ K) at a distance of $730\pm110$ pc (although the existing data and spectral templates are insufficient to rule out an even colder, later-type brown dwarf). Capotauro is thus one of the most distant Y dwarfs found to date, as expected given its discovery in a deep JWST extragalactic survey field. This result demonstrates the value of multi-epoch imaging for identifying substellar contaminants among the most extreme photometric-redshift candidates.
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All authors F.-Y. F. Liu, D. J. McLeod, B. J. Sutlieff, T. J. Dupuy, J. S. Dunlop, X. Chen, R. J. McLure, H.-H. Leung, S. Antonogiannaki, C. Bondestam, E. Laplace, R. Begley, A. C. Carnall, F. Cullen, C. T. Donnan, R. S. Ellis

High Energy Astrophysical Phenomena

Core-Collapse Supernova detections from Einstein Telescope within the Milky Way

I.F. Giudice, A.L. De Santis, M.T. Botticella et al. (+6 more)

Core-collapse supernovae are key drivers of galaxy evolution and promising sources of gravitational waves, which provide a unique probe of the physics driving their explosion mechanism. Third-generation detectors, such as the Einstein Telescope, will dramatically improve the prospects for detecting these signals. This study assesses the capability of the Einstein Telescope, alone and in synergy with next-generation detectors such as Cosmic Explorer, to detect gravitational waves from core-collapse supernovae. We estimate the detection horizons and expected event rates for sources in the Milky Way and nearby satellite galaxies. We employed the GWFish simulation framework, customized to include core-collapse supernovae waveform catalogs from state-of-the-art 3D simulations and stellar population data generated with TRILEGAL. This approach allows us to model gravitational waves detectability as a function of progenitor mass, source position and detector network configuration. Our analysis shows that the Einstein Telescope can detect gravitational waves from PNS-driven core-collapse supernovae up to distances ranging from ~20 to more than 100 kpc with a 90% confidence level, depending on the progenitor mass and waveform, while a combination of this detector in a network can extend the reach up to ~170 kpc in the most favorable cases. For a representative 15 M_sun progenitor, ET (in its 2L configuration) achieves a detection horizon of ~100 kpc, ensuring essentially complete coverage of the Milky Way and partial coverage of the Magellanic Clouds.
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All authors I.F. Giudice, A.L. De Santis, M.T. Botticella, M. Branchesi, G. Pastorelli, L. Girardi, L. Izzo, E. Cappellaro, M. Della Valle

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Oscillations of Dissipative Neutron Stars: The Impact of Hyperonic Reaction Rates

Suprovo Ghosh, Alexander Haber, Nils Andersson et al. (+1 more)

Tidal excitations of stellar oscillation modes during binary neutron-star inspirals offer a powerful probe of the composition of dense matter at supranuclear densities. Chemical equilibration plays a crucial, but often neglected, role in stellar perturbation calculations. If the chemical equilibration timescale is comparable to the oscillation timescale, then viscous effects can damp the modes. If the reactions are fast, some modes can completely disappear since their restoring force vanishes. Typically, these calculations, however, assume either instantaneous chemical equilibrium or no equilibration (frozen composition). Motivated by this, we investigate the effects of finite reaction rates on the oscillation spectrum of neutron stars containing hyperonic matter. We calculate the dominant non-leptonic weak interaction rates and incorporate them into the relativistic perturbation equations through a complex, frequency-dependent dynamical sound speed. We show that finite-rate effects naturally manifest as bulk-viscous dissipation, modifying the properties of both the fundamental ($f$) and gravity ($g$) modes. We further examine the impact on the tidal response by matching stellar perturbations to near-zone boundary conditions, demonstrating how viscous dissipation gives rise to a tidal lag. These results provide a consistent framework connecting microscopic reaction rates and the resulting bulk viscosity to the tidal dynamics of compact binaries, and represent a step towards incorporating viscous dissipation into gravitational-wave models of binary neutron-star inspirals.
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All authors Suprovo Ghosh, Alexander Haber, Nils Andersson, Andrew Rhys Counsell

High Energy Astrophysical Phenomena

Multi-dimensional NLTE radiative transfer for a double detonation Type Ia explosion model in the photospheric phase

F. P. Callan, L. J. Shingles, S. A. Sim et al. (+7 more)

Previous radiative transfer calculations have shown that both multi-dimensionality and NLTE (non local thermodynamic equilibrium) effects impact the synthetic observables predicted for Type Ia supernova explosion models. Here we carry out a 2D NLTE radiative transfer simulation in the photospheric phase for a double detonation model with a 1 M$_{\odot}$ carbon-oxygen core and 0.02 M$_{\odot}$ helium shell. The predicted observables demonstrate that departures from both spherical symmetry and local thermodynamic equilibrium are significant on scales relevant to comparisons with observations. The NLTE treatment leads to a bluer spectral energy distribution, more slowly declining optical-band light curves, changes to the near-infrared light curve shapes, and differences in the evolution of key spectral features. Although substantial viewing-angle variation is predicted for the model, the scale of the variation is not significantly impacted by NLTE effects up to peak. However, after peak, our 2D NLTE simulation retains a strong viewing-angle dependence in its spectra whereas our simulation of the same ejecta model using an approximate NLTE treatment predicts significantly reduced spectroscopic viewing-angle variation. The NLTE treatment leads to improved agreement with normal Type Ia supernovae, primarily due to the increased ionisation state of the simulation, although the absence of a secondary near-infrared maximum suggests that the ejecta remain over-ionised relative to observations after peak. Despite the improved agreement, many viewing angles still show excessive line blanketing, suggesting that the 0.02 M$_{\odot}$ helium-shell mass of the current model is too large to reproduce normal Type Ia supernovae over the majority of lines of sight.
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All authors F. P. Callan, L. J. Shingles, S. A. Sim, C. E. Collins, J. M. Pollin, R. Pakmor, S. Gronow, F. K. Roepke, A. Holas, I. R. Seitenzahl

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Testing the spin-induced multipole moments of compact binary coalescences using the flexible theory-independent framework

Elise M. Sänger, Alessandra Buonanno, Ajit Kumar Mehta et al. (+1 more)

According to the no-hair theorem, the multipole moments of an electrically neutral black hole in general relativity are entirely determined by its mass and spin. However, this is not in general true for compact objects: The multipole moments of neutron stars or exotic compact objects can depend on their formation history and internal processes, which are encoded in an equation of state. Furthermore, their spin-induced multipole moments differ from those of black holes of the same mass and spin, leaving an imprint on the dynamics and emitted gravitational waves of the binary. Gravitational waves can thus be used to test the nature of compact binary coalescences. Here, we present a test of the spin-induced quadrupole and octupole moments of compact objects based on the flexible theory-independent (FTI) framework. FTI is a parameterized inspiral test of general relativity which enables the addition of post-Newtonian coefficient deviations to the gravitational-wave phase of a generic aligned-spin frequency-domain waveform model. We use this test on synthetic signals to study the measurability of spin-induced quadrupole and octupole moments. Next, we apply the test to a subset of signals observed by the LIGO-Virgo-KAGRA Collaboration. Lastly, we present forecasts for next-generation ground-based detectors, such as Einstein Telescope and Cosmic Explorer. Our estimates suggest that these detectors will be capable of placing stringent constraints on the spin-induced quadrupole and octupole moments of $\mathcal{O}(10^{-2})$ and $\mathcal{O}(10^{-1})$ respectively, which is two orders of magnitude tighter than current constraints, and thus on the nature of black holes in a compact binary coalescence.
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All authors Elise M. Sänger, Alessandra Buonanno, Ajit Kumar Mehta, Jan Steinhoff

High Energy Astrophysical Phenomena

Search for gamma-ray spectral lines from dark matter annihilation with the H.E.S.S. Inner Galaxy Survey

H.E.S.S. Collaboration, F. Aharonian, H. Ashkar et al. (+116 more)

Spectral gamma-ray line features are expected as key signatures from dark matter (DM) annihilations of TeV-scale particle DM. Observations of the Galactic Centre with atmospheric Cherenkov telescopes are unique to probe thermal-relic TeV particle DM, well beyond the reach of direct detection and collider searches. We report here on the search for line signals in very-high-energy gamma rays using data from the Inner Galaxy Survey, consisting of 546 hours of H.E.S.S. observations of the inner few degrees of the Galactic Centre. No significant signal is detected. We then compute the exclusion limits on the annihilation line cross section $\langle \sigma v \rangle_{\rm line}$, with a two-dimensional log-likelihood ratio test statistics, exploiting spectral and spatial features of the DM signal. Assuming an Einasto DM density profile for the Milky Way, our results provide the most constraining limits so far, reaching $\langle \sigma v \rangle_{\rm line} = 2.3$ $\times$ $10^{-28}$ and $2.4 \times$ $10^{-27}$ cm$^3$s$^{-1}$ for DM masses of 1 and 10 TeV, respectively. The present limits are used to constrain the widely searched Wino, Higgsino and Quintuplet models. For the first time, thermal Higgsino DM is probed for DM Milky Way models.
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All authors H.E.S.S. Collaboration, F. Aharonian, H. Ashkar, V. Barbosa Martins, R. Batzofin, Y. Becherini, D. Berge, K. Bernlohr, M. Bottcher, C. Boisson, J. Bolmont, F. Brun, B. Bruno, T. Bulik, C. Burger-Scheidlin, S. Casanova, J. Celic, M. Cerruti, A. Chen, M. Chernyakova, J.O. Chibueze, O. Chibueze, B. Cornejo, G. Cotter, J. de Assis Scarpin, M. de Bony de Lavergne, M. de Naurois, E. de Ona Wilhelmi, A. G. Delgado Giler, J. Djuvsland, A. Dmytriiev, K. Egberts, K. Egg, C. Escanuela Nieves, M. D. Filipovic, G. Fontaine, S. Funk, S. Gabici, J.F. Glicenstein, J. Glombitza, P. Goswami, B. Hess, J.A. Hinton, W. Hofmann, T. L. Holch, M. Holler, M. Jamrozy, F. Jankowsky, I. Jaroschewski, I. Jung-Richardt, K. Kasprzak, K. Katarzynski, D. Kerszberg, B. Khelifi, N. Komin, K. Kosack, D. Kostunin, R.G. Lang, S. Lazarevic, A. Lemiere, J.-P. Lenain, P. Liniewicz, A. Luashvili, J. Mackey, D. Malyshev, D. Malyshev, V. Marandon, M. Meyer, A. Mehta, A.M.W. Mitchell, R. Moderski, L. Mohrmann, A. Montanari, E. Moulin, J. Niemiec, L. Olivera-Nieto, M.O. Moghadam, S. Panny, R.D. Parsons, U. Pensec, G. Puhlhofer, A. Quirrenbach, M. Regeard, A. Reimer, O. Reimer, I. Reis, H. Ren, B. Reville, F. Rieger, G. Roellinghoff, G. Rowell, B. Rudak, K. Sabri, V. Sahakian, H. Salzmann, A. Santangelo, M. Sasaki, F. Schussler, J.N.S. Shapopi, W. Si Said, S. Spencer, L. Stawarz, S. Steinmassl, T. Takahashi, T. Tanaka, A.M. Taylor, G. L. Taylor, T. Unbehaun, C. van Eldik, M. Vecchi, C. Venter, J. Vink, T. Wach, S.J. Wagner, A. Wierzcholska, M. Zacharias, A. Zech, W. Zhong, F. Bradascio

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

New Universal Relations for Magnetized Neutron Stars

Byon N. Jayawiguna, Siddarth Ajith, Takuya Katagiri et al. (+2 more)

Unlike the neutron-star mass–radius relation, which depends sensitively on the internal stellar structure through the equation of state of dense nuclear matter, certain neutron-star properties obey approximately universal relations that exhibit only weak dependence on the equation of state. In this paper, we explore new universal relations for magnetized neutron stars. We focus on a purely poloidal dipolar magnetic-field configuration and treat the effects of the magnetic field perturbatively to second order in the field strength. After appropriately normalizing the relevant quantities by the stellar mass and the magnetic-field strength at the pole, we first identify an exact universal relation between the magnetic dipole moment and stellar compactness. We then find approximate universal relations among the magnetic dipole moment, magnetically-induced stellar quadrupole moment, and ellipticity, with fractional variations due to the equation of state at the level of O(10%). We support these numerical findings with analytic estimates for Newtonian polytropes, which reproduce the observed behavior. Among the newly discovered relations, the one connecting the magnetic dipole moment and stellar quadrupole moment may be particularly useful for the analysis of gravitational-wave signals from binaries containing magnetized neutron stars.
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All authors Byon N. Jayawiguna, Siddarth Ajith, Takuya Katagiri, Kent Yagi, Piyabut Burikham