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Physics Astrophysics High Energy Astrophysical Phenomena

astro-ph.HE Watch High Energy Astrophysical Phenomena

Monday 21 September

High Energy Astrophysical Phenomena

Rotating Radio Transient Phases of Isolated Neutron Star Systems and Descendants of Central Compact Objects

Ş. Demirok, Ü. Ertan and A.A. Gençali

Rotating radio transients (RRATs) form an isolated neutron star (INS) population characterized by their sporadic and short radio bursts. In the fallback disc model, it was suggested that most INS populations pass through an RRAT phase during their evolution, and the mechanism producing these bursts could be the enhancement of the flux of open magnetic field lines through the poles of dead pulsars due to penetration of the inner disc into the light cylinder. To test this idea, we determine the RRAT phases that could be produced by this mechanism along the evolutionary curves of the INS families on the period-period derivative ($P$–$\dot{P}$ diagram). These RRAT phases form an RRAT region in the $P$–$\dot{P}$ diagram, which is in agreement with the known RRAT distribution. Using our results, we also investigate the descendants of central compact objects (CCOs). We estimate that the CCOs similar to the three CCOs with measured $P$ and $\dot{P}$ are not likely to become radio pulsars (RPs). The situation is rather different for Calvera, a recently identified CCO. In the model, Calvera-like sources become RPs with lifetimes $ > 10^{8}$ yr. Indeed, there is a cluster of RPs in the region of \PPdot~diagram where descendants of Calvera-like CCOs evolve in our model. We also estimate that they have a very low birth rate, and therefore their immediate descendants may not currently exist in our Galaxy.
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High Energy Astrophysical Phenomena

Fast Radio Bursts Associated with Persistent Radio Sources Prefer Hydrogen-poor Superluminous Supernova Host Environments

Fujia Li, Fei Liu, Di Li et al. (+3 more)

A subset of repeating fast radio bursts (FRBs) is associated with compact persistent radio sources (PRSs). The FRB-PRS hosts differ dramatically from the general FRB host population: they do not follow the distribution of localized non-PRS FRB hosts, nor the SFR-weighted or mass-weighted mock host distributions expected for the general star-forming galaxy population, instead occupying the extreme low-mass, high-sSFR, and low-metallicity end of host-galaxy parameter space. We compare these hosts with well-defined samples of hydrogen-poor superluminous supernovae (SLSNe-I), hydrogen-rich superluminous supernovae (SLSNe-II), and Type II core-collapse supernovae (CCSNe). Using cumulative distribution functions and statistical tests, we find that FRB-PRSs tend to reside in dwarf galaxies with high specific star formation rates and low gas-phase metallicities, even relative to galaxies of similar stellar mass. Their hosts are most similar to those of SLSNe-I, but differ significantly from CCSN hosts, with SLSN-II hosts lying between these populations. These results suggest that FRB-PRSs do not simply trace star formation activity or the general FRB host population, but instead favor SLSN-I-like environments. This preference is consistent with young magnetars formed through low-metallicity massive-star channels, for which SLSN-I-like ejecta imply a characteristic free–free transparency time of ~29 yr at 600 MHz.
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All authors Fujia Li, Fei Liu, Di Li, Dongzi Li, Ziheng Ding, Ran Gao

High Energy Astrophysical Phenomena

Constraints on Axion-like Dark Matter from Cosmic Birefringence with a Polarization Array of Repeating Fast Radio Bursts

Xiaohui Liu, Zi-Yan Yuwen, Yun-Long Zhang et al. (+5 more)

Axion-like dark matter (ALDM) is a well-motivated dark matter candidate whose Chern-Simons coupling to photons can induce cosmic birefringence, producing temporal oscillations and spatial correlation in polarization angle (PA) signals from different sources. Hyperactive repeating fast radio bursts (FRBs) with high linear polarization are a particularly promising probe of such signatures. We develop a Bayesian framework to search for PA oscillations caused by ALDM in individual repeating FRBs, and combine multiple sources in an FRB polarization array (FRBPA) by exploiting correlations arising from the common Earth term. We apply this framework to PA datasets from three well-studied hyperactive repeating FRBs, and constrain the Chern-Simons coupling over a broad range of ALDM masses. For each FRB, we estimate the dark matter density at its host location using a simulation-calibrated halo profile. The inferred dark matter densities are comparable to the fiducial local density $\rho_0 = 0.4~\mathrm{GeV/cm^3}$. The comparable source and Earth dark matter densities, together with the redshift-induced difference between the frequencies of the source and Earth terms, motivate our adoption of the full two-component birefringence model. We find no compelling evidence for ALDM-induced PA oscillations in either the individual source analyses or the joint FRBPA analysis. We place 95% credible upper limits on the Chern-Simons coupling strength as a function of ALDM mass. Across the axion mass from $10^{-23}$ to $10^{-18}~\mathrm{eV}$, the resulting upper limits of the coupling strength of FRBPA lie between $10^{-12.6}$ and $10^{-7.9}~\mathrm{GeV}^{-1}$. Our results establish long-term polarimetric monitoring of hyperactive repeating FRBs as a promising and independent probe of ALDM, with sensitivity expected to improve with longer observational baselines and larger source samples.
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All authors Xiaohui Liu, Zi-Yan Yuwen, Yun-Long Zhang, Zerui Liu, Shiqian Zhao, Shuai Feng, Wei-Yang Wang, Xuelei Chen

High Energy Astrophysical Phenomena

AT2019aalc: An obscured tidal disruption event candidate in an active galactic nucleus revealed by its first flare?

Ying Gu, Xiao Li, Xue-Guang Zhang et al. (+1 more)

AT2019aalc is considered a repeating tidal disruption event (TDE) candidate occurring in an active galactic nucleus (AGN). In this paper, we highlight previously unnoticed but intriguing features that include a brief optical dimming prior to the rise of the main flare and a significantly lower post-flare luminosity compared to the pre-flare level. By applying a time-dependent obscured TDE model to AT2019aalc, we successfully reproduce its light curves with the tidal disruption of a $1.122_{-0.176}^{+0.246}\rm M_\odot$ main-sequence star by a $1.862_{-0.259}^{+0.255} \times 10^7{\rm M_\odot}$ supermassive black hole (SMBH). Both the pre-flare dimming and the reduced post-flare luminosity are attributed to obscuration of the intrinsic AGN emission. The total energy of the event derived from our fit is $1.24\times10^{51}$ ergs and about 0.2 ${\rm M_\odot}$ of debris mass is accreted by the SMBH. In addition, the $g-r$ color of the net flare in AT2019aalc exhibits a continuous reddening trend during the first flare, consistent with a gradual increase in $E(B-V)$ predicted by the obscured TDE model. These results suggest that AT2019aalc can be considered a second member of the recently proposed class of obscured TDE candidates hosted in AGNs. } \keywords{galaxies: active-galaxies: nuclei-quasars: supermassive black holes-quasars: individual (AT2019aalc)-transients: tidal disruption events.
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All authors Ying Gu, Xiao Li, Xue-Guang Zhang, En-Wei Liang

Sunday 20 September

High Energy Astrophysical Phenomena

Eccentricity and Inclination Excitation of Stellar Orbits around merging Black-Hole Binaries

Hao Gao and Hanlun Lei

Identifying the formation channels of merging compact-object binaries remains a fundamental challenge in gravitational-wave (GW) astrophysics. Here, we formulate a generalized framework incorporating both third-body perturbations and post-Newtonian effects to investigate the resonance-driven excitation of eccentricity and/or inclination for stellar orbits around merging black-hole binaries (BHBs). We show that at the quadrupole level, inclination excitation is driven by adiabatic capture into a quadrupole-order resonance, with subsequent resonance escape governed by the conservation of phase-space area. Furthermore, in the coplanar octupole regime, an apsidal precession resonance triggers robust eccentricity growth, where the capture probability depends on the initial conditions. For spatial octupole configurations, we reveal a distinct two-stage evolutionary pathway: the quadrupole-order resonance first excites the orbital inclination, followed by subsequent eccentricity growth driven by the inverse von Zeipel-Lidov-Kozai (ZLK) resonance. Our results indicate that these resonance-driven dynamics could imprint observable kinematic signatures on surrounding stellar populations, thereby offering a novel indirect probe for merging BHBs.
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High Energy Astrophysical Phenomena

A Linear Instability and Damping in the Acoustic Dispersion Relation of Fluids Subject to Inverse Compton Drag

Yiting Wang, Sebastian Heinz and Vladimir Zhdankin

Radiation drag from inverse-Compton scattering of an external radiation field changes the acoustic dispersion relation of a relativistic fluid. We derive the linear dispersion relation and show that, depending on the electron distribution and fluid sound speed, radiation drag either damps both modes or damps one while driving the other unstable. The unstable growth is robust at short wavelengths but slow and overdamped at long wavelengths, where the linear analysis is limited by the background acceleration. The resulting growth and damping rates are of order the bulk radiative acceleration rate, so whenever radiation drag is important for the background flow, its effects on fluid perturbations are also important. A purely damped region exists for a wide range of parameters. Radiation drag also makes acoustic waves dispersive: The phase speed deviates from the ordinary sound speed at longer wavelengths, and approaches the sound speed at short wavelengths. We validate the derived rates using special-relativistic hydrodynamic simulations. We apply the derived relation to astrophysical jets such as gamma-ray bursts, blazars in the broad-line region of the host active galactic nucleus, and quasar jets traveling through the CMB and galactic radiation field. We find that the derived instability, damping and dispersion may be relevant across a range of relativistic outflow conditions.
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High Energy Astrophysical Phenomena

Spectral Analysis of the Egress and Ingress Phases of Cen X-3 with XRISM/Resolve

J. Planelles-Villalva, L. Gu, J.J. Rodes-Roca et al. (+7 more)

We investigate the phase-resolved X-ray spectral evolution of the high-mass X-ray binary Cen X-3 across eclipse ingress and egress, using two out-of-eclipse intervals as references, to constrain the absorbing material and Fe K emitting regions with high-resolution XRISM/Resolve spectroscopy. We model the spectra with SPEX, including interstellar and local wind absorption, a power-law and blackbody continuum, disk reflection, and Gaussian components for Fe XXV and Fe XXVI. We compare the orbital variation of the absorbing column with a smooth CAK wind model and investigate the variability of the Fe K alpha line width. The local absorbing column varies by nearly two orders of magnitude, from N_H^local = 4.25 x 10^22 cm^-2 during pre-ingress to 5.9 x 10^23 cm^-2 at ingress. The excess ingress absorption cannot be reproduced by a smooth wind model alone, suggesting a localized overdense structure along the line of sight. The Fe K alpha width varies from approximately 510 km s^-1 during pre-ingress to 1400 km s^-1 during egress, with intermediate, statistically indistinguishable values of approximately 900 km s^-1 during ingress and post-egress. Highly ionized Fe XXV and Fe XXVI emission is detected throughout the orbit, although fewer components are resolved during ingress. These diagnostics reveal a complex circumstellar environment with localized dense material and multiple reprocessing regions. The results demonstrate the capability of XRISM/Resolve to probe the geometry and kinematics of accretion environments in eclipsing high-mass X-ray binaries.
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All authors J. Planelles-Villalva, L. Gu, J.J. Rodes-Roca, G. Sanjurjo-Ferrín, J. de Plaa, J.M. Torrejón, F. S. Porter, Y. Mochizuki, M. Loewenstein, E. Costantini

High Energy Astrophysical Phenomena

The role of photon fields of local sources in the formation of the cosmic rays energy spectrum

S.E.Pyatovsky and S.K.Machavariani

The influence of photon fields of local sources (LS) on the formation of the cosmic ray (CR) energy spectrum (E0) is considered. A model for the formation of irregularities in the CR spectrum, based on the local source model, is proposed. It is shown that the CR spectrum can be formed as a sum of partial spectra formed near local CR sources during the passage of primary cosmic radiation (PCR) through the photon fields of the sources. Local sources can be the most active stars of various types of variability in the stellar population, - from dwarfs to hypergiants. Studies have shown that the so-called "bump" near E0 = 100 PeV is formed in the photon fields of Mira-type variable stars, which are typically multiple stellar systems, consisting of a red giant and a white dwarf.
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High Energy Astrophysical Phenomena

Observational Evidence of an Internal Shock Collision in the Relativistic Jet of the Nearby Radio Galaxy 3C 111

Kenzo Kawamura, Motoki Kino, Mareki Honma et al. (+21 more)

We report 10 epochs of 22 GHz East Asia To Italy: Nearly Global VLBI (EATING VLBI) observations of the nearby radio galaxy 3C~111 obtained from 2020 to 2023. Combined with VLBA data at 15 and 43 GHz, these observations yield a 64-epoch, multi-frequency sequence of high-resolution radio images. We used high-resolution Bayesian Stokes~I imaging and Gaussian component modeling to derive light curves and knot kinematics. We find evidence that a faster, later-emitted knot catches up with a slower, earlier knot at a deprojected distance of about 10 pc from the central engine. The knot component responsible for this interaction propagated at relativistic speed and exhibited a rise-and-decay evolution over approximately six months. The Stokes~I flux evolution supports the internal shock interpretation, while archival polarization images reveal a temporary increase in fractional linear polarization in the interaction region near the Stokes~I flux maximum. The timing of the 2021 GeV flare suggests that this earlier high-energy event is more naturally associated with activity near the core. These results provide direct evidence for an internal shock in an active galactic nucleus jet and support a hybrid picture in which internal and standing shocks coexist in relativistic jets and may play different roles in their variability.
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All authors Kenzo Kawamura, Motoki Kino, Mareki Honma, Kazuhiro Hada, Paul Tiede, Evgeniya Kravchenko, Marcello Giroletti, Rocco Lico, Kazunori Akiyama, Mieko Takamura, Filippo D'Ammando, Monica Orienti, Gabriele Giovannini, Fumie Tazaki, Bong Won Sohn, Salvatore Buttaccio, Lang Cui, Giuseppe Maccaferri, Andrea Melis, Alexey Melnikov, Carlo Migoni, Matteo Stagni, Kiyoaki Wajima, Takeshi Sakai

High Energy Astrophysical Phenomena

A dynamic magneto-ionic environment around a long-period radio transient

Botao Li, Yongjie Jin, Shike Qu et al. (+5 more)

Faraday rotation provides one of the most direct probes of magnetized plasma along the line of sight, from the large-scale Galactic magnetic field to compact plasma environments local to radio sources. In particular, temporal variations in rotation measure can trace changes in the density, magnetic-field strength, or geometry of the Faraday-rotating medium, as observed in radio pulsars and fast radio bursts. Long-period radio transients (LPTs), a recently identified class of coherent radio sources with periods of hundreds to thousands of seconds, remain poorly explored because their physical nature is still uncertain. Here we present full-Stokes observations of the 421-s LPT source CHIME J0630+25 and report, for the first time, extreme rotation measure (RM) variability from approximately -400 to -1630 rad m^-2. The rapid RM changes occur on short timescales, including a difference of approximately 50 rad m^-2 between two consecutive rotation periods and a sudden change of approximately 536 rad m^-2 within approximately 2500 s. Compared with other radio-emitting sources, CHIME J0630+25 occupies an unusual region of the DM-RM plane: despite its very small DM of approximately 22 pc cm^-3, |RM| reaches over 1.6 x 10^3 rad m^-2, far exceeding that expected from the interstellar medium and pulsars. The fast and large-amplitude RM variations should arise from a compact, structured, and rapidly evolving magneto-ionic environment local to the source, possibly associated with a compact binary system.
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All authors Botao Li, Yongjie Jin, Shike Qu, Chaohua Gao, Wei Wang, Pei Wang, Shumei Jia, Jifeng Liu

Saturday 19 September

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

Renormalized Dynamical Friction in Black-Hole Spacetimes

Jordan Wilson-Gerow

We derive the renormalized local equation of motion for the gravitational self-force on a compact object moving through matter in a black-hole spacetime. We integrate out the environment and metric perturbations on a Schwinger–Keldysh contour, obtaining a causal effective action given by a sum of curved-spacetime Feynman diagrams organized by powers of the mass ratio and environmental density. At leading order, an environmental wake gravitationally backreacts on the worldline. The corresponding diagram contains a logarithmic ultraviolet divergence that renormalizes the leading dissipative fluid–particle coupling. We isolate the divergence with a local large-momentum expansion, in which the curved-spacetime retarded Green's function reduces to its flat tangent-space form. We translate the resulting singularity into a Barack–Ori mode-sum scheme, deriving an analytic puncture and regularization parameters for an ideal-fluid environment. Mode subtraction fixes the divergent part but not the finite Wilson coefficient. For collisionless dust, we determine this coefficient by matching to an exact near-zone calculation for a black hole moving through the medium. This gives a complete renormalization prescription suitable for numerical self-force calculations.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Charged particles and QPO constraints in tidal charge black hole magnetosphere sourced by a current loop

Ozodbek Abdurakhmonov, Javlon Rayimbaev, Inomjon Ibragimov et al. (+3 more)

We investigate the dynamics of charged particles in the dipolar electromagnetic field generated by a stationary current loop around a static black hole in the Randall–Sundrum braneworld model. The current loop is located at the innermost stable circular orbit (ISCO) of the tidal charged black hole, and the azimuthal electromagnetic four-potential is obtained as an exact analytical solution of the Maxwell equations in the curved background. Starting from the Hamilton–Jacobi equation, we derive the effective potential for charged particle motion in both the interior and exterior regions of the current loop, and analyze the dependence of the ISCO radius, angular momentum, energy, and orbital frequency on the tidal charge parameter $b$ and the magnetic coupling parameter $\omega$. We further compute three fundamental frequencies and show that the dipolar loop field revives a nonzero nodal precession frequency even though the background is static and non-rotating. Using these frequencies we construct five twin-peak QPO models (RP, WD, and ER2–ER4) and perform a Markov chain Monte Carlo (MCMC) analysis to constrain the braneworld parameters $(b,\omega)$ from the observed twin-peak QPO frequencies of six black hole sources spanning three mass regimes: GRO~J1655–40, XTE~J1550–564, GRS~1915$+$105, H~1743$+$322, M82~X-1, and Sgr~A$^{*}$. Adopting the epicyclic-resonance ER4 model as the representative framework, we find moderate, non-negligible tidal charges $b\simeq0.3$–$1.0$, while the magnetic coupling remains consistent with zero, $|\omega|\lesssim0.05$. Our results therefore place upper bounds on the tidal charge and on the magnetic coupling strength from astrophysical QPO data.
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All authors Ozodbek Abdurakhmonov, Javlon Rayimbaev, Inomjon Ibragimov, Sherzod Djumanov, Nuraliev Farhod, lkhomjon Makhmudov

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

Surveying the Universe in 4D: Beating Cosmic Variance with Wide-Field Slitless Spectroscopy from HST, JWST, Euclid, Roman, and Beyond

Andreea Petric, Gaël Noirot, Stacey Alberts et al. (+71 more)

We summarize strategies, lessons learned, and future directions from the Space Telescope Science Institute workshop Surveying the Universe in 4D: Beating Cosmic Variance with Wide-Field Slitless Spectroscopy from HST, JWST, Euclid, Roman, and Beyond, held August 24–28, 2026. The workshop examined scientific results, observational and data analysis challenges, extraction tools, and future opportunities. Discussions highlighted (1) the transformative potential of WFSS for the study of transient phenomena, galaxy evolution –both spatially-resolved and within the broader context of the cosmic web–, and rare populations and (2) the synergies among Euclid and Roman surveys, Rubin-LSST monitoring, JWST WFSS, and high-resolution integral-field observations. Participants identified advances in forward modeling and physics-informed machine learning as essential for addressing spectral overlap, crowded fields, and upcoming, very large data volumes. Realizing WFSS's full potential will require community-wide infrastructure, science-ready data products, accessible cloud-based analysis tools, and robust benchmarking of reduction pipelines. Crucially, participants called for systemic changes to properly recognize early-career researchers who invest significant efforts in pipeline, code, and calibration developments that enable WFSS science, and stressed that progress requires collaborative, multidisciplinary practices that optimize the participation and benefits of the next generation.
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All authors Andreea Petric, Gaël Noirot, Stacey Alberts, Russell Ryan, Louis-Gregory Strolger, Vicente Estrada-Carpenter, Mainak Singha, Adrian E. Bayer, Olivier Gilbert, Farhanul Hasan, Mason Huberty, Bingcheng Jin, Xiangyu Jin, Anika Kumar, Kasra Mokhtarpour, Preethi Nair, Eleni Tsiakaliari, Vivian U, Brittany N. Vanderhoof, Arshia Akhtarkavan, Natalia Alvarez-Ibanez, Roman Fernandez Aranda, Tri L. Astraatmadja, Clive Binu, Claire Bolda, Westley Brown, Guillermo Romero Cruz, Mohamed H. Abdullah, Jeremy Favaro, Mason Footh, Helen Fraser, Yuming Fu, Annie Giman, Nicolas Gomez, Massimo Griggio, Peter Gwartney, Aryana Haghjoo, Fabian Hervas-Peters, Jiamu Huang, Sandra Jaison, Jeyhan S. Kartaltepe, Sarah Kendrew, Ivan Kramarenko, Sahana Kumar, Zhaoran Liu, Arianna S. Long, Sangeeta Malhotra, Faezeh Manesh, Jasleen Matharu, Vihang Mehta, Edward M. Molter, Ivelina Momcheva, Zhiwei Pan, Yuxuan Pang, Pallavi Patil, Rachel Plesha, Marc Rafelski, Mitchell Revalski, Jyotika Roychowdhury, Gregory Rudnick, Swetha Sankar, Maya Seagraves, Lu Shen, Sabnam Shrestha, Manuchehr Taghizadeh-Popp, Jo Taylor, Wei Leong Tee, Scott Tompkins, Feige Wang, Xin Wang, Isak Wold, Jerry J.-Y. Zhang, Qianqiao Zhou, Zihao Zuo

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

Energy-momentum-squared gravity: charged quark star solutions with unified interacting matter

Ayan Banerjee, Bobur Turimov, Javlon Rayimbaev et al. (+3 more)

We investigate the equilibrium structure of electrically charged quark stars within the framework of energy-momentum-squared gravity (EMSG), adopting a unified interacting quark-matter equation of state that incorporates perturbative QCD corrections, color superconductivity, and finite-strange-quark-mass effects. By solving the modified Tolman-Oppenheimer-Volkoff equations over a broad range of EMSG coupling strengths and interaction parameters, we show that the inclusion of electric charge substantially increases both the maximum mass and radius compared with neutral configurations. For strong negative couplings and pronounced interaction strengths, the resulting stellar models reach masses close to $3,M_{\odot}$ with compactness ratios of order $0.34$, placing them within the mass range inferred for the secondary component of GW190814, whose nature remains observationally undetermined. The presence of charge reduces the central density at maximum mass by approximately $10$–$15\%$ while maintaining full compliance with causality requirements. Furthermore, comparisons with observational constraints from PSR J1614$-$2230, J0348$+$0432, J0740$+$6620, J0952$-$0607, and recent NICER radius measurements indicate that charged EMSG configurations remain consistent with current astrophysical bounds over a wide parameter space. These results demonstrate that a moderate electric charge, when combined with nonlinear matter-geometry coupling, can support quark stars that are significantly more massive than those predicted in general relativity, underscoring the potential observational relevance of charged compact objects in modified gravity and multimessenger astrophysics.
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All authors Ayan Banerjee, Bobur Turimov, Javlon Rayimbaev, Faisal Javed, Gulnoza Palvanova, Sulton Usanov

High Energy Astrophysical Phenomena

Dark matter self-annihilation as a hidden energy source in white dwarfs

Alvin Cheuk-Nam Chu, Cheuk-Man Yiu, Ching-Hui Lam et al. (+3 more)

White dwarfs (WDs) are compact remnants of stars, supported by electron degeneracy pressure, and their structures are generally considered to be well understood. Significant discrepancies exist between the theoretical and observed white dwarf mass-radius (MR) relations, especially for hot Q-branch white dwarfs with unexplained heating sources. In this study, we explore the potential of WDs as a portal to dark matter (DM) physics by investigating the effect of self-annihilating DM (SADM) admixed in WDs, solving the set of two-fluid hydrostatic equilibrium and heat diffusion equations self-consistently. We obtain empirical formulae for the WD luminosity $L$ and effective temperature $T_\text{eff}$ as functions of the DM mass fraction $f_d$, annihilation cross section $\langle\sigma v\rangle$, and particle mass $m_\chi$, as well as the WD's total mass $M_t$. We also compare the WD MR relations for various $L$, $f_d$, and both Fermionic and Bosonic DM particle statistics, with the observational data. We show that the majority of observed deviations in the WD MR relation can be accounted for by having SADM admixed with $f_d \le 10^{-5}$ and $\langle\sigma v\rangle \ll 3\times10^{-26}$ $\text{cm}^3$ $\text{s}^{-1}$, the thermal relic cross section. Therefore, our results suggest that WDs can be sensitive DM detectors, and DM self-annihilation could provide additional heating in WDs, accounting for their observed extra luminosities.
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All authors Alvin Cheuk-Nam Chu, Cheuk-Man Yiu, Ching-Hui Lam, Peter Siu-Hei Cheung, Fong-Ching Ho, Ming-chung Chu

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Gamma-Ray Echo as a Probe of Supernova Neutrino Emission Anisotropy and Long-Baseline Effects

Garv Chauhan, Cecilia Lunardini and Yago Porto

During a core-collapse supernova (CCSN), the emitted electron antineutrino ($\bar{\nu}_e$) burst initiates inverse beta decay (IBD) in the outer hydrogen layer of the stellar envelope. This leads to the production of a characteristic 511 keV photon signal, termed the Gamma-Ray Echo. The same neutrino burst, when detected on Earth in large neutrino observatories such as Hyper-Kamiokande, will offer information about the $\bar{\nu}_e$ content of the neutrino flux reaching Earth. In this work, we show that comparing the $\bar{\nu}_e$ content inferred from the gamma-ray echo with that inferred from terrestrial neutrino observations during a nearby CCSN event can offer a promising probe of large neutrino emission anisotropies and long-baseline propagation effects. In the latter case, the combined SN-Earth observations effectively act as a near-far detector configuration for neutrino propagation over an astrophysical baseline. We find that, for a near-Earth supernova, anisotropies or non-standard propagation effects at the level of tens of percent can be tested using gamma-ray telescopes with effective areas of $\mathcal{O}(10^4)~\mathrm{ cm^2}$. Therefore, our results motivate the development of the next generation of large effective area gamma-ray telescopes operating in the MeV gap.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Kaluza–Klein Dark-Photon Mediation of Inelastic Dark Matter at LUX-ZEPLIN

Waqas Ahmed and George K. Leontaris

We study a five-dimensional realization of endothermic dark matter motivated by the recent high-recoil LUX-ZEPLIN event. A pseudo-Dirac Standard-Model singlet fermion is localized in the extra dimension and couples to a bulk $U(1)_D$ gauge field. The same localization that suppresses a distant-brane Majorana operator and generates the inelastic splitting also controls the couplings to the Kaluza–Klein (KK) dark-photon tower, producing a localization-filtered mediator propagator. We organize the phenomenology around two representative mass–splitting points: an LZ benchmark, $m_\chi=1.10~\TeV$ and $\delta=365~\keV$, and an IceCube-motivated comparison point, $m_\chi=1.08~\TeV$ and $\delta=566~\keV$. The latter is used only to compare terrestrial and solar kinematics; the published IceCube bound is Higgsino-specific and is not directly imposed on our singlet KK model. At the LZ benchmark with $R^{-1}=0.30~\GeV$ and $m_0=0.10~\GeV$, the KK tower enhances the high-recoil xenon rate by a factor of about four relative to a single dark photon at fixed microscopic coupling. The LZ point lies just below the terrestrial halo speed ceiling, whereas the $566~\keV$ comparison point is inaccessible to ordinary xenon scattering and instead lies in a kinematic regime accessible to solar capture; any neutrino constraint on the present singlet model remains dependent on its capture and annihilation dynamics. The characteristic prediction of the extra-dimensional construction is therefore a correlated interplay of localization, KK spectral distortion, and inelastic kinematics.
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High Energy Astrophysical Phenomena

Stereoscopic gravitational-wave probe: Gravitational lensing of a binary merger in active galactic nuclei

Paul Martens, Samson H. W. Leong, Ryan Zhang et al. (+1 more)

Recent work has shown that, if a large fraction of the LIGO-Virgo-KAGRA compact binary coalescences (CBCs) occur in accretion disks around active galactic nuclei (AGNs), many such AGN-CBC systems will likely experience lensing and produce multiple gravitational-wave (GW) "images" of the CBCs that will become detectable with current or future GW detectors. However, the waveforms produced by such lensed "images" will differ from those produced by other lensing systems because the binary source is orbiting the AGN's central supermassive black hole at a close distance. Here, we show that these systems produce 2 snapshots of the same binary source from 2 different viewing angles. These differences in the effective viewing angle between the images are encoded in the GWs they emit, such that GW detectors can effectively analyse the waveforms from 2 viewpoints. Beyond such "multi-view lensing", the GW images may also differ by their Doppler shift due to the expected relativistic orbital motion of the source around the AGN, an effect which is further amplified by the proximity to the lens. If the AGN's own angular momentum can be related to the binary's orbital angular momentum, we can describe the entire AGN-CBC system using only one additional free parameter compared with a typical point-mass lens system, or with 3 additional parameters when we do not make such an assumption. In this work, we establish a framework of transformation rules that describe both the angles in the 2 points of view, and the Doppler effect that comes from the source's motion around the lens. We also provide the framework to produce consistent AGN-lensed waveforms from any currently available GW waveform. These AGN-CBC systems give 2 unique points of view on a binary merger thus opening up a new window into the merger's properties unlike any other lens system.
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All authors Paul Martens, Samson H. W. Leong, Ryan Zhang, Otto A. Hannuksela

Friday 18 September

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

Black Holes as Frequency-Dependent Filters of Stochastic Gravitational Waves

Sefi Katznelson, Aidan Minger and Stefano Profumo

Black holes ring when perturbed, whereas their response to a stationary gravitational-wave background is a real-frequency scattering problem, not a source of additional quasi-normal-mode lines. We make this standard distinction quantitative by treating a black hole as a frequency-, angle-, and polarization-dependent filter. For an isotropic stationary background around Schwarzschild holes, elastic scattering produces no net monopole signal, so horizon absorption is the only population-level spectral distortion. We calculate this transfer function for Schwarzschild holes in detail, identify its absorptive and phase-delay signatures, and connect the stationary response to the causal ringdown excited by a finite wave packet. We then promote the single-hole result to an angular and polarization transport kernel for a cosmological population. The resulting optical depth is negligible for realistic black-hole populations, including asteroid-mass primordial black holes comprising all dark matter. We then extend the analysis to Kerr holes, for which superradiance allows genuine amplification in selected co-rotating modes, but isotropic incidence and random spin orientations strongly dilute the diffuse signal. Observable effects are therefore more likely in rare, nearby, aligned, rapidly spinning, or transiently illuminated systems than through cumulative cosmological propagation.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

New bounds on light scalars from the tip of the red giant branch

Natnael Debru, Audrey Fung, Saniya Heeba et al. (+3 more)

Light, weakly coupled particles can be copiously produced in the hot and dense interior of stars, and the resulting energy loss can leave observable imprints on entire stellar populations. For instance, additional energy loss from red giant cores delays helium ignition and brightens the tip of the red giant branch (TRGB). We revisit the TRGB bounds on light scalars coupled to electrons, of which the Higgs portal is the prototypical example. In the degenerate cores of red giants, scalar emission is dominated by resonant conversion of longitudinal plasmons, which we compute using finite-temperature field theory. Rather than rescaling neutrino emission rates at fixed benchmark core conditions, we implement this emissivity in the MESA stellar evolution code and self-consistently simulate the evolution of red giants, including the backreaction of the scalar energy loss on the stellar structure. Comparing our predictions with the observed bolometric TRGB magnitudes of 27 Milky Way globular clusters, we exclude scalar-electron couplings $\alpha_{\phi ee} = g_e^2/4\pi > 1.6 \times 10^{-34}$ at 95% confidence for sub-keV masses, improving on previous bounds by nearly two orders of magnitude. In the context of the Higgs portal, this corresponds to an exclusion on values of the mixing angle $\sin\theta > 2.2\times 10^{-11}$, providing the tightest bound for scalar masses in the $\sim 1\,\mathrm{eV} - 10\,\mathrm{keV}$ range.
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All authors Natnael Debru, Audrey Fung, Saniya Heeba, Hugo Schérer, Katelin Schutz, Aaron C. Vincent

High Energy Astrophysical Phenomena

Resolving the Galactic Center Region's Gamma-Ray Emission and Searching for its Neutrino Counterpart with HAWC and IceCube

S. Yun-Carcamo, R. Babu, for the HAWC et al. (+1 more)

The Galactic Center (GC) is a prime candidate for petaelectronvolt cosmic-ray acceleration, with gamma-ray emission observed by the High Altitude Water Cherenkov (HAWC) Observatory extending beyond 100 TeV. We present an analysis of the GC using ~2860 days of HAWC data, with increased exposure and improved sensitivity relative to previous results. The best-fit gamma-ray emission model includes a point source (HAWC J1745-2857) and a Galactic diffuse emission component. Assuming a hadronic origin, we construct the corresponding neutrino signal template and search for it in 12 years of IceCube muon-track data. No significant neutrino excess is found, and we report the first upper limit on the high-energy neutrino flux associated with the multi-component spatial model of the GC derived from HAWC data. The limit is approximately 12 times the nominal neutrino flux predicted from the HAWC gamma-ray model under a hadronic interpretation, and therefore it does not yet test the optically thin hadronic scenario.
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All authors S. Yun-Carcamo, R. Babu, for the HAWC, IceCube collaborations

High Energy Astrophysical Phenomena

The chirping of Lense-Thirring precession in tidal disruption event accretion flows

Andrew Mummery and Eliot Quataert

Tidal disruption event X-ray light curves do not appear to show clear signs of periodic modulation. This is naively somewhat surprising since the stars that are disrupted originate at large scales in the galaxy where they cannot know about the orientation of the black hole spin axis. This should lead to the formation of a misaligned disk that precesses due to Lense-Thirring torques, modulating X-ray emission from the inner disk regions. We argue that in fact the properties which are required for solid-body precession, namely a thick $(H/R\sim {\mathcal O}(1))$ disk, naturally lead to rapid precession period change, with a per-period increase of $\Delta T_{\rm prec}/T_{\rm prec} \sim {\mathcal O}(1-10)$, as the disk spreads to larger radii to conserve angular momentum. In other words the precession of thick TDE disks is aggressively chirped, washing out any possibility of observing multiple cycles other than for fine tuned regions of parameter space. The global disk alignment timescale is equally strongly chirped by the exact same mechanism, meaning that TDE disks will not in general align with the black hole spin axis during a super-Eddington phase, and should generically show global quasi-steady warp profiles at the beginning of any thin disk phase. These results have important implications for interpreting timing features associated with TDE disks, including models for quasi-periodic X-ray eruption timing phenomenology, and the observational properties of TDE disks in the initial transition to the thin disk phase.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR

Inflated Supermassive Stars as Little Red Dots and Progenitors of Supermassive Black Holes

Wenbin Lu

JWST has uncovered an abundant population of compact, red sources at high redshifts, termed little red dots (LRDs). We study whether they could be explained by thermally relaxed, hydrogen-burning, metal-enriched supermassive stars (SMSs). We construct 1D models in hydrostatic and thermal equilibrium, including a radiation-pressure-dominated, CNO-burning core and an outer envelope with metallicity-dependent opacity, non-adiabatic convection, and an effective treatment of super-Eddington surface layers. The luminosity is close to the Thomson-scattering Eddington limit. The Fe-opacity bump drives the formation of a strongly inflated, low-mass envelope, while hydrogen recombination terminates the envelope at a bound photosphere. For M=$10^4$ to $10^6$ Msun and metal mass fractions $Z=10^{-4}$ to $10^{-2}$, we find that the most metal-rich models (Z ~ $10^{-2}$) develop highly inflated envelopes and reach Teff ~ 7000 K. We suggest that such enriched SMSs could instead be assembled through runaway stellar collisions in compact star clusters. The GR instability sets a maximum mass that depends on the core rotation rate. The nonrotating and rotating models have maximum masses $3\times10^5$ to $3\times 10^6$ Msun, and maximum luminosity of the order $10^{44}$ erg/s, comparable to the observed bright-end cutoff of the LRD luminosity function. Core hydrogen depletion can drive initially stable SMSs across the instability threshold after a lifetime of order 1 Myr. If each LRD leaves a black hole retaining most of its mass, the observed LRD abundance implies a present-day remnant density of order $10^{-2}\rm cMpc^{-3}$, consistent with the local abundance of supermassive black holes. Cool SMSs naturally produce weak X-ray and weak high-ionization lines. Non-LTE effects may significantly modify the Balmer features and the continuum opacity, and may lower Teff below our LTE value.
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High Energy Astrophysical Phenomena

Importance of the Resonant Cosmic-Ray Streaming Instability Upstream of Collisionless Shocks

Bricker Ostler, Benedikt Schroer and Damiano Caprioli

Cosmic rays (CRs) escaping collisionless shocks form a dilute, relativistic population whose current amplifies the upstream magnetic field, a process widely attributed to the non-resonant (Bell) instability. Solving the dispersion relation for both cold and finite-spread CR distributions, we show that for the maximum-energy escaping population, the resonant mode can outgrow the non-resonant mode. At slower shocks, this dominance persists for broader CR distributions, and sufficient pitch-angle broadening can even stabilize the non-resonant mode while leaving the resonant mode unstable. Relativistic hybrid particle-in-cell simulations confirm the cold-beam linear theory predictions and, in the nonlinear regime, saturate at $\delta B/B_0 \sim 1$ with significant pitch-angle redistribution. Neglecting the resonant instability thus underestimates magnetic field growth at the very scale needed to confine the highest-energy escaping CRs.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Evidence for a Continuous Hadron–Quark Transition in Cold Dense Matter

Yong-Jia Huang and Bikai Gao

Statistical evidence for a continuous hadron-quark transition is found in this work. Confronting microscopic descriptions connecting the Parity Doublet Model and the Nambu–Jona-Lasinio model with observationally constrained non-parametric equations of state, Bayesian model comparison decisively favors a boundary-free crossover over the conventional first-order Maxwell construction ($\Delta\ln\mathcal{Z} \sim +7.20$) and fixed-boundary crossover ($\Delta\ln\mathcal{Z} \sim +5.16 $). The preferred crossover decouples the intermediate stiffening from the intrinsic stiffness of each phase, allowing both sectors to exhibit physical self-consistency. The chiral-invariant nucleon mass is large, $M_0 = 834^{+28}_{-92}\text{ MeV}$, as expected for a substantial baryon mass surviving chiral restoration. While the quark sector accommodates a small pairing gap $\Delta_{\rm CFL} = 88^{+83}_{-59}\text{ MeV}$ consistent with perturbative QCD limits, avoiding the excessively large gaps $\Delta_{\rm CFL} \gtrsim 200\text{ MeV}$ required by the other constructions. These results demonstrate that a realistic unified description represents a continuous transition deviating substantially from isolated effective models of hadrons and quarks. Exploring genuine phase boundaries is therefore necessary through the emergence of spinodal instabilities within unified frameworks.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

LoTSS of dual AGN: enhanced detectability and prospects for a systematic search

Q. D'Amato, F. Mannucci, E. De Rubeis et al. (+25 more)

Context: Dual active galactic nuclei (DAGN) - systems of two accreting supermassive black holes at kpc-scale separations - trace galaxy mergers and are the progenitors of gravitational-wave sources targeted by pulsar timing arrays and the upcoming Laser Interferometer Space Antenna. However, their radio properties remain poorly constrained, particularly at high redshift. Aims: We demonstrate the detectability of high-redshift DAGN at 144 MHz through sub-arcsec imaging of the LOFAR Two-metre Sky Survey (LoTSS) and characterize their low-frequency radio properties. Methods: We cross-matched 92 spectroscopically confirmed DAGN (z > 0.3, projected separation r_p < 30 kpc) with the LoTSS DR2 catalog and reprocessed international LOFAR telescope (ILT) data for three systems (0.59 < z < 2.39), achieving ~0.3 arcsec resolution at 144 MHz. Multi-frequency analysis and brightness-temperature diagnostics were used to investigate the radio emission. Results: We obtained high-quality ILT images for all three systems. In one source at z = 1.49, both AGN are detected at >5 sigma, making it one of the highest-redshift and faintest radio-detected DAGN. Brightness temperatures confirm AGN-powered emission even in sub-mJy sources. In the other two systems only one AGN is detected; for one, the new data constrain the low-frequency spectrum of a compact steep-spectrum source, indicating that its morphology is driven by jet-ISM interaction rather than the companion galaxy. For the 92 objects sample, the LoTSS detection rate is ~24%, significantly higher than for matched single AGN (~9-10%), suggesting an enhanced detectability of DAGN in the LoTSS. Conclusions: Low-frequency sub-arcsec radio observations provide an efficient, dust-unbiased method to detect and characterize DAGN. This pilot study establishes a benchmark for the forthcoming all-sky ~0.3 arcsec iLoTSS survey and future SKA observations.
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All authors Q. D'Amato, F. Mannucci, E. De Rubeis, I. Prandoni, A. De Rosa, M. Scialpi, M. Kunert-Bajraszewska, A. Janiuk, A. Krauze, L. Battistini, E. Bertola, C. Bracci, A. Chakraborty, M. Ceci, C. Cicone, G. Cresci, A. Marconi, C. Marconcini, E. Nardini, M. Parvatikar, A. Peca, K. Rubinur, P. Severgnini, C. Spingola, L. Ulivi, G. Venturi, C. Vignali, M. V. Zanchettin

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

Super-Chandrasekhar white dwarfs by the evolution of magnetized main-sequence stars: New mass-limits from STARS simulation

Zenia Zuraiq, Banibrata Mukhopadhyay, Achal Kumar et al. (+4 more)

We explore the time evolution of the magnetized main-sequence stars (MSs) to magnetized non-rotating white dwarfs (WDs) with a series of models, capturing modified Hertzsprung-Russell diagram. We use the Cambridge Stellar evolution code, STARS, with modifications by introducing magnetic effects and cooling. We investigate the possible existence of stable, magnetized, massive, super-Chandrasekhar, approximately spherical WDs, away from Chandrasekhar's mass-radius curve. These we refer to as B-WDs. They are inferred from the observations of peculiar over-luminous type Ia supernovae, e.g. SN2003fg. We show that the classical effects of magnetic fields significantly impact MSs and their time evolution to WDs. Moreover, the magnetic field could be decisive in explaining the unusually large radius observed in some sub-Chandrasekhar WDs, e.g. SDSS J123204.19+522548.2, along with the finite temperature effect. We further investigate the stability of magnetized WDs, both below and above the Chandrasekhar limit and confirm the possibility of super-Chandrasekhar B-WDs with new mass limits that depend on the magnetic field geometry, mass accretion from a companion and cooling rates. Therefore, while the "Chandrasekhar limit" may be sacrosanct, its value severely depends on the underlying physics, here the magnetic field.
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All authors Zenia Zuraiq, Banibrata Mukhopadhyay, Achal Kumar, Arnab Sarkar, Alexander J. Hackett, Projjwal Banerjee, Christopher A. Tout

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

Galaxy-SMBH co-evolution in 2,435 DESI disk galaxies and merger-free BH growth in bulgeless disks

Sophie M. Jewell, Rebecca J. Smethurst, Chris J. Lintott et al. (+8 more)

We analyse black hole scaling relations for disk-dominated galaxies, and present evidence for secularly driven galaxy-black hole co-evolution. We do this observationally by looking at “bulgeless” galaxies, where the lack of a stellar bulge suggests a quiet merger history. We first compose a sample of 2,435 disk-dominated galaxies hosting optical broad line active galactic nuclei (AGN) from DESI data, and find a $M_{\mathrm{BH}}$–$M_{*}$ scaling relation of $\log(M_{\mathrm{BH}})= - 3.7^{+0.3}_{-0.3} + 1.00^{+0.03}_{-0.03} \log(M_*)$. From these, we identify 546 bulgeless galaxies hosting AGN, a factor of $\gtrsim 5$ larger than pre-existing samples, and find they follow the same $M_{\mathrm{BH}}$–$M_{*}$ relation as the general disk galaxy sample. Comparing the bulgeless galaxies to those with some bulge component, we find good agreement in the $M_{\mathrm{BH}}$–$M_{*}$ relation (within $3 \sigma$), but disagreement in the $M_{\mathrm{BH}}$–$M_{*, \mathrm{bulge}}$ relation (at $>7 \sigma$). This is the opposite of what is expected from merger-driven co-evolution, suggesting secular growth is significant in establishing observed $M_{\mathrm{BH}}$–$M_{*}$ scaling relations. Furthermore, in a control sample of early-type galaxies we find tentative evidence of increased AGN luminosity compared to the bulgeless sample, but no statistical difference in black hole mass. This suggests the assumed merger-dominated evolutionary history of early-type galaxies does not lead to significantly increased long-term BH growth. These results support numerous recent observational and theoretical studies which suggest secular processes fuel significant supermassive black hole growth and galaxy-black hole co-evolution.
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All authors Sophie M. Jewell, Rebecca J. Smethurst, Chris J. Lintott, Brooke D. Simmons, Ricarda S. Beckmann, Izzy L. Garland, Tobias Géron, Benne W. Holwerda, Karen L. Masters, Ragadeepika Pucha, Ashley Spindler

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

A Quantitative Method to Investigate the Spectral Class Time Evolution of Novae

Maria Kopsacheili, Martín Guerrero and Diego Alejandro Vasquez Torres

Novae are spectroscopically classified as Fe II or He/N according to the dominance of Fe II, or He and N emission lines in their pre-nebular spectra, while spectra exhibiting both are classified as hybrid. Evidence suggests that these spectral classes represent spectral evolution. We investigate this scenario using a large spectroscopic dataset and introduce a quantitative coefficient, $\kappa$, to characterise the relative strength of Fe II and He/N emission. The coefficient is defined as the ratio of the flux of the Fe II ($\lambda5169$) line to the mean flux of five He and N emission lines, with $\kappa>1$ indicating Fe II-dominated spectra and $\kappa<1$ indicating He/N-dominated spectra. We apply this method to 26 novae using spectra from the Astronomical Ring for Amateur Spectroscopy (ARAS) Database and compare the evolution of $\kappa$ with optical light curves. Fifteen of the 24 classical novae and one of the two recurrent novae exhibit at least one transition between Fe II- and He/N-dominated phases, while temporal trends suggest this fraction could approach 90% with complete spectroscopic coverage. The $\kappa$ coefficient closely tracks the optical light curves and repeatedly crosses unity in novae exhibiting jitters, revealing non-monotonic spectral evolution linked to brightness fluctuations. These results support the interpretation of Fe II, He/N, and hybrid spectra as evolutionary stages rather than distinct nova types and establish $\kappa$ as a quantitative tool for tracing nova spectral evolution while reducing biases from incomplete spectroscopic coverage.
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High Energy Astrophysical Phenomena

GRB 220706A: a gamma-ray burst with a month-long engine and a luminous supernova

Benjamin P. Gompertz, Nusrin Habeeb, Dheeraj R. Pasham et al. (+30 more)

While the progenitors of many long gamma-ray bursts (GRBs) are well established as the core collapse of very massive, envelope-stripped, rapidly-rotating stars, it has been suggested that bursts at the extremely long end of the duration distribution may be a separate population of `ultra-long' GRBs. With durations of thousands of seconds or more, these bursts are difficult to reconcile with the engine timescales expected from the compact Wolf-Rayet stars that are typically assumed to produce more `standard' long GRBs. Here, we present observations of GRB~220706A, where X-ray follow-up reveals flaring episodes that last until $\approx 51$ days after trigger. At the measured redshift of $z = 0.8577$, this corresponds to 27 days in the GRB rest frame, and represents the latest central engine activity ever observed in a GRB by a margin of $\approx 21$ rest-frame days. We also identify a likely supernova (SN) which, when accounting for the inferred optical extinction of $0.9 \leq A_V \leq 3.6$ mag (constrained by indirect arguments), has a peak absolute magnitude of $M_r \leq -20.25$, resembling the energetic SN\,2011kl found accompanying ultra-long GRB\,111209A, and consistent with super-luminous SNe. We discuss the implications GRB~220706A has for ultra-long GRB progenitor models and possible powering mechanisms for the extremely late central engine activity.
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All authors Benjamin P. Gompertz, Nusrin Habeeb, Dheeraj R. Pasham, Antonio de Ugarte Postigo, Daniele B. Malesani, Phil A. Evans, Kim L. Page, Ben Rayson, J. Feliciano Agui Fernandez, Michael Bremer, Andrew J. Levan, Genevieve Schroeder, Nial R. Tanvir, Christina C. Thone, Eric Burns, Valerio D'Elia, Massimiliano De Pasquale, Dimple, Dieter Hartmann, Pall Jakobsson, Sylvio Klose, Antonio Martin-Carrillo, Matt Nicholl, Ana M. Nicuesa Guelbenzu, David O'Neill, Giovanna Pugliese, Arne Rau, Andrea Rossi, Jesper Sollerman, Rhaana Starling, Darach Watson, Isabelle Worssam, Makenzie E. Wortley