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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 2 September

High Energy Astrophysical Phenomena

LHAASO-WCDA observed a $\sim$ 5 days TeV-delayed flaring event in blazar 1ES 1959+650

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

We report a day-scale hard lag between GeV and TeV $\gamma$-ray emission from the HBL 1ES~1959+650 in early 2024. Since the LHAASO-WCDA real-time monitoring system began operation in late 2023, multiple TeV flares from this source have been triggered, including the 1st trigger flare on 2024 February 9. A Bayesian-block analysis of the WCDA light curve identifies three TeV flares in 2024. For the second triggered flare, a discrete cross-correlation analysis reveals a $>3\,\sigma$ correlation (relative to uncorrelated red-noise simulations) at a time delay of $\Delta t = 5.0_{-2.1}^{+2.1}$ days, with the TeV emission lagging the GeV. Time-resolved spectroscopy shows that this flare has the softest TeV spectrum among these flares (intrinsic spectral index $\Gamma=3.16\pm0.18$), while the 1st trigger flare is harder ($\Gamma=2.48\pm0.21$). The observed five-day hard lag is difficult to reconcile with a purely cooling-driven temporal ordering and is consistent with scenarios in which particle energization and/or transport may contribute to the evolution. However, the current data do not uniquely identify the underlying mechanism.
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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

High Energy Astrophysical Phenomena

17 Yr of Magnetar Bursts Observed with the Fermi Gamma-ray Burst Monitor

Matt Godwin, Özge Keskin, Mustafa Demirer et al. (+17 more)

The Fermi Gamma-ray Burst Monitor (GBM) has been in operation for over 17 years, during which it has observed more than a thousand bursts from soft gamma repeaters (SGRs), also known as magnetars. Serving as a laboratory for extreme physics, magnetars are a sub-family of neutron stars characterized by extreme magnetic field strength, observed through a combination of persistent and short transient emission across the electromagnetic spectrum. We present the comprehensive GBM catalog of SGR short bursts which supersedes the 5-year catalog of Collazzi et al. 2015. The new catalog contains 1254 SGR short bursts observed over 17 years, providing the longest uninterrupted, high-sensitivity all-sky monitoring of magnetar bursts with unprecedented spectral and temporal resolution. Our catalog contains bursts from 17 unique Galactic sources, with major contributions by bursts from SGR J1935+2154 and SGR J1550-5418. We present overall characteristics of these bursts, such as the durations, spectral parameters for various photon models, fluxes, as well as their comparison with recently published catalogs of other missions and the previous GBM magnetar catalog. The machine readable catalog, as well as burst spectra and response files are made publicly available for the community.
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All authors Matt Godwin, Özge Keskin, Mustafa Demirer, Yi-Jing Yi, Lin Lin, Oliver J. Roberts, Ersin Göğüş, Yuki Kaneko, Michael Briggs, Matthew G. Baring, Eric Burns, David M. Palmer, Boyan A. Hristov, Bagrat Mailyan, Christian Malacaria, Eva Palafox, Chryssa Kouveliotou, Alexander J. van der Horst, Peter Veres, George Younes

Instrumentation and Methods for Astrophysics

GRINTA: a new Probe of the Dynamic Universe

Lorenzo Natalucci, Philippe Laurent, Marica Branchesi et al. (+48 more)

Recent observations of the transient sky at all wavelengths are increasingly revealing the importance of the multi-messenger and multi-wavelength approach. The GRINTA (Gamma-Ray INternational Transient Array Observatory) mission, proposed for launch around the middle of the next decade, is conceived as a small mission with good sensitivity, excellent angular resolution and fast follow-up capability for studying transient sources at timescales from ms to hours, at the same time ensuring optimal integration with multi-messenger networks. The GRINTA mission will carry two complementary payloads to cover in total the 5 keV-10 MeV band, that will detect and localise gamma-ray bursts covering $\sim$ half of the sky and will be able to perform imaging surveys with sub-arcmin resolution. GRINTA will operate in synergy with the most powerful electromagnetic, gravitational wave and neutrino observatories foreseen to be operational after 2035.
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All authors Lorenzo Natalucci, Philippe Laurent, Marica Branchesi, Mariateresa Fiocchi, Lorraine Hanlon, J. Miguel Mas-Hesse, Aline Meuris, Paul 'O Brien, James C. Rodi, Simone Scaringi, Konrad Skup, Norbert Werner, Silvia Zane, Julia Alfonso-Garzon, Biswajit Banerjee, Patrizia Barria, Anthony J.Bird, Soren Brandt, Gabriele Bruni, Floriane Cangemi, Gianluca Castignani, Eric Chassande-Mottin, Sylvain Chaty, Jerome Chenevez, Alexis Coleiro, Francesco Dazzi, Alessio L. De Santis, Phil Evans, Olivier Godet, Diego Gotz, Rene Hudec, Lucien Kuiper, Angela Malizia, Sheila McBreen, Sandro Mereghetti, Manuela Molina, Filip Munz, David Murphy, Gor Oganesyan, Francesca Panessa, Elena Pian, Jakub R{\i}pa, Oliver J. Roberts, Samuele Ronchini, Fabian Schussler, Vojtech Simon, Nial Tanvir, Alexey Uliyanov, Nello Vertolli, Stanislav V{\i}tek, Ugo Zannoni

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Strong Constraints on Higgsino Dark Matter from Solar Capture

Maxim Pospelov and Harikrishnan Ramani

Higgsino dark matter remains one of the most convincing dark matter candidates. It can exist in a “quasi-Dirac" regime, when the splitting between two Majorana components is on the order of $O(\rm few~\,MeV)$ or less. Owing to the strong gravitational pull of the Sun, the DM particles accelerate to up to $\sim 1400$\,km/sec in the solar core, which allows for inelastic scattering on heavy elements and very effective capture onto solar-bound trajectories. We evaluate the expected flux of the neutrinos from the expected $\chi\chi \to W^+W^-,ZZ$ annihilation for the cosmologically preferred mass, $m_\chi \simeq 1.08$\,TeV while keeping the mass splitting $\delta$ as a free parameter. Confronting it with the non-observation of high-energy neutrinos from the Sun by the IceCube experiment, we obtain a robust limit, $\delta>566$\,keV. These limits exclude the interpretation of the recent LZ event in terms of endothermic inelastic scattering of Higgsino dark matter on xenon nuclei.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG

Do Tabular Foundation Models Know Physics? Contamination, Units, and the Deterministic Limit

Wassim Tenachi, Yashar Hezaveh, Laurence Perreault Levasseur et al. (+1 more)

Tabular foundation models (TFMs) learn to fill in tables the way language models fill in text, and tables are arguably the format in which most physical measurement arrives. Did they learn any physics in the process? They are Bayesian by construction, so the question is what their prior contains. We probe it directly, evaluating four of them (TabPFN-3, TabICLv2, TabDPT and Real-TabPFN-2.5) against six baselines on datasets sampled from 316 physical equations, in and out of domain. TFMs dominate, out of the box and after tuning. But we show that their prior can represent neither a noiseless mechanism nor physical units, which is why they interpolate physics without yet being able to act as physical models.
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All authors Wassim Tenachi, Yashar Hezaveh, Laurence Perreault Levasseur, Pierre-Luc Bacon

Cosmology and Nongalactic Astrophysics

Gravitational Imprints of Axion Clouds on Black-Hole Orbital Dynamics

J. Ruz, V. Mungai, F. Kühnel et al. (+4 more)

Black holes of primordial or astrophysical origin immersed in axion dark matter provide a natural laboratory for exploring the interplay between compact objects and ultralight scalar fields. While previous studies have primarily focused on superradiance and horizon-scale phenomena, the gravitational response of the surrounding axion distribution has received comparatively little attention. We investigate the dynamics of particles orbiting Schwarzschild and Kerr primordial black holes embedded in scalar-field dark matter halos. Using first-order perturbation theory, we show that the ambient halo redistributes the gravitationally bound axion cloud, shifting the characteristic radius of the gravitational atom. Numerical integrations of timelike geodesics demonstrate that the maximum orbital response consistently occurs at this perturbed radius, establishing a direct correspondence between the microscopic structure of the axion wavefunction and the macroscopic dynamics of orbiting particles. Our results identify a new purely gravitational signature of scalar-field dark matter around primordial black holes and provide a framework for probing mixed axion–primordial black hole dark matter scenarios.
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All authors J. Ruz, V. Mungai, F. Kühnel, C. Köhn, E. Stamou, J. K. Vogel, B. Guichard

High Energy Astrophysical Phenomena

An Exact Engine for Black-Hole Jets

Yu Wang

For fifty years the Blandford–Znajek mechanism has been a mechanism and not an exact solution: force-free electrodynamics on a prescribed metric, with the jet's own field carrying no weight. Here that field gravitates. A split monopole weighs as much as a magnetic monopole, so its self-gravity is the magnetic Reissner–Nordström geometry; two copies glued across an equatorial current sheet put hole, disk and jet-driving flux into one spacetime, and force-free plasma makes a magnetosphere of it. Three things then follow that no test-field calculation can see. First, a steady jet is impossible. A stationary horizon cannot be heated but a slipping magnetosphere necessarily heats it, so the only stationary state is a dead one corotating with the hole, and a working jet is a black hole in decay at rates the field equations fix rather than assume. Second, flux enters the laws of black-hole mechanics as a charge, sharing one extremality budget with spin. That budget caps the jet power at $c^5/48G$ whatever the mass. Third, the lifetime output is finite: a maximally spinning hole delivers $1-e^{1/4}/\sqrt2=9.2\%$ of its mass and grows its horizon area by exactly $\sqrt e$. The horizon's own moment of inertia vanishes with the irrational exponent $(\sqrt{17}-1)/2$ set by the near-horizon throat, and what is left is a rotating hole whose angular momentum has passed to its own field.
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Earth and Planetary Astrophysics

Revisiting orbital recurrence in the dimmings of Boyajian's star (KIC~8462852)

Hector Socas-Navarro

KIC~8462852 (Boyajian's star) shows deep, asymmetric, and highly irregular dimming events with no simple repetition pattern. A symmetric 1.1% transit detected by TESS in 2019 has been interpreted as a possible giant planet or brown dwarf, while the irregular dips are generally attributed to transiting dust from exocomets or planetesimal fragments. We test whether the broader dip families may nevertheless recur orbitally. Our scenario assumes a major disruption that produced fragments with slightly different periods, causing successive returns to spread progressively in orbital phase. We compare this recurrent model with a null hypothesis of chronologically independent family centers, accounting for the observing window, and marginalize over the recurrence period $P$ and dispersion scale $\sigma_P$. We obtain $B_{10}=44.9$ in favor of recurrence, corresponding to “very strong” evidence on the Jeffreys scale. The maximum-likelihood solution is $P_{\rm ML}=781.6$~d and $\sigma_{P,\rm ML}=80.0$~d, close to the 776.1-d timescale obtained if D800 and the 2019 TESS event are separated by four revolutions. Independently of the timing fit, this period predicts a transit duration of about 20.5~h for the published stellar and transit parameters, in close agreement with the observed $\sim21$~h. The result is conditional on the adopted topology, priors, family definition, and observing selection function, and does not prove orbital recurrence. Nevertheless, the family timings strongly favor this specific recurrent-fragment model over independent occurrence, making progressive orbital phase dispersion a viable and physically motivated interpretation.
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Earth and Planetary Astrophysics

The Hill sphere transits of Beta Pictoris c and the search for another 1981-like event

V.E.C. Bakker, M.A. Kenworthy, R. Stuik et al. (+17 more)

Beta Pictoris is a young and nearby planetary system hosting an edge-on debris disk and at least three gas-giant planets. Their circumplanetary environments could host exomoons and rings, a detection of which would be highly informative for moon and planet formation theories. A photometric fluctuation of about 4% was seen towards Beta Pictoris in 1981, indicating the transit of dust in the system, which could be associated with the Hill spheres of the two inner planets. We search for the origin of the 1981 event by searching for an analogous event in multi-epoch photometry from 2017 to 2023, and look for signs of circumplanetary material in transits of the Hill sphere of Beta Pictoris c. Observations from the BRITE satellite, and the bRing and ASTEP observatories are fitted to a model of the 1981 event to search for a similar event, and also search for a signal consistent with a circumplanetary disk transit using a simple flat disk model. No compelling evidence for a 1981 event during a Hill sphere primary transit is found, although we do find a candidate event around 2019 July 26. Due to the uncertainty in the time of closest projected separation of Beta Pictoris c, a search for a disk during the primary transit of 2018 could not be robustly determined, but bRing photometry for the second primary transit places an upper limit on the dust content of the Hill sphere of ~ $10^{22}$ grams of material. With no compelling detection of an event similar to that seen in 1981 during the transits of Beta Pictoris c in the photometric time series, we rule out the hypothesis that this event was related to the Hill spheres of Beta Pictoris c and Beta Pictoris b. Future observations of the next Hill sphere transit in 2028 can be realised with both ground-based observatories and with PLATO, whose first long duration science pointing will include Beta Pictoris.
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All authors V.E.C. Bakker, M.A. Kenworthy, R. Stuik, K. Zwintz, T. Guillot, S. Vach, J. Wang, J. Kammerer, W. Balmer, S. Lacour, S. Zieba, E.E. Mamajek, G.-D. Marleau, R.B. Kuhn, P. Kalas, Y. De Pra, E.J.W. de Mooij, N. Crouzet, M. Buttu, J.I. Bailey III

Earth and Planetary Astrophysics

Galactic tides in the Solar System within a non-axisymmetric Milky Way model adjusted to Gaia data

Alexandre Bougakov, Yassin Rany Khalil, Marc Fouchard et al. (+4 more)

Context. Galactic tides are external differential forces acting on extended systems immersed in the Galactic potential. They play a key role in the dynamics of comets in the Oort cloud. Aims. We aim to establish the strength of Galactic tides from the non-axisymmetric potential of the Milky Way revealed by the Gaia mission, and how this strength evolves along the Galactic trajectory of the Solar System. Methods. We derived expressions for Galactic tide parameters independently of any simplified trajectory for a star in the Galaxy or any specific symmetry of the Galactic potential. We obtained six parameters, $G_1$ to $G_6$, that quantify the influence of tides. Using the most up-to-date Galactic potential model, extended here to three dimensions, we studied the time evolution of these parameters along the Sun's trajectory using a statistical approach. Results. Even for Galactic trajectories featuring modest radial and vertical excursions, as investigated here, the dominant Galactic parameter, $G_3$, is found to vary by an order of magnitude along the solar trajectory. $G_1$ and $G_2$ reach up to about one half and one quarter, respectively, of $G_3$ along the solar trajectory, whilst parameters $G_4$ to $G_6$ reach up to one tenth of $G_3$. Conclusions. Contrary to what is often assumed, all Galactic tide parameters vary widely along the Galactic trajectory of the Solar System. Two consequences can be expected: First, $G_3$ directly affects the flux of observable long-period comets and the extent of the fossilised Sednoids region; second, $G_1$ and $G_2$, and to a lesser extent, $G_4$ to $G_6$, break the integrability of the dynamics, potentially affecting the long-term structure of the Oort cloud. Additionally, the new parameters $G_4$ to $G_6$, while small for the Solar System, may strongly impact extrasolar systems with a large out-of-the-plane excursion in the Galaxy.
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All authors Alexandre Bougakov, Yassin Rany Khalil, Marc Fouchard, Melaine Saillenfest, Benoit Famaey, Paola Di Matteo, Misha Haywood

High Energy Astrophysical Phenomena

Multiwavelength View of Black Hole X-ray Binary Swift J151857.0-572147

Manoj Mandal, Sachindra Naik, Souvik Manik et al. (+1 more)

We investigate multiwavelength timing and spectral properties of the newly discovered black hole X-ray binary Swift J151857.0-572147 during its 2024 outburst using observations from AstroSat, NuSTAR, NICER, Swift, and MeerKAT. The AstroSat/LAXPC20 power density spectrum reveals a $\sim$8 Hz low-frequency QPO with a quality factor of $\sim2.8$. The broadband X-ray spectrum of the source exhibits prominent reflection features, which are modeled to constrain the geometry and physical properties of the accretion disk. The spectral analysis indicates that the source was in the soft/intermediate spectral state, characterized by a steep power law with a photon index of $\Gamma \approx 2.6$ and a relatively high disk temperature of $\sim0.9$ keV. The reflection modeling suggests a disk inclination of $23-31^{\circ}$ and a highly ionized accretion disk with $\log\xi \sim 3.3$-4.0. The MeerKAT monitoring revealed a strong radio variability that closely tracked the hard X-ray evolution, including a bright radio flare during the hard-to-soft state transition, supporting close coupling between the accretion flow and jet activity. Using the quasi-simultaneous AstroSat, Swift/XRT and MeerKAT observations, we investigated the radio/X-ray correlation and found that Swift J151857.0-572147 follows the established $L_{\rm X}$-$L_{\rm R}$ relation for Galactic black hole X-ray binaries. Its location in the $L_{\rm X}$-$L_{\rm R}$ plane is consistent with that of Galactic black hole X-ray binaries, further supporting its black hole nature.
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All authors Manoj Mandal, Sachindra Naik, Souvik Manik, Sabyasachi Pal

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Ultralight Bosons Explain the Mass-Spin Correlations in the Merging Binary Black Hole Population

Xiao-Xiao Kou, Vuk Mandic, Ran Ding et al. (+1 more)

Ultralight bosons could trigger superradiant instabilities in rapidly spinning black holes, forming oscillating clouds while extracting rotational energy. We consider an extended, superradiance-informed spin distribution model that characterizes possible environment-induced spin variations and compare its predictions with the observed population of merging black hole binaries in the Gravitational-Wave Transient Catalogs (GWTCs). We find that the mass-spin relation predicted by a scalar boson with mass $m_b\sim 10^{-12} \,\rm eV$ is consistent with the GWTCs, with increasing significance from GWTC-3.0 to 5.0. The Bayes factor reaches $\ln B \approx 7.8$ for GWTC-5.0. Intriguingly, this mass range largely coincides with a previous study based on a waveform analysis of the GW190728 gravitational wave event. Our findings provide compelling evidence that a superradiance-informed spin distribution model is highly compatible with the expanding binary black hole population dataset.
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All authors Xiao-Xiao Kou, Vuk Mandic, Ran Ding, Chi Tian

High Energy Astrophysical Phenomena

Feeding The Little Monster: An Accreting Intermediate-Mass Black Hole In A Minor Merger Secondary Galaxy

Marko Mićić and Julia St. Pierre

We report the discovery of a luminous supersoft X-ray source associated with the secondary galaxy in a 10:1 minor merger at $z$=0.216. We identified the system in the 3D-HST survey and observed it serendipitously in more than 100 Chandra observations, providing a combined exposure of 6.6 Msec. The secondary galaxy ($\log$ (M$_*$/M$_\odot$)=8.24) exhibits X-ray emission detected exclusively below 2.0 keV, with no significant hard-band photons. Because the source is low-count, we characterize its spectrum using Bayesian hardness-ratio analysis combined with simulations of physically motivated spectral models folded through the Chandra response files. The observed count rates and hardness ratios are reproduced by a thermal accretion-disk spectrum with rest-frame inner-disk temperatures kT$_{in}$=0.18-0.30 keV and luminosities log(L$_X$/erg s$^{-1}$)=40.5-41.2. Interpreted using a standard thin-disk framework, these properties imply a black hole mass of M$_\bullet$$\approx 8\times10^{2}$–$5\times10^{3}\,M_\odot$ accreting at $\approx$0.2-0.5 of the Eddington rate. Alternative interpretations involving ultraluminous X-ray supersoft sources are disfavored by the source's luminosity, temperature, lack of variability, and the host galaxy's low star-formation rate. Numerical simulations predict that black holes in smaller, secondary galaxies could experience episodic rapid growth during minor mergers. This discovery provides observational support for this scenario and suggests that minor interactions may be an important channel for assembling supermassive black holes in dwarf galaxies.
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Astrophysics of Galaxies

The Neutral Atomic Hydrogen in the solar neighborhood (NeAtHood) project I. Ghost in the shell: Neutral atomic hydrogen in the extended Orion nebula

J. D. Soler, H. Beuther, S. C. O. Glover et al. (+15 more)

The Orion Nebula is the nearest site of ongoing and recent high-mass star formation. It is a unique laboratory for studying the mass, energy, and momentum input from high-mass stars. We present 21-centimeter emission line observations that resolve for the first time the neutral atomic hydrogen (HI) gas in the extended Orion nebula (EON) at a resolution of one arcminute, which corresponds to a physical scale of 0.12 parsecs at the standard distance to the region. Our HI emission maps reveal an expanding shell that matches the EON contours delineated by recent observations of ionized carbon ([CII]) line emission. However, our combination of single-dish and interferometric HI observations suggests 100 solar masses of material for the front hemisphere of the shell, which is lower by roughly a factor of ten than the mass inferred from [CII] observations. This discrepancy suggests that the mass of the nearest wind-blown bubble has been overestimated, although we do not rule out the possibility that a significant amount of molecular hydrogen (H_2) in the shell may account for part of the difference. Our extended 21 cm line maps also reveal uncharted structures in and around the EON. They include a probable secondary bubble and a linear protrusion extending roughly four parsecs from the shell boundary. Our results illustrate the potential of HI interferometric observations to elucidate key aspects of the multiphase structure of star-forming regions and their connection to their surroundings.
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All authors J. D. Soler, H. Beuther, S. C. O. Glover, R. S. Klessen, J. Ott, M. Rugel, J. W. Teh, S. E. Clark, P. Goldsmith, A. Hacar, A. Socci, M. Heyer, M.-Y. Lee, C. E. Murray, D. Seifried, S. Walch, B. Godard, M.-A. Miville-Deschênes

Astrophysics of Galaxies

Can diffuse X-rays be important in driving photoionisation in molecular clouds?

E. I. Makarenko, A. V. Ivlev, S. Bialy et al. (+5 more)

The ionisation balance in molecular clouds is regulated by several ionising sources, including cosmic rays, X-rays, and ultraviolet radiation. Their relative importance depends on the local physical conditions and on the shielding column density. We compute the contribution of the large-scale diffuse X-ray radiation field to the ionisation in molecular clouds in the absence of strong local X-ray sources, such as young stars. Our goal is to quantify its significance relative to the Galactic cosmic rays. Using measurements of diffuse X-ray emission from the first eROSITA all-sky survey, we estimate the depth-dependent X-ray ionisation rate in molecular clouds across different Galactic environments. We consider both the observed diffuse field and a deabsorbed field obtained by correcting for foreground Galactic attenuation using HI4PI line-of-sight column densities in a pixel-by-pixel framework. Diffuse Galactic X-rays are unlikely to dominate the ionisation balance in well-shielded molecular gas ($N_{\mathrm{H}} > 5 \times 10^{21} \mathrm{cm^{-2}}$), where cosmic rays remain the primary ionising agent. At low column densities, the deabsorbed diffuse X-ray field produces ionisation rate of $\zeta_X \sim 10^{-18}\mathrm{s^{-1}}$ at $N_{\mathrm H} \sim 10^{19}\mathrm{cm^{-2}}$, remaining below the lower end of Galactic cosmic ray ionisation rate ($\sim 10^{-17} \mathrm{s^{-1}}$). The X-ray contribution decreases rapidly with increasing shielding, falling to $\zeta_{X}\sim10^{-19}\mathrm{s^{-1}}$ by $N_{\rm H}\sim10^{21}\mathrm{cm^{-2}}$ and to $\zeta_X \sim5\times10^{-21}\mathrm{s^{-1}}$ by $N_{\rm H}\sim10^{22}\mathrm{cm^{-2}}$. Diffuse X-ray may therefore contribute to the thermal and chemical structure of low-extinction material and should be considered when interpreting ionisation tracers in diffuse or cloud-envelope environments.
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All authors E. I. Makarenko, A. V. Ivlev, S. Bialy, X. Zheng, B. A. L. Gaches, P. Caselli, M. Padovani, M. C. H. Yeung

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

Dark Matter at the Kinematic Edge: Interpreting the 248 keV LZ Nuclear-Recoil Candidate

Mattia Di Mauro

The LUX-ZEPLIN (LZ) Collaboration recently reported one event consistent with a $248$ keV nuclear recoil in a $2.84$ tonne-year exposure, with a maximum local significance of $3.4\sigma$ and a global significance of $2.6\sigma$. We investigate whether the dark matter (DM)–nucleon interactions favored by this high-energy event can arise from particle DM models that simultaneously reproduce the observed relic abundance and satisfy indirect-detection constraints. Using the published LZ efficiency and operator significances, we show that elastic spin-independent (SI) scattering poorly explains an isolated high-energy recoil because its spectrum is concentrated at lower energies, whereas elastic spin-dependent (SD) $\mathcal{O}_4$ scattering remains viable. Endothermic scattering instead naturally suppresses the low-energy rate and shifts the recoil spectrum toward the observed energy. A thermal pseudo-Dirac fermion with an off-diagonal vector interaction provides a simple realization of this mechanism. For $m_\chi\simeq1$ TeV, the relic-density requirement predicts $\sigma_N\simeq6.5\times10^{-43}\,\mathrm{cm}^2$, while a splitting $\delta\simeq297$ keV shifts the recoil spectrum into the LZ event region. Present-day indirect-detection signals can be strongly suppressed because freeze-out proceeds mainly through coannihilation, while the excited state is depleted at late times. A thermal Higgsino provides a more predictive realization: its relic abundance fixes the mass near $1.1$ TeV, while a splitting $\delta\simeq 377$ keV is required to reproduce the event. This interpretation is testable through the associated gamma-ray line signal. Overall, combining direct detection, relic density, and indirect detection significantly restricts the viable interpretations of the LZ event and provides concrete targets for future searches.
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Earth and Planetary Astrophysics

Drift-dominated dust evolution. A multiwavelength analysis of dust rings in CY Tau and DoAr25

Anastasia Topalidou, Nienke van der Marel, Paola Pinilla et al. (+3 more)

Context. Protoplanetary disks are the birthplaces of planets, and understanding the distribution and evolution of dust within them is essential for tracing the early stages of planet formation. Aims. Following the DSHARP survey, we aim to constrain the radial distribution of the dust surface density and the maximum emitting grain size in the disks of CY Tau and DoAr 25 and assess the relative importance of dust trapping and radial drift in shaping the dust population in disks. Methods. We present multiwavelength continuum observations of CY Tau and DoAr 25 from ALMA at 2.4 and 1.25 mm and archival VLA data at 8.8 mm. Combining the observations with dust continuum forward modeling, we sought to infer a radial profile of the two systems of the dust surface density and maximum emitting grain size. Results. For DoAr 25, the results reveal a prominent dust ring at 111 AU and evidence for large (centimeter-sized) grains extending to the outer disk. In contrast, CY Tau exhibits a more compact and smoother structure, with both the dust surface density and grain size decreasing monotonically with radius. A tentative shoulder feature in the radial profiles, located between 20-40 AU, may point to a marginal substructure, possibly a weak dust trap. Conclusions. DoAr 25 shows evidence for a dust trap capable of halting inward drift, while CY Tau exhibits behavior consistent with evolution dominated by radial drift. Together, these results highlight how dust evolution processes shape the disk morphology and grain-size distributions, even in the low-mass stellar regime.
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All authors Anastasia Topalidou, Nienke van der Marel, Paola Pinilla, Haochang Jiang, Osmar M. Guerra-Alvarado, Brodie J. Norfolk

Instrumentation and Methods for Astrophysics

3.5-meter Segmented-Mirror Robotic Space Telescope Mission White Paper III. Key Scientific Mission: Exoplanet Science with a Coronagraph

Juhan Kim, Sang Hyun Lee, Yong-Woo Kang et al. (+22 more)

This volume defines the exoplanet science program enabled by the dedicated high-contrast coronagraph in the baseline science payload of the 3.5-meter Segmented-Mirror Robotic Space Telescope. The observatory architecture incorporates the optical interfaces, wavefront sensing and control, pointing stability, and operations software required for coronagraphic observations from the outset. The observing strategy gives priority to the nearest stellar systems because they provide the most accessible laboratories for planetary exploration and the most likely destinations of future interstellar missions. The diffraction limit sets a reflected-light horizon of roughly 10–15 pc for planets at 1 AU and roughly 50–80 pc for Jupiter analogs. Within those horizons, the telescope can image nearby giant planets, obtain reflected-light spectra of their atmospheres, survey young systems and circumstellar disks, and support the habitability and biosignature programs that larger future missions will pursue. The wide-field imager complements the coronagraph through transit photometry, occurrence-rate statistics, and long-term monitoring of stellar magnetic activity. A systematic census of the nearest stellar neighbors provides a lasting reference for exoplanet science and future space exploration.
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All authors Juhan Kim, Sang Hyun Lee, Yong-Woo Kang, Jeong-Yeol Han, Sungwook E. Hong, Bongkon Moon, Donguk Song, Juhyung Kang, Myeong-Gu Park, Sang Chul Kim, Chung-Uk Lee, Sangmo Tony Sohn, Arman Shafieloo, David Parkinson, Hong Soo Park, Dohyeong Kim, Chan Park, Jungjoo Sohn, Young-Beom Jeon, Jong-Hak Woo, Hyung Mok Lee, Hong Bae Ann, Myungkook James Jee, Mansoo Choi, Changbom Park

Instrumentation and Methods for Astrophysics

3.5-meter Segmented-Mirror Robotic Space Telescope Mission White Paper II. Key Scientific Mission: Wide-Field Cosmology and Galaxy Evolution

Juhan Kim, Yong-Woo Kang, Sang Hyun Lee et al. (+22 more)

The 3.5-meter Segmented-Mirror Robotic Space Telescope uses an image slicer for all spectroscopic observations. The planning baseline uses $R \simeq 1000$ for the wide survey and retains selectable $R \simeq 5000$ bands for precision line measurements. The central science case is a dense emission-line galaxy redshift survey for baryon acoustic oscillations and redshift-space distortions. Supernova and quasar programs exploit the stability, multiplexing, and repeatability of space operations. The supernova tier measures rest-frame U and near-ultraviolet magnitudes that separate optical twins at subgroup precision to $z \simeq 0.9$–$1.1$ in standard visits and to $z \simeq 1.3$–$1.5$ in ten-hour stacks. Every wide-survey tile receives three spectroscopic orientations, and a joint scene reconstruction uses their different overlap geometries to recover the spectra. The flagship survey covers 100–300 deg$^2$ and targets $10^6$–$3 \times 10^6$ emission-line galaxies. A deep pencil-beam tier and a supernova time-domain tier complement the wide survey. The same observations provide a census of ultra-diffuse and low-surface-brightness galaxies, map intracluster light, and test cold, self-interacting, and fuzzy dark matter through dwarf-galaxy structure and low-mass halo abundance.
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All authors Juhan Kim, Yong-Woo Kang, Sang Hyun Lee, Jeong-Yeol Han, Sungwook E. Hong, Bongkon Moon, Donguk Song, Juhyung Kang, Myeong-Gu Park, Sang Chul Kim, Chung-Uk Lee, Sangmo Tony Sohn, Arman Shafieloo, David Parkinson, Hong Soo Park, Dohyeong Kim, Chan Park, Jungjoo Sohn, Young-Beom Jeon, Jong-Hak Woo, Hyung Mok Lee, Hong Bae Ann, Myungkook James Jee, Mansoo Choi, Changbom Park

Instrumentation and Methods for Astrophysics

3.5-meter Segmented-Mirror Robotic Space Telescope Mission White Paper I. Overall Architecture and Scientific Mission

Yong-Woo Kang, Sang Hyun Lee, Juhan Kim et al. (+22 more)

We present the preliminary science concept and mission architecture of a 3.5-meter segmented-mirror robotic space telescope currently under study. The observatory is conceived as a versatile platform supporting wide-field cosmology and galaxy evolution, direct imaging and characterization of nearby planetary systems, time-domain and multi-messenger observations, compact-object studies, and Solar-System small-body science. These programs share requirements for angular resolution, photometric stability, rapid target acquisition, spectroscopy, and long-term observing efficiency. The telescope employs an 18-segment 3.5-meter primary mirror for high-angular-resolution imaging from the near-ultraviolet through the optical and near-infrared. The current baseline covers 0.2–1.5 $\mu$m, with the wavelength for diffraction-limited performance to be set by the final wavefront-error budget. Wide-field imaging is intended for deep surveys, precision photometry, and repeated monitoring over approximately 10' $\times$ 10' to 30' $\times$ 30'. Spectroscopic modes with $R \sim 1000$ and higher-resolution options approaching $R \sim 5000$ are being considered for galaxy surveys, transient classification, compact-object spectroscopy, and targeted studies. A dedicated coronagraph is also being studied for direct observations of nearby exoplanetary systems, with a current raw-contrast goal of order $10^{-8}$ and further gains expected from calibration and post-processing. Candidate mission configurations include the Sun–Earth L2 region and alternative Earth orbits, with the final choice driven by science performance, thermal stability, communications, operations, and mission cost. This paper defines the current science requirements, baseline technical configuration, and engineering trade space for further development of the 3.5mST concept.
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All authors Yong-Woo Kang, Sang Hyun Lee, Juhan Kim, Jeong-Yeol Han, Sungwook E. Hong, Bongkon Moon, Donguk Song, Juhyung Kang, Myeong-Gu Park, Sang Chul Kim, Chung-Uk Lee, Sangmo Tony Sohn, Arman Shafieloo, David Parkinson, Hong Soo Park, Dohyeong Kim, Chan Park, Jungjoo Sohn, Young-Beom Jeon, Jong-Hak Woo, Hyung Mok Lee, Hong Bae Ann, Myungkook James Jee, Mansoo Choi, Changbom Park

Earth and Planetary Astrophysics

Photometric characterization of near-Earth asteroids: rotation, taxonomy, and candidate evidence for internal cohesion

A. Carbognani, A. Buzzoni, M. Barbetta et al. (+1 more)

We present the results of a survey of previously uncharacterized near-Earth asteroids (NEAs) conducted between the second half of 2024 and the first months of 2026 using broadband $BVR_{c} I_{c}$ photometry and time-resolved lightcurve observations. Color indices were obtained for 14 NEAs of the 15 observed, with a dimension range between 0.11 and 2.5 km, and used to derive taxonomic classifications through comparison of a sample of reference reflectance curves. The sample appears to be dominated by S-, X-, and C-complex and V-type asteroids; absolute magnitudes and effective diameters were estimated using taxonomically appropriate albedos. Rotation periods were determined or constrained for several targets. Some large objects appear to rotate faster than the classical cohesionless spin barrier at $P\simeq 2.2$~h, although in some cases the period determinations remain tentative due to limited temporal coverage. A cohesive rubble-pile model provides a plausible explanation for the observed rapid rotation within the uncertainties of the derived physical parameters, and modest cohesive strengths of order $10^{2}$–$10^{4}$~Pa are sufficient to account for the observed rotation rates.
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All authors A. Carbognani, A. Buzzoni, M. Barbetta, R. Gualandi

Astrophysics of Galaxies

Constraining reionization-era Ly$\alpha$ escape with JELS-MUSE: a highly complete H$\alpha$-selected sample at $z\sim6.1$

A. L. Patrick, K. J. Duncan, Z. Li et al. (+16 more)

The Ly$\alpha$ escape fraction, $f_{\rm{esc}}^{\rm{Ly}\alpha}$, probes both the interstellar medium (ISM) conditions governing ionizing photon escape and the rising neutral fraction of the IGM through the Epoch of Reionization (EoR). Characterising the intrinsic, ISM-driven distribution of $f_{\rm{esc}}^{\rm{Ly}\alpha}$ before IGM attenuation becomes dominant is essential to interpret the observed decline in Ly$\alpha$ visibility through the EoR. We present $f_{\rm{esc}}^{\rm{Ly}\alpha}$ measurements for a highly complete, H$\alpha$-flux-limited sample of 24 star-forming galaxies at $z \approx 6.1$, drawn from the JWST Emission Line Survey (JELS) and observed in Ly$\alpha$ with VLT/MUSE as part of the JELS-MUSE Large Area Survey. We detect Ly$\alpha$ in 12 of 24 sources and a Ly$\alpha$ emitter fraction of $X_{\rm{Ly}\alpha} = 33 \pm 12$ per cent using the canonical EW(Ly$\alpha$) $> 25 \, \mathring{\rm{A}}$ definition. Incorporating non-detections via reverse Kaplan-Meier survival analysis yields $\langle f_{\rm{esc}}^{\rm{Ly}\alpha} \rangle = 0.07^{+0.04}_{-0.03}$, consistent with an independent stacked-flux estimate of $0.08^{+0.02}_{-0.02}$. Using reionization simulations matched to the area, depth, and redshift range of our survey, we find that all galaxies are expected to experience broadly similar IGM transmission, so we postulate that the large scatter in $f_{\rm{esc}}^{\rm{Ly}\alpha}$ reflects genuine ISM-driven variance rather than differences in the surrounding IGM. Among the detections, higher $f_{\rm{esc}}^{\rm{Ly}\alpha}$ galaxies tend to have lower nebular dust attenuation, bluer UV slopes, and lower stellar mass, consistent with feedback-regulated escape through localised, low-column-density ISM channels around star-forming regions. These results benchmark intrinsic Ly$\alpha$ escape at the end of reionization, against which IGM suppression at $z > 7$ can be interpreted.
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All authors A. L. Patrick, K. J. Duncan, Z. Li, C. A. Pirie, A. M. Swinbank, L. C. Keating, S. R. Flury, R. Begley, P. N. Best, M. Brinch, A. C. Carnall, F. Cullen, J. S. Dunlop, E. Ibar, J. Matthee, D. J. McLeod, A. Puglisi, H. M. O. Stephenson, J. P. Stott

Solar and Stellar Astrophysics

Solar Soft X-ray Coronal Dimming in a Failed Eruption Associated with Plasma Cooling

Xinyue Wang, Astrid M. Veronig, Hechao Chen et al. (+1 more)

Coronal dimmings are observed as sudden and localized reductions in the extreme-ultraviolet and X-ray emission of the solar corona. Traditionally, significant dimmings of spectral lines formed at temperatures of 1-2 MK are regarded as indicators of coronal mass ejections (CMEs), reflecting the density depletion caused by plasma escaping into interplanetary space. In this Letter, we report a peculiar deep coronal dimming event predominantly observed in high-temperature spectral lines following an M8.8-class confined solar flare associated with a failed filament eruption. Sun-as-a-star measurements from the Geostationary Operational Environmental Satellite and the Extreme Ultraviolet Variability Experiment reveal intensity reductions exceeding 30% in soft X-ray (SXR) and measurable decreases in Fe XVIII (6.5 MK) and Fe XX (9.3 MK). Spatially resolved observations from the Atmospheric Imaging Assembly demonstrate that the dimming originates from the active region core, while the Solar Terrestrial Relations Observatory-A shows no evidence for CME-driven mass loss. Differential emission measure analysis reveals plasma at temperatures >5 MK cooling into lower temperatures, supporting plasma cooling as the dominant contributor to the hot-band dimming rather than CME-associated plasma escape. This event demonstrates that deep hot SXR dimmings can occur without substantial CME-driven mass loss, suggesting that alternative physical mechanisms may also account for unresolved stellar dimmings in addition to the commonly inferred CME signatures.
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All authors Xinyue Wang, Astrid M. Veronig, Hechao Chen, Hui Tian

High Energy Astrophysical Phenomena

Are jet speeds governed by accretion modes?

Hong Tu, Xinwu Cao and Andrzej A. Zdziarski

Relativistic jets are observed in both stellar-mass black hole X-ray binaries (BHXRBs) and active galactic nuclei (AGNs), yet their bulk Lorentz factors differ systematically—those in black hole X-ray binaries are typically below $\sim2$, whereas AGN jets can reach $\sim50$. The origin of this discrepancy remains unclear. Searching the literature, we compile a sample of 333 AGNs with well-measured jet component motions, consisting of 270 quasars, 47 BL Lac objects, 10 FRI, and 6 FRII galaxies. We find that quasars/FRIIs exhibit minimal bulk Lorentz factors ranging from $\sim$1.0 to 41.5, with a mean of 11.5 (median 9.5). In contrast, BL Lac objects/FRIs show $\Gamma_{\rm jet}\sim$1.0–21.9, averaging 4.2 (median 1.5). These values, particularly the median, closely resemble those of BHXRBs, implying a strong correlation between jet speed and accretion mode. The Lorentz factor of a magnetically driven jet is mainly determined by the ratio of the magnetic pressure to rest mass energy density at the jet base. In BL Lacs/FRIs/BHXRBs, the field is maintained by the advection-dominated accretion flow (ADAF), and the gas at the ADAF surface is magnetically driven into the jets. In quasars/FRIIs, the field is maintained by the disc, while the jet base is connected to the corona. Our model calculations show that the disc field is always much stronger than that of the ADAF, and therefore leads to a larger $\Gamma_{\rm jet}$, which can explain the systematic difference in $\Gamma_{\rm jet}$ between these two types of sources.
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Solar and Stellar Astrophysics

Visual Discovery of Fading Events in the Wolf-Rayet Star WR 80

Rod Stubbings

Long-term visual and CCD V-band monitoring of the heavily reddened Wolf-Rayet star WR 80 from 2017-2026 reveals optical fading events that depart from its long-term stable baseline. On 26 April 2017 (JD 2457870), I discovered a deep minimum using a 22-inch (0.56-m) telescope, with the source plunging from a baseline of magnitude 14.6 down to magnitude 15.8. This 6-day event was subsequently verified via archival ASAS-SN V-band records. In July 2018, my visual observations identified a short duration fade to magnitude 15.4 that went undetected in concurrent electronic V band data streams, indicating a masking effect likely caused by near-infrared red leak contamination in the CCD filters. Following a stable phase recorded by continuous CCD V-band tracking from 2023 through early 2026, a mid-2026 visual detection caught a full 16-day fading event reaching a minimum magnitude of 15.3. These combined datasets establish that WR 80 undergoes highly variable optical obscuration events.
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High Energy Astrophysical Phenomena

Stars as triggers of interstellar gas entrainment in relativistic jets

B. Longo, M. Perucho, J.M. Martí et al. (+2 more)

Low-power extragalactic jets are known to be decelerated and dissipate large amounts of energy within their host galaxies. However, the exact process by which this occurs is still elusive. The aim of this work is to probe the role of stars as triggers of jet mass-loading, deceleration and dissipation in Fanaroff-Riley type I radio galaxies. This is motivated by a theoretical model that proposes that stars interacting with the jet boundaries could facilitate entrainment of interstellar medium (ISM) gas into jets, favouring mixing and dissipation. We have performed a numerical experiment of stars entering a relativistic flow, using a relativistic hydrodynamics code. Our setup is limited to the interaction of three stars with the jet boundary, in order to assess the results in a limited, controlled, environment, although this number of stars may be plausible in the inner kpc-region of a massive galaxy. Our results allow us to estimate the amount of entrained ISM gas as the stars enter the jet. We show that the entrainment temporally induced on scales of tens of parsecs and thousands of years by evolved stars is comparable to the initial jet mass rate. The way in which this entrainment happens is by the creation of a low pressure region behind the stellar objects, which drags ambient gas into the jet flow. Our results confirm that stars interacting with the jet boundaries, and acting as catalysts of ISM/shear gas entrainment, can significantly contribute to jet mass-load and deceleration.
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All authors B. Longo, M. Perucho, J.M. Martí, V. Bosch-Ramon, Y. Hoche

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Dark Matter as the Z_2 Partner of the Standard Model Higgs Boson

Yasunori Nomura

A possible gamma-ray excess from the Galactic halo favors dark matter with a mass of several hundred GeV. In previous work, we found that an electroweak scalar doublet is a particularly economical, and nearly uniquely selected, interpretation among simple renormalizable thermal dark-matter models. We point out that its unbroken Z_2 symmetry is exactly equivalent to an interchange symmetry between two Higgs doublets, making dark matter the Z_2-odd partner of the Standard Model Higgs boson and suggesting that the two doublets may share a common weak-scale origin. We connect this model to the recently reported 248 keV nuclear-recoil event in the LUX-ZEPLIN experiment. For dark-matter masses of 440–600 GeV, a technically natural, mass-dependent neutral-state splitting of order 350 keV defines a narrow strip near the kinematic boundary where the fixed off-diagonal Z interaction can produce the observed recoil. Because the scattering probes the extreme high-velocity tail of the Galactic distribution, this interpretation predicts a large annual modulation, with future events preferentially occurring around early summer. Neither observation is yet conclusive, but their common interpretation is sharply testable.
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High Energy Astrophysical Phenomena

Transient discs around isolated accreting neutron stars

Marina D. Afonina, Anton V. Biryukov, Sergei B. Popov et al. (+1 more)

Mature, isolated neutron stars can accrete from the interstellar medium. Due to turbulence, the accreted gas can have a substantial angular momentum and form a disc around the compact object. In this paper, we perform a population synthesis of isolated neutron stars in the Milky Way that specifically tracks the possibility of disc formation, which typically requires a low spatial velocity of the compact object ($\lesssim 40$ km s$^{-1}$). In general, weak magnetic fields favour disc formation as the magnetosphere occupies a smaller volume. Still, even in the case of fields decaying exponentially over a characteristic timescale of $\sim 1.5$ Gyr, we find that for several realistic models of propeller spin-down, only a small fraction of accretors (down to $\sim 0.02$ %) attain discs. However, disc-accreting isolated neutron stars are relatively numerous among the brightest sources. We estimate that their number can reach a few hundred at X-ray fluxes of $\gtrsim 10^{-14}$ erg s$^{-1}$ cm$^{-2}$. We speculate that disc-accreting isolated neutron stars can manifest as long-period radio transient sources via electron cyclotron maser emission, predicting spectra and critical conditions for quenching.
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All authors Marina D. Afonina, Anton V. Biryukov, Sergei B. Popov, Arthur G. Suvorov

Instrumentation and Methods for Astrophysics

CHARA/SPICA: The six-telescope visible combiner and near-infrared fringe tracker for the CHARA Array

D. Mourard, P. Bério, C. Bailet et al. (+43 more)

The suite called Stellar Parameters and Images with a Cophased Array (SPICA) has two interferometric instruments installed at the focus of the CHARA Array located at Mount Wilson, CA. SPICA is made of SPICA-VIS, a fiber-fed six-beam visible spectrograph with three spectral resolutions, and SPICA-FT, a six-beam near-infrared fringe tracker for the fast stabilization of the fringes. SPICA is opening access to imaging in the visible domain with an unprecedented angular resolution down to 0.2 milliarcseconds. It has been designed around a large survey of fundamental parameters of stars over the Hertzsprung- Russell diagram, aiming at understanding the deviations from the standard empirical relations of stellar physics as a function of activity: limb darkening, multiplicity, rotation, winds, and environments. SPICA makes use of the advanced technologies in electron multiplying detectors in the visible and electron- avalanche photodiode arrays in the near-infrared. It benefits from the newly commissioned adaptive optics on the one-meter telescopes of the array. The modules of the visible instrument, SPICA-VIS, optimize the injection of light into single-mode fibers for spatial filtering before spectral dispersion in the image plane. The fringe tracker, SPICA-FT, performs group-delay and phase-delay tracking for six beams in the H band. SPICA-FT can use an all-in-one or ABCD encoding of the fringe signals. SPICA is operational on sky and is close to reaching the expected performance in low spectral resolution, in particular, for the Interferometric Survey of Stellar Parameters (ISSP). More work is still needed to achieve the ultimate performance in terms of sensitivity and to allow operations with higher spectral resolutions.
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All authors D. Mourard, P. Bério, C. Bailet, A. Caci, J. Dejonghe, P. Geneslay, S. Lagarde, D. Lecron, A. Meilland, F. Morand, N. Nardetto, C. Pannetier, K. Perraut, S. Rousseau, D. Salabert, N. Ebrahimkutty, R.V. Ibañez Bustos, J. Jonák, R. Ligi, H. Nowacki, F. Patru, M. Vrard, L. Bourgés, G. Mella, N. Anugu, T. ten Brummelaar, C. Farrington, D. Gies, J. Jones, R. Koehler, K. Kubiak, C. Lanthermann, R. Ligon, G. Schaefer, N. Scott, N. Turner, J. Monnier, S. Kraus, J.B. Le Bouquin, T. Gardner, M. Gutierrez, N. Ibrahim, E. Aristidi, Y. Caujolle, C. Giordano, A. Ziad

Solar and Stellar Astrophysics

Multiplicity of Cool Stars and their Evolution

Matthew I. Swayne, Leen Decin, Theo Khouri et al. (+12 more)

Making up a sizeable portion of the galactic census, stellar multiples are experiencing a renaissance. Enabling the study of multiple strands of the study of cool stars, stellar multiples have been found and characterised in great numbers by the missions of the last decade, allowing the exploration of stellar parameters and populations, observation of stellar interactions, studies into stellar formation and evolution, and characterisation of circumbinary systems. This exciting explosion of science is only set to continue, with future missions set to offer even further insights into the topic. Within these proceedings we will summarise the presentations and discussions on cool stellar multiplicity within our splinter sessions at the 23rd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, as we examine the present state of the field and look to what the future may bring.
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All authors Matthew I. Swayne, Leen Decin, Theo Khouri, Ayush Moharana, Léa Planquart, John Southworth, Nikki J. Miller, José A. Caballero, Orsolo De Marco, Krzysztof G. Hełminiak, Swetlana Hubrig, Valentin D. Ivanov, Pierre Kervella, Thibault Merle, Dorota M. Skowron