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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 18 December

Astrophysics of Galaxies

Unveiling the population of massive quenched galaxies at $z\ge2$ in the COLIBRE simulations - I. Galaxy demographics

Ángel Chandro-Gómez, Claudia del P. Lagos, Chris Power et al. (+14 more)

The James Webb Space Telescope has uncovered a substantial population of Massive ($M_{\star} > 10^{10}\,\mathrm{M_{\odot}}$), Quenched Galaxies (MQGs) in the early Universe ($z \ge 2$), whose properties challenge current galaxy formation models. In this series, we examine this population of MQGs within the new COLIBRE cosmological hydrodynamical simulations, which introduce key innovations in their sub-grid physics. In this first paper, we find a dependence of MQG number densities on both mass resolution and the Active Galactic Nucleus feedback implementation, as well as a significant impact from potential observational uncertainties. Using the fiducial $(200\,\rm cMpc)^3$ volume L200m6 simulation, which provides adequate volume, mass and spatial resolution to study these systems, we report number densities and stellar mass functions in broad agreement with the latest observations. The predicted quenching and formation timescales are qualitatively consistent with observational inferences, indicating extended formation (medians $t_{50}\approx0.5-1.5\,\mathrm{Gyr}$) followed by rapid quenching (medians $t_{\mathrm{q}}\lesssim0.6\,\mathrm{Gyr}$) with strong starburst episodes. Leveraging the state-of-the-art physics in COLIBRE, the model predicts that MQGs have dust and $\rm H_{2}$ fractions more than $1$~dex lower than their massive star-forming counterparts; generally consistent with the (scarce) observational estimates. MQGs and massive star-forming systems show broadly similar stellar sizes and kinematics, suggesting that size or morphological transformations occur after quenching in COLIBRE. Our results provide robust predictions for MQGs and show that tensions with observations are reduced when an effective observational uncertainty is forward-modelled.
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All authors Ángel Chandro-Gómez, Claudia del P. Lagos, Chris Power, William M. Baker, Alejandro Benítez-Llambay, Evgenii Chaikin, Harry G. Chittenden, Camila Correa, Carlos S. Frenk, Filip Huško, Robert J. McGibbon, Themiya Nanayakkara, Sylvia Ploeckinger, Alexander J. Richings, Matthieu Schaller, Joop Schaye, James W. Trayford

High Energy Astrophysical Phenomena

Fastest or Significant: A Systematic Framework for Validating Global Minimum Variability Timescale Measurements of Gamma-ray Bursts

S. Bala, P. Veres, A. Goldstein et al. (+3 more)

The minimum variability timescale (MVT) is a key observable used to probe the central engines of Gamma-Ray Bursts (GRBs) by constraining the emission region size and the outflow Lorentz factor. However, its interpretation is often ambiguous: statistical noise and analysis choices can bias measurements, making it difficult to distinguish genuine source variability from artifacts. Here we perform a comprehensive suite of simulations to establish a quantitative framework for validating Haar-based MVT measurements. We show that in multi–component light curves, the MVT returns the most statistically significant structure in the interval, which is not necessarily the fastest intrinsic timescale, and can therefore converge to intermediate values. Reliability is found to depend jointly on the MVT value and its signal-to-noise ratio ($\mathrm{SNR}_{\mathrm{MVT}}$), with shorter intrinsic timescales requiring proportionally higher $\mathrm{SNR}_{\mathrm{MVT}}$ to be resolved. We use this relation to define an empirical MVT Validation Curve, and provide a practical workflow to classify measurements as robust detections or upper limits. Applying this procedure to a sample of Fermi-GBM bursts shows that several published MVT values are better interpreted as upper limits. These results provide a path toward standardizing MVT analyses and highlight the caution required when inferring physical constraints from a single MVT measurement in complex events.
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All authors S. Bala, P. Veres, A. Goldstein, R. Sonawane, R. Samanta, S. Iyyani

Earth and Planetary Astrophysics

Physics-Informed Neural Networks for Modeling the Martian Induced Magnetosphere

Jiawei Gao, Chuanfei Dong, Chi Zhang et al. (+6 more)

Understanding the magnetic field environment around Mars and its response to upstream solar wind conditions provide key insights into the processes driving atmospheric ion escape. To date, global models of Martian induced magnetosphere have been exclusively physics-based, relying on computationally intensive simulations. For the first time, we develop a data-driven model of the Martian induced magnetospheric magnetic field using Physics-Informed Neural Network (PINN) combined with MAVEN observations and physical laws. Trained under varying solar wind conditions, including B_IMF, P_SW, and {\theta}_cone, the data-driven model accurately reconstructs the three-dimensional magnetic field configuration and its variability in response to upstream solar wind drivers. Based on the PINN results, we identify key dependencies of magnetic field configuration on solar wind parameters, including the hemispheric asymmetries of the draped field line strength in the Mars-Solar-Electric coordinates. These findings demonstrate the capability of PINNs to reconstruct complex magnetic field structures in the Martian induced magnetosphere, thereby offering a promising tool for advancing studies of solar wind-Mars interactions.
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All authors Jiawei Gao, Chuanfei Dong, Chi Zhang, Yilan Qin, Simin Shekarpaz, Xinmin Li, Liang Wang, Hongyang Zhou, Abigail Tadlock

Solar and Stellar Astrophysics

Bayesian Smooth-Fit Extrapolation of the $^{12}\mathrm{C}+{}^{12}\mathrm{C}$ Astrophysical $S$ Factor

A. M. Mukhamedzhanov

A Bayesian analysis of the astrophysical \(S\) factor for the \(^{12}{\rm C}+{}^{12}{\rm C}\) fusion reaction is presented using available low-energy information at carbon–carbon relative energies \(E <3.5~{\rm MeV}\), including direct measurements and recent inverse-kinematics data. The goal of the global Bayesian fit is not to reproduce the local resonance-by-resonance structure of the \(^{12}{\rm C}+{}^{12}{\rm C}\) system, but rather to constrain the smooth global component of \(S^{*}(E)\) using the direct and inverse-kinematics constraints. The resulting posterior \(S^{*}(E)\) lies systematically below the traditional FCZ75 reference normalization over the energy interval considered. For example, at \(E=1.5~{\rm MeV}\) the median posterior value is \(S^{*}(1.5~{\rm MeV})=1.20\times10^{16}~{\rm keV\,b}\), whereas the Fowler–Caughlan–Zimmerman reference value is \(S^{*}_{\rm FCZ75}=3.0\times10^{16}~{\rm keV\,b}\) [W.~A. Fowler, G.~R. Caughlan, and B.~A. Zimmerman, Annu. Rev. Astron. Astrophys. 13, 69 (1975)]. Thus, the updated posterior favors a lower smooth low-energy trend and does not support a sharp increase of \(S^{*}(E)\) as the energy decreases. The astrophysical consequence of the analysis is assessed through the thermonuclear reaction rate \(N_A\langle\sigma v\rangle\). The resulting median rate is lower than the CF88 analytic rate [G.~R. Caughlan and W.~A. Fowler, At. Data Nucl. Data Tables 40, 283 (1988)] over the temperature interval considered, with \(R_{\rm present}/R_{\rm CF88}\simeq0.33\)–\(0.46\) for \(0.3\leq T_9\leq1.2\). At higher temperatures, where the Gamow window extends above the upper end of the adopted integration interval, the calculated rate should be regarded as a truncated rate rather than a complete stellar rate.
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High Energy Astrophysical Phenomena

The SKAO Pulsar Timing Array

Ryan M. Shannon, N. D. Ramesh Bhat, Aurelien Chalumeau et al. (+23 more)

Pulsar timing arrays (PTAs) are ensembles of millisecond pulsars observed for years to decades. The primary goal of PTAs is to study gravitational-wave astronomy at nanohertz frequencies, with secondary goals of undertaking other fundamental tests of physics and astronomy. Recently, compelling evidence has emerged in established PTA experiments for the presence of a gravitational-wave background. To accelerate a confident detection of such a signal and then study gravitational-wave emitting sources, it is necessary to observe a larger number of millisecond pulsars to greater timing precision. The SKAO telescopes, which will be a factor of three to four greater in sensitivity compared to any other southern hemisphere facility, are poised to make such an impact. In this chapter, we motivate an SKAO pulsar timing array (SKAO PTA) experiment. We discuss the classes of gravitational waves present in PTA observations and how an SKAO PTA can detect and study them. We then describe the sources that can produce these signals. We discuss the astrophysical noise sources that must be mitigated to undertake the most sensitive searches. We then describe a realistic PTA experiment implemented with the SKA and place it in context alongside other PTA experiments likely ongoing in the 2030s. We describe the techniques necessary to search for gravitational waves in the SKAO PTA and motivate how very long baseline interferometry can improve the sensitivity of an SKAO PTA. The SKAO PTA will provide a view of the Universe complementary to those of the other large facilities of the 2030s.
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All authors Ryan M. Shannon, N. D. Ramesh Bhat, Aurelien Chalumeau, Siyuan Chen, H. Thankful Cromartie, A. Gopukumar, Kathrin Grunthal, Jeffrey S. Hazboun, Francesco Iraci, Bhal Chandra Joshi, Ryo Kato, Michael J. Keith, Kejia Lee, Kuo Liu, Hannah Middleton, Matthew T. Miles, Chiara M. F. Mingarelli, Aditya Parthasarathy, Daniel J. Reardon, Golam M. Shaifullah, Keitaro Takahashi, Caterina Tiburzi, Riccardo J. Truant, Xiao Xue, Andrew Zic, The SKAO Pulsar Science Working Group

High Energy Astrophysical Phenomena

Probing neutron star interiors and the properties of cold ultra-dense matter with the SKAO

Avishek Basu, Vanessa Graber, Marcus E. Lower et al. (+19 more)

Matter inside neutron stars is compressed to densities several times greater than nuclear saturation density, while maintaining low temperatures and large asymmetries between neutrons and protons. Neutron stars, therefore, provide a unique laboratory for testing physics in environments that cannot be recreated on Earth. To uncover the highly uncertain nature of cold, ultra-dense matter, discovering and monitoring pulsars is essential, and the SKA will play a crucial role in this endeavour. In this paper, we will present the current state-of-the-art in dense matter physics and dense matter superfluidity, and discuss recent advances in measuring global neutron star properties (masses, moments of inertia, and maximum rotation frequencies) as well as non-global observables (pulsar glitches and free precession). We will specifically highlight how radio observations of isolated neutron stars and those in binaries – such as those performed with the SKA in the near future – inform our understanding of ultra-dense physics and address in detail how SKAO's telescopes unprecedented sensitivity, large-scale survey and sub-arraying capabilities will enable novel dense matter constraints. We will also address the potential impact of dark matter and modified gravity models on these constraints and emphasise the role of synergies between the SKA and other facilities, specifically X-ray telescopes and next-generation gravitational wave observatories.
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All authors Avishek Basu, Vanessa Graber, Marcus E. Lower, Marco Antonelli, Danai Antonopoulou, Manjari Bagchi, Prasanta Char, Paulo C. C. Freire, Brynmor Haskell, Huanchen Hu, David I. Jones, Banibrata Mukhopadhyay, Micaela Oertel, Nanda Rea, Violetta Sagun, Benjamin Shaw, Jaikhomba Singha, Benjamin W. Stappers, Tinn Thongmeearkom, Anna L. Watts, Patrick Weltevrede, The SKA Pulsar Science Working Group

High Energy Astrophysical Phenomena

Testing Gravity with Binary Pulsars in the SKA Era

V. Venkatraman Krishnan, L. Shao, V. Balakrishnan et al. (+21 more)

Binary (and trinary) radio pulsars are natural laboratories in space for understanding gravity in the strong field regime, with many unique and precise tests carried out so far, including the most precise tests of the strong equivalence principle and of the radiative properties of gravity. The Square Kilometre Array (SKA) telescope, with its high sensitivity in the Southern Hemisphere, will vastly improve the timing precision of recycled pulsars, allowing for a deeper search of potential deviations from general relativity (GR) in currently known systems. A Galactic census of pulsars will, in addition, will yield the discovery of dozens of relativistic pulsar systems, including potentially pulsar – black hole binaries, which can be used to test the cosmic censorship hypothesis and the “no-hair” theorem. Aspects of gravitation to be explored include tests of strong equivalence principles, gravitational dipole radiation, extra field components of gravitation, gravitomagnetism, and spacetime symmetries. In this chapter, we describe the kinds of gravity tests possible with binary pulsar and outline the features and abilities that SKA must possess to best contribute to this science.
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All authors V. Venkatraman Krishnan, L. Shao, V. Balakrishnan, M. Colom i Bernadich, A. Carelo, A. Corongiu, A. Deller, P. C. C. Freire, M. Geyer, E. Hackmann, H. Hu, Z. Hu, J. Kunz, M. Kramer, K. Liu, M. E. Lower, X. Miao, A. Possenti, D. Perrodin, D. S. Pillay, S. Ransom, I. Stairs, B. Stappers, The SKA Pulsar Science Working Group

High Energy Astrophysical Phenomena

Understanding Pulsar Wind Nebulae with the SKA

Joseph D. Gelfand, C.-Y. Ng, B. Posselt et al. (+9 more)

Produced by the interaction between the “pulsar wind” powered by the rotational energy of a neutron star and its surroundings, the study of pulsar wind nebulae (PWNe) provides vital insight into the physics of neutron star magnetospheres and ultra-relativistic outflows. Spatially-resolved studies of the continuum and polarized radio emission of these sources are vital for understanding the production of $e^\pm$ in the magnetospheres of neutron stars, the acceleration of these particles to $\gtrsim10^{15}~{\rm eV}$ energies, and the propagation of these particles within the PWN as well as the surrounding interstellar medium. The significant improvements in sensitivity, dynamic range, timing capabilities offered by the Square Kilometer Array have the potential to significantly improve our understanding of the origin of some of the highest energy particles produced in the Milky Way.
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All authors Joseph D. Gelfand, C.-Y. Ng, B. Posselt, Mallory S. E. Roberts, Subir Bhattacharyya, Shi Dai, Rene Breton, Benjamin Stappers, Andrea Possenti, Jason Hessels, Yifan Sun, Moaz Abdelmaguid

Astrophysics of Galaxies

Exploring the magnetic field structure of the Milky Way with pulsars in the SKA era

Jun Xu, J. L. Han, Weicong Jing et al. (+1 more)

The magnetic field structure of the Milky Way can offer critical insights into the origin of galactic magnetic fields. Measurements of magnetic structures of the Milky Way are still sparse in far regions of the Galactic disk and halo. Pulsars are the best probes for the three-dimensional structure of the Galactic magnetic field, primarily owing to their highly polarized short-duration radio pulses, negligible intrinsic Faraday rotation compared to the contribution from the medium in front, and their widespread distribution throughout the Galaxy across the thin disk, spiral arms, and extended halo. In this article, we give an overview of Galactic magnetic field investigation using pulsars. The sensitive SKA1 design baseline (AA4) will increase the number of known pulsars by a factor of around three, and the initial staged delivery array (AA*) will probably double the total number of the current pulsar population. Polarization observations of pulsars with the AA* telescopes will give rotation measures along several thousand lines of sight, enabling detailed exploration of the magnetic structure of both the Galactic disk and the Galactic halo.
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All authors Jun Xu, J. L. Han, Weicong Jing, The SKA Pulsar Science Working Group

High Energy Astrophysical Phenomena

Exploring Galactic plasma with pulsars in the SKA era

C. Tiburzi, M. T. Lam, D. J. Reardon et al. (+14 more)

The ionised media that permeate the Milky Way have been active topics of research since the discovery of pulsars in 1967. In fact, pulsars allow one to study several aspects of said plasma, such as their column density, turbulence, scattering measures, and discrete, intervening structures between the neutron star and the observer, as well as aspects of the magnetic field throughout. Such sources of information allow us to characterise the electron distribution in the terrestrial ionosphere, the Solar Wind, and our Galaxy, as well as the impact on other experiments involving pulsars, such as Pulsar Timing Arrays. In this article, we review the state-of-the-art in plasma research using pulsars, the aspects that should be taken into consideration for optimal plasma studies, and we provide future perspectives on improvements enabled by the SKA.
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All authors C. Tiburzi, M. T. Lam, D. J. Reardon, N. K. Porayko, M. Mevius, S. Koch Ocker, S. C. Susarla, J. R. Dawson, A. Deller, G. M. Shaifullah, M. Walker, W. Jing, F. A. Iraci, N. D. R. Bhat, M. Geyer, L. Levin, M. Keith

High Energy Astrophysical Phenomena

Understanding pulsar magnetospheres with the SKAO

L. S. Oswald, A. Basu, M. Chakraborty et al. (+22 more)

The SKA telescopes will bring unparalleled sensitivity across a broad radio band, a wide field of view across the Southern sky, and the capacity for sub-arraying, all of which make them the ideal instruments for studying the pulsar magnetosphere. This paper describes the advances that have been made in pulsar magnetosphere physics over the last decade, and details how these have been made possible through the advances of modern radio telescopes, particularly SKA precursors and pathfinders. It explains how the SKA telescopes would transform the field of pulsar magnetosphere physics through a combination of large-scale monitoring surveys and in-depth follow-up observations of unique sources and new discoveries. Finally, it describes how the specific observing opportunities available with the AA* and AA4 configurations will achieve the advances necessary to solve the problem of pulsar radio emission physics in the coming years.
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All authors L. S. Oswald, A. Basu, M. Chakraborty, B. C. Joshi, N. Lewandowska, K. Liu, M. E. Lower, A. Philippov, X. Song, P. Tarafdar, J. van Leeuwen, A. L. Watts, P. Weltevrede, G. Wright, J. Benacek, A. Beri, S. Cao, P. Esposito, F. Jankowski, J. C. Jiang, A. Karastergiou, K. J. Lee, N. Rea, D. Vohl, The SKA Pulsar Science Working Group

High Energy Astrophysical Phenomena

Understanding the Neutron Star Population with the SKAO telescopes

L. Levin, M. Bagchi, M. Burgay et al. (+13 more)

The known population of non-accreting neutron stars is ever growing and currently consists of more than 3500 sources. Pulsar surveys with the SKAO telescopes will greatly increase the known population, adding radio pulsars to every subgroup in the radio-loud neutron star family. These discoveries will not only add to the current understanding of neutron star physics by increasing the sample of sources that can be studied, but will undoubtedly also uncover previously unknown types of sources that will challenge our theories of a wide range of physical phenomena. A broad variety of scientific studies will be made possible by a significantly increased known population of neutron stars, unravelling questions such as: How do isolated pulsars evolve with time; What is the connection between magnetars, high B-field pulsars, and the newly discovered long-period pulsars; How is a pulsar's spin-down related to its radio emission; What is the nuclear equation of state? Increasing the known numbers of pulsars in binary or triple systems may enable both larger numbers and higher precision tests of gravitational theories and general relativity, as well as probing the neutron star mass distribution. The excellent sensitivity of the SKAO telescopes combined with the wide field of view, large numbers of simultaneous tied-array beams that will be searched in real time, wide range of observing frequencies, and the ability to form multiple sub-arrays will make the SKAO an excellent facility to undertake a wide range of neutron star research. In this paper, we give an overview of different types of neutron stars and discuss how the SKAO telescopes will aid in our understanding of the neutron star population.
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All authors L. Levin, M. Bagchi, M. Burgay, A. T. Deller, V. Graber, A. Igoshev, M. Kramer, D. Lorimer, B. Posselt, T. Prabu, K. Rajwade, N. Rea, B. Stappers, T. M. Tauris, P. Weltevrede, The SKAO Pulsar Science Working Group

High Energy Astrophysical Phenomena

Galactic Centre Pulsars with the SKAO

F. Abbate, A. Carleo, S. Chatterjee et al. (+19 more)

The detection of a pulsar closely orbiting our Galaxy's supermassive black hole - Sagittarius A* - is one of the ultimate prizes in pulsar astrophysics. The relativistic effects expected in such a system could far exceed those currently observable in compact binaries such as double neutron stars and pulsar white dwarfs. In addition, pulsars offer the opportunity to study the magneto-ionic properties of Earth's nearest galactic nucleus in unprecedented detail. For these reasons, and more, a multitude of pulsar searches of the Galactic Centre have been undertaken, with the outcome of just seven pulsar detections within a projected distance of 100 pc from Sagittarius A*. It is currently understood that a larger underlying population likely exists, but it is not until observations with the SKA have started that this population can be revealed. In this paper, we look at important updates since the publication of the last SKAO science book and offer a focused view of observing strategies and likely outcomes with the updated SKAO design.
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All authors F. Abbate, A. Carleo, S. Chatterjee, J. Cordes, P. B. Demorest, G. Desvignes, R. P. Eatough, E. Hackmann, Hu Z., M. Kramer, J. Lazio, K. J. Lee, K. Liu, I. Rammala-Zitha, S. M. Ransom, G. Saowanit, L. Shao, P. Torne, R. Wharton, J. Wongphechauxsorn, W. Zhu, The SKAO Pulsar Science Working Group

High Energy Astrophysical Phenomena

Pulsars in Globular Clusters With the SKAO

Manjari Bagchi, Federico Abbate, Vishnu Balakrishnan et al. (+15 more)

Because of their extreme stellar densities, globular clusters are highly efficient factories of X-ray binaries and radio pulsars: per unit of stellar mass, they contain about 1000 times more of these exotic objects. Thus far, 345 radio pulsars have been found in globular clusters. These can be used as precision probes of the structure, gas content, magnetic field, and dynamic history of their host clusters; some of them are also highly interesting in their own right because they probe exotic stellar evolution scenarios as well as the physics of dense matter, accretion, and gravity; one of them (PSR~J0514$-$4002E) might even be the first pulsar - black hole system known. Deep searches with SKA-MID and SKA-LOW will only require one to a few tied-array beams, and can be done during early commissioning of the telescope, before an all-sky pulsar survey using hundreds to thousands of tied-array beams is feasible. Even a conservative approach predicts new discoveries only with the core of SKA-MID AA*, and the full AA* and eventually AA4 is expected to increase the number of discoveries even more, leading to more than doubling the current known population. This offers a great opportunity for early SKAO pulsar science, even before all the collecting area is in place. On the other hand, a more optimistic prediction calls for a 4-5 times growth of the population, leading to a total of about 1700 pulsars to be detectable with SKA-MID AA4 configuration in all Galactic GCs visible by SKA telescopes. Thus, a dedicated search for pulsars in globular clusters will fully exploit the best possible natural laboratories to study many branches of physics and astrophysics, including properties of dense matter, stellar evolution, and the dynamical history of the Galactic globular cluster systems.
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All authors Manjari Bagchi, Federico Abbate, Vishnu Balakrishnan, Miquel Colom i Bernadich, Bhaswati Bhattacharyya, Arunima Dutta, Paulo C. C. Freire, Kriisa Halley, Jason W. T. Hessels, Sangeeta Kumari, Duncan R. Lorimer, Andrea Possenti, Rouhin Nag, Scott M. Ransom, Alessandro Ridolfi, Vivek Venkatraman Krishnan, Weiwei Zhu, The SKA Pulsar Science Working Group

High Energy Astrophysical Phenomena

A Square Kilometre Array Pulsar Census

E. F. Keane, V. Graber, L. Levin et al. (+8 more)

Most of the pulsar science case with the Square Kilometre Array (SKA) depends on long-term precision pulsar timing of a large number of pulsars, as well as astrometric measurements of these using very long baseline interferometry (VLBI). But before we can time them, or VLBI them, we must first find them. Here, we describe the considerations and strategies one needs to account for when planning an all-sky blind pulsar survey using the SKA. Based on our understanding of the pulsar population, the performance of the now-under-construction SKA elements, and practical constraints such as evading radio frequency interference, we project pulsar survey yields using two complementary methods for a number of illustrative survey designs, combining SKA1-Low and SKA1-Mid Bands 1 and 2 in a variety of ways. A composite survey using both Mid and Low is optimal, with Mid Band 2 focused in the plane. We find that, given its much higher effective area and survey speed, the best strategy is to use SKA1-Low to cover as much sky as possible, ideally also overlapping with the areas covered by Mid. In our most realistic scenario, we find that an all-sky blind survey with Phase 1 of the SKA with the AA* array assembly will detect $\sim10,000$ slow pulsars and $\sim 800$ millisecond pulsars (MSPs) if SKA1-Mid covers the region within $5\deg$ of the plane, while higher latitudes will be covered with SKA1-Low. The yield with AA4 is $\sim 20\%$ higher. One could increase these numbers by increasing the range covered by SKA1-Mid Bands 1 and 2, at the cost of a considerably longer survey. The pulsar census will enable us to set new constraints on the uncertain physical properties of the entire neutron star population. This will be crucial for addressing major SKA science questions including the dense-matter equation of state, strong-field gravity tests, and gravitational wave astronomy.
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All authors E. F. Keane, V. Graber, L. Levin, C. M. Tan, O. A. Johnson, C. Ng, C. Pardo-Araujo, M. Ronchi, D. Vohl, M. Xue, The SKA Pulsar Science Working Group

High Energy Astrophysical Phenomena

Pulsar Science with the SKA Observatory

Bhal Chandra Joshi, Aris Karastergiou, Marta Burgay et al. (+1 more)

The large instantaneous sensitivity, a wide frequency coverage and flexible observation modes with large number of beams in the sky are the main features of the SKA observatory's two telescopes, the SKA-Low and the SKA-Mid, which are located on two different continents. Owing to these capabilities, the SKAO telescopes are going to be a game-changer for radio astronomy in general and pulsar astronomy in particular. The eleven articles in this special issue on pulsar science with the SKA Observatory describe its impact on different areas of pulsar science. In this lead article, a brief description of the two telescopes highlighting the relevant features for pulsar science is presented followed by an overview of each accompanying article, exploring the inter-relationship between different pulsar science use cases.
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All authors Bhal Chandra Joshi, Aris Karastergiou, Marta Burgay, The SKA pulsar science working group

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Unraveling the anomaly in the production of $^{60}$Fe nucleus in massive stars

Samapti Lakshan, Le Tan Phuc, Deepak Pandit et al. (+6 more)

The production of $^{60}$Fe is crucial for nucleosynthesis in massive stars and supernovae. In this work, by using the microscopic EP+IPM (exact pairing plus the independent-particle model) for the nuclear level density (NLD) and extended EP+PDM (exact pairing plus phonon damping model) for the $\gamma$-ray strength function (gSF), we re-evaluate the substantial enhancement of $^{60}$Fe production recently reported in {\it A. Spyrou et al., Nat. Comm. 15, 9608 (2024)}, which was attributed to an unexpectedly large Maxwellian-averaged cross section (MACS). Our analysis demonstrates that this enhancement indeed originates from the choice of NLD, which, despite being constrained to reproduce the total NLD and gSF data, lacks a reliable spin dependence, a critical input for Hauser-Feshbach calculations of nuclear reaction rate. In contrast, our predictions yield a significantly lower MACS, calling the claimed enhancement into question. In particular, our approach highlights the microscopic nature of the low-energy enhancement of the gSF, the so-called upbend resonance, which arises from strong particle-particle ($pp$) and hole-hole ($hh$) excitations that emerge only at finite temperature, thereby further reinsisting on the invalidity of the Brink-Axel hypothesis in this low-energy region. Overall, our study reopens the question on the long-standing problem of $^{60}$Fe production in massive stars.
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All authors Samapti Lakshan, Le Tan Phuc, Deepak Pandit, Srijit Bhattacharya, Le Thi Quynh Huong, Nguyen Dinh Dang, Balaram Dey, Nguyen Ngoc Anh, Nguyen Quang Hung

High Energy Astrophysical Phenomena

Inferring the Intrinsic Energy Function of FRB 20220912A

Xiaohui Liu, Wei-Yang Wang, Weicong Jing et al. (+2 more)

The statistical analysis of fast radio burst (FRB) samples from repeaters may suffer from a band-limited selection effect, which can bias the observed distribution. We investigated the impact of this selection bias on the energy function through simulations and then applied our analysis to the particular case of FRB 20220912A. Our simulations show that, in the sample of bursts observed by the Five hundred meter Aperture Spherical Telescope (FAST), assuming a unimodal intrinsic energy distribution, the band selection effect alone is insufficient to produce a bimodal energy distribution; only the bimodal central frequency distribution can achieve this. The bursts' energy of FRB 20220912A that primarily fell within the observing band showed no significant correlation with the central frequency. In contrast, bursts with higher central frequency tend to exhibit narrower bandwidth and longer duration. The distribution of the intrinsic energy can be modeled as a log-normal distribution with a characteristic energy of $8.13 \times 10^{37}$ erg, and a power-law function with the index of $1.011 \pm 0.028$. In contrast to the initial energy function reported by \cite{2023ApJ...955..142Z}, the low-energy peak vanishes, and the high-energy decline becomes steeper, which implies the low-energy peak is an observational effect. The bimodality of the energy distribution seems to originate from the intrinsic radiation mechanism.
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All authors Xiaohui Liu, Wei-Yang Wang, Weicong Jing, Xuelei Chen, Jinlin Han

Earth and Planetary Astrophysics

Axisymmetric Modeling of DSHARP Dusty Disks: Asymmetric Structures and Inner-Disk Dispersal

Masataka Aizawa, Takayuki Muto and Munetake Momose

High-resolution observations of Class II protoplanetary disks frequently reveal annular structures that may indicate the presence of embedded planets. In this study, we model brightness profiles and geometries for 16 dusty disks in the DSHARP observations to identify asymmetric substructures, including possible planet-induced signatures. We find no compelling evidence for circumplanetary emission in these systems. We identify a possible one-armed spiral in Elias 27; while previous studies report an $m=2$ spiral, the morphology of the newly identified spiral agrees with a spiral for a possible protoplanet. Although non-detection of circumplanetary emission is consistent with low expected luminosities, the absence of additional dust spirals except for Elias 27 may constrain properties of potential embedded planets given their theoretical detectability. The analyses further suggest that spiral amplitudes and phases correlated with gap and ring locations in WaOph 6 and IM Lup, appearing as deflections of spirals in images. Five disks exhibit strong residual asymmetries attributable to the vertical extent of their dust layers. We find that the brightness temperature of inner disks ($1$-$5$ au) declines with stellar age on a $\sim 3$ Myr timescale, while the total flux shows no clear decreasing trend. This trend is consistent with the presence of pressure bumps that retain large dust grains at outer radii, while allowing the inner disks to disperse. The universality of disk dispersal timescale at millimeter wavelengths, observed in both the extended DSHARP disks and the compact disks from previous demographic surveys, may constrain timing of planet formation, including habitable planets.
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Instrumentation and Methods for Astrophysics

Graph Neural Networks for Interferometer Simulations

Sidharth Kannan, Pooyan Goodarzi, Evangelos E. Papalexakis et al. (+1 more)

In recent years, graph neural networks (GNNs) have shown tremendous promise in solving problems in high energy physics, materials science, and fluid dynamics. In this work, we introduce a new application for GNNs in the physical sciences: instrumentation design. As a case study, we apply GNNs to simulate models of the Laser Interferometer Gravitational-Wave Observatory (LIGO) and show that they are capable of accurately capturing the complex optical physics at play, while achieving runtimes 815 times faster than state of the art simulation packages. We discuss the unique challenges this problem provides for machine learning models. In addition, we provide a dataset of high-fidelity optical physics simulations for three interferometer topologies, which can be used as a benchmarking suite for future work in this direction.
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All authors Sidharth Kannan, Pooyan Goodarzi, Evangelos E. Papalexakis, Jonathan W. Richardson

Astrophysics of Galaxies

Gas Accretion from a Neighbouring Galaxy Fuels the Low-luminosity AGN in NGC 4278

Jin-Long Xu, Nai-Ping Yu, Ming Zhu et al. (+4 more)

How a seemingly `dead' host galaxy provides fuel for its active galactic nuclei (AGN) remains an unresolved problem. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we present a new high-sensitivity atomic-hydrogen (HI) observation toward the nearby elliptical galaxy NGC 4278 and its adjacent region. From the observation, we found that external gas accretion from a neighbouring galaxy fuels the low-luminosity AGN in NGC 4278 through tidal interactions. The accreted gas entering NGC 4278 exhibits a rotating gas disk. And the accreted galaxy has been gas-poor and has an HI to stellar mass ratio of about 0.02. Due to the process of gas accretion, it is likely that relativistic jets are generated in the AGN of NGC 4278. The emission of TeV gamma rays in NGC 4278 is likely to be associated with the newly accreted HI gas.
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All authors Jin-Long Xu, Nai-Ping Yu, Ming Zhu, Chuan-Peng Zhang, Xiao-Lan Liu, Mei Ai, Peng Jiang

Wednesday 17 December

Astrophysics of Galaxies

Astrometric and Spectroscopic Analysis of IC 2714: An Open Cluster Hosting a Lithium-Rich Giant

T. Flaulhabe, N. Holanda, G. Tautvaišienė et al. (+7 more)

Open clusters serve as laboratories to study and evaluate stellar evolution and Galactic chemical evolution models. Chemical peculiarities, such as lithium-rich giants, are rarely observed in these stellar systems. This work focuses on eight red giants (#005, #028, #034, #053, #087, #121, #126, and #190) previously reported as members of the Galactic cluster IC 2714. We conducted a detailed investigation using high-resolution spectroscopy, supplemented with data from the Gaia DR3 catalog. Besides deriving the cluster's fundamental parameters, we provide the most thorough chemical characterization of IC 2714 to date, reporting the abundance of 23 species, including light elements (Li, C, N, O), odd-Z elements (Na, Al), $\alpha$-elements (Si, Ca, Ti, Mg), iron-peak elements (Sc, Cr, Ni), $\textit{s}$-process-dominated elements (Y, Zr, Ba, La, Ce, Nd) and $\textit{r}$-process elements (Sm, Eu). We also present the carbon isotopic ratios $^{12}$C/$^{13}$C for the first time for seven stars. One particular star (#087) exhibits a high lithium abundance ($\log \varepsilon$(Li)$_{\rm NLTE}$ = $+$1.54 dex) and a slightly higher projected rotational velocity ($v \sin i$ = 6.7 km s$^{-1}$). Our results suggest that the analyzed stars are in the core-helium-burning phase of evolution, where the most lithium-rich giants are found. Combining astrometric probabilities and chemical abundances, we conclude that two giants (#028 and #034) might not be cluster members.
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All authors T. Flaulhabe, N. Holanda, G. Tautvaišienė, O. J. Katime Santrich, F. F. S. Maia, B. P. L. Ferreira, W. J. B. Corradi, C. B. Pereira, M. Carlos, S. Daflon

Solar and Stellar Astrophysics

Direct calculation of steady-state hydrodynamic solar wind solutions with newtonian viscosity

Roger B. Scott, Stephen J. Bradshaw, Mark G. Linton et al. (+2 more)

Steady-state solutions to the Navier-Stokes equations are known to admit solutions that are singular at the sonic point. Consequently, inviscid solar wind models require special treatment of the solution near the sonic points, and this has proven to be a significant impediment to efficient modeling of the solar wind. In this paper we revisit the governing hydrodynamic equations for the expanding solar wind, with the inclusion of the classical (Newtonian) viscous stress , and we show how this inclusion eliminates the singularities that emerge from the inviscid equations. This result has been previously reported and used to generate solar wind profiles from initial conditions in the asymptotic limit; however, those studies did not include realistic treatments of the inner corona, and generally rejected the prospect of extrapolating solutions outward from the Sun into the heliosphere. Here, we expand this method to include external heating and optically thin radiative losses and show that solutions can be computed from initial conditions near the solar surface, thereby capturing the entire range of scales from below the transition region to the outer heliosphere in a single solution. Our approach is to cast the steady-state Navier-Stokes equations as a system of five coupled, ordinary differential equations (ODEs), which we solve using conventional methods, without any special treatment of the governing equations in the vicinity of the sonic point. The representative solutions that we present here demonstrate the utility and efficiency of this extrapolation method, which is considerably more realistic than commonly used analytical or empirical models. This method provides a direct approach to generating accurate solar wind profiles subject to observationally motivated initial conditions near the solar surface, at a fraction of the computational cost of comparable relaxation-based models.
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All authors Roger B. Scott, Stephen J. Bradshaw, Mark G. Linton, Chris Lowder, Leonard Strachan

Astrophysics of Galaxies

LSTM-MDNz: Estimating Quasar Photometric Redshifts with an LSTM-Augmented Mixture Density Network

Jianzhen Chen, Zhijian Luo, Liping Fu et al. (+4 more)

Quasar photometric redshifts are essential for studying cosmology and large-scale structures. However, their complex spectral energy distributions cause significant redshift-color degeneracy, limiting the accuracy of traditional methods. To overcome this, we introduce LSTM-MDNz, a novel end-to-end deep learning model combining long short-term memory networks (LSTM) with mixture density networks (MDN). The model directly uses multi-band photometric fluxes and associated errors as wavelength-ordered sequential inputs, eliminating the need for manual feature engineering while enabling simultaneous point estimation and probability distribution function (PDF) prediction of quasar redshifts. We integrate data from four major sky surveys-SDSS, DESI-LS, WISE, and GALEX-to assemble a sample of over 550,000 spectroscopically confirmed quasars ($0 \leq z_{\mathrm{spec}} \leq 5$) across 14 ultraviolet to infrared bands for model training and testing. Experimental results show that using all 14 bands yields optimal performance, with a normalized median absolute deviation ($\sigma_{\mathrm{NMAD}}$) of 0.037 and an outlier rate ($f_{\mathrm{out}}$) of 3.5% on the test set. These values represent reductions of 29% and 56%, respectively, compared to the commonly adopted SDSS+WISE band set. Probability integral transform ($\mathrm{PIT}$) and continuous ranked probability score ($\mathrm{CRPS}$) analyses confirm that the predicted PDFs align closely with the true redshift distribution. Band-ablation experiments further highlight the essential role of ultraviolet and infrared data in alleviating color degeneracy and reducing systematic bias. This study demonstrates the effectiveness of multi-band fusion in improving quasar photo-z accuracy and offers a ready-to-use estimation framework for future surveys like LSST, CSST, and Euclid.
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All authors Jianzhen Chen, Zhijian Luo, Liping Fu, Zhu Chen, Hubing Xiao, Shaohua Zhang, Chenggang Shu

High Energy Astrophysical Phenomena

Exploring the Galactic Plane: A Comparative Study of Fermi-LAT Sources and HESS's Non-Detection at TeV Energies

François Brun, Baptiste Le Nagat-Neher, Marianne Lemoine-Goumard et al. (+2 more)

The HESS Galactic Plane Survey (HGPS), published in 2018, presented a decade of very-high-energy (VHE) gamma-ray observations along the Galactic plane. This study was accompanied by the release of several maps in FITS format, offering a detailed view of the region. The flux upper-limits from these HGPS maps can be compared to the high-energy (HE) spectra of sources catalogued by the Fermi-LAT in the same region. For some sources, extrapolating the Fermi-LAT flux into the VHE range predicts flux values exceeding the upper-limits set by HESS. In this work, we present the results of this comparison and highlight the sources that are of particular interest for future VHE observations.
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All authors François Brun, Baptiste Le Nagat-Neher, Marianne Lemoine-Goumard, Marie-Hélène Grondin, Paul Fauverge

High Energy Astrophysical Phenomena

HEGS : Revisiting a decade of H.E.S.S. extragalactic observations

François Brun, David Sanchez, Andrew M. Taylor et al. (+2 more)

During its first phase, from 2004 up to the end of 2012, the H.E.S.S. (High Energy Stereoscopic System) experiment observed the extragalactic skies for more than 2700 hours. These data have been re-analysed in a single consistent framework, leading to the derivation of a catalog of 23 sources. In total, about 5.7% of the sky was observed, allowing for several additional studies to be conducted: source variability, extragalactic gamma-ray background light, and comparison with the Fermi-LAT catalogues. In this contribution, we discuss these results and present the high-level data (catalogs, maps) released to the astrophysical community.
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All authors François Brun, David Sanchez, Andrew M. Taylor, Matteo Cerruti, Jean-Philippe Lenain

Solar and Stellar Astrophysics

IPA. Accretion rate of a low-mass Class 0 protostar, measured via mid-infrared fluorescent OH emission

Dan M. Watson, Mayank Narang, Caeley V. Pittman et al. (+41 more)

The earliest stages of star formation are highlighted by complex interactions between accretion, outflow, and radiative processes, which shape the chemical and physical environment of the emerging protostar. James Webb Space Telescope observations of the low-mass, low-luminosity Class 0 protostar IRAS 16253-2429 reveal a central compact source. This object exhibits a rich mid-infrared emission spectrum of OH pure rotational lines and $\rm CO_2$ ro-vibrational lines. Unusually for a young stellar object, it has no mid-infrared line emission from $\rm H_2O$ to match the other molecules. We demonstrate that the emitting OH molecules arise from UV photodissociation of $\rm H_2O$ in its second absorption band at $\lambda = 114-145$ nm, and that the OH emission is a fluorescent cascade starting with highest-excitation rotational states. This situation offers the opportunity of using the infrared OH spectrum to measure the UV flux from the central protostar. Thereby we determine the disk-star accretion rate to be $3 \times 10^{-10} \ M_\sun \ {\rm year^{-1}}$, and demonstrate that the system luminosity arises mostly from the protostar's photosphere rather than from accretion luminosity. The result is in accord with the measured outflow rate of IRAS 16253-2429 and lies within the outflow/accretion-flow rate trend often inferred for protostars; and with episodic accretion as the dominant mechanism by which this protostar has grown.
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All authors Dan M. Watson, Mayank Narang, Caeley V. Pittman, Himanshu Tyagi, Robert Gutermuth, Adam E. Rubinstein, Neal J. Evans II, Lee W. Hartmann, S. Thomas Megeath, P. Manoj, Catherine C. Espaillat, Nuria Calvet, Alessio Caratti o Garatti, Ewine F. van Dishoeck, Tyler L. Bourke, Joel D. Green, Carey M. Lisse, Pamela Klaassen, Leslie W. Looney, Pooneh Nazari, David A. Neufeld, John J. Tobin, Scott J. Wolk, Guillem Anglada, Prabhani Atnagulov, Henrik Beuther, Nashanty G. C. Brunken, Samuel Federman, Elise Furlan, Nolan Habel, Nicole Karnath, Hendrik Linz, James Muzerolle Page, Mayra Osorio, Riwaj Pokhrel, Rohan Rahatgaonkar, Will R. M. Rocha, Patrick D. Sheehan, Katerina Slavicinska, Thomas Stanke, Amelia M. Stutz, Lukasz Tychoniec, Yao-Lun Yang, William J. Fischer

Astrophysics of Galaxies

ASKAP discovery of a 30 kpc bipolar outflow from the edge-on disk of the nearby spiral galaxy ESO 130-G012

Baerbel S. Koribalski, Roland M. Crocker, Ildar Khabibullin et al. (+6 more)

We present the discovery of a large-scale, limb-brightened outflow, extending at least 30 kpc above and below the star-forming disk of the edge-on galaxy ESO 130-G012 (D = 16.9 Mpc). Partially obscured by Galactic foreground stars and dust, this optically unremarkable, low-mass galaxy reveals one of the largest known hourglass-shaped outflows from the full extent of its bright stellar disk. The outflow was discovered in 944 MHz radio continuum images from the Australian Square Kilometre Array Pathfinder (ASKAP) obtained as part of the "Evolutionary Map of the Universe" (EMU) project. Its height is at least 3x that of the stellar disk diameter (~10 kpc), while its shape and size most resemble the large biconical, edge-brightened FUV and X-ray outflows in the nearby starburst galaxy NGC 3079. The large-scale, hourglass-shaped outflow of ESO 130-G012 appears to be hollow and originates from the star-forming disk, expanding into the halo with speeds close to the escape velocity before likely returning to the disk. Given ESO 130-G012's modest star formation rate, the height of the outflow is surprising and unusual, likely made possible by the galaxy's relatively low gravitational potential. Follow-up observations are expected to detect hot gas inside the bipolar outflow cones and magnetic fields along the X-shaped outflow wings. Neutral gas may also be lifted above the inner disk by the outflow.
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All authors Baerbel S. Koribalski, Roland M. Crocker, Ildar Khabibullin, Anna Ivleva, Klaus Dolag, Umberto Maio, Ralf-Juergen Dettmar, Jacco Th. van Loon, Stanislav Shabala

Astrophysics of Galaxies

MAGellanic Outflow and chemistry Survey (MAGOS): Hot cores in the LMC

Takashi Shimonishi, Kei E. I. Tanaka, Yichen Zhang et al. (+3 more)

The Large Magellanic Cloud (LMC) provides a key laboratory for exploring the diversity of star formation and interstellar chemistry under subsolar metallicity conditions. We present the results of a hot core survey toward 30 massive protostellar objects in the LMC using the Atacama Large Millimeter/submillimeter Array (ALMA) at 350 GHz. Continuum imaging reveals 36 compact sources in total, among which line analyses identify 9 hot cores and 1 hot-core candidate, including two newly identified sources. We detect CO, HCO+, H13CO+, HC15N, HC3N, SiO, SO, SO+, NS, SO2, 34SO2, 33SO2, CH3OH, 13CH3OH, HCOOH, HCOOCH3, CH3OCH3, C2H5OH, H2CCO (tentative), and hydrogen recombination lines from hot cores. CH3OCH3, a complex organic molecule larger than CH3OH, is detected for the first time in a hot core outside the LMC bar region. All hot cores show stronger emission in the high-excitation SO line compared to non-hot-core sources, suggesting that its strong detection will be useful for identifying hot-core candidates in the LMC. Chemical analysis reveals a spread of more than two orders of magnitude in CH3OH abundances, with some sources deficient in COMs. In contrast, SO2 is detected in all hot cores, and its abundance shows a good correlation with rotational temperature. The hot cores without CH3OH detections are all located outside the LMC bar region and are characterized by either high luminosity or active star formation in their surroundings. A combination of locally low metallicity, active star formation in the vicinity, and high protostellar luminosity may jointly trigger the COM-poor hot core chemistry observed in the LMC.
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All authors Takashi Shimonishi, Kei E. I. Tanaka, Yichen Zhang, Kenji Furuya, Yu Cheng, Asako Sato

Earth and Planetary Astrophysics

The Sesquinary Catastrophe on Deimos can reconcile its excited past with its dynamically cool present

Kaustub P. Anand, Matija Ćuk and David A. Minton

The origins of the Martian moons Phobos and Deimos are highly debated, and hypotheses include formation from an impact-generated circum-Martian disk or from capture of asteroids. With the impact scenario, Deimos (or its precursors) were formed or were pushed out beyond the synchronous orbit of Mars. Moons interior to the synchronous orbit, including Phobos (or its precursors), would tidally evolve and resonances between these moons could potentially excite Deimos' orbit. This contradicts Deimos' present-day orbit of low eccentricity ($0.00027$) and moderate inclination ($1.8^\circ$ to the Laplace plane). Tidal dissipation within Deimos is too inefficient for eccentricity damping, and without alternative mechanisms, Deimos' present-day orbit places strong constraints on the evolution of any inner moons. We propose that a runaway collisional cascade called the "sesquinary catastrophe” acts as a natural barrier that prevents Deimos from having a more excited orbit. Using N-body simulations with collisional fragmentation, we show that if Deimos was more excited, it would undergo a sesquinary catastrophe and break apart into a Roche-exterior debris disk. Using a measure of sesquinary orbital excitation called $q$, our simulations and previous works suggest that breakup occurs for $q \gtrsim 8$ on timescales of $\sim 10^{3-4}$ years. If Deimos was destroyed in a sesquinary catastrophe and re-accreted from a (likely collisionally) damped debris disk, it should be a porous sand-pile moon, consistent with its smooth surface. The sesquinary catastrophe can be applied to other Deimos-like planetary moons at $q \gtrsim 8$.
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