High Energy Astrophysical Phenomena
Colour evolution in the radio afterglow of GRB 241025A
S. Giarratana, O. S. Salafia, L. Nava et al. (+10 more)
We present the observing campaign of the afterglow of GRB241025A, a gamma-ray burst (GRB) whose
prompt emission has been simultaneously detected by Swift, Einstein Probe,
Fermi/GBM, SVOM, Konus-Wind and VZLUSAT-2 3U CubeSat. Our multi-wavelength campaign comprises
radio, near-infrared, Optical and X-ray observations. The afterglow was clearly detected in all bands. We performed a semi-empirical fit of the data, showing that the afterglow behaviour can be reasonably reproduced by a single component, i.e. an ultra-relativistic shock. However, the results from the semi-empirical fit are inconsistent with the predicted
evolution from the standard afterglow model in the slow cooling regime. Specifically, we found that at early times the synchrotron self-absorption frequency $\nu_a$ should be at higher frequencies with respect to the ones sampled by our campaign, in order to explain the observed colour
evolution in
radio, namely the spectral
evolution in time. To reconcile the prediction from the standard model with the observed data set, we fit the observations with a semi-analytical model, including a multiplicative factor $\tau_{enh}$ to the optical depth which, in turn, artificially increases $\nu_a$. We found that the
radio colour
evolution, together with the near-infrared, optical and X-ray emission, can be described reasonably well by a forward shock from a structured jet, provided that the optical depth in the shocked material is enhanced by a factor $\tau_{enh}=500$. We suggest that such enhancement in the optical depth can result from a population of cold electrons in the downstream material, i.e. electrons that were not accelerated by
Fermi I process at the shock front, in agreement with the theoretical expectations previously reported in the literature. Overall, our work underscores the importance of systematic, multi-frequency, multi-epoch
radio follow-ups of these extreme events.
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All authors S. Giarratana, O. S. Salafia, L. Nava, G. Ghirlanda, M. Giroletti, S. Antier, M. Pillas, T. Hussenot-Desenonges, A. Iskandar, M. Tanasan, G. Oganesyan, N. Di Lalla, N. Omodei
Instrumentation and Methods for Astrophysics
$J$ and $H$ band sky brightness measurements from polar day to polar night at Dome A, Antarctica
Jinji Li, Bin Ma, Haonan Yang et al. (+9 more)
The near-infrared (NIR) sky brightness is a fundamental parameter for evaluating the performance of ground-based infrared observatories. Dome~A on the Antarctic plateau offers exceptional atmospheric conditions, yet its NIR sky background has not been continuously monitored. We present the first continuous $J/H$-band measurements of the sky background at Dome~A from polar day to polar night, and characterize their median levels and temporal variability. The Antarctic Infrared Binocular
Telescope (AIRBT), operating in the $J$ and $H$ bands, obtained continuous fixed-pointing observations from February to May 2024, which were used to measure the NIR sky background. The median sky brightness is $5.2/2.9$ and $15.3/13.4~\mathrm{mag~arcsec^{-2}}$ in $J/H$ bands during daytime and nighttime, respectively. The twilight–nighttime boundaries occur at
solar elevations of $-9.3^\circ$ in $J$ and $-7.4^\circ$ in $H$. At the same
solar elevation, the NIR sky background during the polar night is darker by about $0.1$ and $0.4~\mathrm{mag~arcsec^{-2}}$ in the $J$ and $H$ bands compared with the period of regular day–night alternation. During the polar-night period, the nighttime sky brightness in the $H$ band shows a more evident association with the sunspot number, while the corresponding trend in the $J$ band is weaker. These results reveal systematic differences in sky background between polar and non-polar environments and between polar night and regular day–night cycles. The measured sky brightness may be elevated, as the observations were conducted near
solar maximum, highlighting the importance of long-term monitoring across the
solar cycle.
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All authors Jinji Li, Bin Ma, Haonan Yang, Pu Lin, Zhongnan Dong, Michael C. B. Ashley, Lu Feng, Yi Hu, Zhaohui Shang, Yun Shi, Shijie Sun, Xu Yang
Astrophysics of Galaxies
Distance Determination of Southern Galactic Plane Supernova Remnants with the Mopra CO Survey and DECaPS 3D Dust Map
Fupeng Liu, He Zhao, Biwei Jiang et al. (+2 more)
Accurate distance measurements to
supernova remnants (SNRs) are crucial for understanding their physical properties, evolutionary processes, and role in the
Galactic interstellar medium (ISM) cycle. In this study, we apply for the first time to the southern
Galactic plane a distance determination method that utilizes CO emission data from the Mopra survey to identify molecular clouds (MCs) interacting with SNRs. By combining this with extinction-distance profiles from the DECaPS three-dimensional (3D) extinction map, we directly measure the distances to the associated MCs, thereby obtaining precise distances to the remnants. To overcome the extinction-missing bias in extremely dense regions where the 3D map suffers from a deficit of background
stars, we supplement our analysis with two-dimensional (2D) extinction maps as cross-validation. Applying this method, we have derived precise distances for nine SNRs: G290.1-0.8 (7.32+0.60/-0.47 kpc), G292.2-0.5 (10.85+0.43/-0.68 kpc), G296.1-0.5 (4.59+0.18/-0.19 kpc), G296.8-0.3 (8.74+0.40/-0.29 kpc), G298.6-0.0 (6.50 +/- 0.21 kpc), G312.4-0.4 (3.60+0.19/-0.23 kpc), G332.4-0.4 (2.66+0.23/-0.15 kpc), G335.2+0.1 (2.76+0.37/-0.31 kpc), and G353.6-0.7 (1.81+0.18/-0.14 kpc). Additionally, we established a robust lower distance limit of 1.34 kpc for G351.7+0.8.
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All authors Fupeng Liu, He Zhao, Biwei Jiang, Jun Li, Zhe Zhang
Cosmology and Nongalactic Astrophysics
meer21cm: an Analysis Pipeline and Comprehensive Toolkit for HI Intensity Mapping
Zhaoting Chen, Steven Cunnington, Daniel Tassie et al. (+23 more)
We present meer21cm, a comprehensive python package for cosmological data analysis of single-dish HI intensity mapping surveys. This package is simple to use, with a modularised code structure designed for interactive usage. meer21cm is designed for data analysis, with particular focus on the UHF-band observation of MeerKAT Large Area Synoptic Survey (MeerKLASS). We explicitly impose meer21cm to be survey-oriented, ensuring consistent modelling of observational effects in the clustering power spectrum with the survey specifications and data analysis choices. meer21cm covers a large range of data analysis procedures post calibration, including data read-in, foreground cleaning, power spectrum estimation, mock simulation, transfer function corrections and parameter inference. It handles both meer21cm intensity maps and overlapping
galaxy catalogues, allowing for multi-tracer and cross-correlation analysis between MeerKLASS and optical
galaxy surveys. Tested with a simulated survey of ten $750\,$deg$^2$ sky patches in the
redshift sub-band $0.6\,{<}\,z\,{<}\,0.8$, the meer21cm pipeline achieves per-cent accuracy in the power spectrum estimation for $k \in [0.02, 0.2]\,{h{\rm Mpc}^{-1}}$, with deviations $\lesssim 0.5\sigma$ between the mock and the model power spectra, where $\sigma$ is the signal variance. The meer21cm package is publicly available and easy to install, with a comprehensive documentation website at https://meer21cm.readthedocs.io
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All authors Zhaoting Chen, Steven Cunnington, Daniel Tassie, Alkistis Pourtsidou, Laura Wolz, Gabriele Autieri, Matilde Barberi-Squarotti, José Luis Bernal, Phil Bull, Stefano Camera, Isabella P. Carucci, Brandon Engelbrecht, José Fonseca, Karin Fornazier, Keith Grainge, Jiakang Han, Wenkai Hu, Melis O. Irfan, Piyanat Kittiwisit, Yichao Li, Sefa Pamuk, Mario G. Santos, Marta Spinelli, Jingying Wang, Amadeus Witzemann, Boyan Zhao
Earth and Planetary Astrophysics
TESS's First Bound Microlensing Planet: A Binary Microlensing Event Revealing a Planetary Companion toward the Galactic Plane
Mallory Harris, Diana Dragomir, Etienne Bachelet et al. (+2 more)
We report the discovery of
Gaia23bra b, the first gravitationally bound microlensing
planet detected by the Transiting
Exoplanet Survey Satellite (TESS). Initially flagged as a single-lens event by the
Gaia Science Alerts system,
Gaia23bra was serendipitously observed by TESS over two consecutive sectors. During those TESS sectors, the light curve of the event displayed caustic-crossing features characteristic of a binary-lens event. Joint modeling of
Gaia and TESS photometry with pyLIMA, supplemented by
stellar parameter inference using pyLIMASS, suggests a K
dwarf ($M_L = 0.79^{+0.19}_{-0.17}\,M_\odot$) hosting a Jovian
planet with $M_P = 1.63_{-0.38}^{+0.42}\,M_{\rm Jup}$ at a projected separation of $a_{\perp,\min} \approx 4.8\,\mathrm{AU}$. This result underscores the synergy between high-cadence photometry and long-baseline monitoring for robust microlensing characterization. Its location along the
Galactic Plane highlights TESS's unexpected capacity for microlensing science through its all-sky coverage and its potential to detect
planets in regions beyond the
Galactic Bulge.
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All authors Mallory Harris, Diana Dragomir, Etienne Bachelet, Michael Fausnaugh, Samson Johnson
Solar and Stellar Astrophysics
Revisiting atmospheric Roche lobe overflow in symbiotic binaries
Tan Liu, Natalia Ivanova, Philipp Podsiadlowski et al. (+5 more)
Classical binary
evolution models predict dynamically unstable mass transfer in symbiotic
stars with high mass ratios, leading to a common envelope. However, many observed S-type symbiotic systems show long-lived interaction, suggesting that an additional stabilizing mechanism may be at work. We investigate whether atmospheric Roche-lobe overflow can prolong the mass-transfer phase and help reconcile theory with observations. We implement the Rapid Unified Mass Transfer framework in MESA and compute a grid of white-
dwarf–
giant binaries covering a wide range of donor masses, mass ratios, and orbital periods. We then compare the resulting lifetimes and evolutionary tracks with well-constrained
Galactic S-type symbiotic systems. For convective
giant donors, our models recover stable mass transfer up to $q \simeq 1.5$, while atmospheric overflow strongly extends the symbiotic phase. RGB and early-AGB systems with $q \lesssim 1.5$ can remain interacting for up to $10^6$ yr at $\dot{M} \gtrsim 10^{-9},M_{\odot},{\rm yr}^{-1}$, much longer than the commonly assumed $\sim 10^3$ yr pre-common-envelope lifetime. In these systems, the orbit shrinks mildly and may re-expand after mass-ratio reversal. Systems with higher mass ratios still evolve toward a common envelope, but even for $q \simeq 2$–$4$ the symbiotic phase can last $10^4$–$10^5$ yr. The synthetic distribution in the orbital-period–mass-ratio plane and individual evolutionary tracks are broadly consistent with observed S-type symbiotic binaries, including recurrent novae. The RUMT framework, which incorporates atmospheric RLOF, provides an explanation for the long-term stability of many symbiotic binaries and may account for their high observed occurrence rate.
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All authors Tan Liu, Natalia Ivanova, Philipp Podsiadlowski, Joanna Mikołajewska, Zheng-Wei Liu, Xuefei Chen, Xiangcun Meng, Zhanwen Han
Astrophysics of Galaxies
Post-starburst Galaxies with Active Galactic Nucleus: Properties and Evolutionary Sequences
Junjie Huang, Yanmei Chen, Yong Shi et al. (+7 more)
Post-starburst (PSB)
galaxies, identified by strong Balmer absorption and weak nebular emission, provide a key laboratory for studying rapid quenching. Using the final data release of the SDSS-IV MaNGA survey, we follow the traditional PSB selection criteria of Chen et al. (2019) and develop a new method to identify regions that simultaneously exhibit PSB features and
nuclear activities (AGN-PSBs). Our final sample comprises 48 AGN-PSBs, 92 central PSBs (CPSBs), 89 ring-like PSBs (RPSBs), and 828 irregular PSBs (IPSBs). We find the global and spatially resolved properties of CPSBs and RPSBs are consistent with the results of Chen et al. (2019). In this work, we focus on the properties of AGN-PSBs, comparing them with CPSBs, RPSBs, and control
galaxies. Similar to CPSBs and RPSBs, AGN-PSBs show positive $\mathrm{D}_{n}4000$ gradients relative to negative $\mathrm{D}_{n}4000$ gradients of their controls, which indicates younger
stellar populations in the central region than that in the outskirt. Among the three sub-types, high-mass CPSBs (H-CPSBs, with $\log(M_{*}/M_{\odot})>9.5$) display the highest incidence of merger remnants and gas–
star kinematic misalignment, consistent with a merger/interaction-dominated origin. AGN-PSBs and RPSBs, however, show lower and comparable fractions of merger remnants and gas–
star kinematic misalignment, favoring less violent external mechanisms. Based on radial profiles of mass-weighted age and $V_{\rm star}/\sigma_{\rm star}$, we suggest that RPSBs can evolve into AGN-PSBs, whereas H-CPSBs likely follow a distinct evolutionary pathway. The existence of RPSBs and IPSBs also indicates that AGN feedback is not a necessary condition for the formation of PSB.
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All authors Junjie Huang, Yanmei Chen, Yong Shi, Cheng Li, Zhuo Cheng, Ho-Hin Leung, Vivienne Wild, Qiusheng Gu, Qihang Cheng, Ying Yu
High Energy Astrophysical Phenomena
Polarization Architecture of Steady GRMHD Jets from the Horizon to Infinity
Zhenyu Zhang, Yehui Hou, Yu Song et al. (+2 more)
We develop a semi-analytic framework for stationary, axisymmetric GRMHD jets that efficiently generates resolved polarized images from the near-horizon region out to $\sim 10^5\,r_g$ across a broad parameter space, enabling rapid exploration of how
gravity and magnetohydrodynamic flows imprint scale-dependent signatures on jet morphology and polarization. We identify a new scale-dependent separation in polarimetric diagnostics. Outside the
photon ring,
plasma loading strongly modifies the polarization-angle profile of the integrated jet-layer emission through inertia-driven winding of the
magnetic field. At large image-plane radii, the polarization angle follows a power-law in radius, with an index determined by the jet collimation profile. Near the horizon, in contrast, jets converge to a universal polarization pattern controlled solely by black hole
spin. This convergence is hierarchical: differences in velocity and
magnetic-field structure are erased first, whereas collimation-dependent differences persist to smaller radii, thereby allowing these effects to be disentangled. These results establish a largely achromatic polarimetric diagnostic that connects GRMHD jet dynamics to resolved image structure, with direct implications for high-resolution polarimetry and for constraining black hole
spin and jet formation.
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All authors Zhenyu Zhang, Yehui Hou, Yu Song, Yosuke Mizuno, Bin Chen
Cosmology and Nongalactic Astrophysics
Gravitational Waves from Primordial Black Holes: Connecting Low-Frequency Scalar-Induced Signatures to High-Frequency Binary Mergers
Ashu Kushwaha
Formation of
primordial black holes (PBHs) requires a significant enhancement of
curvature perturbations. This enhancement generates a twofold gravitational wave (GW) signature: a low-frequency
stochastic background of scalar-induced GWs (SIGWs) and a distinct high-frequency signal from subsequent PBH binary mergers. Assuming a monochromatic PBH mass function, we use PBH abundance constraints on the
primordial curvature power spectrum to evaluate the
stochastic SIGW background. We also compute the
stochastic GW background from mergers of the corresponding PBH binaries, incorporating merger-rate suppression effects to obtain realistic estimates. Furthermore, we derive a model-independent correspondence between the characteristic frequencies of these two signals. This unified framework links these otherwise distinct GW channels, enabling the same
primordial fluctuations to be probed across widely separated frequency bands.
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Cosmology and Nongalactic Astrophysics
Lattice study of primordial black hole formation in bumpy axion inflation
Masahiro Kawasaki, Kai Murai and Shunsuke Tsuchida
We study
primordial black hole (PBH) formation in
axion $U(1)$ inflation using
lattice simulations. In
axion $U(1)$ inflation with a bumpy potential, the
curvature perturbations can be enhanced in a narrow range of wavenumbers, potentially leading to PBH formation. After confirming that our
lattice simulations reproduced the known
curvature power spectra for chaotic inflation and simple
axion $U(1)$ inflation, we calculate the
curvature power spectrum in the bumpy
axion inflation model in the strong backreaction regime. We find that large
curvature perturbations are generated, which lead to PBH production with an abundance sufficient to account for dark matter.
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Earth and Planetary Astrophysics
The influence of lunar tidal potential on clock frequencies at different positions on Earth
Hongbin Zhang, Yanyue Gao and Baocheng Zhang
With the advancements in clock timing technology, increasingly smaller time differences can be distinguished. Therefore, it is critical to investigate the fractional frequency shift of clocks at different locations on Earth. In this paper, we study it systematically under the influence of a subtle lunar
tidal potential based on a new method. Our calculations in the geocentric
Fermi frame show that when two clocks are located at the same latitude, the longitude difference changes the fractional frequency shift between them. A similar phenomenon occurs when there is a difference in latitude between two clocks on the ground at the same longitude. Interestingly, when the Moon's longitude changes, the phase and amplitude of the lunar
tidal fractional frequency shift between two clocks with the same longitude difference will change, while the change in the Moon's latitude only affects the amplitude of the fractional frequency shift of these two clocks. Our results provide useful information for the calibration and synchronization of clocks on Earth.
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Solar and Stellar Astrophysics
The Sun's chemical peculiarity: disentangling Galactic chemical evolution and planetary engulfment in solar twins
Mia Babatsikos, Fan Liu, Amanda Karakas et al. (+5 more)
Recent observational studies have suggested that the Sun may be chemically peculiar relative to the majority of
solar twins. Here, we re-analyse high-resolution, high signal-to-noise spectra of 79 nearby
solar twins using a differential spectroscopic approach and
Bayesian framework to test whether the Sun's chemical peculiarity arises from
Galactic chemical
evolution (GCE) or planetary ingestion. Using the spectroscopic tool Korg, we obtain highly precise, validated atmospheric parameters and abundances for 18 elements, with an average abundance precision of 0.015dex (3.5%). Employing an independent
Bayesian indicator, we disentangle GCE and planetary engulfment signatures from other processes influencing
stellar composition, including intrinsic abundance scatter. Our results indicate that the chemical peculiarity of the Sun relative to the average
solar twin is largely driven by GCE effects, with 62.3$\pm$5.8% of our sample exhibiting abundance patterns well-described by GCE trends. We further identify 2–6
solar twin candidates exhibiting chemical signatures consistent with planetary engulfment that warrant further investigation. These findings reinforce the importance of accounting for GCE effects when interpreting
solar twin abundance patterns, and suggest that the Sun may not be chemically peculiar relative to the majority of
solar twins.
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All authors Mia Babatsikos, Fan Liu, Amanda Karakas, Ilya Mandel, Lachlan Passenger, Megan Bedell, Sharon Wang, Zimo Cheng
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Gravitational Waves from Multiple First-Order Phase Transitions in a Scenario with Early Matter Domination
Rouzbeh Allahverdi and Fazlollah Hajkarim
Non-standard cosmological histories with epochs of early matter domination (EMD) arise in various top-down models of the early universe. Typically, in the latter stage of EMD, temperature decreases more slowly than in a radiation dominated universe because of
entropy generation from decay of the species that drives EMD. A time-dependent decay rate can significantly modify this picture and even lead to a period with increasing temperature. We study non-monotonic temperature
evolution in a well-motivated scenario of EMD with a time-dependent decay rate that can give rise to multiple first-order phase transitions in both cooling and heating phases. The spectra of the ensuing gravitational waves (GW) exhibit characteristic features such as multiple peaks and a distinct behavior at high frequencies. These features allow us to determine the phase transition temperature as well as the reheating temperature at the end of the EMD. The future GW detectors can therefore provide a probe for the new physics and a window to the early thermal history.
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Instrumentation and Methods for Astrophysics
Periodic Radio Technosignature Search toward 3I/ATLAS with FAST
Jian-Kang Li, Zhen-Zhao Tao, Tong-Jie Zhang et al. (+1 more)
3I/ATLAS, the third confirmed interstellar object discovered in the
Solar System, provides a unique opportunity for targeted technosignature searches. We report a periodic
radio technosignature search toward 3I/ATLAS using the Five-hundred-meter Aperture Spherical
Telescope (FAST) L-band multibeam receiver. To search for periodically modulated signals and distinguish center-beam-dominated candidates from multibeam
radio-frequency interference, we apply canonical polyadic decomposition (CPD) to the multibeam dynamic spectra. CPD factorizes the multibeam data tensor into a set of separable components, with associated time, frequency, and beam signatures. Candidate components are then selected through periodogram and autocorrelation diagnostics. We find no credible artificial periodic
radio technosignature above 0.146 W is detected from the direction of 3I/ATLAS. This search expands the range of signal types explored for this target by including periodic modulated signal, and illustrates that CPD is a promising framework for multibeam periodic technosignature searches.
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All authors Jian-Kang Li, Zhen-Zhao Tao, Tong-Jie Zhang, Men-Quan Liu
Instrumentation and Methods for Astrophysics
Development of a Retrieval-Augmented Generation Virtual Assistant for Enhanced Information Discovery at Rubin Observatory
Leanne P. Guy, Connor Yablonski, Aaron M. Meisner et al. (+5 more)
The NSF-DOE Vera C. Rubin Observatory will generate petabytes of data through the Legacy Survey of Space and Time (LSST) over the next decade, enabling discoveries across a broad range of astrophysical fields. Alongside these data products, Rubin maintains a large but heterogeneous collection of supporting documentation, including operational guides, technical notes, and scientific papers. Because this material is distributed across multiple platforms and formats, staff and scientists often struggle to efficiently locate accurate, up-to-date information. Many resources also reside on internal systems, limiting the ability of general-purpose
language models to provide reliable answers to Rubin-specific questions. To address these challenges, we explore the use of
Retrieval Augmented Generation (RAG) to improve information discovery. We present a prototype RAG-based virtual assistant that delivers context-aware, factual, conversational access to Rubin's vast and heterogenous documentation ecosystem. The system integrates material from multiple sources and enables semantic search through a conversational interface, using Weaviate for
embeddings, LangChain for query orchestration, and an OpenAI GPT model as the LLM backend. By grounding responses in domain-specific knowledge, the assistant reduces
hallucinations, improves accuracy, and demonstrates the potential of RAG to enhance access to distributed knowledge, streamline workflows, and support effective use of LSST data products.
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All authors Leanne P. Guy, Connor Yablonski, Aaron M. Meisner, Guillem Megias Homar, Merlin Fisher-Levine, Eman E. Ali, Tiger J. Hu, Christopher W. Stubbs
Solar and Stellar Astrophysics
Numerical Investigation of Efficient Electron Acceleration at an Unsteady Solar Flare Loop-Top
Yoshiaki Sato, Takafumi Kaneko, Noriyuki Narukage et al. (+1 more)
Using magnetohydrodynamic (MHD) fields and guiding-center test-particle calculations, this study investigates how time-dependent loop-top dynamics modulate the adiabatic energization of electrons in a
solar flare. Our results indicate that a time-varying loop-top structure enhances acceleration efficiency compared to a quasi-steady one. In the quasi-steady velocity field, the net acceleration is suppressed due to the decelerating effect of betatron cooling. Conversely, in the unsteady velocity field, the betatron mechanism readily accelerates electrons within the compressed
magnetic field at the edge of the loop-top. These findings suggest that the acceleration of electrons at the loop-top is driven not only by the static shape of the
magnetic structure but also by dynamic events such as plasmoid collisions. While previous studies have primarily focused on acceleration processes within the reconnection
outflow, such as at termination shocks or within plasmoids, our research highlights the importance of the acceleration and deceleration processes at the exit point where electrons escape from the loop-top.
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All authors Yoshiaki Sato, Takafumi Kaneko, Noriyuki Narukage, Shinsuke Takasao
Instrumentation and Methods for Astrophysics
Architecture and Validation of the CRS F-Engine for the CHORD Radio Telescope
Ian Hendricksen, Jean-François Cliche, Matt Dobbs et al. (+1 more)
We introduce the design of the t0.technology Control and Readout System (CRS) F-Engine that will be used for the Canadian Hydrogen Observatory and
Radio transient Detector (CHORD), a new
radio interferometer currently being commissioned at the Dominion
Radio Astrophysical Observatory (DRAO) in Canada. The CRS F-Engine will directly digitize and channelize 1024 individual RF signals from the 512 dual-polarized dishes of the core array using an array of 128 CRS boards, a multi-purpose microwave readout platform using an AMD Zynq Ultrascale+ RF-System-on-Chip (RFSoC) architecture. The CRS supports the required analog and digital signal processing and is appropriately scalable, with rack-mountable crates each supporting up to 16 CRS boards, equipped with a backplane for distribution of power, common clock and time synchronization signals, and a full-mesh network for intra-crate data transmission. Implemented on the CRS boards is the chFPGA firmware which supports the digitization of 8 analog signals at 3.2 GSPS and channelizes them with a CASPER-based PFB/FFT into 8,192 frequency bins with ~195 kHz of resolution, which are then re-quantized into (4 + 4i) bits for data offload to an external X-Engine. chFPGA supports multiple post-channelization signal processing options through separate bitstream files for different applications, such as a 100 GbE packet assembler-transmitter for CHORD to feed channelized data to its external GPU-based X-Engine, as well as FPGA-based N^2 correlators, including a single-board (N = 8) correlator (the “Pocket Correlator"), and a multi-board corner-turn engine coupled with a half-CRS crate (N = 64) correlator. We demonstrate the performance of chFPGA by injecting a wideband Gaussian noise source into a CRS board running the Pocket Correlator firmware, and find that recovered digitized timestream and channelized data are in excellent agreement with expectations.
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All authors Ian Hendricksen, Jean-François Cliche, Matt Dobbs, Joshua Montgomery
High Energy Astrophysical Phenomena
X-ray Fourier lag-frequency spectra modulated by stochastic turbulent acceleration in the jets of high-frequency-peaked BL Lac
Guang-Cheng Xiao, Wen Hu, Da-Guo Jiang et al. (+4 more)
X-ray interband time lags are key diagnostics of jet physics and are frequently detected in high-frequency peaked BL Lac (HBL) objects at different epochs with various X-ray
telescopes. In this work, we theoretically investigate
Fourier lag-frequency spectra using a generic one-zone leptonic model incorporating the
stochastic turbulent acceleration (STA), which plays a crucial role in shaping the emitted
photon spectra. We demonstrate that the competition between STA, radiative cooling, and escape processes not only gives rise to two well-defined time-lag regimes: hard/positive and soft/negative lags, but also reveals the existence of a transition between the two regimes. Our results indicate that time lags in the transitional and soft-lag regimes can be clearly amplified and modified by STA's suppression of high-energy electron cooling, and nonlinear synchrotron self-Compton (SSC) cooling can further amplify the emergence of time lags. We conclude that the adopted model offers a unifying quantitative framework for interpreting the diverse time-lag signatures observed in the X-ray
flares of HBLs. Additionally, SSC cooling effects can account for the relatively large lags observed in TeV-bright
flares, as well as the observed trend between lag amplitude and
flare duration: the larger the
flare duration, the larger the lag.
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All authors Guang-Cheng Xiao, Wen Hu, Da-Guo Jiang, Jun-Xian Wang, Zhen-Yi Cai, Da-Hai Yan, Fang-Wu Lu
High Energy Astrophysical Phenomena
Bolometric correction factor and radiative efficiency for the super-Eddington accretion flow in tidal disruption events
Yongxin Wu, Erlin Qiao, Xuan Fang et al. (+3 more)
The estimate of the bolometric luminosity and the radiative efficiency are two key aspects for understanding the properties of the
accretion flow around a supermassive black hole (BH). In this paper, we focus on the estimate of the bolometric luminosity and the radiative efficiency of the early super-Eddington
accretion flow in
tidal disruption events (TDEs). Specifically, we first perform radiation hydrodynamic simulations of super-Eddington
accretion flow in TDE environment, and then calculate the corresponding emergent spectra with the method of post processing for the simulation data. Based on the emergent spectra, we calculate the isotropic-equivalent X-ray bolometric correction factor $k_\mathrm{bol}$ and the radiative efficiency $\eta$ of the super-Eddington
accretion flow. We find that both $k_\mathrm{bol}$ and $\eta$ are BH mass and viewing-angle dependent. $k_\mathrm{bol}$ is in the range of about a few tens to a few thousands, and $\eta$ is in the range of $\sim 10^{-3}-10^{-1}$ for BH mass in the range of $10^{6-7}M_\odot$ and the viewing angle in the range of $0^{\rm o}-90^{\rm o}$. Finally, we apply the derived $k_\mathrm{bol}$ and $\eta$ to some specific TDEs to estimate the accreted mass during an event, which can significantly alleviate the so-called missing energy problem in TDEs.
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All authors Yongxin Wu, Erlin Qiao, Xuan Fang, Yiyang Lin, Jifeng Liu, Meng Guo
Instrumentation and Methods for Astrophysics
Efficient high-order explicit symplectic splitting methods for post-Newtonian Hamiltonian systems
Yujie Jiang and Lijie Mei
The nonseparability of post-Newtonian (PN)
Hamiltonian systems typically necessitates the use of computationally expensive implicit integrators. Recent research overcomes this limitation by
embedding the dynamics into a doubled phase space, which enables the development of explicit
symplectic methods. However, existing specially designed explicit integrators suffer from order reduction for high-order methods when the time stepsize is small, i.e., $h <\varepsilon^3$. In this paper, we propose a novel extension and splitting approach for the doubled
Hamiltonian, under which specially designed explicit
symplectic integrators can be constructed. It is shown that the proposed integrators achieve genuine high-order convergence without order reduction and take advantage of the small PN parameter $\varepsilon$. Numerical results from simulations with 2PN spinning binaries demonstrate superior long-term conservation of invariants and significantly higher computational efficiency compared to both implicit methods and existing explicit splitting techniques.
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High Energy Astrophysical Phenomena
Signatures of Two Distinct Epochs of FRB 20240114A from January to August 2024 Based on its Energy and Waiting Time Analysis
Xiao Li, Ying Gu and En-Wei Liang
A comprehensive analysis of the energy and waiting time distributions of the bursts from FRB 20240114A detected by the Five-hundred-meter Aperture Spherical
Radio Telescope between 28 January and 29 August 2024 is presented. For the full sample, its energy distribution cannot be fitted with the simple power-law (SPL),bent power-law (BPL), thresholded power-law (TPL) or Band function models, and its waiting time distribution excluding intervals shorter than 0.5 s cannot be fitted with the Poisson or Weibull models. Nevertheless, for the subsamples with more than 50 bursts in single-day observations, their energy distributions can be fitted with the BPL or TPL models, and their waiting time distributions are better described by a Weibull model. It is noted that the best-fitting BPL parameter $\beta$ is approximately invariant within the epochs before and after 21 March 2024, with an average of $\bar \beta_b = 1.006 \pm 0.074$ and $\bar \beta_a = 1.236 \pm 0.183$ (one standard deviation), respectively. Most subsamples from the later epoch have a smaller burst rate parameter $r$ in the Weibull model than those from the earlier epoch. The majority of bursts with $E>10^{39}$ erg occurred in the earlier epoch. The energy distributions in the high-energy range ($> 6\times10^{37}$ erg) differ significantly between the two epochs, and power-law fits to $dN/dE$ yield indices of $-1.97_{-0.02}^{+0.02}$ and $-2.34_{-0.06}^{+0.06}$, respectively. The median of the waiting time distribution of the later epoch is larger than that in the earlier epoch. These results suggest that the two epochs may be dominated by different types of bursts, possibly attributed to changes in the physical properties of the emission region.
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Solar and Stellar Astrophysics
Detection of Doppler velocity differences between ions and neutrals in an erupting prominence
Yuwei Huang, Kiyoshi Ichimoto and Tetsu Anan
We performed a spectroscopic observation of an erupting prominence occurred on the
solar limb on 2015 May 8th in He I 706.5 nm, O I 777.2 nm triplet and Ca II 849.8 nm lines to investigate differences in the Doppler velocity between ions and neutrals in a
plasma strongly accelerated by the Lorentz force. We found that the ion-neutral velocity difference between Ca II and He I reached an order of 15 km s-1. On the other hand, the velocity difference between Ca II and O I was significantly smaller than that between Ca II and He I. This result can be interpreted as the formation of O I 777.2 nm lines in the erupting prominence is mainly contributed by the recombination from O II ions through charge transfer with hydrogen atoms, resulting in a behavior close to ions. According to an order estimate of the collisional friction among He I atoms and
protons, the observed velocity difference between Ca II and He I implies the acceleration of the eruption reaching about 150 times of
solar gravity. We propose a new method to evaluate the ionization degree of hydrogen from the velocity differences observed in Ca II, He I and O I lines.
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Earth and Planetary Astrophysics
CHEOPS observations of V1298 Tau: updated planetary densities and implications on the early evolution of the young system
Hinna Shivkumar, Sérgio Gomes, Jean-Michel Désert et al. (+9 more)
The young (10-30 Myr) multi-
planet system V1298 Tau presents a unique opportunity to probe the early formation and
evolution of young systems. We present new CHEOPS observations of the three innermost
planets, yielding high-precision planetary radii ($\sim$5-11 $R_\oplus$ ) and improving the radius ratios (Rp/Rs) by 30-71% compared to previous multiple TESS observations. Combined with refined period and mass determinations from transit-timing variation (TTV) measurements, we derive revised bulk densities (0.06-0.23 g/cm$^3$) for these
planets. We find that the innermost
planet c is denser compared to the outermost
planet at the 3.4-$\sigma$ level, while the bulk densities of the three outermost
planets are consistent within the reported uncertainties. These bulk densities suggest differing envelope mass fraction across the system, indicating differential atmospheric
evolution in the young system. We further assess the early dynamical state of the V1298 Tau system and find that within the range of simulations performed we find no evidence for present-day mean-motion resonance trapping. As an independent diagnostic, we compute the forced eccentricities and low Normalized Angular Momentum Deficit (NAMD) exhibited by the system. Our simulations suggest that no past dynamical excitation is required to explain the present orbital architecture.
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All authors Hinna Shivkumar, Sérgio Gomes, Jean-Michel Désert, John Livingston, John Lopez, Vatsal Panwar, James Sikora, Saugata Barat, Pierre F. L. Maxted, Thomas G. Wilson, Antonija Oklopčić, Silvia Toonen