Astrophysics of Galaxies
Dynamical evolution timescales for the supermassive black hole system in the galaxy NGC 7727 (Arp 222)
P. Berczik, M. Ishchenko, O. Veles et al. (+5 more)
Context. A dual active
galactic nucleus candidate with a separation of only 500 pc was recently found in NGC 7727. According to the hierarchical merging scenario, such objects would be expected to merge on a timescale of a few hundred Myr. However, estimating the accurate merging timescales for the two
nuclei is still a complex challenge. Aims. Using our numerical N-body code, we can trace the full
evolution of central black holes during all phases: dynamical friction of unbound black holes, binary black hole formation, hardening of the system due to two-body scattering, and emission of gravitational waves leading to the final merger. Methods. Our model has next components: the bulge contains two dense
stellar nuclei, each of which hosts a black hole. The most massive black hole in the center of the
galaxy has a mass of 1.54x10^8 Msol and the least massive black hole in the offset second stripped
nucleus has a mass of 6.33x10^6 Msol. We followed the dynamical
evolution of the system up to a final separation of four Schwarzschild radii. The black holes were added as special relativistic particles and their equation of motion contains a full post-Newtonian approximation - 2.5 term. Results. Initially, the black holes are not gravitationally bound and, thus, the system spends more than 60 Myr in the phase of dynamical friction while tightening the orbit. The two-body scattering phase takes place from 60 Myr up to 120 Myr. In the last 10 Myr, the black hole's separation is seen to be rapidly shrinking due to the gravitational wave emission. Starting from the physical separation observed today, the total merging time in our model is 130 (10) Myr. Conclusions. These results have implications for the statistics of strong sources of gravitational waves at low frequencies, namely, systems engaged in an advanced state of are expected to be
prime sources for the LISA mission to observe.
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All authors P. Berczik, M. Ishchenko, O. Veles, M. Sobolenko, K. Voggel, C.M. Boily, E. Polyachenko, R. State
Instrumentation and Methods for Astrophysics
Millimeter-Wavelength Lens-Absorber-Coupled Ti/Al Kinetic Inductance Detectors
Alejandro Pascual Laguna, Victor Rollano, Aimar Najarro-Fiandra et al. (+4 more)
This work presents Ti/Al bi-layer Microwave Kinetic Inductance Detectors (MKIDs) based on lens-coupled spiral absorbers as the quasi-optical coupling mechanism for millimeter-wavelength radiation detection. From simulations, the lens-coupled absorbers provide a 70% lens aperture efficiency in both polarizations over an octave band with a spiral array absorber and over 10% relative bandwidth with a single spiral. We have fabricated and measured two devices with bare Ti/Al MKIDs: a 3x3 cm chip with 9 pixels to characterize the optical response at 85 GHz of the two variations of the absorber; and a large format demonstrator with 253 spiral-array pixels showing potential towards a large format millimeter-wavelength camera. We estimate a sensitivity of 1 $\mathrm{mK}\cdot\mathrm{Hz}^{-0.5}$ and a 95% detector yield.
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All authors Alejandro Pascual Laguna, Victor Rollano, Aimar Najarro-Fiandra, David Rodriguez, Maria T. Magaz, Daniel Granados, Alicia Gomez
Astrophysics of Galaxies
A quest for sulfur-bearing refractory species. Identification of CaS in the interstellar medium
A. Tasa-Chaveli, Á. Sánchez-Monge, A. Fuente et al. (+10 more)
The recent detection of refractory molecules in massive
star-forming regions provides a means of probing the innermost regions of disks around massive
stars. These detections also make it possible to explore the chemical composition of refractories through gas-phase observations. In this regard, identifying refractory compounds containing sulfur could reveal potential connections between sulfur and refractories, as well as help determine the sulfur budget in these extreme environments. We find convincing evidence of a reliable detection of CaS, and tentative detections of KS and KSH in the disk G351.77-mm1. These are the first ever identifications of these species in the interstellar medium. The CaS, KS, and KSH column densities are about 3 orders of magnitude lower than those of the abundant sulfur compounds SO$_2$, CH$_3$SH and SiS, proving that these species are not the major reservoir of sulfur at the spatial scales probed by our observations. Higher angular resolution observations at different wavelengths are required to confirm these detections, which are of paramount importance to gain insights into the formation of gas-phase refractory molecules.
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All authors A. Tasa-Chaveli, Á. Sánchez-Monge, A. Fuente, A. Ginsburg, H. S. P. Müller, Th. Möller, P. Rivière-Marichalar, D. Navarro-Almaida, G. Esplugues, P. Schilke, M. Rodríguez-Baras, S. Thorwirth, L. Beitia-Antero
Solar and Stellar Astrophysics
The Role of Asteroseismology in Understanding Mass Loss in Red Giants
Sibel Örtel and Mutlu Y{\i}ld{\i}z
Red
giant stars play a key role in advancing our understanding of
stellar mass loss. However, its initial mass and the amount of mass lost during this phase remain uncertain. In this study, we investigate the asteroseismic signatures of mass loss and the parameters that influence it. We examine six
stars identified as red
giant branch (RGB)
stars in the APOKASC-2 catalog. Assuming these
stars are on their first ascent of the RGB, we construct interior models. The resulting model ages are significantly older than the age of the
Galaxy, indicating that these
stars are likely experiencing mass loss and evolving toward the red clump (RC) phase. The minimum possible initial masses are estimated using the mass-
metallicity diagram, from which we infer that the minimum mass lost by these
stars ranges from $0.1$-$0.3{\rm M}_{\odot}$. Models constructed with an initial minimum mass yield the maximum possible age of the
star. The ages of these models fall within the range of 9-9.5Gyr. For two
stars, asteroseismic parameters confirm RC classification. Due to degeneracies in the HR diagram, distinguishing between internal structure models is challenging; however, asteroseismic constraints provide clear differentiation. Although mass-loss and mass-conservation models have similar $M$, $R$, and $T_{\rm eff}$ values, $\Delta\nu$s determined from the $l$=0 modes in the mass-loss models are 5-10$\%$ higher than observed. This discrepancy may arise from differences in internal structure. Finally, evolutionary model grids are used to examine how initial mass and $Z$ affect mass loss. Mass loss increases with increasing
metallicity and decreases with increasing initial mass, regardless of the adopted value of $\eta$.
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Solar and Stellar Astrophysics
Is there a unique asteroseismic interior model for the solar-like oscillating KIC 7747078?
Sibel Örtel, Mutlu Y{\i}ld{\i}z and Z. Çelik
Asteroseismology provides a direct observational window into the structure and
evolution of
stars. While spectroscopic and photometric methods only provide information about the surface properties of
stars, asteroseismology, through the analysis of oscillation frequencies, offers comprehensive information about the deep
stellar interior as well as the surface. The scattering of effective temperature (Teff) determined from the spectrum and degeneracy in the Hertzsprung Russell diagram poses challenges in developing a unique interior model for a single
star. Although observational asteroseismic data partially lift this degeneracy, the best model that meets all asteroseismic constraints is not obtained. Most models reported in the literature typically address the large separation Dnu constraint between oscillation frequencies, which is a critical issue, especially in post main sequence
stars. Reference frequencies, influenced by helium ionisation zone induced glitches in oscillation frequencies, are instrumental in refining models. Using the high
metallicity derived from the colors of the Kepler Legacy
star KIC 7747078, we obtain the masses of models M as 1.208 Msun and 1.275 Msun using the reference frequencies and individual frequencies as constraints, respectively. By applying the chi2 method using these reference frequencies, Dnu, and surface
metallicity determined from the spectrum, we develop a unique
star model with a mass of 1.171 pm 0.019 Msun, a radius of 1.961 pm 0.011 Rsun, an effective temperature of 5993 K, an initial
metallicity of 0.0121, and an age of 5.15 pm 0.29 Gyr. A significant advantage of this method is that Teff emerges as an output, not a constraint. The mixed mode oscillation frequencies of this model align well with the observations.
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Instrumentation and Methods for Astrophysics
Measurements of the Birks' coefficient of GAGG:Ce using hard X-rays
Merlin Kole and Nicolas De Angelis
Inorganic scintillators continue to be widely used within astrophysical X-ray and gamma-ray detectors. This is in part thanks to the development of new scintillators, such as GAGG:Ce, as well as the availability of new scintillator readout sensors such as Silicon Photomultipliers and Silicon Drift Detectors. In order to use such scintillator materials for spectrometry or polarimetry, a detailed understanding of their response is important. One parameter that can affect the scintillator performance, particularly at lower
photon energies, is their Birks' coefficient, which correlates the relative light yield to the ionization energy density. While for many high-Z inorganic scintillators this effect can be ignored, for GAGG:Ce this appears to not be the case. Here we provide a measurement of the Birks' coefficient for GAGG:Ce using data from a detector irradiated in the 20-80~keV energy range at the LARIX-A X-ray beam in Ferrara, Italy. While the effects due to Birks' law are visible below 30 keV, they also significantly influence the performance of GAGG:Ce performance near one of the K-edges, affecting both the measured gain and the energy resolution. Here, we use beam test data to derive the Birks' coefficient from GAGG:Ce. The results indicate that for usage in hard X-ray and soft gamma-ray missions, this coefficient has a significant effect on the measurements.
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High Energy Astrophysical Phenomena
Spectral nature of Sco X-1 observed using the X-ray SPECtroscopy and Timing (XSPECT) payload on-board XPoSat
V. P. Shyam Prakash, Vivek K. Agrawal, Rwitika Chatterjee et al. (+3 more)
Scorpius X-1 is the brightest and first discovered X-ray source in the sky. Studying this source in the low-energy band has been challenging in the past due to its high brightness. However, with the X-ray SPECtroscopy and Timing (XSPECT) payload on-board Indias first X-ray Polarimetry Satellite (XPoSat), we have the capability to study the source despite its very high brightness, thanks to the fast (1 ms) readout of the instrument. We investigate the
evolution of the spectral and timing properties of Sco X-1 across the horizontal, normal, and flaring branch, as observed with XSPECT. We examine changes in the spectral parameters as a function of position on the color-color diagram (CCD). Spectral studies indicate that the soft X-ray emission can be modeled using a multicolor disk component, with the inner disk temperature ranging from 0.6 to 0.8 keV. The hard component is described by a Comptonized continuum using either the nthComp or Comptb model with electron temperatures from 2.4 to 4.7 keV and optical depth between 5 and 14. Additionally, we observe the presence of an iron K-alpha line at 6.6 keV and an iron K-beta line at 7.6 keV. Both spectral models suggest a steep rise in Comptonization flux as well as disk flux in the flaring branch. An increase in
neutron star blackbody temperature and inner disk temperature are also observed during flaring. The Z-track is driven by changes in the optical depth of the corona, the Comptonization flux and the disk flux and the inner disk temperature. No quasi-periodic oscillations are detected in any branch, suggesting their association with the high-energy spectrum.
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All authors V. P. Shyam Prakash, Vivek K. Agrawal, Rwitika Chatterjee, Radhakrishna Vatedka, Koushal Vadodariya, A. M. Vinodkumar
High Energy Astrophysical Phenomena
Rapid onset of a Comptonisation zone in the repeating tidal disruption event XMMSL2 J140446.9-251135
R. D. Saxton, T. Wevers, S. van Velzen et al. (+11 more)
We report here on observations of a
tidal disruption event, XMMSL2 J1404-2511, discovered in an XMM-Newton slew, in a quiescent
galaxy at z=0.043. X-ray monitoring covered the epoch when the
accretion disc transitioned from a thermal state, with kT~80 eV, to a harder state dominated by a warm, optically-thick corona. The bulk of the coronal formation took place within 7 days and was coincident with a temporary drop in the emitted radiation by a factor 4. After a plateau phase of ~100 days, the X-ray flux of XMMSL2 J1404-2511 decayed by a factor 500 within 230 days. We estimate the black hole mass in the
galaxy to be $M_{BH}=4\pm{2}\times10^{6}$
solar masses and the peak X-ray luminosity $L_{X}\sim6\times10^{43}$ ergs/s. The optical/UV light curve is flat over the timescale of the observations with $L_{opt}\sim 2\times10^{41}$ ergs/s. We find that TDEs with coronae are more often found in an X-ray sample than in an optically-selected sample. Late-time monitoring of the optical sample is needed to test whether this is an intrinsic property of TDEs or is due to a selection effect. From the fast decay of the X-ray emission we consider that the event was likely due to the partial stripping of an evolved
star rather than a full
stellar disruption, an idea supported by the detection of two further re-brightening episodes, two and four years after the first event, in the SRG/eROSITA all-sky survey.
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All authors R. D. Saxton, T. Wevers, S. van Velzen, K. Alexander, Z. Liu, A. Mummery, M. Giustini, G. Miniutti, F. Fuerst, J. J. E. Kajava, A. M. Read, P. G. Jonker, A. Rau, D.-Y. Li
Astrophysics of Galaxies
HR-pyPopStar II: high spectral resolution evolutionary synthesis models low metallicity expansion and the properties of the stellar populations of dwarf galaxies
I. Millán-Irigoyen, M. Mollá, M. Cerviño et al. (+1 more)
Low
metallicity stellar populations are very abundant in the Universe, either as the remnants of the past history of the Milky Way or similar spiral
galaxies, or the young low
metallicity stellar populations that are being observed in the local
dwarf galaxies or in the high-z objects with low metal content recently found with JWST. Our goal is to develop new high-spectral-resolution models tailored for low-
metallicity environments and apply them to analyse
stellar population data, particularly in cases where a significant portion of the
stellar content exhibits low
metallicity. Methods. We used the state-of-the-art
stellar population synthesis code HR-pyPopStar with available
stellar libraries to create a new set of models focused on low
metallicity stellar populations. We have compared the new spectral energy distributions with the previous models of HR-pyPopStar for
solar metallicity. Once we verified that the spectra, except for the oldest ages that show some differences in the molecular bands of the TiO and G band, are similar, we reanalysed the high resolution data from the globular cluster M 15 by finding a better estimate of its age and
metallicity. Finally, we analysed a subsample of mostly
star-forming
dwarf galaxies from the MaNGA survey we found similar
stellar mass-mean
stellar metallicity weighted by light to other studies that studied
star forming
dwarf galaxies and slightly higher mean
stellar metallicity than the other works that analysed all types of
dwarf galaxies at the same time, but are within error bars.
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All authors I. Millán-Irigoyen, M. Mollá, M. Cerviño, M.L. García-Vargas
Astrophysics of Galaxies
Dust scattering halo of 4U 1630-47: High resolution X-ray and mm observations constrain source and molecular cloud distances
E. Kalemci, M. Díaz Trigo, E. Oztaban et al. (+8 more)
We re-investigated the distance to the black hole X-ray binary 4U 1630-47 by analyzing its
dust scattering
halo (DSH) using high-resolution X-ray (Chandra) and millimeter (APEX) observations.
Dust scattering
halos form when X-rays from a compact source are scattered by interstellar
dust, creating diffuse ring-like structures that can provide clues about the source's distance. Our previous work suggested two possible distances: 4.9 kpc and 11.5 kpc, but uncertainties remained due to low-resolution CO maps. We developed a new methodology to refine these estimates, starting with a machine learning approach to determine a 3D representation of molecular clouds from the APEX
dataset. The 3D maps are combined with X-ray flux measurements to generate synthetic DSH images. By comparing synthetic images with the observed Chandra data through radial and azimuthal profile fitting, we not only measure the source distance but also distinguish whether the molecular clouds are at their near or far distances. The current analysis again supported a distance of 11.5 kpc over alternative estimates. While the method produced a lower reduced chi-squared for both the azimuthal and radial fits for a distance of 13.6 kpc, we ruled it out as it would have produced a bright ring beyond the APEX field of view, which is not seen in the Chandra image. The 4.85 kpc estimate was also excluded due to poor fit quality and cloud distance conflicts. The systematic error of 1 kpc, arising from uncertainties in determining molecular cloud distances, dominates the total error.
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All authors E. Kalemci, M. Díaz Trigo, E. Oztaban, A. A. Abbasi, T. Stanke, J. A. Tomsick, T. J. Maccarone, A. Saraçyakupoğlu, E. von Nussbaum, J. C. A. Miller Jones, B. Bahçeci
Instrumentation and Methods for Astrophysics
Accelerating cosmological simulations on GPUs: a portable approach using OpenMP
M. D. Lepinzan, G. Lacopo, D. Goz et al. (+5 more)
In this work we present the porting to Graphics Processing Units (GPUs, using OpenMP target directives) and optimization of a key module within the cosmological {\pinocchio} code, a Lagrangian Perturbation Theory (LPT)-based framework widely used for generating dark matter (DM)
halo catalogs. Our optimization focuses on a specific segment of the code responsible for calculating the collapse time of each particle involved in the simulation. Due to the embarrassingly parallel nature of this computation, it represents an ideal candidate for GPU offloading. As part of the porting process, we developed fully GPU-native implementations of both cubic spline and bilinear interpolation routines, required for evaluating collapse times. Since GNU Scientific Library (GSL) does not support GPU offloading, these custom implementations run entirely on the GPU and achieve residuals of only $\sim0.003\%$ when compared to the CPU-based implementation of GSL. Comparative benchmarking on the LEONARDO (NVIDIA-based) and SETONIX (AMD-based) supercomputers reveals notable portability and performance, with speedups of~4x and up to~8x, respectively. While collapse time calculation is not a primary bottleneck in the overall workflow, the acceleration reduces full production runs by $\sim 100$ seconds each leading to a cumulative saving of $\sim 160000$ Standard-h ($\sim28$ hours wall time) across thousands of simulations. Roofline analysis confirms that our GPU porting achieves over 80% of the theoretical FP64 peak performance, confirming efficient compute-bound execution. This work demonstrates that OpenMP directives offer a portable, effective strategy for accelerating large-scale cosmological simulations on heterogeneous hardware.
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All authors M. D. Lepinzan, G. Lacopo, D. Goz, G. Taffoni, P. Monaco, P. J. Elahi, U. Varetto, M. Cytowski
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
PINNGraPE: Physics Informed Neural Network for Gravitational wave Parameter Estimation
Leigh Smith, Matteo Scialpi, Francesco di Clemente et al. (+1 more)
Weakly-modelled searches for gravitational waves are essential for ensuring that all potential sources are accounted for in detection efforts, as they make minimal assumptions regarding source morphology. While these searches primarily target generic transient sources, they are also highly effective at identifying a broad range of compact binary coalescences, demonstrated by the weakly-modelled search
algorithm coherent WaveBurst being the first to detect GW150914. Despite their ability to detect compact binaries with diverse properties, the accurate estimation of source parameters from their output remains to be a challenging task. To overcome this, we leverage physics-informed neural networks, which serve as a powerful tool for parameter estimation by applying physical constraints through the universal differential equation governing a compact binary system. With this approach, we rapidly infer the mass parameters of binary black hole merger systems to within 7% from only the time-frequency representation of the gravitational wave signal.
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All authors Leigh Smith, Matteo Scialpi, Francesco di Clemente, Michał Bejger
Solar and Stellar Astrophysics
The chemical DNA of the Magellanic Clouds III. The first, extragalactic Mg-K anticorrelation: the LMC globular cluster NGC 1786
Deimer Antonio Alvarez Garay, Alessio Mucciarelli and Lorenzo Monaco
In this work we derived [K/Fe] and [Mg/Fe] abundance ratios for six
stars of the old globular cluster NGC 1786 in the Large Magellanic Cloud. We employed high-resolution spectra acquired with the MIKE spectrograph mounted at the Magellan/Clay
telescope. We found a clear Mg-K anticorrelation among the analyzed
stars. In particular, the Mg-poor
stars ([Mg/Fe] < 0.0 dex) are enriched by ~ 0.25 dex in [K/Fe] compared to the Mg-rich
stars ([Mg/Fe] > 0.0 dex). This finding makes NGC 1786 the first globular cluster residing in an external
galaxy in which such extreme chemical anomaly has been detected. The observed trend nicely agrees with those observed in
Galactic globular clusters hosting Mg-poor
stars, such as NGC 2808, and Omega Centauri suggesting that such chemical anomaly is an ubiquitous feature of old, massive, and metal-poor
stellar systems and it does not depend on the properties of the parent
galaxy in which the cluster formed. Also, Na-O and Mg-Al anticorrelations were detected among the
stars of NGC 1786. The newly discovered Mg-K anticorrelation reinforces the idea that
stars capable of activating the complete MgAl cycle are responsible for the observed chemical anomalies in these clusters. In this context, asymptotic
giant branch
stars seem to be a valuable model since they are able to produce K while depleting Mg. However, the precise and complete physics of this model remains a subject of debate.
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Instrumentation and Methods for Astrophysics
The simulation chain for the Terzina Cherenkov telescope on board the NUSES space mission
M. Abdullahi, R. Aloisio, F. Arneodo et al. (+74 more)
The Terzina
telescope is designed to detect ultra-high energy
cosmic rays (UHECRs) and Earth-skimming
neutrinos from a 550 km low-Earth orbit (LEO) by observing Cherenkov light emitted by Extensive Air Showers (EAS) in the Earth's atmosphere pointing towards the
telescope and in the field of view. In this contribution, a simulation chain for the Terzina
telescope on board the NUSES mission will be presented. The chain encompasses all stages of the detection process, from event generation and EAS modelling with CORSIKA and EASCherSim to Geant4-based simulations of the
telescope's geometry and optics, followed by modelling of the trigger system and silicon photomultiplier (SiPM) response. The Geant4 module includes the real CAD model of the
telescope structure and optical components, with aspherical lenses manually implemented to ensure accurate representation of the optical efficiency and point spread function in Geant4. This comprehensive pipeline, developed using modular C++ code and Python tools for event analysis and reconstruction, produces detailed performance assessments of a
telescope operating in a LEO mission but can be adapted for any high altitude Cherenkov
telescope, making it a versatile tool for future observatory designs. The possibility of modelling balloons in the atmosphere has also been developed.
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All authors M. Abdullahi, R. Aloisio, F. Arneodo, S. Ashurov, U. Atalay, F. C. T. Barbato, R. Battiston, M. Bertaina, E. Bissaldi, D. Boncioli, L. Burmistrov, F. Cadoux, I. Cagnoli, E. Casilli, D. Cortis, A. Cummings, M. D'Arco, S. Davarpanah, I. De Mitri, G. De Robertis, A. Di Giovanni, A. Di Salvo, L. Di Venere, J. Eser, Y. Favre, S. Fogliacco, G. Fontanella, P. Fusco, S. Garbolino, F. Gargano, M. Giliberti, F. Guarino, M. Heller, T. Ibrayev, R. Iuppa, A. Knyazev, J. F. Krizmanic, D. Kyratzis, F. Licciulli, A. Liguori, F. Loparco, L. Lorusso, M. Mariotti, M. N. Mazziotta, M. Mese, M. Mignone, T. Montaruli, R. Nicolaidis, F. Nozzoli, A. Olinto, D. Orlandi, G. Osteria, P. A. Palmieri, B. Panico, G. Panzarini, D. Pattanaik, L. Perrone, H. Pessoa Lima, R. Pillera, R. Rando, A. Rivetti, V. Rizi, A. Roy, F. Salamida, R. Sarkar, P. Savina, V. Scherini, V. Scotti, D. Serini, D. Shledewitz, I. Siddique, L. Silveri, A. Smirnov, R. A. Torres Saavedra, C. Trimarelli, P. Zuccon, S. C. Zugravel
High Energy Astrophysical Phenomena
Analysis of the Supernova Remnant IC 443 using H.E.S.S. Data
Alison M. W. Mitchell, Lukas Grosspietsch and Tina Wach
IC 443 is a well-known
supernova remnant that stands out due to its interaction with a dense molecular cloud, creating a complex environment where shocks can efficiently accelerate particles to high energies. This makes it a key target for investigating the mechanisms of
cosmic-ray acceleration and gamma-ray production, particularly in the context of
supernova remnants as potential sources of PeV
cosmic rays. This work presents a first analysis of the region as observed by H.E.S.S.. We detect extended very-high-energy gamma-ray emission from IC 443, consistent with previous observations by VERITAS and MAGIC. A multi-wavelength comparison incorporating data from
Fermi-LAT, MAGIC, and VERITAS strongly supports a hadronic origin of the observed emission, and highlights the presence of relativistic
protons interacting with the surrounding molecular cloud. These findings reinforce the role of IC 443 as a key laboratory for studying
supernova remnants as
cosmic-ray accelerators and their interaction with their surrounding mediums.
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High Energy Astrophysical Phenomena
Hunt for the mHz variability in the TESS and XMM-Newton observations of nova-like cataclysmic variables
Andrej Dobrotka, Jozef Magdolen and Martin Melicherčík
We analysed the flickering of selected nova-like cataclysmic variables observed by the TESS satellite and XMM-Newton. We searched for break frequencies ($f_{\rm b}$) in the corresponding power density spectra (PDS), and for any long-term
evolution. We found a new optical $f_{\rm b}$ in three nova-like systems and confirmed that the value of this frequency is clustered around 1 mHz. V504 Cen and V751 Cyg show possible X-ray counterparts of $f_{\rm b}$ that had previously only been seen in MV Lyr. This points towards the very central disc for source localisation. We investigated a previously proposed correlation between white
dwarf mass and $f_{\rm b}$, but thanks to the new measurements we do not conclude its existence. V3885 Sgr and V1193 Ori show flaring activity in the long-term light curve during which TESS observations were made. The corresponding PDSs show changes in shape and disappearance of $f_{\rm b}$. TT Ari and SGRt 062340.2-265715 exhibit smooth changes in the long-term optical light curve, and the corresponding TESS observations show variable $f_{\rm b}$ during these changes. $f_{\rm b}$ is higher for lower brightness, which was seen only in MV Lyr so far.
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High Energy Astrophysical Phenomena
A supermassive black hole under the radar: Repeating X-ray variability in a Seyfert galaxy
Matteo Imbrogno, Andrea Sacchi, Giovanni Miniutti et al. (+4 more)
In the last few years, a few supermassive black holes (SMBHs) have shown short-term (of the order of hours) X-ray variability. Given the limited size of the sample, every new addition to this class of SMBHs can bring invaluable information. Within the context of an automated search for X-ray sources showing flux variability in the Chandra archive, we identified peculiar variability patterns in 2MASX J12571076+2724177 (J1257), a SMBH in the Coma cluster, during observations performed in 2020. We investigated the long-term
evolution of the flux, together with the
evolution of the spectral parameters throughout the Chandra and XMM-Newton observations, which cover a time span of approximately 20 years. We found that J1257 has repeatedly shown peculiar variability over the last 20 years, on typical timescales of $\simeq20-30$ ks. From our spectral analysis, we found hints of a softer-when-brighter behaviour and of two well-separated flux states. We suggest that J1257 might represent a new addition to the ever-growing size of relatively low mass SMBHs ($M\simeq10^6-10^7\mathrm{M}_\odot$) showing extreme, possibly quasi-periodic X-ray variability on short time scales. The available
dataset does not allow for a definitive classification of the nature of the variability. However, given the observed properties, it could either represent a quasi-periodic oscillation at particularly low frequency or be associated with quasi-periodic eruptions in an AGN with peculiar spectral properties.
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All authors Matteo Imbrogno, Andrea Sacchi, Giovanni Miniutti, Francesco Tombesi, Gian Luca Israel, Enrico Piconcelli, Roberta Amato
Solar and Stellar Astrophysics
Modeling the Excitation, Propagation and Damping of Quasi-Periodic Fast Magnetosonic Waves in Realistic Coronal Active Region Magnetic Field Structures
Leon Ofman, Tongjiang Wang, Xudon Sun et al. (+1 more)
Quasi-periodic fast propagating magnetosonic waves (QFPs) were discovered in the
solar corona in EUV since the launch of SDO spacecraft more than a decade ago. The QFP waves are associated with
flares and coronal mass ejections (CMEs) providing information on
flare pulsations as well as on the
magnetic field by MHD wave seismology. Previous models of QFP waves used primarily idealized
magnetic active region structures. However, more realistic active region numerical models are needed to improve the application of coronal seismology to observations of waves in coronal structures. Here, we extend the previous models by including realistic
magnetic configuration based on an observed coronal active region in a case study using AR 11166 observed on March 10, 2011 by SDO/AIA, using potential field extrapolation of photospheric
magnetic field with realistic gravitationally stratified density structure { with typical coronal temperature} in our resistive 3D MHD model. We aim at reproducing the observed QFPs properties, such as directionality, propagation, reflection, nonlinearity, and damping of these waves. We model various forms of excitation of QFPs through time dependent boundary conditions, and localized pulses at the base of the corona. We produce synthetic emission measure (EM) maps from the 3D MHD modeling results to facilitate comparison to EUV observations. We find that the present more realistic model provides better qualitative agreement with observations compared to previous idealized models, improving the study of QFP wave excitation, propagation and damping in coronal ARs, with potential applications to coronal seismology.
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All authors Leon Ofman, Tongjiang Wang, Xudon Sun, Meng Jin
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Suppression of scalar perturbations due to a heavy axion
Kai-Ge Zhang, Jian-Feng He, Chengjie Fu et al. (+1 more)
A fast-rolling
axion can transfer its kinetic energy to gauge fields via the Chern-Simons coupling, leading to copious production of gauge quanta during inflation. The amplified gauge fields act as a source for both scalar and tensor perturbations. In this work, we propose a mechanism for suppressing scalar perturbations while sourcing strong tensor perturbations. We present an implementation of such a mechanism, demonstrating that sourced tensor perturbations are expected to be detected by upcoming next-generation CMB experiments.
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All authors Kai-Ge Zhang, Jian-Feng He, Chengjie Fu, Zong-Kuan Guo
Solar and Stellar Astrophysics
Band Splitting in m-Type II radio Bursts and their Role in Coronal Parameter Diagnostics
Pooja Devi, Ramesh Chandra, Rositsa Miteva et al. (+2 more)
Type II
radio bursts are signatures of shock waves generated by
solar eruptions, observed at
radio wavelengths. While metric (m) type II bursts originate in the lower corona, their longer-wavelength (up to kilometers) counterparts extend into interplanetary space. A rare but valuable feature observed in some type II bursts is band splitting in their dynamic spectra, which provides crucial insights into physical parameters such as shock speed, Alfvén Mach number, Alfvén speed, and coronal
magnetic field strength (B). In this study, we investigate band-splitting in 44 m-type II
radio bursts observed by the
Radio Solar Telescope Network during
solar cycle 24 (2009 – 2019). These events exhibit splitting in both fundamental and harmonic bands and are analyzed under both perpendicular and parallel shocks. All events are associated to
solar flares and 41 (93 %) with the coronal mass ejections. Shock speeds, derived using a hybrid coronal density model proposed by \cite{Vrsnak2004}, range from $\approx$ 350 to 1727 \kms. The relative bandwidth (BDW) of the split bands remains constant with frequency and height. Alfvén Mach numbers indicate moderate shock strength (1.06 – 3.38), while Alfvén speeds and $B$ vary from $\approx$ 230 – 1294 \kms\ and $\approx$ 0.48 – 7.13 G, respectively. Power-law relationships are established as $BDW \propto f_L^{-0.4}$ and $BDW \propto R^{\sim1}$, while the coronal
magnetic field decreases with height as $B \propto R^{\sim-3}$. These results enhance our understanding of shock dynamics and
magnetic field structures in the
solar corona.
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All authors Pooja Devi, Ramesh Chandra, Rositsa Miteva, M. Syed Ibrahim, Kamal Joshi
Earth and Planetary Astrophysics
JCMT detection of HCN emission from 3I/ATLAS at 2.1 AU
Iain M. Coulson, Yi-Jehng Kuan, Steven B. Charnley et al. (+8 more)
We report the detection of HCN ($J=3-2$) rotational emission from comet 3I/ATLAS at a heliocentric distance of 2.13 AU with the James Clerk Maxwell
Telescope (JCMT). Observations were conducted from 07 August 2025 and 14 September 2025 (UT) using the $^{\prime}\overline U^{\prime}\overline u$ heterodyne receiver and ACSIS spectroscopic backend. The HCN line was detected at $>6\sigma$ on 14 Sep 2025 (UT) and a production rate of $Q({\rm HCN})=(4.0\pm1.7)\times10^{25}\ {\rm s}^{-1}$ was derived by non-LTE radiative transfer modelling. Preliminary estimates of the HCN/H$_2$O and CN/HCN abundance ratios suggest values similar to
Solar System comets.
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All authors Iain M. Coulson, Yi-Jehng Kuan, Steven B. Charnley, Martin A. Cordiner, Yo-Ling Chuang, Yueh-Ning Lee, Min-Kai Lin, Stefanie N. Milam, Bannawit Pimpanuwat, Nathan X. Roth, Michał Żółtowski
Cosmology and Nongalactic Astrophysics
Gravitational lensing by a spiral galaxy I: the influence from bar's structure to the flux ratio anomaly
Xikai Shan, Yunpeng Jin and Shude Mao
Gravitational lens flux ratio anomalies are a powerful probe of small-scale mass structures, often attributed to dark matter subhalos. However, baryonic components can also play a significant role. This study investigates, for the first time, the impact of bars on flux ratio anomalies. We conduct a systematic analysis using barred
galaxies from the Auriga simulations. First, we model the projected mass distribution with the Multi-Gaussian Expansion formalism. This method yields smooth lens potentials that preserve the primary bar structure while mitigating numerical noise. We then perform strong
lensing simulations and quantify flux ratio anomalies by measuring their deviation from the theoretical cusp-caustic relation, denoted as $R_{\text{cusp}}$. Our primary finding is a strong, statistically significant correlation between the flux ratio anomaly magnitude and the strength of higher-order even
Fourier modes. Specifically, the strengths of the boxy/peanut and hexapole components show an exceptionally tight correlation with $R_{\text{cusp}}$, with Spearman correlation coefficients of $r = 0.85$ and $0.89$, and p-values on the order of $10^{-6}$ and $10^{-8}$, respectively. This demonstrates that flux ratio anomalies are highly sensitive to complex, non-axisymmetric bar features. We conclude that flux ratio anomalies can be powerful indicators of bar morphology. Failing to account for such morphology can lead to misinterpreting
lensing signatures and potentially overestimating the dark matter subhalo population.
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High Energy Astrophysical Phenomena
TeV Emission from PSR B1055-52 with HESS: Evidence for a Pulsar Halo
Tina Wach and Alison M. W. Mitchell
Pulsar halos are a recently identified class of TeV $\gamma$-ray sources, offering valuable insights into the
evolution of
pulsar systems at the highest energies. However, only a handful of such sources have been detected so far, making each new identification critical for understanding the properties of the population as a whole. We report the first detection of extended very-high-energy (VHE) $\gamma$-ray emission around PSR~B1055$-$52 using observations from the H.E.S.S. array. This middle-aged
pulsar, previously grouped together with Geminga and PSR~B0656$+$14 as part of the “Three Musketeers”, has now been confirmed to host a TeV
pulsar halo, making it the third detected system of its kind, and the first TeV
pulsar halo discovered in the southern hemisphere. Our analysis performed in an energy range of $0.3-60\,$TeV, reveals gamma-ray emission with a one sigma extension of $(2.05 \pm 0.32)^\circ$. The analysis indicates that the emission extends beyond the region which was observed with H.E.S.S.. No significant spectral variation is detected across the emission. The
diffusion coefficient derived for this
halo is significantly lower than the standard ISM value, aligning with findings in the Geminga
halo and indicating that slow
diffusion may be a common property of
pulsar halos. The detection of this new TeV
pulsar halo provides a crucial data point for studying the population-wide properties of
pulsar halos, their impact on
cosmic-ray propagation, and their role as a source of
Galactic electrons and positrons.
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Astrophysics of Galaxies
A z ~ 0.4 Galaxy Reflecting the high-redshift Little Red Dots: An Extended Starburst with an Overmassive Black Hole
Xiaoyang Chen, Kohei Ichikawa, Masayuki Akiyama et al. (+10 more)
One of the most remarkable discoveries of JWST is a population of compact, red sources at z > 4, commonly referred to as Little Red Dots (LRDs). Spectroscopic identifications reported that most LRDs are active
galactic nuclei (AGNs), which are preferentially found around z ~ 6 and could imply a key phase in the formation and growth of black holes (BHs) in the early universe. Photometric surveys at lower
redshift have recently been carried out to trace their
evolution across
cosmic time, and a small number of LRD-like
galaxies have been spectroscopically identified at both
Cosmic Noon and in the local universe. Here we report the discovery of one of the lowest-z LRD-like
galaxies, J204837.26-002437.2 (hereafter J2048) at z = 0.4330, using new Gemini-N/GMOS IFU observations combined with archival multi-band photometric SED data. The GMOS data reveal extended blue emission from starburst with a
star formation rate of 400
solar mass per year, together with an extended, highly fast ionized
outflow. This is the first spectroscopic confirmation of extended host emission and
outflow in an LRD-like
galaxy, providing a unique laboratory for understanding the nature of their high-
redshift counterparts. Moreover, J2048 would host an extremely overmassive BH with a BH-to-
stellar mass ratio of ~ 60%, with the BH mass and host
stellar mass estimated to be 10^10.2 and 10^10.4
solar masses, respectively. We discuss the origin and evolutionary fate of J2048, and the implications that such low-z analogs have for interpreting the properties of high-z LRDs.
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All authors Xiaoyang Chen, Kohei Ichikawa, Masayuki Akiyama, Kohei Inayoshi, Akio K. Inoue, Masafusa Onoue, Yoshiki Toba, Jorge A. Zavala, Tom J. Bakx, Toshihiro Kawaguchi, Kianhong Lee, Naoki Matsumoto, Bovornpratch Vijarnwannaluk
High Energy Astrophysical Phenomena
H.E.S.S. observations of SN 2024ggi
Jowita Borowska-Naguszewska, Robert Brose, Bernardo Cornejo et al. (+3 more)
Supernova (SN) explosions interacting with dense circumstellar medium are considered to be very promising sites for efficient
cosmic-ray (CR) acceleration and subsequent emission of neutral-pion-decay gamma rays. These environments share similarities with already detected gamma-ray novae, but with much greater available energy content, so it is important to characterize their emission in the very-high-energy range. We present the results of H.E.S.S. observations of one such candidate source - SN 2024ggi, located in NGC 3621 at a distance of 7.24 Mpc. A total of 30 hours of data, gathered throughout a month of post-explosion observations, provide flux upper limits that are used to constrain source parameters, offering meaningful insights for theoretical predictions. We exclude bright gamma-ray emission in the first day after explosion, and later upper limits are consistent with wind densities derived from optical observations.
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All authors Jowita Borowska-Naguszewska, Robert Brose, Bernardo Cornejo, Jonathan Mackey, Robert Daniel Parsons, Fabian Schüssler
Astrophysics of Galaxies
Wide-field GMRT imaging of X-shaped Radio-Galaxies: Spectral properties of 4C32.25 and 4C61.23
E. Retana-Montenegro
We present wide-field upgraded
Giant Metrewave
Radio Telescope (uGMRT) images of the fields around the X-shaped
radio-
galaxies (XRGs) 4C32.25, 4C61.23, and MRC 2011-298 obtained at 400 MHz. The observations are calibrated using the extreme peeling method to account for direction-dependent effects across the field of view, as previously applied to Low-frequency array (LOFAR) data. Our 400 MHz images capture in fine detail the
radio-morphology of the XRGs, as well as other serendipitous
radio-sources located in these fields. We use these images along with archival low-frequencyand high-frequency
radio data to investigate the spectral properties of the XRGs 4C32.25 and 4C61.23. Under the assumption of conditions corresponding to the maximum
radio-source age, we estimate the spectral ages of both the primary lobes and the wings. These ages indicate that the wings are the oldest component of the XRGs and are a product of past
radio activity. Moreover, we have used the
radio images available to derive high-resolution spectral index maps for these two XRGs. We find that the spectral index steepens from the primary lobes towards the wings, consistent with our spectral age estimates. These results suggest that precessional and backflow models explain the X-shaped
radio-morphology of 4C32.25 and 4C61.23, respectively. Finally, taking advantage of our wide-area images, we identify several serendipitous diffuse
radio-sources located in our XRG fields and cross-reference them with previous surveys.
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Astrophysics of Galaxies
Self-lensing binaries in globular clusters – predictions for ELT
Grzegorz Wiktorowicz, Matthew Middleton, Mirek Giersz et al. (+4 more)
Self-
lensing (SL) represents a powerful technique for detecting compact objects in binary systems through gravitational microlensing effects, when a compact companion transits in front of its luminous partner. We present the first comprehensive study of SL probability within globular cluster (GC) environments, utilizing synthetic
stellar populations from MOCCA simulations to predict detection rates for the Extremely Large
Telescope (ELT). Our analysis incorporates finite-size lens effects for white
dwarf (WD) lenses and the specific observational characteristics of the ELT/MICADO instrument. We find that present-day GCs contain 1-50 SL sources with magnifications $\mu_\mathrm{sl} > 1+10^{-8}$, strongly dependent on initial binary fraction, with systems dominated by WD lenses paired with low-mass main-sequence companions. The predicted populations exhibit characteristic bimodal magnitude distributions with peaks at $m \approx 24$ and 32 mag at 10 kpc distance, and typical Einstein ring crossing times of $\tau_\mathrm{eff} \sim 2$ hours. ELT observations should achieve detection efficiency of 0.015-10 sources in $\sim150$ nearby GC after a year of observations depending on distance and survey strategy, with nearby clusters ($D \lesssim 10$ kpc) offering the highest yields. Multi-year monitoring campaigns with daily cadence provide order-of-magnitude improvements over single observations through enhanced photometric precision and increased detection probability. Our results demonstrate that coordinated ELT surveys of
Galactic GCs represent a viable approach for probing hidden binary populations and compact object demographics in dense
stellar environments, with comprehensive programs potentially yielding up to 10-100 well-characterized SL sources after first 5 years of observations suitable for statistical studies of binary
evolution in extreme environments.
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All authors Grzegorz Wiktorowicz, Matthew Middleton, Mirek Giersz, Adam Ingram, Adam McMaster, Abbas Askar, Lucas Hellström
High Energy Astrophysical Phenomena
Features in the Cosmic Ray Energy Spectrum Observed with Telescope Array Surface Detectors
Jihyun Kim, Dmitri Ivanov and Gordon Thomson
Ultra-high energy
cosmic rays (UHECRs) are extremely energetic charged particles that originate from outer space. The
Telescope Array (TA) experiment, the largest UHECR observatory in the Northern Hemisphere, has provided high-precision measurements of the
cosmic ray energy spectrum due to its stable operation and efficient data collection. These measurements have revealed three significant spectral features: the ankle, shoulder, and cutoff. Analyzing these features is crucial for understanding the origin and propagation of UHECRs. In this talk, we will present the latest energy spectrum measured by the TA surface detectors and discuss the observed differences in the UHECR energy spectrum between the northern and southern skies.
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High Energy Astrophysical Phenomena
Medium-scale anisotropies measured by Telescope Array surface detectors
Jihyun Kim, Dmitri Ivanov, Kazumasa Kawata et al. (+2 more)
The
Telescope Array (TA) experiment, the largest observatory for ultra-high energy
cosmic rays in the Northern Hemisphere, has identified two medium-scale anisotropies: the TA Hotspot near the constellation Ursa Major and an excess in the direction of the Perseus-Pisces supercluster. Studying these medium-scale anisotropies may provide insights into the origins of ultra-high energy
cosmic rays. This presentation will explore an oversampling analysis of TA surface detector data to evaluate these medium-scale event excesses and will present the latest findings on the TA Hotspot and the Perseus-Pisces supercluster excess.
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All authors Jihyun Kim, Dmitri Ivanov, Kazumasa Kawata, Hiroyuki Sagawa, Gordon Thomson
Astrophysics of Galaxies
Probing the Low Radio Frequency Emission in PG Quasars with the uGMRT – II
Sanna Gulati, Silpa Sasikumar, Preeti Kharb et al. (+3 more)
We present results from uGMRT 685 MHz observations of 87 QSOs belonging to the Palomar Green (PG)
quasar sample with $z<0.5$.
Radio emission is detected in all sources except for 3
radio-quiet (RQ) sources, viz., PG 0043+039, PG 1121+422, and PG 1552+085. The
radio-loud (RL) $-$ RQ dichotomy persists at 685 MHz with only 1 source, PG 1216+069, changing its classification from RQ to RL. Approximately 1/3 of the detected RQ
quasars display AGN-dominated
radio emission while the rest may show additional contributions from
stellar-related processes. Consistent with this, the RL and RQ
quasars occupy distinct tracks on the `fundamental plane' of black hole activity. We find that RL
quasars have $\log_{10}(L_{685\,\mathrm{MHz}}/\mathrm{W\,Hz}^{-1}) > 25.5$, while RQ
quasars have ${\log_{10}(L_{685\,\mathrm{MHz}}/\mathrm{W\,Hz}^{-1})} <23.5$. Furthermore, the
radio sizes display the RQ$-$RL divide as well with RQ sources typically having sizes $\lesssim30$ kpc, with only 16 ($\sim22$%) RQ sources having sizes between 30 and 100 kpc where there is an overlap with RL
quasar sizes. A strong correlation exists between 685 MHz
radio luminosity and black hole mass which is tightened when
accretion rate is considered, highlighting the important role played by the
accretion rate and
accretion disk structure in jet production. We found no difference in the minimum-energy
magnetic field strengths of the
radio cores of RL and RQ
quasars; however, different assumptions of source volume and volume filling factors may apply. High-resolution X-ray observations and
radio-X-ray flux comparisons are needed to independently test the `
magnetic flux paradigm'.
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All authors Sanna Gulati, Silpa Sasikumar, Preeti Kharb, Luis C. Ho, Salmoli Ghosh, Janhavi Baghel