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Physics Astrophysics

astro-ph Watch Astrophysics

Sunday 24 May

High Energy Astrophysical Phenomena

Shear Particle Acceleration in Structured Gamma-Ray Burst Jets: IV. Thermal vs. Non-thermal Emission of the Jet Cocoon

Zi-Qi Wang, Xiao-Li Huang, Hai-Ming Zhang et al. (+1 more)

A distinct thermal or quasi-thermal spectral component is occasionally observed in gamma-ray burst (GRB) prompt emission spectra. Taking GRB 090902B as a case study, we investigate its origin within a structured jet framework, in which the outflow consists of an ultra-relativistic uniform core surrounded by a structured cocoon. In the weak-scattering regime with inefficient shear acceleration, electrons pre-energized in the thin jet-cocoon interaction layer are further heated in the mixed jet-cocoon (MJC) region, forming a quasi-thermal electron distribution. Parameterizing the radial temperature profile of electrons as a power law with index $q_T$, we demonstrate that both the peak flux and spectral width of the thermal component are sensitive to maximum temperature $T_{\max}$ and $q_T$. Combined with the synchrotron emission of shock-accelerated electrons in the jet core, our model reproduces both the quasi-thermal component in the keV-MeV range and the broadband non-thermal emission observed in the time-integrated and time-resolved spectra of GRB 090902B. A comparative analysis of GRB 240825A within a shear-acceleration dominated (strong-scattering) scenario shows that shear-accelerated electrons produce broader spectra than thermalized electrons in the weak-scattering regime. These results indicate that GRB spectral diversity likely arises from the additional emission component originating in the MJC region under different physical conditions.
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All authors Zi-Qi Wang, Xiao-Li Huang, Hai-Ming Zhang, En-Wei Liang

Astrophysics of Galaxies

Exploring biases in derived stellar parameters and the ionizing photon production efficiency

Ravi Jaiswar, Anshu Gupta, Elisabete da Cunha et al. (+8 more)

Constraining the timescale and manner in which the Epoch of Reionization (EoR) occurred is a major JWST science goal. However, any constraints on the stellar or ionizing parameters (xi ion) of galaxies in the EoR must contend with biases introduced by both the data and the models used. We explore three techniques that use spectroscopic and photometric data as well as three different spectral energy distribution (SED) fitting codes, each comprised of multiple star formation history, stellar population synthesis, dust, and photoionization prescriptions to determine their relative influence on stellar parameters and xi ion. We use z=3 EoR analog galaxies due to their reliable photometric coverage (improved physical constraints) in comparison to direct EoR sources and potential for direct Lyman Continuum escape research. For this population the median stellar mass can vary by over 0.6 dex and the SFR by more than 0.9 dex. Further, the xi ion can vary by over 1.1 dex for individual sources when comparing spectroscopic and photometric derivations, or by more than 0.5 dex when fitting SEDs with different models. As such, the choice of methodology can have significant consequences for the derived xi ion and the subsequent sources of reionization. We find that the presence of a redshift evolution for xi ion is dependent on the method adopted for its derivation, where a consistent method yields an evolutionary trend with redshift in extreme emitters while an indiscriminant selection of studies does not. The model, method and data dependence of the xi ion parameter is undeniable even for a homogeneous population.
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All authors Ravi Jaiswar, Anshu Gupta, Elisabete da Cunha, Cathryn M. Trott, Andrew Battisti, A. J. Hedge, Robin Cook, Sabine Bellstedt, Jordan DSilva, Luke Davies, Juno Li

Solar and Stellar Astrophysics

Cyclotron breaking: a mechanism for parallel ion cyclotron waves to heat the fast solar wind

Evan L. Yerger, Benjamin D. G. Chandran, Vincent David et al. (+2 more)

The $\textit{Parker Solar Probe}$ ($\textit{PSP}$) mission has observed near-continuous power in parallel ion cyclotron waves (PICWs) in the young, fast solar wind. These waves are unlikely to be directly produced by the turbulent cascade and are likely born of a local instability; yet, they are observed to both cool – and heat – the plasma. We propose that these observations can be self-consistently explained as the natural consequence of PICWs propagating in the inhomogeneous solar wind after they have been driven unstable. In this work, we argue that strong proton heating by a turbulent cascade of oblique ICWs will result in PICWs being driven unstable in a process known as quasi-linear focusing. Because the power in the turbulent cascade is concentrated at scales above the turbulent transition region, PICWs will be driven unstable within a range of wave numbers parallel to the background magnetic field, $k_\parallel$, that is bounded from above by $k_{\parallel\rm P}^*$, corresponding to the start of the transition region. As unstable PICWs propagate away from the sun to regions of lower proton density, their $k_\parallel$, multiplied by the proton inertial length $d_{\rm p}$, increases. Eventually, the $k_\parallel d_{\rm p}$ of the PICWs becomes larger than $k_{\parallel\rm P}^*d_{\rm p}$ and the waves damp, heating the solar wind. We call this effect `cyclotron breaking', in analogy with ocean waves breaking on the shore. We then discuss the testable predictions of the theory, including a distinct heating signature in which PICWs cool fast protons and heat slow protons at any given heliocentric distance $r$. Finally, we conjecture that cyclotron breaking can lead to net heating by PICWs if the power emitted as PICWs decreases sufficiently rapidly with $r$ that local emission of PICWs is overwhelmed by the local damping of PICWs generated closer to the sun.
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All authors Evan L. Yerger, Benjamin D. G. Chandran, Vincent David, Trevor A. Bowen, Stuart D. Bale

Astrophysics of Galaxies

Small and Complex II: Characterizing the Disk and Stellar Envelope of Edge-on $z \sim 0$ Massive Compact Galaxies

A. Schnorr-Müller, K. Slodkowski Clerici, F. Pinna et al. (+7 more)

We present multi-component photometric decompositions of $r$-band Hyper Suprime-Cam images for a sample of 75 edge-on massive compact galaxies (MCGs) at $z < 0.1$, selected as $+2\sigma$ outliers in the stellar mass-velocity dispersion relation and $-2\sigma$ outliers in the velocity dispersion-size relation. MCGs are composed of compact bulges and disks embedded within stellar envelopes of unclear physical nature. Comparing MCGs to a mass- and redshift-matched control sample of non-compact edge-on S0 galaxies with a similar three-component structure, we find that the smaller sizes of MCGs are not driven by a single component. MCGs host more compact bulges and envelopes ($R_\mathrm{e,bulge} \sim 0.3$ versus $0.5$kpc; $R_\mathrm{e,env} \sim 4.4$ versus $5.7$kpc), as well as shorter and thicker disks ($h_R \sim 1.1$ versus $1.7$kpc; $h_R/z_0 \sim 3.9$ versus $5.3$). The sizes of the structural components are coupled, suggesting their formation processes are linked. Median bulge- and disk-to-total flux fractions are similar in both samples, with $B/T \sim 0.3$ and $D/T \sim 0.4$. Envelope ellipticities span $\epsilon_\mathrm{env} \sim 0$-$0.7$, with MCGs exhibiting rounder envelopes. Low- and high-ellipticity envelopes are broadly consistent with stellar halos and thick disks, respectively. However, the nature of intermediate ellipticity envelopes remains ambiguous from photometry alone. The coupling between component sizes, together with the survival of a substantial disk component, argues against dry minor mergers as the dominant envelope-building mechanism. A comparison with 8 relic galaxies reveals that MCGs and relics share similar bulge-disk-envelope structures and follow the same component size-mass relations, consistent with belonging to a common structural family.
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All authors A. Schnorr-Müller, K. Slodkowski Clerici, F. Pinna, R. Merib-Dias, M. Trevisan, T. V. Ricci, F. Ferrari, A. C. Santiago-Menezes, W. L. Becker, F. Palacios

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

Thermal Spin Polarization Driven by Nuclear Spin-Orbit Coupling in Neutron Star Pasta

Hiroyuki Tajima, Yuta Sekino, Hiroshi Funaki et al. (+3 more)

We discuss anomalous spin polarization on the surface of nuclear pasta in a neutron star, driven by a nuclear spin-orbit interaction. We present an effective two-band model of surface-localized neutrons near the nuclear pasta. The central point is the emergence of a Rashba-type spin-orbit hybridization generated by the neutron–nucleus spin-orbit force in the presence of the strong density gradient normal to the pasta surface. Starting from a single-particle Hamiltonian with a central potential and a standard nuclear spin-orbit interaction, we show that the surface spin polarization occurs due to the thermal inhomogeneity even in the absence of a magnetic field. Our study links neutron-star physics and solid-state spintronics and would contribute to understanding the interplay between spin dynamics and strong magnetic fields.
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All authors Hiroyuki Tajima, Yuta Sekino, Hiroshi Funaki, Shota Kisaka, Nobutoshi Yasutake, Mamoru Matsuo

High Energy Astrophysical Phenomena

Radio Study of G76.9+1.0 Pulsar Wind Nebula

Haotian Qiu, Yunlei Huang, C-Y. Ng et al. (+3 more)

Pulsar Wind Nebulae (PWNe) are key astrophysical laboratories for high energy phenomena. Specifically, radio observations and related polarimetry are essential probes to understand acceleration and transport, as well as PWN interaction with environment. We aim to better study the multi-wavelength morphology and magnetic geometry of \gname\ PWN (a system between early and middle ages). We conduct high resolution VLA observations at 3 cm (X band), 6 cm (C band), and 13 cm (S band) and compare them with the archival Chandra X-ray data. We also performed spectral analysis and radio polarimetry based on our radio observations. Our new VLA observations reveal a north-south double-lobed PWN bracketing a bridge-like feature, with the pulsar clearly resolved at C and S bands. The polarization fraction reaches 30% across all bands, with the bridge region showing ordered north-south magnetic fields aligned with the X-ray torus elongation, while the southern outer lobe exhibits fields not following such a direction and the northern lobe displays a more chaotic configuration. Notably, we detect a significant radio-X-ray anti-correlation near the pulsar, with bright radio emission appearing just beyond the compact X-ray PWN boundary, multiwavelength spectral analysis suggest distinct particle populations. The radio PWN spectral index steepens from $\alpha\sim-0.3$ in the inner bridge to $<-1.0$ in the outer lobes, yet we suggest it is less likely related to synchrotron cooling. We tried to use a thick torus model with toroidal $B$-field to reproduce observed features; the result implies possible particle deceleration in the radio PWN. The equipartition magnetic field strength is estimated to be $\sim$15.3\,$\mu$G.
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All authors Haotian Qiu, Yunlei Huang, C-Y. Ng, Lili Yang, Sujie Lin, Yihan Liu

Astrophysics of Galaxies

Puzzling Ultra-Diffuse Galaxy Evolution (PUDGE). II. A transformation pathway from ultra-diffuse galaxies to compact dwarfs in galaxy clusters

Nataša Pavlov and Ana Mitrašinović

Ultra-diffuse galaxies (UDGs) and compact dwarfs (CDs) occupy opposite extremes of the structural parameter space of dwarf galaxies, yet their spatial distributions in clusters suggest a possible evolutionary connection. Observational studies have reported a pronounced anticorrelation between the two populations interpreted as evidence that CDs represent tidally stripped remnants of diffuse progenitors, a scenario that implicitly assumes a compact stellar nucleus must be present at infall to survive environmental processing. We tested this hypothesis using the IllustrisTNG cosmological simulation (TNG100) by examining the UDG and CD populations in seven galaxy clusters and tracing the evolutionary histories of 112 present-day CDs. We confirm that TNG100 reproduces the observed spatial anticorrelation, with CDs concentrated within $d/R_{200} \lesssim 0.2$ and UDGs preferentially inhabiting the cluster outskirts. Tracing CDs back in time, we identified eight systems whose progenitors undergo a transient UDG phase, with extremely high gas fractions ($f_{\rm gas} \gtrsim 0.8$), immediately before cluster infall. In all eight systems, a vast majority of the present-day stellar mass was assembled after the epoch of maximum spatial extent, and the peak star formation rate during the transformation is the highest each galaxy achieves across its entire lifetime. The UDG progenitors show no prominent stellar cores before infall, demonstrating that the compact component of the resulting CD is not an exposed preexisting nucleus but is instead freshly built through starburst-driven star formation during the stripping process itself. Our results reveal a physically motivated UDG-to-CD transformation pathway driven entirely by cluster environment that is fundamentally distinct from classical tidal stripping scenarios and highlight the critical role of gas richness as a prerequisite for this channel.
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Solar and Stellar Astrophysics

Mass distribution of neutron stars in binary systems

Zhe Hu, GuoLiang Lv, ChunHua Zhu et al. (+5 more)

It is known that the mass distribution of the known neutron stars (NSs) exhibits a bimodal pattern. The origin of this distribution remains a subject of debate. We constructed a super-Eddington accretion model for accreting neutron stars and investigated the mass growth and distribution of these stars using the population synthesis method. We find, in our model, the mass growth of NSs depends on the binary orbital period and the mass of the donor star. Our results can successfully account for the bimodal distribution of NS masses. The peak distribution of NS masses at around ~ 1.8 Msun primarily originates from NS binary systems where the donor star mass is less than ~ 1.6 Msun and the orbital period is shorter than 20 days; while, NS systems that may undergo common envelope evolution and these NSs can account for the mass peak at 1.4 Msun.
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All authors Zhe Hu, GuoLiang Lv, ChunHua Zhu, Sufen Guo, Helei Liu, Lin Li, Zhuowen Li, Zhenwei Li

High Energy Astrophysical Phenomena

QPEs from Warped Disk Collisions with EMRIs: Brightness-Recurrence Diagram and Gravitational-Wave Follow-up

Bo-An Chen, Bei You, Giovanni Miniutti et al. (+11 more)

Quasi-Periodic Eruptions (QPEs) display correlated long/short and strong/weak patterns that remain unexplained by existing flat-disk collision models. We propose that these features arise from an extreme-mass-ratio inspiral (EMRI) colliding with a warped accretion disk, likely formed after a tidal disruption event. The warp modulates both recurrence time and burst energy, encoding the disk geometry – and thus the spin of the central supermassive black hole (SMBH) – into the X-ray light curve. We introduce the Brightness-Recurrence Diagram (BRD) to visualize this correlation, where QPE bursts trace an elliptical trajectory driven by the EMRI's apsidal precession; the tilt of this ellipse encodes whether the EMRI is prograde or retrograde relative to the SMBH spin. Applying this model to the prototypical QPE source GSN 069 successfully reproduces the observed patterns. The data are consistent with either a prograde stellar secondary or a retrograde stellar-mass black hole. In the stellar-mass black hole scenario, ongoing orbital decay could render the EMRI detectable by LISA within a few decades, facilitating gravitational-wave follow-up and independent multimessenger constraints on the system.
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All authors Bo-An Chen, Bei You, Giovanni Miniutti, Ning Jiang, Zhen Pan, Tao Yang, Xi-Long Fan, Kai Liao, Xu-Heng Ding, Zong-Hong Zhu, Shuai-Kang Yang, Sai-En Xu, Han He, Xiao Fan

High Energy Astrophysical Phenomena

Pulse Modulation as a Signature of the Asteroid-Neutron Star Collision Model for High-Energy Transients

Partha Bagchi, Biswanath Layek, Dheeraj Saini et al. (+3 more)

Asteroid-neutron star collision models have been proposed as possible sources of high-energy transients, such as gamma-ray bursts (GRBs) and fast radio bursts (FRBs). The sequence of events following the impact of the asteroid and finally dissolving into the neutron star can have several other observable consequences. We propose that due to the development of the off-diagonal moment of inertia (MI) components, the merger's aftermath can lead to the wobbling of the pulsar (assuming the neutron star happens to be a pulsar). Using sample values of various parameters, viz., size, shape, the locations of the deposits, and the pre-existing pulsar deformation parameter ($\eta$), we calculate the detailed pulse profile modulation of the pulsar. We observe a distinct pattern of pulse profile modulation on a characteristic timescale enhanced by a factor of $1/\eta$ compared to the pulse timing. Importantly, even small changes in the MI components, of order $\epsilon$, can produce large pulse profile modulations of order $\epsilon/\eta$ (depending on the relative location of asteroid material deposition). Thus, if an asteroid-neutron star collision is responsible for a high-energy transient, the associated pulse profile modulation may serve as a falsifiable observational signature of such an event.
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All authors Partha Bagchi, Biswanath Layek, Dheeraj Saini, Anjishnu Sarkar, Ajit M. Srivastava, Deepthi Godaba Venkata

Cosmology and Nongalactic Astrophysics

Preliminary cosmological results using extreme accretors Quasar formalism

Rodrigo Sandoval-Orozco, Castalia Alenka Negrete, Paola Marziani et al. (+1 more)

We revisited the xA Quasar formalism from the cosmological point of view, where a completely cleaned and standardized sample is compiled from different literature references. This allowed us to test three different cosmological models including $w$CDM and $w_0w_a$CDM and $\Lambda$CDM resulting in a Hubble constant estimation of $H_0 = 69.8 \pm 2.2$~$\mathrm{km\,s^{-1}\,Mpc^{-1}}$ for the compiled sample alone and $H_0=69.0 \pm 0.9$~$\mathrm{km\,s^{-1}\,Mpc^{-1}}$ when combined with Type I Supernovae (SNIa), Cosmic Chronometers and the Cosmic Microwave Background (CMB) distance priors. Using both the $w$CDM and $w_0w_a$CDM a weak Bayesian preference for the dynamical dark energy models over the $\Lambda$CDM model was found. A comparative analysis was performed with other AGN based methods in cosmology like the Reverberation Mapping, the X-Ray and UV non-linear relation and the Angular distance measurements. We conclude that the significant intrinsic dispersion is a key issue present in all samples. Overcoming this dispersion is key to establish xA and other AGN samples as robust and precise cosmological probes.
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All authors Rodrigo Sandoval-Orozco, Castalia Alenka Negrete, Paola Marziani, Jackson Levi Said

Solar and Stellar Astrophysics

High-precision K2/TESS Photometry and HERMES Spectroscopy of Four Bright Field Stars

Otto Trust, Santosh Joshi, Benard Nsamba et al. (+13 more)

Space-based photometry from K2 and TESS, coupled with high-resolution spectroscopy, provides a unique opportunity to re-examine the variability and chemical nature of four bright stars (HD 73135, BD +19$^\circ$ 2045, BD +19$^\circ$ 2046, and TYC 1395-855-1), which were poorly characterised by the original ground-based campaign under the Nainital-Cape survey. We aim to establish the nature of the variability, chemical properties, and evolutionary status of these stars. We analysed ground-based Johnson $BV$ photometry combined with K2 and TESS time-series data to establish the nature of their variability. Using high-resolution HERMES spectroscopy, we determined their spectral classifications and chemical abundances. In addition, we used the inferred spectroscopic constraints with grid-based evolutionary modelling to derive their corresponding masses, radii, and ages. The frequency analysis reveals a diversity of low-amplitude variability across the sample. HD 73135 shows a persistent modulation near 1.5 d that is most consistent with rotation, although an ellipsoidal-binary interpretation cannot yet be excluded, while BD +19$^\circ$ 2045 exhibits multiple low-frequency signals and is identified as a new candidate $\gamma$ Doradus $g$-mode pulsator. BD +19$^\circ$ 2046 and TYC 1395-855-1 are non-variable or only marginally variable in K2 but display coherent low-frequency modulation in TESS of uncertain origin. Spectroscopically, HD 73135 is the only chemically peculiar star in the sample and shows a clear Am abundance pattern, whereas the other three stars are chemically normal. These results demonstrate the value of combining legacy survey data with contemporary photometric and spectroscopic analysis.
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All authors Otto Trust, Santosh Joshi, Benard Nsamba, Sharon Aol, Owen Vermeulen, Ronald Ssembatya, Peter De Cat, Patricia Lampens, Sydney A. Barnes, Partha P. Goswami, Athul Dileep, Surath C. Ghosh, Pramod S. Kumar, Edward Jurua, Mrinmoy Sarkar, Sarabjeet S. Bedi

High Energy Astrophysical Phenomena

The Evolution of Cataclysmic Variables Under Various Magnetic Braking Prescriptions

Wen-Shi Tang, Xiang-Dong Li, Zhe Cui et al. (+2 more)

Recent studies revealed discrepancies between observations and the predictions of the standard magnetic braking (MB). Although alternative models have been broadly discussed in neutron star binaries, they have not been systematically tested in cataclysmic variables (CVs). In this work, we investigate the performance of four MB models in CVs: the standard MB, the Convection And Rotation Boosted (CARB) model, the $\tau$-boosted model, and the saturated, boosted, and disrupted (SBD) model. We find that both the CARB and $\tau$-boosted models appear too strong so that it fails to reproduce the location of the period gap in CVs, indicating that they are not appropriate for CVs. Furthermore, we present a comparison between the standard MB and the SBD models. Compared with the standard model, although the SBD model can better reproduce some observational features, it also exacerbates certain discrepancies between theory and observations. We also find that different prescriptions for the convective turnover timescale have a significant impact on the results in the non-standard MBs. Finally, we discuss the impact of the SBD model on the formation and evolution of AM CVn.
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All authors Wen-Shi Tang, Xiang-Dong Li, Zhe Cui, Zhu-Ling Deng, Wei-Min Gu

High Energy Astrophysical Phenomena

SN~2018erx: A fast-evolving, dust-reddened Type Icn supernova with broad C II emission lines

Kaustav K. Das, Anjasha Gangopadhyay, Mansi M. Kasliwal et al. (+17 more)

We present the discovery and characterization of SN~2018erx (ZTF18abkmbpy), a fast-evolving, unusually red, interacting stripped-envelope supernova. Spectroscopically, SN~2018erx shows broad \ion{C}{2} emission with characteristic widths of $\sim\!3800$~km~s$^{-1}$, consistent with interaction with carbon-rich circumstellar material and a Type~Icn core-collapse SN classification. Photometrically, it evolves rapidly, rising from half-maximum to peak in 2.1~d and declining back in 3.1~d. Semi-analytical CSM-interaction modeling favors a compact, shell-like CSM with $M_{\rm CSM}\approx0.3\,M_\odot$, $R_0\approx0.7$~AU, and a low ejecta mass of $M_{\rm ej}\approx0.11\,M_\odot$. The radioactive yield is also small, with $M_{\rm Ni}\lesssim(3$–$5)\times10^{-3}\,M_\odot$, placing SN~2018erx at the low end of the H-poor distribution. At +29~d after peak, we detect a near-infrared excess consistent with pre-existing local circumstellar dust, with $M_{\rm d}\sim10^{-6}$–$10^{-5}\,M_\odot$. Together, the rapid evolution, strong local reddening, carbon-rich emission, and dust point to a multi-component circumstellar environment: a dense inner interaction region from enhanced pre-SN mass loss and an outer dusty layer from an earlier mass-loss episode roughly $10$–$200$~yr before core collapse. These properties favor an ultra-stripped core-collapse explosion of a low-mass He star in a binary system, with fallback-modified Wolf–Rayet collapse or merger-driven mass loss remaining possible alternatives. SN~2018erx provides rare insight into the mass-loss history of stripped-envelope SNe and suggests that dust-enshrouded explosions of this kind may be underrepresented in optical surveys.
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All authors Kaustav K. Das, Anjasha Gangopadhyay, Mansi M. Kasliwal, Jesper Sollerman, Daniel A. Perley, Steve Schulze, Christoffer Fremling, Michael W. Coughlin, Kishalay De, Avishay Gal-Yam, Ariel Goobar, Matthew Graham, Frank J. Masci, Takashi J. Moriya, Josiah Purdum, Sam Rose, Ben Rusholme, Nikhil Sarin, Roger Smith, Daichi Tsuna

Saturday 23 May

Instrumentation and Methods for Astrophysics

White dwarf planetary systems in the ultraviolet

Jamie Williams, Amy Bonsor, Boris Gänsicke et al. (+9 more)

Almost every known planet host will evolve into a white dwarf, and the surviving planetary material will continue to orbit this stellar remnant. Asteroids perturbed onto star-grazing orbits will become disrupted, forming an accretion disk which causes "enrichment" of the otherwise pure hydrogen or helium atmosphere. Measurements of these photospheric abundances give detailed insights into the interior compositions of exo-planetesimals with an accuracy not possible for intact exoplanets around main sequence stars. This method has revealed the diversity of rocky material in our solar neighborhood, including primitive, chondritic planetesimals, fragments of planetary cores, and even analogues of Kuiper belt objects. The planetesimal abundances can be used as an input to interior structure models. The far-ultraviolet is a key wavelength range for this field because it contains strong transitions for almost every element of interest, many of which are undetectable using ground-based optical spectroscopy. Without the FUV, we will no longer have access to the C, N, P, S content of exoplanetary bodies and thus will no longer be able to probe how volatiles interact with refractories, which is crucial to understanding planet formation-and even the origin of life. The medium resolution and high sensitivity of COS on HST has been indispensable in determining the compositions of dozens of exo-planetesimals. However, the only two medium resolution FUV-capable spectrographs are currently onboard HST, with no plans for replacements until the 2040s. An extension to the HST mission is critical for the field of white dwarf planetary systems, because the loss of FUV capability would leave us blind to volatiles. Boosting the orbit of HST would allow us to measure volatile abundances, determine the rocky planetary occurrence rate, investigate differentiation, and probe for photospheric abundance variability.
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All authors Jamie Williams, Amy Bonsor, Boris Gänsicke, Joseph Guidry, JJ Hermes, Lou Baya Ould Rouis, Laura Rogers, Pier-Emmanuel Tremblay, Snehalata Sahu, Andrew Swan, David Wilson, Siyi Xu

Instrumentation and Methods for Astrophysics

Exploring Space Weather From Young Solar-like Stars as Windows to Exoplanetary Habitability

V. S. Airapetian, K. Namekata, K. France et al. (+10 more)

Young solar-like stars are efficient generators of magnetic activity, superflares, coronal mass ejections (CMEs), and stellar energetic particles. These phenomena drive the early evolution of stars and shape the habitability of exoplanets. The Hubble Space Telescope (HST), with its unmatched far-ultraviolet (FUV) and near-ultraviolet (NUV) sensitivity, provides a uniquely powerful window into these processes one that no current or near future facility can replicate. This white paper articulates four interconnected science questions that require Hubble continued operation and targeted observing programs over the next 10 to 15 years, enriched by new multi-wavelength insights from deep X-ray surveys of open clusters. We describe required instrument capabilities, critical synergies with contemporaneous missions (JWST, Chandra, XMM Newton, TESS, and the Nancy Grace Roman Space Telescope), and the fundamental role Hubble observations will play in calibrating and informing the design of the Habitable Worlds Observatory (HWO). We advocate for large scale coordinated campaigns targeting young solar-like stars as the highest priority science program for the coming decade.
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All authors V. S. Airapetian, K. Namekata, K. France, T. Sextro, M. Jin, J. Hu, T. Shi, K. V. Getman, E. D. Feigelson, J. Schlieder, M. McElwain, K. G. Carpenter, D. Sur

Solar and Stellar Astrophysics

Deep Learning-Enabled Prediction of Geoeffective CMEs Using SOHO and SDO Observations

Zhaoxin Yan, Jason T. L. Wang, Haimin Wang et al. (+5 more)

Understanding and forecasting the geoeffectiveness of a coronal mass ejection (CME) is crucial for protecting infrastructure in the near-Earth space environment and on Earth. In this study, we present a novel fusion model to forecast the geoeffectiveness of CME events. Our model combines convolutional neural networks for feature learning and a prediction network for feature fusion and event classification. The model is trained by observations from instruments including the Large Angle Spectroscopic Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). The trained model is then used to predict whether an Earth-reaching CME will cause a geomagnetic storm and/or the probability that the CME will cause such a storm. Experimental results based on a five-fold cross validation scheme demonstrate the good performance of our fusion model, achieving a mean true skill statistic (TSS) score of 0.703 when the model is used as a deterministic prediction tool, and a mean Brier score of 0.095 when the model is used as a probabilistic forecasting tool, where a TSS score of 1 or a Brier score of 0 indicates perfect performance. This work contributes to forecasting the causal relationship between Earth-directed CMEs and geomagnetic storms in solar-terrestrial interactions.
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All authors Zhaoxin Yan, Jason T. L. Wang, Haimin Wang, Harim Lee, Ju Jing, Yan Xu, Chunhui Xu, Vasyl Yurchyshyn

Astrophysics of Galaxies

A Three-Decade VLBI Study of the Nucleus in the Lobe-Dominated Quasar 3C207

D. H. Hough, J. P. Linick, E. L. Danielson et al. (+8 more)

We present results from very-long-baseline-interferometry (VLBI) observations of the nucleus in the lobe-dominated quasar 3C207. These observations were completed at 8.4 or 10.7 GHz (X-band) from 1981 to 2010, spanning 29 years. The nucleus of 3C207 is the strongest and most variable in the 3CR complete sample of LDQs, which is under study to test relativistic jet models over a wide range of jet orientation angles. Images have typical resolutions of ~0.5-1.0 milliarcseconds (mas) and sensitivities of ~0.1-0.2 mJy beam^{-1}. The VLBI core region has flux density outbursts at mean intervals of ~7 yr; two of these are multiple outbursts from a stationary "true: core that feeds a "swinging component" ~0.5 mas to the east. The position angle (PA) of the swinging component shows a long-term increase of ~40{\deg}, with a short-term reversal of ~10{\deg}. A one-sided, curved VLBI jet extends ~25 mas eastward, with components spanning a PA range of ~25{\deg}. The jet components have average apparent transverse velocities ~10c. One component shows apparent acceleration from 7c to 14c at 2-3 mas from the true core, where the flow is redirected toward PA ~90{\deg}. Another component shows marginal evidence for apparent deceleration. Individual jet components expand until reaching the recollimation zone. Our results are consistent with a physical model in which 3C207 has quasi-periodic outbursts, jet precession by ballistic components on a conical surface with a small opening angle, and a recollimation process that modifies component motions and narrows the conical geometry on a scale of ~100 pc.
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All authors D. H. Hough, J. P. Linick, E. L. Danielson, S. M. Escobedo, H. D. Ibaroudene, B. D. Sadler, N. A. Polito, R. C. Vermeulen, C. E. Aars, C. L. Newton, T. A. Rector

Cosmology and Nongalactic Astrophysics

Gravitational Waves from Post-Inflationary Magnetism: Direct and Scalar-Induced Contributions

Subhasis Maiti

We study stochastic gravitational waves generated in a post-inflationary magnetogenesis scenario with time-dependent gauge couplings during inflation and reheating. In this setup, magnetic anisotropic stress directly sources gravitational waves, while the induced curvature perturbations generate an additional scalar-induced GW component. We compare the spectral behavior of the two contributions and find that the magnetic component dominates the peak amplitude, whereas the scalar-induced contribution becomes important on larger scales. For blue magnetic spectra with $n_{\rm b}\geq3/2$, both spectra follow the universal infrared scaling $\Omega_{\rm GW}(f\ll f_{\rm peak})\propto f^3$. However, their ultraviolet behaviors differ significantly for $f>f_{\rm peak}$, leading to distinct spectral features. For suitable reheating and magnetogenesis parameters, the resulting GW signal naturally extends into the nano-Hz range relevant for pulsar timing array observations, while remaining consistent with current bounds. The distinct spectral features of the two components may provide a useful probe of reheating dynamics and primordial magnetogenesis.
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High Energy Astrophysical Phenomena

Model dependence of XRISM black-hole spin constraints in Cyg X-1

Andrzej A. Zdziarski, Swadesh Chand, Michal Szanecki et al. (+2 more)

We study the persistent black hole X-ray binary Cyg X-1, recently observed by XRISM Resolve and simultaneously by NICER and NuSTAR in its hard spectral state. We confirm the result of Draghis et al. that fits of the Resolve data alone with the simplest available relativistic reflection model, relxill, yield a black hole spin parameter close to the maximum, $a_* = 0.99$. However, fitting with an improved, Comptonization-based model, relxillCp, yields a low $a_*=0.0^{+0.17}$. A similarly low range is obtained with another Comptonization-based model, reflkerrD. Then, fits to the combined data require two Comptonization models but are consistent with any spin value. We conclude that the spin value of Cyg X-1 is strongly model-dependent. However, low spin values are consistent with the constraints from gravitational waves. All of the models constrain the inner disk radius to be <10 gravitational radii, which is consistent with a recent finding of the weakness of thermal reverberation in Cyg X-1. The suggested source geometry is that of an outflowing disk corona, which was also proposed to explain the X-ray polarization observed from this source.
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All authors Andrzej A. Zdziarski, Swadesh Chand, Michal Szanecki, Gulab Dewangan, Barbara De Marco

High Energy Astrophysical Phenomena

New galaxy cluster in the Zone of Avoidance SRGe CL0512.7+3712. Discovery and multi-wavelength characterization

Ildar Khabibullin, Eugene Churazov, Natalya Lyskova et al. (+9 more)

The census of massive clusters of galaxies in the local Universe is almost complete, thanks to their prominent observational signatures at X-ray, optical, and sub-mm wavelengths. Nevertheless, a number of such systems are likely to be missing and hidden behind the plane of our Galaxy, where high interstellar absorption as well as strong contamination by foreground stellar and diffuse sources prevent detection of even the brightest and the most massive ones. Here we report the discovery and multiwavelength characterization of such a cluster in the zone of avoidance (ZoA) SRGe CL0512.7+3712 in the data of SRG/eROSITA all-sky survey. Combining the data of radio, optical, and infrared surveys, we identify overdensity of possible red sequence galaxies, as well as the candidate brightest cluster galaxy. Follow-up optical and X-ray observations confirm that the newly found object is a massive ($M_{500c}=(4-5)\cdot 10^{14}M_{\odot}$, $kT\approx 5 $ keV) galaxy cluster at redshift $z=0.0745$ with possible indications of unrelaxed dynamical scale. Location and elongation of this cluster is consistent with an expectation from the large-scale structure at this redshift, and it might be a part of an extended overdensity of such objects in the Galactic Anticenter direction. Examination of X-ray, radio, and infrared data in the locations of ZoA, where similar objects are expected to be found based on the large-scale structure properties, might reveal another $\sim10$ clusters at this redshift in future.
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All authors Ildar Khabibullin, Eugene Churazov, Natalya Lyskova, Ilfan Bikmaev, Eldar Irtuganov, Mikhail Suslikov, Igor Zaznobin, William R. Forman, Ralph Kraft, Rashid Sunyaev, Alexei Moiseev, Arkadiy Sarkisyan

High Energy Astrophysical Phenomena

Timing and Spectral Studies of PSR J2022+3842 with NICER and NuSTAR

Jia-Ning Hu, Xiang-Hua Li, Xian-Ao Wang et al. (+6 more)

We report on the long-term timing analysis of PSR J2022+3842 using observations from the Neutron Star Interior Composition Explorer (NICER), along with spectral properties derived from joint observations with NICER and the Nuclear Spectroscopic Telescope Array (NuSTAR). Two large glitches are identified around MJD 58335 with $\Delta\nu=25.35(2)\times10^{-6}$ Hz and MJD 58875 with $\Delta\nu=52.078(6)\times10^{-6}$ Hz. Furthermore, phase-resolved spectroscopy reveals that the X-ray emission is well described by a power-law model across different phase intervals. The phase-integrated X-ray spectrum (1-79 keV) has a photon index of $\Gamma=1.22(7)$, yielding an unabsorbed 0.5-10 keV flux of $8.9(6)\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$. The main pulse spectrum (1.2-79 keV) and the inter-pulse spectrum (1-70 keV) are harder with $\Gamma=1.17(4)$ and $\Gamma=1.03^{+0.07}_{-0.06}$ separately, producing an unabsorbed 0.5-10 keV flux of $33.2(2)\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$ and $29(3)\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$. Investigation of the pulse profile evolution with time shows that no significant variations were observed.
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All authors Jia-Ning Hu, Xiang-Hua Li, Xian-Ao Wang, Han-Long Peng, Shi-Qi Zhou, Wen-Tao Ye, Shi-Jie Zheng, Ze-Jun Jiang, Ming-Yu Ge

Solar and Stellar Astrophysics

Observational Technological Innovations and Future Development of the Lijiang Coronagraph

Xuefei Zhang, Yu Liu, Tengfei Song et al. (+5 more)

As a core ground-based coronal observation facility in China's low-latitude high-altitude regions, the Lijiang Coronagraph leverages the natural advantages of Lijiang Astronomical Observation Station, including its 3200 m altitude and low atmospheric turbulence. It has undergone a full development process, from introduction via Chinese-Japanese cooperation to independent innovation and iteration. This paper systematically summarizes its core technological innovations: upgrade of the automatic operating system, integration of the dual-band observation system, stray light suppression based on image differencing before and after cleaning, and high-precision image calibration and registration. These advances have significantly improved observation efficiency and data quality, laying a solid foundation for high-quality observations. Scientifically, the data reveal that 1.1 solar radii is a highly correlated region between coronal green line brightness and magnetic field intensity. The study also confirms a strong correlation between the coronal green line and the SDO/AIA 21.1 nm extreme ultraviolet band (correlation coefficient: 0.89-0.99), supporting early warning research on Coronal Mass Ejections (CMEs). These results provide key data for verifying coronal heating mechanisms and exploring the origin of the slow solar wind. The experience from the Lijiang Coronagraph not only lays a foundation for China's next-generation large-aperture coronagraphs, but also accelerates progress in low coronal observation capabilities, enabling the country to build internationally competitive capabilities in this field. The system is also an important part of the global coronal observation network.
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All authors Xuefei Zhang, Yu Liu, Tengfei Song, Mingyu Zhao, Xiaobo Li, Mingzhe Sun, Feiyang Sha, Xiande Liu

Astrophysics of Galaxies

FASTAR – II. Semi-resolved evolutionary stellar population models

Ignacio Martín-Navarro, Alexandre Vazdekis, Luis Peralta de Arriba et al. (+12 more)

Standard evolutionary synthesis models rely on the assumption of a fully sampled stellar initial mass function (IMF). Under this assumption, the age, chemical composition, and IMF uniquely define the predicted absorption spectra. However, with current instrumentation pushing observations towards higher spatial resolutions and lower surface brightnesses, the assumption of a fully sampled IMF does not always hold true. Here we present the semi-resolved version of the FASTAR models, a comprehensive set of evolutionary synthesis predictions able to reproduce the stochastic behavior of discretely-sampled IMFs. Semi-resolved FASTAR predictions share the same evolutionary principles, ingredients, and features of the integral (fully sampled IMF) version of the FASTAR models, expanding a range of ages from 20 Myr to 14 Gyr, metallicities between -2.5 < [M/H] < +0.3, and several IMF functional forms. Detailed spectroscopic measurements can be carried out within the 3,540-7,400 A wavelength range, and low-resolution spectral energy distributions can also be synthesized over a wider 2,000-to-12,000 A coverage. Semi-resolved FASTAR models also depend on the number of stars contributing to the observed spectra, which determines the effective sampling of the different stellar evolutionary phases along the isochrones. This incomplete sampling implies that semi-resolved FASTAR models are inevitably stochastic. On top of the inherent stochasticity of the models, derived quantities such as equivalent widths, colors, or mass-to-light ratios might present strong deviations compared to standard fully sampled simple stellar population models. This stochasticity dilutes the boundary between model predictions and data, promoting new sampling-based inference approaches. FASTAR semi-resolved models allow for the effective exploration of the parameter space thanks to their optimized, JAX-based computation.
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All authors Ignacio Martín-Navarro, Alexandre Vazdekis, Luis Peralta de Arriba, Isaac Alonso Asensio, Patricia Iglesias Navarro, Eirini Angeloudi, Francesco La Barbera, Miguel Cerviño, Katja Fahrion, Tereza Jerabkova, Michael A. Beasley, Jesús Falcón-Barroso, Marc Huertas-Company, Sebastián F. Sánchez, Prashin Jethwa

Astrophysics of Galaxies

Changing-look Active Galactic Nuclei from SDSS, LAMOST and DESI Surveys

Guohai Chen, Wenxin Yang, Xuhong Ye et al. (+4 more)

Results. We identify 45 CLAGNs, of which 40 are newly reported. The sample is dominated by turn-off events, comprising 43 turn-off and 2 turn-on sources. This may be because Type 2 AGNs either lack a detectable broad-line region or have their broad emission lines obscured by circumnuclear dust, making turn-on events more difficult to identify. Using DESI spectra as a third spectroscopic epoch, we identified 12 RCLAGNs. Of the 14 newly identified CLAGNs with three-epoch spectroscopic coverage, 7 objects, i.e. 50%, are confirmed as RCLAGNs. In the previously reported sample, 5 out of 16 objects with available DESI spectra, corresponding to ~31%, exhibit repeating CL behaviour. The relatively high incidence of repeated CL behaviour suggests that CL transitions are associated with recurrent physical processes, such as accretion-rate fluctuations or accretion-disk instabilities. In the logM_BH–log(L_bol/L_Edd) plane, the RCLAGNs display a clear high–low–high accretion-state evolution, indicating a close connection between repeated CL behaviour and recurrent variations in accretion power. The rest-frame upper limits on the transition timescales are ~10 yr for the first transition and 4 yr for the second transition.
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All authors Guohai Chen, Wenxin Yang, Xuhong Ye, Zhiqiang Chen, Zhiyuan Pei, Hubing Xiao, Junhui Fan

Solar and Stellar Astrophysics

Radiative MHD Studies of Solar Spicules: Driving Mechanisms and the Role of Background Magnetic Field

Jin Li, Lei Ni, Robertus Erdélyi et al. (+3 more)

We conduct 2.5D radiative magnetohydrodynamic (MHD) simulations to investigate the driving mechanisms of the solar spicules in coronal holes and how the different background magnetic fields affect their formation. The simulation model includes the upper convection zone, photosphere, chromosphere, and lower corona. We run several cases with different background magnetic fields to primarily explore the effects of magnetic field strength and inclination on the characteristics of the formed spicules, such as the maximum height, lifetime, maximum upward velocity, and deceleration. According to the results, we find that a weaker background magnetic field tends to cause solar spicules that exhibit higher heights, longer lifetimes and faster maximum upward velocities. Additionally, when the background magnetic field inclines, the generated spicules incline accordingly; compared with those in a vertical magnetic field, the spicules in the inclined magnetic field are relatively longer, with smaller decelerations, longer lifetimes and lower maximum upward velocities. Meanwhile, by tracking and analyzing the formation processes of the spicules in two cases with different magnetic field strengths, we find that most of the spicules are mainly driven by shock waves induced by convective and turbulent motions around the solar surface, while less than one third of the spicules are primarily driven by high-velocity reconnection outflows. These results provide a more in-depth basis for the theoretical understanding of the driving mechanisms and formation processes of solar spicules.
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All authors Jin Li, Lei Ni, Robertus Erdélyi, Jun Lin, Xiaoli Yan, Guanchong Cheng

Solar and Stellar Astrophysics

Evolution of a long-period Cataclysmic Variable from the viewpoint of the donor star: the case of SDSS J085210.48+783246.6

G. Tovmassian, D. Belloni, I. Mora Zamora et al. (+8 more)

Cataclysmic variables were long considered to be close binaries consisting of a white dwarf and a Roche-lobe-filling, near-zero-age main-sequence (ZAMS) red or brown dwarf. Recent massive surveys have uncovered an increasing number of binaries with similar spectral characteristics but harboring secondary stars that have undergone nuclear evolution and partial envelope stripping, many with orbital periods far exceeding the normal upper limits for ordinary CVs. We present a detailed study of a newly discovered CV with a 17.109 h period and determine its basic stellar parameters. We also discuss the evolutionary paths leading to the formation of these extremely long-period cataclysmic variables. We consider the implications of the new evolutionary hypothesis on their further evolution into double-degenerate binaries.
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All authors G. Tovmassian, D. Belloni, I. Mora Zamora, B.T. Gaensicke, S. Zharikov, J. Echevarria, M.R. Schreiber, P. D'Avanzo, P. Ochner, R. Ashley, K. Inight

Astrophysics of Galaxies

The 3D Structure and Kinematics of the Local Disk-Halo Interface: Intermediate-velocity Clouds are the Minority of High-altitude Clouds in the Solar Neighborhood

Theo J. O'Neill, Andrew K. Saydjari, Catherine Zucker et al. (+4 more)

Studies of the Milky Way's disk-halo interface have historically identified inflowing and outflowing gas incompatible with disk rotation on the basis of radial velocity, leading to the well-known categories of intermediate-velocity clouds (IVCs) and high-velocity clouds (HVCs). In this work, we leverage recent progress in 3D dust mapping of the Solar Neighborhood to perform the first 3D spatial search for anomalous-velocity clouds at the local disk-halo interface. We identify 1,695 dust clouds within 1.25 kpc of the Sun (with altitudes ranging between z=-646 pc to z=+928 pc) by applying a topological structure finding method to a parsec-resolution 3D dust map. We then evaluate the morphological similarity between these clouds and HI 21 cm emission to measure cloud kinematics, and construct a sample of 519 clouds with high-confidence distances, 3D morphologies, and radial velocities. Among these are several IVCs (embedded within the well-known Intermediate Velocity Arch complex) now identified in 3D for the first time, enabling direct measurement of their distances, sizes, densities, masses, pressures, and dust-to-gas ratios. We observe a pronounced asymmetry in the vertical distribution of all clouds in the Solar Neighborhood, with $(2.9 \pm 0.2) \times$ more clouds in the Northern Galactic hemisphere than the Southern above altitudes at which IVCs are present ($|z| \geq 480$ pc). IVCs make up only 18% of the total number of clouds located at these high altitudes, with the remainder having low velocities – highlighting the importance of accounting for low-radial-velocity structures when evaluating the local disk-halo interface and modeling feedback-driven Galactic fountain flows.
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All authors Theo J. O'Neill, Andrew K. Saydjari, Catherine Zucker, Eric W. Koch, Robert A. Benjamin, Philipp Frank, Stephanie Yoshida

Cosmology and Nongalactic Astrophysics

Constraining the Potential Index $n$ of the Early Dark Energy Model Using Cosmic Birefringence from Planck and ACT

Kedi Zhang and Lu Yin

Cosmic birefringence and the Hubble tension represent compelling challenges to the standard $\Lambda$CDM model. The early dark energy (EDE) model with potentials $V(\phi) \propto [1-\cos(\phi/f)]^n$ offer a unified framework to address both anomalies through energy injection near matter-radiation equality and parity-violating Chern–Simons coupling to photons. While previous studies have focused on $n=3$, the dependence of the birefringence signal on the potential index $n$ remains largely unexplored. We perform a comprehensive statistical analysis of axion-like EDE models with $n=2$, $n=3$, and $n=\infty$, using $EB$ cross-polarization data from Planck-$EB$ and ACT-$EB$. The $n=2$ model is severely disadvantaged, displaying extreme coupling values ($gM_{\rm pl} \approx 69.912$ for Planck, $-40.726$ for ACT), large $\chi^2_{\rm min}$ (144.52 and 86.93), and $\Delta \chi^2<1$ with many local minials. Conversely, $n=3$ achieves the best fits ($\chi^2_{\rm min} = 65.70$ and $48.08$) with consistent couplings ($gM_{\rm pl} = -0.210 \pm 0.024$ and $-0.158 \pm 0.025$) that accurately reproduce observations across all angular scales. We checked that the $n=3$ configuration represents the optimal choice for simultaneously addressing the Hubble tension and cosmic birefringence within a theoretically viable framework.
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Friday 22 May

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

First results of a high sensitivity and transportable Ring Laser Gyroscope

A. Basti, G. Carelli, G. Di Somma et al. (+6 more)

Within the GINGER project, aimed at installing an array of large frame ring laser gyroscopes for fundamental physics tests and as part of a geophysics observatory located in the underground laboratory at Gran Sasso, Italy (LNGS-INFN), we are developing a ring laser gyroscope design to reduce spurious rotation of instrumental origin and the ability to extend the cavity side length from 1.5 up to 5 m, thanks to the implementation of suitable spacers. The new design led to a prototype, called TRIO, with a side length of 1.52 m, conceived as a transportable instrument. The present paper reports on several preliminary measurements of the Earth angular velocity carried out with TRIO. Results have the twofold objective to assess the instrument performance in the present geometrical configuration and to test validity of the design in view of the GINGER project. To this aim, data obtained with TRIO are compared with typical data acquired with other, previously made, gyroscope prototypes, including the large frame GINGERINO already in operation at the Gran Sasso underground site.
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All authors A. Basti, G. Carelli, G. Di Somma, A.D.V. Di Virgilio, F. Fuso, R. Macchia, E. Maccioni, P. Marsili, A. Pasqualetti