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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 14 October · still arriving

Solar and Stellar Astrophysics

High-Frequency Transverse Waves in Chromospheric Fibrils Revealed by DKIST

Qifan Dong, Xiaoli Yan, Zhike Xue et al. (+4 more)

Chromospheric fibrils are ubiquitous dynamical structures that can support magnetohydrodynamic waves and may contribute to energy transport in the solar atmosphere. Using high-resolution observations from the Visible Broadband Imager (VBI) onboard the Daniel K. Inouye Solar Telescope (DKIST), we investigate transverse oscillations of H$\alpha$ fibrils. Our observations encompass both quiet-Sun and active regions. The results reveal that high-frequency transverse oscillations are highly prevalent in fibrils across different magnetic environments. The detected oscillations exhibit typical periods of 56 $\pm$ 49 s, displacement amplitudes of 37 $\pm$ 25 km, velocity amplitudes of 6 $\pm$ 4 km\,s$^{-1}$, and phase velocities of 21 $\pm$ 13 km\,s$^{-1}$. Under typical chromospheric conditions, the estimated wave energy flux ranges from 20 to 200 W\,m$^{-2}$. The characteristics of these transverse oscillations are consistent with those of Alfvénic kink-mode waves. Our results reveal the existence of the high-frequency, small-amplitude transverse waves in chromospheric fibrils and providing new constraints on their contribution to the chromospheric and coronal heating.
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All authors Qifan Dong, Xiaoli Yan, Zhike Xue, Liheng Yang, Jincheng Wang, Yadan Duan, Zhe Xu

Solar and Stellar Astrophysics

Evidence for Suppressed Non-thermal Broadening in a Flare Ribbon from Stereoscopic Observations

Ziwen Huang, L. P. Chitta and L. Teriaca

Flare ribbons mark the footpoints of newly reconnected magnetic loops and are commonly associated with strong plasma flows and enhanced non-thermal broadening of transition-region lines due to impulsive energy deposition. However, the mechanisms governing energy transport into flare ribbons remain uncertain, particularly under different magnetic field configurations. We investigate the energy deposition process at a flare ribbon near a sunspot by determining the physical nature of its small-scale downflows. We study small-scale downflows in a remote ribbon during the M7.7-class event on 30 September 2024, using coordinated observations from SDO, IRIS, and Solar Orbiter. We use stereoscopic imaging from Solar Orbiter and IRIS to detect plane-of-sky motions on small scales (200 km). We conduct spectroscopic analysis of IRIS Si IV profiles, complemented by C II and Mg II diagnostics. Apparent downflow speeds measured from Solar Orbiter imaging (limb view) are 85-130 km/s, while IRIS images (disk view) reveal plane-of-sky speeds of 70-85 km/s. In contrast, IRIS Si IV profiles at the brightest ribbon pixels are well approximated by a single Gaussian, with minimal Doppler shifts and unexpectedly small non-thermal widths (10 km/s). Peak Si IV emission also coincides with a deeper Mg II central reversal, while electron densities are one to two orders of magnitude higher than typical quiet-Sun values. The absence of significant line-of-sight velocities and non-thermal broadening differs from typical flare-ribbon behavior. Our results are consistent with a scenario in which plasma motions are guided by highly inclined (nearly horizontal) magnetic fields in chromospheric canopy and are not accompanied by strong turbulence or wave motions. This study suggests that flare ribbons can exhibit a wide diversity of lower-atmospheric responses and emphasizes the critical role of magnetic field geometry.
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Astrophysics of Galaxies

Microcaustics: Fast GPU-Accelerated Dynamical Microlensing of Time-Dependent Extended Sources

Joshua Fagin, Connor Stone, James Hung-Hsu Chan et al. (+7 more)

Gravitational microlensing probes unresolved quasar accretion disc structure and compact objects in lens galaxies and is an important systematic in strong-lens time-delay cosmography. Most analyses use static microlensing map simulations because evolving individual microlenses and caustics is computationally prohibitive. We present Microcaustics, a GPU-accelerated Python package built on PyTorch for dynamical microlensing of time-dependent extended sources in strong gravitational lenses. It combines a local-exact/far-field deflection solver, source-directed lens-plane scouting with temporal reuse, and biquadratic inverse polygon mapping (IPM). GPU batching and fused Triton rasterization accelerate the calculation, while binary caustic labels track source-centred crossings. Across three simulated quadruply lensed quasar systems, our package generates a 10-year, 147-frame multiband light curve in an amortized median of 0.68 s (0.88 s with labels) on a consumer GPU with a median light-curve RMSE of 0.35 mmag, while recovering every reference source-centred caustic crossing. At comparable map accuracy, the batched throughput is 780 times higher than that of a recent CUDA IPM implementation and extrapolates to a speedup of millions relative to classic GPU-D. We demonstrate that our IPM converges as $N_{\rm ray}^{-0.84}$, approaching the idealized $N_{\rm ray}^{-1}$ convergence rate of piecewise-affine IPM and improving upon the $N_{\rm ray}^{-1/2}$ inverse ray-shooting rate. We also introduce a GPU-resident general relativistic and reverberating quasar source model and demonstrate our method with an evolving supernova source. These advances make fully dynamical stellar fields practical for Bayesian and simulation-based inference.
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All authors Joshua Fagin, Connor Stone, James Hung-Hsu Chan, Sophia Miskiewicz, Henry Best, Paras Sharma, Matthew O'Dowd, Laurence Perreault-Levasseur, Yashar Hezaveh, Simon Birrer

High Energy Astrophysical Phenomena

Constraint on particle mass of dark matter based on XTE J1814-338 observation and DANS model

Lin Wang and Dehua Wen

The small observed radius of neutron star XTE J1814-338 (with mass of $1.21_{-0.05}^{+0.05}$ $M_{\odot}$ and radius of $7_{-0.4}^{+0.4}$ $\rm{km}$) poses a great challenge to the traditional neutron star model composed of normal nuclear matter. The dark matter admixed neutron star (DANS) model provides a clue to solve this challenge. By employing the self-interacting fermionic dark matter model, we investigate the effects of dark matter parameters including the particle mass, self-interaction strength, and mass fraction of dark matter on the properties of DANSs. Our results indicate that the joint constraints from the observation of XTE J1814-338 and the astrophysical limits on the dark matter self-interaction cross section derived from observations of different colliding galaxy clusters can provide effective constraints on the particle mass of dark matter. Specifically, to simultaneously satisfy the small radius of XTE J1814-338 and the self-interaction limit, the particle mass of self-interacting fermionic dark matter is constrained to the range from sub-GeV to a few GeV.
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Solar and Stellar Astrophysics

Post-merger rotational evolution of magnetised single hot subdwarfs results in slow rotation due to magnetic braking

Facundo D. Moyano, Zhengwei Liu, Zhanwen Han et al. (+3 more)

Single hot subdwarfs are believed to form through mergers of helium-core white dwarfs, which can lead to large-scale magnetic fields generated during the merger, and may be observable at the surface once they evolve into the stable core-helium burning phase. As a post-merger product, the orbital angular momentum of the binary system that forms it, could lead to a rapidly rotating hot subdwarf. But previous models were not able to explain the rather slow rotational velocities of observed single hot subdwarfs. Motivated by recent detections of surface magnetic fields in hot subdwarfs in the range 200 - 500 kiloGauss, we explore in this work the role of large-scale magnetic fields on their rotational evolution via rotating stellar evolution models. We find that large-scale stable magnetic fields can extract angular momentum efficiently from the star via coupling to stellar winds, producing slowly rotating single hot subdwarfs and thus providing a possible explanation to both the long rotation periods provided by asteroseismology and low spectroscopic rotational velocities. This hints magnetic braking could be an important component of the rotational properties of low-mass stellar mergers.
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All authors Facundo D. Moyano, Zhengwei Liu, Zhanwen Han, Xuefei Chen, Tiara Battich, Philipp Podsiadlowski

High Energy Astrophysical Phenomena

Correlation of galactic very-high-energy gamma-ray sources detected by LHAASO with high-energy neutrinos

Long-Yu Zhang and Kai Wang

We conducted an investigation into the possible correlation between very-high-energy (VHE, $E>$ 0.1 TeV) gamma-ray sources, as identified by the Large High Altitude Air Shower Observatory (LHAASO), and high-energy neutrino events captured by the IceCube Neutrino Observatory. For this analysis, we utilized the First LHAASO catalog, which comprises 90 VHE gamma-ray sources, and the IceCube Event Catalog of Alert Tracks (IceCat-1), which includes 348 track-like neutrino events. Through Monte Carlo simulations, we assessed the correlations between the neutrino events and LHAASO sources, achieving the best p-values of 0.237, 0.312, and 0.115, respectively, for all LHAASO sources, KM2A sources, and WCDA sources. These findings imply that the spatial coincidence between LHAASO sources and neutrino alerts is relatively weak. Furthermore, under the assumption that gamma-rays are exclusively generated through hadronic interactions, we estimated the most optimistic theoretical neutrino fluxes from LHAASO sources and compared them with the IceCube observed fluxes. The results indicate that the majority of these sources are improbable counterparts to the detected neutrinos. In conclusion, LHAASO sources could be potential galactic neutrino emitters but currently do not exhibit compelling evidence, thereby underscoring the necessity for elevated sensitivity levels in forthcoming detection instruments like IceCube-Gen2.
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Instrumentation and Methods for Astrophysics

Development and characterization of a millimeter-wave circular polarization observation method using a quarter-wave plate with Simons Array

Kana Sakaguri, Darcy R. Barron, Yuji Chinone et al. (+17 more)

We have developed and demonstrated a method for measuring circular polarization at 90 GHz by combining a quarter-wave plate (QWP) and a continuously rotating half-wave plate (HWP). While many bolometric experiments at millimeter wavelengths focus on measuring linear polarization, observations of circular polarization in millimeter waves may open a new window into astrophysics and cosmology. We present a novel approach to circular-polarization search using linear-polarization-sensitive detectors by incorporating a QWP in the optics. The Simons Array was originally designed for precise linear polarization measurements, and we subsequently installed a QWP in front of the receiver targeting 90 GHz. The QWP converts incident circular polarization to linear polarization, allowing detection with our detectors. Laboratory measurements demonstrate a QWP conversion efficiency of 99.0%. We apply our method to observations of unpolarized and linearly polarized bright sources, Jupiter and Tau A. Using these observations, we establish the calibration and characterize the instrumental leakages relevant to circular polarization measurements. The measured polarization efficiency adopted for Stokes $V$ is $46\pm2$%, and the measured U-to-V leakage is $-11.7\pm5.1$%. We measure a circular polarization fraction of $V/I=0.78\pm0.42$% for Tau A, showing no significant detection and providing a consistency check of the calibration and systematic-uncertainty treatment. These results establish the instrument response model and calibration parameters used for the companion circular-polarization source search.
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All authors Kana Sakaguri, Darcy R. Barron, Yuji Chinone, Matthew Ryan Chu, Nicole Farias, Takuro Fujino, Masaya Hasegawa, Masashi Hazumi, Haruaki Hirose, Jennifer Ito, Oliver Jeong, Daisuke Kaneko, Brian Keating, Akito Kusaka, Adrian T. Lee, Lindsay Ng Lowry, Richard Plambeck, Shahed Shayan Arani, Praween Siritanasak, Satoru Takakura

Cosmology and Nongalactic Astrophysics

Cosmology with strong gravitational lenses

Tommaso Treu

Three of the most pressing open questions in cosmology – the nature of dark energy and dark matter, and the growing tension in the value of the Hubble constant H$_0$ – call for cosmological probes that are independent of, and complementary to, traditional methods. Strong gravitational lensing offers exactly that: a purely gravitational probe of the universe's expansion history and matter distribution, sensitive to dark matter's presence regardless of whether it interacts with light. Time-delay lenses and multiplane lenses can measure H$_0$ and the dark energy equation of state directly, while the distortion of lensed images can reveal the abundance and internal structure of dark matter subhalos. After a brief theoretical and historical introduction, I review recent breakthroughs enabled by JWST and by advances in lens modeling and stellar dynamics. Examples include the recent measurement of H$_0$ with 3% precision in flat $\Lambda$ cold dark matter cosmology, and a tentative detection of dark matter self-interaction. Strong lensing is entering a pivotal era: wide-field surveys with Euclid, Rubin, and Roman, and radio surveys with the Square Kilometer Array, are poised to increase the number of known strong lenses by orders of magnitude, positioning strong lensing to play a central role in answering these open questions in the decade ahead.
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High Energy Astrophysical Phenomena

A possible evolutionary connection between high-mass X-ray binary pulsars and isolated rotation-powered pulsars

Jun Yang

We investigate the long-term spin evolution of high-mass X-ray binary (HMXB) pulsars in the Small Magellanic Cloud (SMC) using archival measurements of spin periods and period derivatives from XMM-Newton, Chandra, and RXTE. In the P-|dP/dt| plane, the HMXB pulsars follow an approximately linear relation in log-log space with a slope of 1.02 +/- 0.11, similar to the trend shown by the youngest isolated rotation-powered pulsars (RPPs; e.g., Manchester et al., 2005; Lorimer and Kramer, 2005). For comparison, young RPPs from the ATNF Pulsar Catalogue give slopes that depend strongly on the characteristic-age cut: 1.10 +/- 0.16 for characteristic ages below 10,000 years and 0.72 +/- 0.08 for characteristic ages below 100,000 years. The full non-recycled population shows no significant correlation. The HMXB pulsars lie in the same characteristic-age range (approximately 1,000-10,000 years) as the youngest RPPs, but at spin periods two to three orders of magnitude longer. Reference characteristic-age contours in the HMXB P-|dP/dt| plane are roughly parallel to this relation, consistent with a continuous evolutionary sequence.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Radion/Dilaton portal freeze-in dark matter in extra-dimensional theories

Amrita Mukherjee, George Sanamyan and Dipan Sengupta

We perform a comprehensive analysis of a radion/dilaton portal freeze-in dark matter in models of stabilized warped extra-dimensions. We show that the relic abundance of a generic dark matter particle (scalars, vectors, or fermions) is obtained via the conformal coupling of the radial mode in a consistent model stabilized warped extra- dimensions; our calculations show that in scenarios where the reheating temperature is much smaller than the radion mass, keV-TeV scale dark matter particles can saturate the relic density. We perform a comprehensive analysis of a radion/dilaton portal freeze-in dark matter in models of stabilized warped extra-dimensions. We show that the relic abundance of a generic dark matter particle (scalars, vectors, or fermions) is obtained via the conformal coupling of the radial mode in a consistent model stabilized warped extra- dimensions; our calculations show that in scenarios where the reheating temperature is much smaller than the radion mass, keV-TeV scale dark matter particles can saturate the relic density. Furthermore, we show that the model is subject to Lyman-alpha constraints in the keV-GeV range, providing a unique, model-independent probe of this sector. Our calculations extend previous attempts to calculate the freeze-in relic abundance in extra-dimensional portals by providing a consistent theoretical calculation of matrix elements, clearly laying out the underlying motivation and assumptions and providing a comprehensive account of the cosmological constraints on the model.
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Astrophysics of Galaxies

Barflow: Modeling Gas Kinematics of Bar-Driven Flows

Seungwon Baek, Woong-Tae Kim, Taehyun Kim et al. (+2 more)

We present self-consistent $N$-body/hydrodynamical simulations of isolated, Milky Way-like galaxies with stellar and gaseous disks. By varying the initial gas fraction, we find that gas delays bar formation and, in the most gas-rich model, suppresses it by exciting higher-order spiral modes and promoting early central mass growth. Once a bar forms, continued gas inflow and gravitational torques weaken the bar and inhibit its secular slowdown, keeping bars in the gas-bearing models shorter and predominantly in the fast-bar regime, while the gas-free bar evolves into the slow-bar regime. Stars and gas respond differently to the same barred potential. While the mean stellar velocity field is well described by a smooth bisymmetric pattern, the cold and warm gas follow elongated, $x_1$-like streamlines with sharp shock-induced velocity transitions, producing sawtooth-like radial and archlike tangential velocity profiles. Despite these strong noncircular motions, their azimuthally averaged tangential velocities closely follow the circular velocity over most of the disk. By contrast, the hot gas is dominated by stellar feedback and thermal pressure and is largely decoupled from the ordered bar-driven flow. To describe these bar-driven gas flows, we introduce the barflow model, a phenomenological description of non-sinusoidal gas streaming motions with a radially varying shock-front phase. Mock line-of-sight velocity-fitting experiments show that the barflow model recovers the intrinsic rotation curve, bar-driven velocity perturbations, and radial gas transport more accurately than the conventional bisymmetric model.
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All authors Seungwon Baek, Woong-Tae Kim, Taehyun Kim, Dajeong Jang, SungWon Kwak

Instrumentation and Methods for Astrophysics

Optimal Design of Shaped Pupil Lyot Coronagraph for China's Large Segmented Telescope

Kaining Yang, He Sun, Bin B. Ren et al. (+7 more)

China's next-generation large telescopes, such as the Expandable Aperture Segmented Telescope (EAST) and the Large Optical/Infrared Telescope (LOT), are being planned as flagship facilities for high-angular-resolution astronomy, including the direct imaging and characterization of exoplanetary systems (e.g., exoplanets, circumstellar disks). However, their segmented, centrally obscured apertures present significant challenges for coronagraph design: diffraction from segmented gaps and spiders severely limit contrast, particularly at small inner working angles (IWAs). To address this, we investigate an optimal Shaped Pupil Lyot Coronagraph (SPLC) architecture tailored for these telescopes, which combines a binary shaped pupil apodizer, a focal-plane occulting mask, and a Lyot stop to suppress stellar glare and enhance contrast. We further augment the coronagraph design with a two-deformable-mirror (2-DM) adaptive optics (AO) system to correct atmospheric turbulence and residual aberrations. End-to-end simulations based on site parameters for Lenghu in Qinghai Province and assuming idealized extreme AO (ExAO) correction demonstrate that the optimized 2DM-SPLC designs can achieve raw contrasts of order 10^-6-10^-7 in the V, H, and K bands, providing an upper-bound estimate of the system performance. The simulated performance highlights the advantages of the SPLC in mitigating diffraction from segmented and centrally obscured pupils while maintaining a small IWA and practical throughput, indicating that the 2DM-SPLC is a promising coronagraphic architecture for high-contrast exoplanet imaging on China's future large segmented telescopes.
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All authors Kaining Yang, He Sun, Bin B. Ren, Fabo Feng, Yiyun Wu, Jinxin Liu, Linbo Cao, Ruobing Dong, Feng Long, Wei Wang

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

Magnetically Charged Black Holes from Grand Unified Theory

Tanmay Vachaspati and Anja Wachowitz

Grand Unified models of particle physics inevitably give rise to magnetic monopoles. Often the model will also contain a weakly broken discrete symmetry that leads to the formation of biased domain walls that survive for a limited period in cosmology. For a range of the discrete symmetry breaking parameter, domain walls can collapse to form magnetically charged extremal black holes lighter than $\simeq 1\, {\rm kg}$ but these are not expected to survive until the present epoch due to Hawking evaporation and Schwinger pair production of monopoles. If the parameter is smaller still, the black holes may be astrophysical, with mass greater than $10^{15}\, {\rm g}$ and with sub-extremal magnetic charge: $Q \simeq 10^8$ (for our canonical choice of parameters). The cosmological energy density in residual magnetic monopoles depends on the discrete symmetry breaking parameter and for sufficiently small values of the parameter, the magnetic monopole density can satisfy all observational constraints.
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Astrophysics of Galaxies

Simulations of Dust Content and Attenuation in $z=5-15$ Galaxies

Dhruv T. Zimmerman, Jed McKinney, Desika Narayanan et al. (+10 more)

Correctly modeling the dust attenuation law in galaxies is essential to properly inferring their growth and physical properties. With the rapid discovery of $z>6$ galaxies by JWST and lack of constraints on the properties of dust at these redshifts, we must turn to theoretical models to predict the properties of dust at these redshifts. In this paper, we develop a theoretical foundation for the nature of high-redshift attenuation laws. We analyze $107$ cosmological zoom-in simulations of galaxies run with the SMUGGLE galaxy formation model. SMUGGLE includes an explicitly modeled multiphase interstellar medium and a state-of-the-art dust model with a self-consistently evolving dust grain size distribution. We forward model these simulations with the radiative transfer package POWDERDAY to produce synthetic spectra and attenuation curves for a set of $z=5-15$, $M_*\sim10^{6.5}-10^{10}\; \mathrm{M}_{\odot}$ galaxies. We find evidence for flatter attenuation curves than the commonly used locally-calibrated literature attenuation laws assumed when modeling high-redshift galaxies. The vast majority of our attenuation curves also lack the 2175 Angstrom absorption feature. Our attenuation laws do not evolve strongly over $z=15-5$, which we attribute to relatively constant fractions of small grains up to $z=4$ in our simulations. We present a set of simulation-informed priors on dust attenuation law parameterization that could be implemented in SED fitting codes. There is an anti-correlation between galaxy mass and attenuation curve slope and positive correlation between galaxy mass and $A_V$, which we attribute to dust growth becoming efficient in our massive galaxies with $\log{M_*/\mathrm{M}_{\odot}}\gtrsim9$ and with ISM conditions above a critical metallicity threshold.
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All authors Dhruv T. Zimmerman, Jed McKinney, Desika Narayanan, Caitlin M. Casey, John Chisholm, Alex M. Garcia, Michelle C. Jecmen, Jessica Kelley-Derzon, Federico Marinacci, Julian B. Muñoz, Laura V. Sales, Ethan Savitch, Paul Torrey

Earth and Planetary Astrophysics

Emission spectroscopy of KELT-2A b with Gemini-North/IGRINS-2: hints of a stellar C/O ratio and sub-stellar metallicity

Yuya Hayashi, Stevanus K. Nugroho, Shota Notsu et al. (+13 more)

We present the results of high-resolution emission spectroscopy of the hot Jupiter KELT-2A~b using IGRINS-2 on the Gemini-North telescope, covering the $H$- and $K$-bands at a spectral resolution of $R \sim 45{,}000$. Observations were carried out over five nights, covering both pre- and post-eclipse orbital phases. Stellar and telluric contaminations are removed via singular value decomposition. We detect $\rm H_2O$ at a signal-to-noise ratio of {6.57}, confirming the previous result at a higher significance. While $\rm ^{12}CO$ is identified in the log-likelihood map near the expected planetary velocity, a definitive detection of $\rm ^{12}CO$ remains elusive given the current data quality. We perform atmospheric retrieval both with IGRINS-2 data alone and jointly with archival Spitzer/IRAC photometric data points. The retrieved temperature–pressure profile is non-inverted, consistent with prior observations. {From the joint fit we constrain the water abundance to} $\rm log(H_2O) = {-3.78^{+0.27}_{-0.20}}$ {with the free chemistry model}. {The chemical equilibrium model yields} $\rm C/O={ 0.19^{+0.12}_{-0.07}}$, $\rm [C/H]=-0.81^{+0.41}_{-0.34}$, and $\rm [O/H] = -0.37^{+0.27}_{-0.17}${: the C/O ratio agrees with the stellar value, while the carbon and oxygen abundances are moderately depleted relative to the host star, though still consistent at the $\sim2\sigma$ level.} If confirmed, {this combination of a stellar C/O ratio with a sub-stellar metallicity is difficult to reconcile with gas accretion between the $\rm{H_2O}$ and CO snowlines, which predicts a super-stellar C/O. It instead points to the accretion of metal-depleted gas outside the CO snowline with only limited planetesimal enrichment, and hence to a disk-free, high-eccentricity migration history.}
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All authors Yuya Hayashi, Stevanus K. Nugroho, Shota Notsu, Changeat Quentin, Peter C. B. Smith, Krishna Kanumalla, Michael R. Line, Jorge A. Sanchez, Tomohiro C. Yoshida, Kazumasa Ohno, Hideko Nomura, Taiki Kagetani, Norio Narita, Kiyoe Kawauchi, Akihiko Fukui, Enric Palle

Solar and Stellar Astrophysics

Magnetic Reconnection Governs the Entire Lifecycle of Solar Eruptive Magnetic Flux Rope

Xinkai Bian, Chaowei Jiang, Qingjun Liu et al. (+3 more)

While magnetic flux ropes (MFRs) are widely accepted to exist prior to many solar eruptions, the physical mechanism responsible for triggering and subsequently driving their eruptions remains debated. Classical models commonly attribute eruption onset to ideal magnetohydrodynamic instabilities, particularly the torus instability, while magnetic reconnection is often regarded as a secondary process. Using high-resolution three-dimensional MHD simulations, we investigate the eruption of an MFR that forms self-consistently through flux cancellation driven by converging motions and photospheric diffusion following an initial shearing phase. The pre-eruption MFR rises quasi-statically and reaches a height where the decay index exceeds the classical torus instability threshold, yet the system continues to evolve quasi-statically without eruption. Instead, eruption begins only when the current sheet beneath the MFR becomes sufficiently thin for magnetic reconnection to set in. Increasing numerical resolution systematically delays the eruption onset, whereas the decay index at eruption onset remains nearly unchanged, demonstrating that the onset is governed by reconnection rather than torus instability. During the eruption, magnetic reconnection continuously converts surrounding sheared arcades into newly reconnected twisted flux that merges with the pre-eruption MFR and continuously to build the erupting MFR. A component-resolved analysis of the Lorentz force work further shows that the newly reconnection flux contributes predominantly to the main acceleration phase. These results demonstrate that magnetic reconnection plays a central role throughout the entire lifecycle of the eruptive MFR: it builds the MFR, directly triggers its eruption, and provides the dominant driving of the eruption.
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All authors Xinkai Bian, Chaowei Jiang, Qingjun Liu, Xueshang Feng, Pingbing Zuo, Yi Wang

High Energy Astrophysical Phenomena

Search for Sub-Solar Mass Binaries in the First and Second Part of LIGO's Fourth Observing Run O4a-O4b

Keisi Kacanja, Kanchan Soni and Alexander H. Nitz

The observation of sub-solar mass neutron stars and black holes would signify a new class of astrophysical objects since these systems are not expected to form via standard stellar evolution. We present the first sub-solar mass search for binaries consisting of neutron star or black holes that uses the data from both the second part (O4b) and first part (O4a) of the fourth observing run of the Advanced LIGO detectors. The search covers primary masses 0.1 to 2 $M_\odot$ and secondary masses 0.1 to 1 $M_\odot$. Tidal effects up to $7\times10^5$ are accounted for in extremely low-mass neutron stars. No statistically significant candidates are identified. We place a $90\%$ confidence upper limit on the merger rate $\mathcal{R}_{90}$ for sub-solar mass black holes and neutron stars to be $< 5.2\times10^{2}\,\textrm{Gpc}^{-3}\,\textrm{yr}^{-1}$ for a chirp mass of 0.5 $M_\odot$, a factor $2.2 \times$ lower compared to previous O1-O4a searches. We constrain the effective local dark matter fraction to be $\tilde{f}_\textrm{PBH}<0.6\%$ for $M_{\textrm{PBH}}=0.8 \,M_\odot$, approximately $1.5$ factor improvement to previous O1-O4a constraints. Given our model assumptions, our local dark matter fraction constraints are $2-7$ times lower than the OGLE microlensing survey for $M_{\textrm{PBH}}\ge{0.6}~M_\odot$.
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Earth and Planetary Astrophysics

ExoEcho: Exoplanet Ephemerides Change Observations. III. A JWST Survey for Transit Timing Variations of 37 Exoplanets

Yunke Wu, Zixin Zhang, Xinyue Ma et al. (+6 more)

Transit timing variations (TTVs) provide a powerful probe of planetary dynamics and orbital evolution. We extend the ExoEcho project by incorporating James Webb Space Telescope (JWST) transit observations and analyze 84 light curves of 37 exoplanets, including 20 hot Jupiters, 11 Neptune-like planets, and 6 super-Earths. We derive updated transit ephemerides and conduct a systematic search for long-term and periodic TTV signals. We identify two strong TTV candidates, including HATS-6~b and HAT-P-18~b. The hot Jupiter HATS-6~b exhibits a long-term trend with $\dot{P} = 230.5 \pm 46.8\ \mathrm{ms\ yr^{-1}}$, potentially driven by tidal interactions with its host star. In addition, the Neptune-like planet HAT-P-18~b shows periodic TTV signal with amplitude of $92.9 \pm 13.7$~s. We also show that the previously claimed positive period derivative in WASP-121~b is inconsistent with our new transit timing data. Although continued monitoring is required to confirm these findings, our results demonstrate the potential of JWST for high-precision transit timing and extend TTV studies beyond the traditional hot-Jupiter population to lower-mass exoplanets.
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All authors Yunke Wu, Zixin Zhang, Xinyue Ma, Wenqin Wang, Siqi Guo, Cong Yu, Shang-Fei Liu, DiChang Chen, Bo Ma

Astrophysics of Galaxies

Large-scale Environmental Dependence of AGN Activity Revealed by JWST Pa$\alpha$ Emitters

Danyang Jiang, Linhua Jiang, Shuqi Fu et al. (+7 more)

The role of the large-scale environment in regulating AGN activity remains an open question. We investigate the Mpc-scale environments of 70 AGNs at $z=1.1$-$1.5$ using a highly complete sample of 3,419 Pa$\alpha$ emitters with accurate spectroscopic redshifts from JWST slitless spectroscopic survey. This dataset allows us to robustly trace the environments and quantify the environmental dependence of AGN properties. We measure the eighth-nearest-neighbor surface density of Pa$\alpha$ emitters around each AGN, probing $\sim$1.5 pMpc scale environments. We find that this environmental density exhibits a weak positive correlation with radio luminosity. Radio-bright AGNs tend to reside in statistically denser environments than their radio-faint counterparts. The environmental density also has a positive correlation with the Eddington ratio and a weak negative correlation with the central black hole mass, implying more efficient black hole accretion in dense environments. We construct Pa$\alpha$ luminosity functions (LFs) in AGN environments and find that they are systematically elevated relative to the field Pa$\alpha$ LF. In addition, their faint-end slopes are shallower, suggesting accelerated galaxy growth and enhanced quenching of star formation. As Pa$\alpha$ emitters trace gas-rich, star-forming galaxies, our results support a scenario in which the large-scale cold gas promotes AGN activity at cosmic noon.
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All authors Danyang Jiang, Linhua Jiang, Shuqi Fu, Zijian Zhang, Jie Chen, Chenxi Bao, Yihe Wang, Junya Arita, Darshan Kakkad, Jan-Torge Schindler

Astrophysics of Galaxies

Hot Molecular Hydrogen in Galaxies at Redshift ~ 0.2-1.5 Revealed by JWST

Jie Chen, Linhua Jiang, Shuqi Fu et al. (+5 more)

Molecular hydrogen (H$_2$) is the fundamental component of the molecular gas reservoir that fuels star formation and black hole growth. While prominent hot H$_2$ emission ($\gtrsim 1000$ K) has been explored in nearby galaxies, its excitation mechanisms at higher redshifts remain poorly constrained. We present a systematic study of hot molecular gas traced via ro-vibrational H$_2$ emitters at z~0.2-1.5 using JWST slitless spectroscopy. Exploiting JWST's great sensitivity to near-infrared H$_2$ ro-vibrational transitions such as H$_2$ 1-0 S(1), we build a sample of 144 H$_2$-luminous galaxies and characterize their multi-wavelength properties. About 96.5% and 80% of these galaxies are detected in the radio and far-infrared (FIR) bands, respectively, and their hot H$_2$ emission strongly correlates with the radio and FIR radiation. Based on radio excess, X-ray emission, and optical diagnostics, 62 sources (43%) exhibit significant AGN activity. The H$_2$ line luminosities of the sample show a sublinear dependence on radio luminosity, while the relation between the H$_2$ luminosities and total infrared luminosities is approximately linear after excluding the radio-excess sources. These scaling relations suggest that star formation provides a baseline contribution to hot H$_2$ excitation, while radio-excess sources require an additional contribution from AGN-related processes such as jet- or wind-driven shocks. These results reveal a multi-channel excitation scenario and shed new light on the interplay between star formation, AGN activity, and the interstellar medium during galaxy evolution.
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All authors Jie Chen, Linhua Jiang, Shuqi Fu, Zijian Zhang, Danyang Jiang, Jing Wang, Ran Wang, Darshan Kakkad

Tuesday 13 October · still arriving

Astrophysics of Galaxies

A JWST View of Cosmic Star Formation from $z\sim0$ to 9 with Hydrogen Recombination Lines in the COSMOS and GOODS-N fields

Shuqi Fu, Linhua Jiang, Christopher J. Conselice et al. (+9 more)

We combine wide-area COSMOS-3D observations with deeper GOODS-N data from JWST/NIRCam F444W wide-field slitless spectroscopy to trace cosmic star formation over $z\sim0$–9. The observations cover approximately $0.33~\mathrm{deg}^2$ in COSMOS and $60.9~\mathrm{arcmin}^2$ in GOODS-N, with typical $3\sigma$ integrated line-flux limits of $3.2\times10^{-18}$ and $1.04\times10^{-18}~\mathrm{erg\,s^{-1}\,cm^{-2}}$, respectively. The common $3.9$–$5.0\,\mu$m wavelength window probes Br$\alpha$, Br$\beta$, Pa$\alpha$, Pa$\beta$, H$\alpha$, and H$\beta$ across the local Universe, cosmic noon, and reionization. Our final sample contains 9146 galaxies, including 7883 in COSMOS and 1263 in GOODS-N. COSMOS constrains luminous emitters, while GOODS-N extends the luminosity functions toward fainter sources. We measure dust-corrected line luminosities, account for line-detection completeness, and convert the six lines to equivalent H$\alpha$ luminosities assuming Case B recombination. Schechter fits reveal an increase in the characteristic H$\alpha$-equivalent luminosity toward cosmic noon. Integrating the resulting star formation rate functions above $0.24\,M_\odot\,\mathrm{yr}^{-1}$, we trace the cosmic star formation rate density from the local Universe to reionization. The combined Brackett, Paschen, and Balmer measurements are broadly consistent with the canonical UV- and IR-based cosmic star formation history at $z\lesssim6$. Fixed-slope tests show that the H$\beta$ estimate at $z\sim8$ remains sensitive to the external photometric faint-end constraint and extrapolation below our spectroscopic limit. These measurements provide complementary constraints on the distribution and integrated rate of star formation across cosmic time.
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All authors Shuqi Fu, Linhua Jiang, Christopher J. Conselice, Zijian Zhang, Danyang Jiang, Jie Chen, Louis Quilley, Fengwu Sun, Ronaldo Laishram, Alberto Traina, Bahareh S. Salmasi, Duncan Austin

Astrophysics of Galaxies

Deep X-ray View of a Distant Protocluster Anchored by a Quasar at $z=6.63$: No Evidence for Enhanced X-ray AGN Activity

Shouyi Wang, Feige Wang, Jinyi Yang et al. (+22 more)

Whether dense environments accelerate SMBH growth during cosmic reionization remains uncertain because X-ray constraints on $z>6$ protoclusters are rare. We analyze $\sim865$ ks of Chandra observations of J0910-0414 quasar field, a massive protocluster at $z=6.63$. We construct a catalog of 251 X-ray sources and search for AGN among 21 spectroscopically confirmed members, excluding the central quasar. This is the first systematic X-ray AGN census in a $z>6$ protocluster; none of the members is individually detected. Stacking all members ($\sim17$ Ms total exposure) yields no significant signal and limits the average rest-frame 2-10 keV luminosity to $\langle L_{\rm 2-10~keV}\rangle\leq9.54\times10^{42}~\rm erg~s^{-1}$. The null result gives a central 90% Jeffreys upper bound of $f_{\rm AGN}<0.09$. After accounting for the spatially varying sensitivity, the field Compton-thin X-ray luminosity function predicts $N_{\rm exp,field}=0.0356$ AGN in the surveyed volume. Assuming the overdensity profile of AGNs in this protocluster is the same as that of galaxies determined by Wang et al. (2024), the expected AGN count becomes $N_{\rm exp}=0.131$. Zero detections then imply a one-sided 90% upper limit of $\eta_{\rm rel}<17.5$ on any additional X-ray AGN enhancement beyond that associated with the galaxy overdensity. Although $\eta_{\rm rel}<17.5$ permits more than an order-of-magnitude enhancement, the data show no significant excess of X-ray-detectable AGN in J0910-0414 protocluster. The present X-ray data may miss heavily obscured, intrinsically X-ray-weak, or intermittently accreting SMBHs; the non-detection therefore does not rule out AGNs among the member galaxies.
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All authors Shouyi Wang, Feige Wang, Jinyi Yang, Bin Luo, Xiangyu Jin, Fan Zou, Jaclyn B. Champagne, Xiaohui Fan, Elaina Malczewski, Fabio Vito, Xue-Bing Wu, Eduardo Bañados, Fuyan Bian, Thomas Connor, Tiago Costa, Anna-Christina Eilers, Emanuele Paolo Farina, Joseph F. Hennawi, Hyunsung D. Jun, Jiang-Tao Li, Chiara Mazzucchelli, Klaudia Protušová, Fabian Walter, Zhibo Yu, Minghao Yue

Solar and Stellar Astrophysics

Transients and Stellar Activity as Revealed by Ultraviolet Diagnostic Tracers

Richard de Grijs, Martin A. Barstow, Deepak Chahal et al. (+5 more)

Ultraviolet (UV) observations offer unique insights into transient and variable astrophysical phenomena, from the Sun and nearby stars to supernovae and star-forming galaxies. Here, we summarise and review the diagnostic power of the UV spectrum for probing the physical conditions, dynamics and energetics of these events. We trace the historical development of UV astronomy from early satellite missions to the current landscape shaped by the Hubble Space Telescope, the GALaxy Evolution eXplorer, the Neil Gehrels Swift Observatory and AstroSat/UVIT. Particular emphasis is placed on resonance lines such as Mg II $h$ and $k$, C II, Si IV, C IV and N V, which probe the (solar and) stellar chromosphere and transition region, revealing magnetic heating, shocks and mass loss across stellar types. We examine UV diagnostics of stellar flares, pre-main-sequence activity and rotation–activity correlations, linking them to exoplanetary irradiation and habitability. We then explore the UV view of supernova shock breakout and early-time emission, as well as the far-UV mapping of young stellar populations and hierarchical star formation in the Magellanic Clouds. Together, these aspects illustrate how the UV connects small-scale plasma processes to galactic-scale star formation. Despite remarkable progress, UV transient astronomy remains limited by instrument availability and cadence. Forthcoming missions promise to transform this field by capturing the rapid, luminous phenomena that define the dynamic Universe.
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All authors Richard de Grijs, Martin A. Barstow, Deepak Chahal, Fabio Favata, Xiaoting Fu, Ana I. Gómez de Castro, Sipra Hota, Firoza Sutaria

Astrophysics of Galaxies

The Contribution of Mergers and Accretion to Dark Matter Halo Assembly: An Excursion Set Theory Approach

Hamed Kameli

We study the relative contributions of mergers and accretion to the assembly of dark matter haloes within the framework of Excursion Set Theory (EST). We extend a variance-discretized merger-tree algorithm, which recursively reconstructs all branches of a complete merger tree and introduces a merger-ratio criterion for distinguishing mergers from accretion. The method is validated by comparing the resulting progenitor distributions with the analytical conditional first up-crossing distribution, showing excellent agreement over a wide range of halo masses and redshifts. We find that the accretion contribution depends strongly on the adopted merger-ratio threshold. For large merger ratios ($MR=0.1$–$0.25$), accretion accounts for up to $\sim70\%$ of the mass growth of massive haloes, whereas including all resolved mergers ($MR=10^{-6}$) reduces the accretion contribution to $\sim40\%$. These values are in good agreement with previous N-body simulation results. The accreted mass exhibits a nearly self-similar distribution in the mass-redshift plane, with the dominant contribution arising from progenitors in the range $10^{-3}M_0 \lesssim M \lesssim 10^{-1}M_0$ and predominantly at $0.5 \lesssim z \lesssim 2$. Our results demonstrate that EST-based merger trees provide an accurate and computationally efficient framework for investigating halo assembly and quantifying the relative roles of mergers and accretion in hierarchical structure formation.
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Solar and Stellar Astrophysics

Twisted Pseudodisk and Asymmetric Mass Accretion on the Circumstellar Disk II: Parameter Survey

Masahiro N. Machida, Shingo Hirano and Shantanu Basu

Using three-dimensional magnetohydrodynamic simulations accounting for ohmic dissipation, we investigate the long-term evolution of the infalling envelope for $\sim 100,000$\,yr after protostar formation. The primary control parameter is the initial misalignment angle $\theta_0$ between the rotation axis and the magnetic field, varied from $0^\circ$ to $90^\circ$. In all misaligned models ($\theta_0 \ne 0^\circ$), the pseudodisk (or infalling envelope) surrounding the circumstellar disk develops a highly distorted and complex morphology. Gas accretion from the envelope proceeds through discrete, channel-like flows, producing asymmetric streams rather than axisymmetric infall. Protostellar outflows are launched even in these complex environments, and inflow and outflow regions are strongly interwoven. Outflows transport angular momentum anisotropically, leading to time-dependent changes in disk orientation and outflow direction, which further enhance envelope asymmetry. We examine the relative orientation between gas flows and magnetic fields and find that, although statistical tendencies exist, accretion streams cannot be uniquely characterized as either parallel or perpendicular to the magnetic field, particularly in strongly misaligned cases. We also show that most infalling gas accretes at nearly the free-fall velocity, with only a minor fraction significantly slowed within the pseudodisk. Asymmetric accretion and stream-like structures persist beyond 10,000\,au, demonstrating that large-scale asymmetry can arise intrinsically. Our results show that complex streams and asymmetric envelopes naturally emerge from magnetized core physics, even in the absence of initial turbulence or external gas accretion.
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Earth and Planetary Astrophysics

The Limits of Tidal Circularization and Atmospheric Escape for Mini-Neptunes and Super-Earths: The Case of TOI-2257 b

M. K. A. Olohoy, Y. A. D. Gelani and R. Barnes

With a 35-day orbital period and $\sim$0.5 eccentricity, TOI-2257 b occupies a sparsely populated corner of transiting mini-Neptune parameter space and may lie near the orbital distance at which tidal and atmospheric escape process become negligible. To test this hypothesis, we performed simulations of the combined stellar, tidal, and atmospheric evolution and confirmed that TOI-2257 b does lie near this boundary, regardless of whether it formed with or without a primordial hydrogen envelope. In the mini-Neptune scenario, we find that all cases retain an envelope of at least 0.02 M$_\oplus$ for 8 Gyr, but that the envelope mass can be halved if it was initially larger than 0.2 M$_\oplus$. We find that tidal evolution only occurs for cases with initial envelope masses larger than 0.02 M$_\oplus$ because their radii are large enough to generate significant torques. In the super-Earth scenario, the planet could lose $\sim$10 Earth ocean masses of surface water during the $\sim$75 Myr pre-main sequence and therefore could be habitable if it formed with $\gtrsim$2x Earth's surface water mass. The predicted tidal heating surface flux tends to be similar to Io, with no cases approaching the flux required to drive a runaway greenhouse. We find that if the planet is rocky, then eccentricities larger than 0.62 today are strongly disfavored, implying that larger eccentricities could confirm the gaseous nature of the planet. These results suggest that TOI-2257 b could provide valuable constraints on mini-Neptune properties and new insight into the radius valley shape as a function of eccentricity.
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Solar and Stellar Astrophysics

Tracing Accretion and Inner-Disk Gas Evolution in the Orion Nebula via Br-alpha and CO

Konstantin V. Getman, Maria Claudia Ramirez-Tannus, Jenny Frediani et al. (+17 more)

We present a systematic spectroscopic study of hydrogen Brackett-alpha (Br-alpha) and carbon monoxide (CO) fundamental-band (4.3-5.2 micron) emission from a homogeneous sample of 0.2-1.5 Msun pre-main-sequence (PMS) stars in the Orion Nebula observed with JWST/NIRSpec-MOS as part of our Chandra-JWST project. Using 73 Br-alpha and 46 CO spectra, we investigate correlations between warm-gas emission, stellar properties, accretion, and environment with censored correlation and regression analyses accounting for multiple testing. Br-alpha luminosity correlates strongly with accretion luminosity (Lacc), even after excluding sources within 2' of Theta1 Ori C, the nebula's main ionizing O-type star, whose radiation may bias proplyd Lacc estimates. This supports Br-alpha as a robust empirical tracer of accretion in PMS stars. Br-alpha also correlates with visual extinction (Av) and more weakly with stellar bolometric luminosity and mass. CO fundamental-band luminosities likewise correlate positively with Lacc and Av, relationships that persist in a larger combined JWST/NIRSpec+MIRI sample spanning multiple star-forming regions. In contrast to Br-alpha, CO luminosity shows no significant dependence on basic stellar properties, suggesting that warm molecular gas is governed primarily by accretion and local disk conditions. The weaker correlations of the Spitzer/IRAC spectral slope with Lacc and Av suggest that warm inner-disk gas may evolve or disperse faster than optically thick dust. Overall, the CO results tentatively indicate declining warm-gas emission as disks evolve, modulated by accretion-powered thermal and ultraviolet excitation, although variations in emitting area inherited from natal core conditions may also contribute.
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All authors Konstantin V. Getman, Maria Claudia Ramirez-Tannus, Jenny Frediani, Kevin L. Luhman, Eric D. Feigelson, Bayron Portilla-Revelo, Christian Rab, Valentin Brunn, Jan Forbrich, Thomas J. Haworth, Rens Waters, Arjan Bik, Charles J. Law, Andrew J. Winter, Vladimir S. Airapetian, Abygail R. Waggoner, Michael A. Kuhn, L. Ilsedore Cleeves, Sergio A. Dzib, Marco Padovani

Earth and Planetary Astrophysics

Paleo-heat flux estimates across Enceladus derived from flexural response of the ice shell

Chelsea Eakins, Francis Nimmo and Paul Schenk

Saturn's moon Enceladus has active plumes suggestive of locally high heat fluxes at present, and the present-day heating is reasonably well characterized. However, the moon's thermal history is not well understood. In this study, we model flexural deformation of chasmata and dorsae in various regions of Enceladus to find the effective elastic thickness of the ice shell and constrain temporal and spatial variations in heat flux. We find paleo-heat fluxes of 60-$\geq$350 mWm$^{-2}$, with most clustered around 125-200 mWm$^{-2}$. Present day measured heat fluxes at the South Polar Terrain (SPT) are comparable to our estimated paleo-heat fluxes in non-SPT regions. Our paleo-heat fluxes, however, are significantly higher than the corresponding present day heat fluxes for the same locations inferred from shell thickness maps. This suggests that regions outside the SPT experienced a past episode of heating (heat fluxes in excess of 100mWm$^{-2}$) followed by a cooling and thickening ice shell. A relatively constant paleo-heat flux for terrains of different ages (determined from crater densities) supports the "resonance locking" hypothesis of dissipation in Saturn and might imply a long-lived resonance between Enceladus and Dione. Our results suggest that Enceladus's tidal heating appears to have been consistent over time. Consistent peak heating at Enceladus could support a long-lived subsurface ocean, which has important consequences for astrobiology and the habitability of the outer solar system.
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Solar and Stellar Astrophysics

Chandra-JWST Probing the Effects of Moderate X-Ray Superflares on Protoplanetary Disks

Konstantin V. Getman, Kevin L. Luhman, Bayron Portilla-Revelo et al. (+17 more)

Powerful X-ray flares from young stars may rapidly alter the physical and chemical conditions of their planet-forming disks, but direct observational tests remain scarce. We present a Chandra-JWST/NIRSpec study of infrared spectral variability associated with pre-main-sequence (PMS) X-ray flares in the Orion Nebula. Combining six Chandra/ACIS-I observations with three NIRSpec-MOS visits, we analyze two-epoch spectra of 10 X-ray Flare stars and 12 matched non-flaring Controls among 84 observed disk-bearing PMS stars. We investigate three diagnostics: narrow 2.8-4.3 micron features, HI Br-alpha, and the CO fundamental band. Flare stars show tentative evidence for relatively fewer variable narrow features at longer wavelengths than Controls, while feature incidence decreases strongly with projected distance from the dominant ionizing O star Theta1 Ori C. Most classifiable features appear in absorption. These properties suggest that at least some features may arise in externally irradiated disk atmospheres and/or associated photoevaporative flows, with their apparent epoch-to-epoch variability potentially reflecting spatial sampling of such locally structured material rather than intrinsic temporal changes. Br-alpha behaves differently: flare stars show systematically stronger variability and uniquely exhibit absorption-core profiles, suggesting control by magnetospheric accretion and stellar magnetic processes rather than disk irradiation. The CO fundamental band shows no significant flare-associated variability, consistent with thermochemical models predicting weak responses to moderate X-ray superflares. This pilot study demonstrates the potential of coordinated Chandra-JWST observations to probe how young stellar magnetic activity affects planet-forming environments, motivating future monitoring to build larger superflare samples and extend them into the rare X-ray mega-flare regime.
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All authors Konstantin V. Getman, Kevin L. Luhman, Bayron Portilla-Revelo, Christian Rab, Valentin Brunn, Eric D. Feigelson, Arjan Bik, Jan Forbrich, Jenny Frediani, Thomas J. Haworth, Charles J. Law, Marco Padovani, Maria Claudia Ramirez-Tannus, Andrew J. Winter, Vladimir S. Airapetian, L. Ilsedore Cleeves, Sergio A. Dzib, Michael A. Kuhn, Abygail R. Waggoner, Rens Waters

Instrumentation and Methods for Astrophysics

Studying the Near-horizon Jet of M87 using Millimeter Balloon-borne VLBI stations

Felix M. Thiel, Dominic W. Pesce, Mayukh Bagchi et al. (+2 more)

In this paper we present synthetic Very Long Baseline Interferometry (VLBI) observations of M87 between a near-future configuration of the Event Horizon Telescope (EHT) and one or multiple 2.5 m-class balloon-borne VLBI stations on a northern transatlantic flight trajectory launching from Kiruna, Sweden. These balloon-borne VLBI stations have the advantage of operating above 99.5% of the atmosphere and their motion allows for efficient sampling of the uv-plane. Assuming frequency phase transfer between 230 and 86 GHz we run these simulations using a modified version of the ngehtsim software package. Our simulations demonstrate the ability of such a VLBI array to probe M87 at the jet base adding baselines down to 0.2 G$\lambda$ for a single balloon-VLBI station and 0.07 G$\lambda$ for three balloon VLBI stations. Using the Bayesian imaging software Comrade.jl, we demonstrate the recovery of jet structures up to 150 $\mu$as in size for a single balloon and up to 300 $\mu$as in size with three balloons. Finally, we test the improvement in jet image fidelity by computing the normalized cross-correlation (NXCOR) and normalized-root-mean-square error (NRMSE) between the image reconstruction and ground truth. We find a factor of 1.2 improvement in the jet NRMSE for a single balloon and a factor of 1.3 improvement for 3 balloons as compared to EHT-only simulations.
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All authors Felix M. Thiel, Dominic W. Pesce, Mayukh Bagchi, Laura M. Fissel, Lindy Blackburn