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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 28 September

High Energy Astrophysical Phenomena

Investigating signatures of extinct PeVatron activity in supernova remnants IC 443 and W51 C

Silvia Celli and Giovanni Morlino

Context. Supernova remnants (SNRs) are renewed sources of non-thermal particles and the main contributors of Galactic cosmic rays (CRs). Recent ultra-high energy (UHE) gamma-ray data from middle-aged SNRs, such as IC 443 and W51 C, highlight the key role of these systems for particle acceleration. Understanding SNR contribution to PeV CRs requires a detailed modelling about how accelerated particles escape their shocks and are released inside the Galaxy. Aims. We aim at critically assessing the SNR paradigm for the origin of Galactic CRs by investigating the expected secondary radiation produced by hadronic collisions of confined and escaping protons in SNRs, and compare these to recent UHE observations. Methods. Through a time-dependent analytical model describing particle acceleration at the SNR forward shock, we investigate particle escape from the shock expanding into uniform environment and diffusing inside and outside the SNR. Results. Our results support the interpretation that the gamma-ray emission from W51 C and IC 443 is due to hadronic emission from both confined and escaping protons, allowing us to derive robust constraints on the particle maximum energy, the magnetic field amplification process, and the CR acceleration efficiency in these systems. Conclusions. We find that the acceleration efficiency is in the range 1 - 10% (2 - 12%) when the spectrum of accelerated particles is proportional to p^-4 (p^-4.3) and the in-situ diffusion coefficient is suppressed by a factor of 3-10 compared to the average Galactic value. On the other hand, the particle maximum energy ever achieved falls, by a factor of a few, below the PeV energy required to explain the CR knee in the context of SNRs only.
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Instrumentation and Methods for Astrophysics

I2C@2024: an interferometric imaging contest in 2024

Florentin Millour, Mathis Houllé, Jeremy Perdigon et al. (+6 more)

Images in optical long-baseline interferometry have seen a boost in the recent years thanks to new techniques and recipes invented by the community. These images are more and more used for science interpretation and not only illustration, and their fidelity has improved significantly, thanks mainly to the increase in the number of telescopes used in interferometers. The focus today is to improve their reliability and dynamic range. With this contest, we follow up the quest introduced in 2004 of comparing the state of the art image reconstruction software for long-baseline interferometry. This is done in a festive way in the form of an imaging contest, where the organizers propose simulated datasets of targets, whose brightness distributions are meant to be blindly retrieved using various algorithms by the contestants. A prize is offered to the winner of the contest. This year is not different from previous ones and we proposed to the contestants tools to compare their reconstructed images with original images. These tools are now distributed, together with example datasets and images, enabling further tests at home of any image reconstruction tool.
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All authors Florentin Millour, Mathis Houllé, Jeremy Perdigon, Julien Drevon, Ryan Norris, Rebecca Proni, Alexis Matter, Ferreol Soulez, Eric Thiebaut

Cosmology and Nongalactic Astrophysics

MATISSE in the era of GRAVITY+

Florentin Millour, Anthony Soulain, Stéphane Lagarde et al. (+28 more)

MATISSE, the mid-infrared spectro-interferometric imager of the Very Large Telescope Interferometer (VLTI), has been feeding on the light corrected by the GRAVITY+ Adaptive Optics (GPAO) systems since the retirement of MACAO on the four Unit Telescopes in 2024. We report the assessment of the new MATISSE performance with GPAO, based on commissioning observations obtained in 2024 and 2025 and compared with archival MACAO observations of the same stellar sources. The instrumental visibility transfer function is more stable in the L band, while its typical value in the L and N bands is unchanged; the visibility signal-to-noise ratio is consistent with, or better than, the values reported at the initial MATISSE commissioning. The correlated flux increases by 20–30% in GRA4MAT mode thanks to a better fringe tracking performance, and the total flux injected into the instrument increases by a factor of 1.3 to 1.4 (up to 1.7) in the L band at low spectral resolution, with no measurable loss in the N band. Combined with the new K-band fringe-tracking limits enabled by GPAO, this translates into a sensitivity gain of a factor 2 to 6 in the L and M bands, a confirmation of the N-band limits similar to the MACAO era. We then report the performances of MATISSE with the GPAO's laser guide stars in November and December 2025. The updated noise figures follow the exposure time calculator predictions in LM LOW and MED and come out better than them in N LOW, the L-band transfer function is stable at the few percent level between observing blocks an hour apart, and correlated fluxes, differential phases and closure phases are recovered down to a 10\,mJy target. Embedded young stellar objects and AGN are now within reach, thanks to the better performances on red targets brought by the lasers. We finally discuss the science cases opened by this gain and the case for a future upgrade of the instrument.
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All authors Florentin Millour, Anthony Soulain, Stéphane Lagarde, Alexis Matter, Valentin Fleury, Farin Drewes, Mathis Houllé, Jules Scigliuto, Bruno Lopez, Anthony Meilland, G. Petrov Romain, Philippe Berio, Anthony Berdeu, Guillaume Bourdarot, Sylvestre Lacour, Mathias Nowak, Jean-Baptiste Le Bouquin, Antoine Mérand, Frank Eisenhauer, Julien Woillez, Miguel Montargès, Diogo Ribeiro, Taro Shimizu, Jens Kammerer, Xavier Haubois, Stefan Gillessen, Pierre Cruzalèbes, Frédéric Gonté, Walter Jaffe, James Leftley, Nicole Nesvadba

Instrumentation and Methods for Astrophysics

The best of all worlds: gravitational-wave transient detection with multiple pipelines

Nikolas Moustakidis, Theofilos Moustakidis, Deep Chatterjee et al. (+2 more)

The search for gravitational-wave transients (modeled and unmodeled) as performed by the LIGO-Virgo-KAGRA collaborations and the broader community typically involves multiple detection algorithms, often redundant and sometimes complementary. We here address the problem of combining such detection algorithms in order to maximize the noise vs signal discrimination power of such an astrophysical search that utilizes multiple analysis pipelines. Using a machine learning approach, we construct a neural network-based classifier that utilizes information (or lack thereof) from all participating pipelines in the search for compact binary coalescences in LIGO-Virgo-KAGRA's realtime (and offline) processing of gravitational-wave data. We benchmark the method with simulated (astrophysical) signals and real noise from the instruments and obtain receiver operating characteristic curves to quantify its performance. We show how this leads to an effectively new, combined pipeline that outperforms any single pipeline alone or other logical combinations of them. This is particularly critical for real-time operations of the LIGO-Virgo-KAGRA detectors as such combination of detection methods can lead to increased robustness in identifying astrophysical sources and to reduction of the number of false alerts that may otherwise be sent out as astronomical telegrams. Our method also aims in simplifying the presentation of astrophysical results out of the LIGO-Virgo-KAGRA detectors by combining all participating pipelines in the astrophysical searches as well as optimizing resources by the broader multi-messenger astrophysics community in following up astronomical alerts for gravitational-wave transient events.
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All authors Nikolas Moustakidis, Theofilos Moustakidis, Deep Chatterjee, Anastasios Tefas, Erik Katsavounidis

Solar and Stellar Astrophysics

First results from PADRE/MeDDEA: X-rays from a flare and its CME

Muriel Zoë Stiefel, Säm Krucker, Olivier Limousin et al. (+22 more)

The MeDDEA hard X-ray spectrometer onboard NASAs PADRE CubeSat operates four flight-spare detectors from the Solar Orbiter/STIX instrument. This paper aims to evaluate the accuracy of the MeDDEA calibration and to demonstrate that MeDDEA data are ready for scientific exploitation. Using the first joint observations between MeDDEA and STIX, we investigate faint HXR emission associated with an escaping CME relative to the emission from the full flare. The first large flare observed by MeDDEA is analyzed, and the MeDDEA spectrum is compared with simultaneous observations from Fermi/GBM and ASO-S/HXI. From the Solar Orbiter viewpoint, the flare is highly limb-occulted allowing STIX to isolate high coronal emission associated with the CME while MeDDEA observed the full flare. We combined spectral fitting with HXR/EUV imaging from STIX, HXI, and AIA to investigate the locations and energetics of the flare- and CME-associated HXR sources. The MeDDEA spectral observations are in agreement with FERMI/GBM and ASO-S/HXI within 10 percent in the energy range of 18-30 keV. The CME-associated photon flux observed by STIX in the nonthermal range is faint at about 1 percent of the flare photon flux. The energy content of the thermal component associated with the CME, on the other hand, is found to be of the same order of magnitude as the thermal energy of the flare loop, at least for a filling factor of unity. Imaging information from STIX in combination with AIA reveals that the emission measured by STIX is located within the associated CME. We report that MeDDEA provides scientifically reliable spectral observations and is ready for scientific use.
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All authors Muriel Zoë Stiefel, Säm Krucker, Olivier Limousin, Niharika Godbole, Gwendoline Marc, Amir Caspi, Kyle Gregory, Ace Stratton, Diana Renaud, Aline Meuris, Laura A. Hayes, André Csillaghy, Pascal Saint-Hilaire, Juan Camilo Buitrago Casas, Christopher Smith, Savannah Sky Perez-Piel, Anton Tremsin, Elizabeth Warren, Bradley Pafchek, Eliad Peretz, Carlos Urdiales, Reynaldo Gonzalez, Chris M. Moeckel, Juan Carlos Martinez Oliveros, Steven Christe

Cosmology and Nongalactic Astrophysics

Localized Enhancements of the Primordial Power Spectrum and the Abundance of Early Bright Galaxies

Shaghayegh Yavari, Hamed Kameli and Shant Baghram

Recent observations of bright galaxies at high redshifts by the James Webb Space Telescope have motivated renewed interest in cosmological mechanisms that can enhance the abundance of early massive dark matter halos. We study a phenomenological modification of the primordial curvature power spectrum in the form of a localized Gaussian enhancement. The modified spectrum is propagated to the linear matter power spectrum, the smoothed density variance, and the Sheth-Tormen halo mass function. We show that a bump centered at small scales can selectively enhance the abundance of rare high-redshift halos and, through a fixed semi-analytic mapping between halo mass and ultraviolet luminosity, shift the bright end of the UV luminosity function toward JWST measurements. The enhancement becomes more pronounced at higher redshift due to the exponential sensitivity of the rare-halo tail to the variance. We emphasize that the effect is limited by small-scale power-spectrum constraints, particularly Lyman-$\alpha$ forest data, and should be interpreted as a partial cosmological contribution rather than a complete solution to the JWST galaxy tension.
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Astrophysics of Galaxies

Far-Ultraviolet diffuse emission as a tracer of Galactic extinction at the North Galactic Pole

Swagat Bordoloi, P. Shalima, Rupjyoti Gogoi et al. (+2 more)

Interstellar extinction at high Galactic latitude is often traced by thermal dust emission, but the conversion from infrared surface brightness to reddening is sensitive to grain properties and temperature. We test dust-scattered far-ultraviolet (FUV) and near-ultraviolet (NUV) diffuse emission as a high-resolution extinction tracer towards the North Galactic Pole (NGP), where E(B-V) < 0.1 mag. Using the GALEX diffuse maps of Murthy (2014), we build FUV and NUV intensity maps at 6' resolution over the region b > 70 deg and compare them with the Planck E(B-V) map at matched resolution. A direct pixel-to-pixel regression gives only moderate correlations (rho = 0.536 for FUV, 0.243 for NUV) owing to high per-pixel scatter from H2 fluorescence, line emission, and photon-counting noise; we therefore construct per-pixel GALEX uncertainty maps and apply a centroid-fitting method that fits the mean intensity in bins of E(B-V) after rejection of outliers via iterative sigma-clipping, recovering tight relations (rho = 0.993 for FUV, 0.976 for NUV). We find the best-fit relations for the FUV and NUV intensity per 6'x6' pixel: FUV = 2285.3 E(B-V) + 278.6 and NUV = 1517.6 E(B-V) + 547.2 (photons/cm^2/s/sr/A), inverted to produce a 601x601 GALEX reddening map. GALEX E(B-V) correlates strongly with HI column density from the all-sky HI4PI survey (rho = 0.991). We validate the maps using SDSS quasars as extragalactic extinction calibrators: quasar extinctions from the GALEX and Planck maps agree with a correlation of 0.99 and a slope of 0.986. Comparison with the Pan-STARRS1 stellar reddening map of Schlafly et al. (2014) shows the GALEX-based values have a smaller mean difference (0.039 mag) than the Planck-based values (0.064 mag). These results establish dust-scattered FUV diffuse emission as a viable alternative to thermal-dust extinction maps at high Galactic latitude.
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All authors Swagat Bordoloi, P. Shalima, Rupjyoti Gogoi, Jayant Murthy, Oleg Malkov

High Energy Astrophysical Phenomena

Jet Forecast: Timing of Discrete Jet Ejections of Stellar-Mass Black Holes Anticipated via X-ray Properties

Toshihiro Kawaguchi and Kazutaka Yamaoka

The radio – soft $\gamma$-ray data of the Galactic black hole binary XTE J1859+226 showed that discrete jets are launched when the inner radius of the accretion disk ($R_{\rm in}$) rapidly approaches the innermost stable circular orbit (ISCO). Given the correlations among the X-ray fractional variability amplitude (rms), $R_{\rm in}$, and the X-ray hardness, previous phenomenological findings related to jet ejections (“jet line” and sharp drops of rms) also indicate that the rapid shrinkage of $R_{\rm in}$ down to the ISCO turns on the jet formation. In order to make clear how these properties appear in other objects, we investigated the X-ray and radio data of XTE J1550-564, GX 339-4, and MAXI J1820+070. We found that all the four sources show drops of $R_{\rm in}$ and rms 1-10 days ahead of a jet activity, and exhibit no huge jumps of the accretion rates prior to jet ejections. XTE J1859 and MAXI J1820 show the jet activities under sub-Eddington accretion. Models for the jet production that require an enhancement of $\dot{M}$ or a super-Eddington accretion rate are unlikely. Another behavior common to multiple sources is the curved shape of the rms–$R_{\rm in}$ correlation. Therefore, monitoring of $R_{\rm in}$ seems to be suitable to predict the timing of jet ejections. When both $R_{\rm in}$ and rms continuously decrease and when $R_{\rm in}$ is about to reach the ISCO, alerts can be circulated as a “jet forecast” for triggering Target-of-Opportunity observations.
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Earth and Planetary Astrophysics

Surveying exogenous species in Saturn with ALMA. II. Detecting and Mapping HCN

T. Fouchet, T. Cavalié, R. Moreno et al. (+3 more)

Several external sources (the rings, the satellites, cometary impacts, interplanetary dust particles) supply material to the upper atmosphere of Saturn. The signature of this external influx has been documented on the ionospheric electronic and ionic densities, and in the stratosphere on oxygenated molecules (CO, CO2, H2O). We search for the chemical signature of the external sources in nitrogen-bearing species in Saturn's stratosphere. We have targeted the HCN(4-3) rotational line and mapped its emission line at the planet limb with ALMA in 2018 with configuration C43-3, providing a synthetic beam of 0.61"x0.50". HCN was detected at all observable latitudes from 20{\deg}S to 60{\deg}N. The HCN abundance was measured at two independent pressure levels, 0.1 and 1 hPa. The measured volume mixing ratios are latitudinally uniform within uncertainties at both pressure levels. The mean vmr is $(7\pm 2)\times 10^{-11}$ and $(4\pm 1)\times 10^{-12}$ at 0.1 and 1 hPa respectively. This corresponds to a mean column-density of $(4\pm 1)\times 10^{12}$ cm$^{-2}$, and a total nitrogen mass of $(3.7 \pm 0.9)\times 10^{10}$ g. The steep vertical profile suggests that another loss mechanism, possibly sticking or heterogeneous chemistry on aerosols, is active besides photodissociation. The huge influx of material detected in the ring plane by Cassini left no detectable chemical signature on HCN. The detected HCN mass seems compatible with several sources: the ring rain at mid-latitudes, Enceladus, or an old cometary impact. The detected HCN could also be a chemical product of internal N2 transported from the deep atmosphere up to the stratosphere.
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All authors T. Fouchet, T. Cavalié, R. Moreno, S. Guerlet, E. Lellouch, D. Bardet

High Energy Astrophysical Phenomena

From Choked to Successful: The Role of Black Hole Spin in Collapsar Jet Breakout

Rushikesh Sonawane, Krishna Kumar and Shabnam Iyyani

Long gamma-ray bursts (LGRBs) are believed to originate from the core collapse of massive Wolf-Rayet (WR) stars, leading to the formation of a spinning black hole that powers a relativistic jet. The prompt emission is produced once the jet emerges from the stellar envelope. We perform 2D axisymmetric RHD simulations using the PLUTO code to model semi-self-consistent, accretion-powered jets launched by Kerr black holes. For the two progenitor models, we adopt black hole masses of $4 M_{\odot}$ and $5 M_{\odot}$ corresponding to WR stars of $10 M_{\odot}$ and $25 M_{\odot}$, respectively. Unlike previous studies, our simulations employ continuous jet injection, with the injected power linked to black hole spin and accretion through an empirical relation motivated by GRMHD simulations, enabling a controlled exploration of jet energetics over $10^{48}$-$10^{52}\,\mathrm{erg\,s^{-1}}$. We investigate jet breakout for WR progenitors of $10\,M_{\odot}$ and $25\,M_{\odot}$ and identify a critical spin threshold: jets are choked for $a \leq 0.001$ and successfully break out for $a > 0.001$. The breakout time ($t_B$) shows a correlation with jet luminosity ($L_{\rm jet}$) and spin ($a$), revealing three regimes: Newtonian ($a \lesssim 0.03$), relativistic ($a \gtrsim 0.3$), and intermediate. A dichotomy is observed in jet head velocity at breakout, with $\beta_h \gtrsim 0.8$ for high-spin and $\beta_h \sim 0.35$-$0.8$ for lower spins. In the Newtonian regime, simulations yield $t_B \propto L_{\rm jet}^{-0.48}$, steeper than analytical predictions, with systematically longer breakout times indicating modified jet-head scaling. In the relativistic regime, calibrated analytical models show improved agreement, with simulations indicating efficient jet propagation.
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Earth and Planetary Astrophysics

Planetesimal formation facilitated by streaming instability in weak pressure bumps

Magnus S. Sørensen-Taylor, Anders Johansen and Troels Haugbølle

Planetesimal formation via the streaming instability of small pebbles in protoplanetary discs requires enhanced solid concentrations relative to the solar metallicity, $Z\simeq 0.01$. We investigate here whether pile-ups in weak axisymmetric pressure bumps are sufficient to trigger strong particle concentrations via the streaming instability. Using high-resolution 2D shearing box simulations with millimetre-to-centimetre pebbles, we explore the behaviour of the streaming instability in the presence of a non-reinforced pressure bump. We find that even very weak bumps, with gas density amplitudes as low as $A = 0.04$ relative to the background, produce dense particle filaments via the streaming instability for all tested Stokes numbers at solar metallicity in the inner disc. Outer disc regions require slightly stronger bumps ($A \geq 0.14$) to form filaments at a solar metallicity, though the necessary bump amplitude is substantially lowered when the metallicity is increased to $Z = 0.02$. Our results suggest that weak, non-reinforced pressure bumps can act as focal points for planetesimal formation via the streaming instability in small pebbles, in contrast to previous studies which used reinforcement to maintain the pressure bump. Additionally, we introduce a pressure-bump-dependent clumping criterion, $(Z/\chi)_\mathrm{crit} \approx 0.3$, where $\chi = \Pi_\mathrm{min}^2/\Pi_0$ reduces to the background pressure gradient $\Pi_0$ in the absence of a pressure bump. This criterion encapsulates the scale of solid pile-ups at lower pressure gradients and accurately predicts the onset of strong clumping based on the results of our simulations. With pressure bump signatures being common features of observed young discs and magnetohydrodynamical simulations, the results of our 2D simulations imply that weak pressure bumps may be major cradles for planetesimal formation in protoplanetary discs.
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Astrophysics of Galaxies

Exploring the observed properties of JWST Little Red Dots with cosmological simulations and dust radiative transfer

Saksham Chandna, Fabio Di Mascia, Simona Gallerani et al. (+6 more)

JWST has uncovered compact high-redshift (z>=4) sources, dubbed Little Red Dots (LRDs), characterised by a distinct V-shaped continuum. Their nature remains debated since broad-line AGN signatures coexist with non-AGN continua, marked by weak X-ray and mid-IR emission. We investigate which properties of LRDs naturally emerge within simulations of massive AGN host galaxies and which require additional physics. We post-process two cosmological zoom-in simulations of the same massive halo, one including black hole growth and AGN feedback (AGNfid) and the other with only star formation and stellar feedback (SFonly). We analyse snapshots spanning z=6-9 to probe different evolutionary stages. Using SKIRTv8, we develop a forward-modelling framework exploring various dust models, dust-to-metal ratios, and intrinsic AGN spectra. We generate mock spectra and images to apply JWST observational LRD selection criteria. Not designed to model LRDs, our AGNfid simulations naturally reproduce their properties: V-shaped continua, compact morphologies with rest-UV complexity, UV luminosities, attenuations, overmassive BHs, sub-Eddington accretion, and Balmer break strengths (~1-2) typical of most LRDs. Spectral decomposition reveals that the rest-UV continuum is dominated by stellar emission, whereas the optical continuum stems from a dust-attenuated AGN. Dust geometry and AGN-to-stellar contribution drive photometric differences between LRDs and Little Blue Dots. Our results suggest that LRDs do not necessarily represent a distinct class of objects. Instead, their defining properties can arise in massive AGN host galaxies from the interplay between stellar emission, an obscured central engine, and dust geometry. Super-Eddington accretion, dust-free gas columns, evolved stellar populations, and photoionisation modelling are required to test whether this framework reproduces the diversity of observed LRDs.
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All authors Saksham Chandna, Fabio Di Mascia, Simona Gallerani, Stefano Carniani, Pierluigi Rinaldi, Roberta Tripodi, Milena Valentini, Alessia Tortosa, Luca Zappacosta

Earth and Planetary Astrophysics

Activity in White Dwarf Debris Disks II: WISE Mission Traces a Decade of Disk Evolution and Persistence

Hiba Tu Noor, Jay Farihi and Scott J. Kenyon

This study presents multi-epoch photometry from the Wide-field Infrared Survey Explorer to investigate variability in white dwarf debris disks, utilizing the full 14.5 yr mission datasets pre- and post-cryogen. Unambiguous variations are detected across the bulk of the 52 confirmed dusty white dwarfs and are consistent with universal variability after correcting for the sensitivity of WISE relative to Spitzer. Some disk light curves exhibit trends such as possible oscillations, sudden brightening, and steadily decaying fluxes, but all infrared excesses persist utterly. On baselines longer than 0.5 yr, flux changes are significantly skewed toward decreases, in contrast to the symmetric distribution found at shorter baselines with Spitzer, consistent with gradual dust depletion over time. Disk emission generally becomes redder when dimmer and bluer when brighter, consistent with changes in the grain size distribution following collisions, although five disks exhibit the opposite trend possibly due to dust production near apastron. A moderate positive correlation is observed between disk luminosity and photospheric Ca abundance, consistent with the accretion of disk material in an optically thin configuration. Taken together with the Spitzer legacy of dusty white dwarfs, these results provide a comprehensive view of debris disk variability and provide empirical constraints on models of disk structure and evolution.
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Astrophysics of Galaxies

DREAMS: Taking the Temperature of a Massive Galaxy at z ~ 11

L. Parente, E. Vanzella, M. Messa et al. (+15 more)

We present a detailed photometric and spectroscopic analysis of Janus-11, a $z=10.7933 \pm 0.0006 $ galaxy magnified by a factor 1.6 by the galaxy cluster MACS J0416. It was observed with JWST/NIRCam as part of the PEARLS program and with JWST/NIRSpec MSA as part of the DREAMS program. It has M$_{\rm UV}=-19.78^{+0.12}_{-0.11}$, and its stellar mass of log(M*/M_sun) = 8.75 (+0.08/-0.10) places it among the most massive known $z>10$ galaxies, while its $A_V=0.54\pm0.09$ mag and UV slope of $\beta=-1.71\pm0.26$ are compatible with a red monster classification, albeit among the least obscured members of this population: this could hint at a transition from the red monster to the blue monster phase. Moreover, the [OIII]4363 detection allows for the highest-redshift metallicity measurement based on the [OIII]4363 direct method to date of $12 + \log(O/H) = 7.74^{+0.11}_{-0.10}$, together with an electron temperature of $T_e$(O$^{++}$) = $(2.1 \pm 0.2)\times10^4$ K. Its spatially resolved nature, with an effective radius of $136 \pm 9$ pc, together with the narrow FWHM of the emission lines ($\lesssim 230$ km s$^{-1}$, or $\sigma_v \lesssim 100$ km s$^{-1}$), and the lack of significant detections of high-ionization emission lines and broad components, favor an SFG classification, although an AGN contribution cannot be excluded. Janus-11 joins the small sample of spectroscopically confirmed and characterized sources at $z>10$, providing new information on massive systems with non-negligible dust attenuation and well-measured metallicity in this epoch.
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All authors L. Parente, E. Vanzella, M. Messa, A. Zanella, K. Nakajima, M. Ouchi, R. A. Windhorst, M. Talia, Y. Harikane, Y. Ono, A. M. Koekemoer, P. Bergamini, M. Meneghetti, P. Rosati, Y. Xu, H. Umeda, Y. Zhang, Y. Isobe

High Energy Astrophysical Phenomena

Emission and cooling of a newborn quark star

Mikalai Prakapenia and Gregory Vereshchagin

It has long been believed that newborn quark stars are inefficient emitters because the quark plasma frequency is so high that it suppresses electromagnetic radiation across the entire spectrum up to energies of several tens of MeV. Here, we show that significant electromagnetic emission can instead originate from the electrosphere of a quark star, where the plasma frequency is much lower, approximately 40 keV. As a result, the cooling of a newborn quark star is expected to proceed through two distinct observational epochs. During the first epoch, blackbody radiation is emitted from the photosphere of an optically thick relativistic wind generated near the electrosphere. Over the course of a few days following the star's formation, the photospheric temperature decreases from several MeV to about 22 keV. During the second epoch, the blackbody spectrum evolves into a narrow feature centered around 40 keV, and the emission gradually fades. This spectral evolution provides a characteristic signature of the electrosphere surrounding compact astrophysical objects and may be detectable with current or future X-ray observatories.
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High Energy Astrophysical Phenomena

Prompt and Afterglow Constraints on the Central Engine of GRB 240825A

Daban Mohammed Saeed, Rahim Moradi, Chen-Wei Wang et al. (+2 more)

GRB 240825A shows unprecedented temporal and spectral features that constrain the properties of its inner engine: (1) a prompt emission three-component spectrum consisting of a Band function continuum, a quasi-thermal bump, and a hard MeV tail; and (2) an X-ray afterglow fitted by a power-law decay with index $1.29 \pm 0.02$; and (3) a $6.37 \pm 0.05$ Hz quasi-periodic oscillation (QPO) identified in the 100-300 keV band during the 2.07-3.25 s time interval, coinciding with the photospheric radiation phase. We compare two central-engine candidates: (a) a newborn millisecond magnetar undergoing multipolar spin-down, free precession, and global magnetoelastic oscillations of its interior; and (b) a Kerr black hole powering a Blandford-Znajek jet subject to Lense-Thirring disk precession. In principle, both channels can reproduce the observed QPO frequency but impose different constraints on the energetics, temporal evolution, and the origin of the oscillation. We first demonstrate that the X-ray afterglow is quantitatively reproduced by a hexapolar magnetar spin-down model with an initial spin period of $P_0 \simeq 1.38$ ms and a surface field of $B_{\rm hexa} \simeq 2.04 \times 10^{16}$ G. The decay index measures a braking index rather than the field multipolarity, does not exclude a fallback-regulated flow, and leaves $P_0$ and $B_{\rm hexa}$ uncertain by a factor of a few. In this scenario, magnetic or magnetoinertial dynamics of the star interior provide a plausible explanation of the QPO without invoking extreme stellar deformations. Although a black hole engine cannot be firmly excluded, the combined prompt and afterglow observational properties of GRB 240825A favor a long-lived magnetar central engine.
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All authors Daban Mohammed Saeed, Rahim Moradi, Chen-Wei Wang, Brwa Shukur Ismael, Marco Muccino

Cosmology and Nongalactic Astrophysics

The separate universe approach with non minimal coupling to gravity

Hugo Holland and Julien Grain

In this paper we extend a study of the validity conditions of the separate universe approach of cosmological perturbations to models of inflation with multiple fields that are non minimally coupled to gravity. The separate universe approach effectively describes the universe as a collection of homogeneous and isotropic patches, leading to an effective description of cosmological perturbations at large scales. This approximation is a necessary step in stochastic inflation and in the $\delta \N$ formalism. We study and compare the dynamics of cosmological perturbation theory at large scales to the dynamics derived in the separate universe picture for non linear sigma models where we have allowed a non minimal coupling between the fields and gravity. We found that the separate universe approach adequately reproduces the dynamics of the large scale perturbations, provided the wavelength of the modes considered is greater than a list of lower bounds derived from the background evolution of the model we consider. These lower bounds are then compared to those derived in the classically equivalent Einstein frame description of the Jordan frame model at hand. In particular these conditions are derived and compared for a Higgs-like toy model of inflation in the large field limit.
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Earth and Planetary Astrophysics

The precipitation of protons and electrons in Jupiter's auroral regions: a statistical comparison based on Juno/JEDI data

B. Benmahi, N. André, V. Hue et al. (+8 more)

Energetic electrons dominate the energy precipitated into Jupiter's auroral regions, but protons precipitate along the same field lines, with a contribution that remains poorly constrained. We statistically compare the precipitating energy flux of protons and electrons in two of Jupiter's auroral sub-regions, the polar (PE) and main (ME) emission regions. We use Juno/JEDI data from PJ3 to PJ66. The magnetic footprint of the spacecraft, computed with the JRM33 and CON2020 field models, is assigned to one of the two sub-regions, and the precipitating energy flux of each species is obtained by integrating over the loss cone the mean differential intensity measured within it. In both sub-regions, the median proton energy flux is 52 to 223 times lower than that of the electrons, and the total precipitated proton power is less than 2% of the electron power. Proton fluxes are broadly distributed across the sub-regions, with higher values in the ME than in the PE. Protons play a secondary role in Jupiter's auroral energy budget, radiating an estimated 5 to 9 GW in the UV per sub-region, pending a dedicated proton transport modelling. Their Doppler signature in the red wing of the Lyman-$\alpha$ line, undetected by HST and difficult to access with Juno/UVS, is a key observable for the upcoming Juice and Europa Clipper missions.
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All authors B. Benmahi, N. André, V. Hue, Z.-Y. Liu, G. Gronoff, B. Mauk, B. Bonfond, T. Stallard, M. Blanc, M. Devinat, M. Barthélémy

Astrophysics of Galaxies

Before fragmentation: from uniform clouds to stellar clusters

A. Giannetti, T. Pillai, J. Kauffmann et al. (+4 more)

Our study of the early stages of fragmentation in massive clumps has revealed a striking anomaly: $\sim15\%$ of the CoCoA sample exhibit no fragmentation at all. These sources could represent the initial conditions before core formation. We investigate whether these sources are indeed at the onset of core formation, and whether gravity or turbulence dominates their early fragmentation. We study the transition from uniform gas to active cluster formation, and compare contrasting predictions of turbulence- and gravity-dominated models of clump fragmentation through ALMA observations of three massive clumps spanning this phase. The fragmented source exhibits higher average $n$(H$_2$) and a core-to-envelope density contrast 5-6 times larger than the minimally fragmented sources. All sources display pc-scale velocity differences comparable to their linewidths and gravitational velocities. This suggests that the linewidth is dominated by the large-scale motions, and that the latter are driven by gravity. The high CH$_3$OH abundances and the mass build-up timescales align with astrochemical models where complex molecules form at intermediate densities before the appearance of cores. All independent diagnostics in our analysis are consistent with the minimally fragmented clumps being an early evolutionary phase, potentially marking the onset of core fragmentation. If turbulence were the primary driver of fragmentation, sources with comparable Mach numbers should exhibit similar structural properties. Instead, we observe significant variations in density contrast and fragmentation. These findings challenge turbulence-supported models and lend support to hierarchical, gravity-driven models of clump fragmentation, where large-scale ordered motions account for a significant fraction of the observed linewidths and drive the evolution of the clump toward increasingly dense and fragmented states.
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All authors A. Giannetti, T. Pillai, J. Kauffmann, A. Palau, E. Vazquez-Semadeni, K. Morii, P. Sanhueza

Solar and Stellar Astrophysics

Limits on eccentricity excitation by tidally enhanced mass loss in Wolf-Rayet binaries

Viktória Fröhlich and Zsolt Regály

Wolf–Rayet (WR) binaries frequently display high orbital eccentricities, and their eccentricity distributions are inconsistent with that of high-mass Galactic field binaries at high significance. This raises the question of whether these eccentricities are primordial or generated during the WR phase. We test whether a tidal enhancement of the mass-loss rate can pump the eccentricity of a WR binary on a sample of 14 WR systems. We model each system as a variable-mass two-body problem and integrate the orbital evolution over the WR lifetime under three prescriptions: i) adiabatic isotropic mass loss, ii) equilibrium-tide circularization, and iii) a tidally enhanced, pericenter-focused mass loss in which the companion-facing reduction of the effective surface gravity raises the local Eddington parameter. Adiabatic mass loss can not change eccentricity and affects only the orbital separation, which increases by up to a factor of ~20. Tidal circularization is effective only in the tightest orbits, which are compatible with the observed systems only for high mass-loss rates, a regime in which any primordial eccentricity is erased. The tidally enhanced mass loss channel pumps the eccentricity by only $\leq10^{-4}$, three to four orders of magnitude below the observed values, and therefore cannot be the responsible mechanism. We conclude that the high eccentricities of WR binaries are predominantly primordial rather than generated by mass loss during the WR phase.
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Solar and Stellar Astrophysics

Doppler Velocity Variation near the Solar Limb in the Solar Photosphere Observed with Hinode

Akie Moritsuka, Yukio Katsukawa and Ryohtaroh T. Ishikawa

The Doppler velocity and bisector of photospheric lines show significant center-to-limb variation. This variation has been considered to be caused by the projection angle of the granular convection which has a corrugated surface. This study aimed to show the spectral line shifts up to limb and investigate how these shifts are caused by granular convection. We analyzed the Fe I 630.15 nm absorption line by spatially resolving the granulation very close to the limb using datasets of polar observations obtained with the Spectro-polarimeter (SP) of the Solar Optical Telescope (SOT) onboard Hinode. We also analyzed the Fe I 630.15 nm emission line, which was observed within 1" above the limb. This study revealed the following: 1) the spatially averaged spectral lines showed an increase in redshift toward the limb, then became constant, and finally became nearly zero, 2) the Doppler velocities of granules, which were classified as bright and non-magnetic regions, showed as increase in redshifts toward the limb, 3) the bisector of granules changed more than that of the intergranules, and 4) the emission lines showed small blueshifts. These results indicate that the increase in redshift toward the limb is caused by the increase in the redshift of granules. Because the bisector reflects the atmospheric velocity along the line-of-sight, our observations can be interpreted as suggesting that the line-forming region in granules is geometrically thicker than that in intergranules.
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Earth and Planetary Astrophysics

Energy distributions of precipitating electrons in Jupiter's auroral regions from combined Juno/JADE and Juno/JEDI measurements

B. Benmahi, V. Hue, N. André et al. (+17 more)

Jupiter's auroras are produced by magnetospheric electrons precipitating into its atmosphere. Juno/JADE and Juno/JEDI together measure these electrons from 100 eV to 1 MeV. However, their auroral spectra are poorly reproduced by the widely used kappa distribution, hereafter the classical single-kappa distribution. We aim to statistically characterize the energy flux distributions of precipitating auroral electrons and to derive a new phenomenological 4-kappa distribution better suited to JADE+JEDI data. We build mean energy flux distributions in six auroral sub-regions (polar, main, and outer emissions in both hemispheres), combining JADE and JEDI data from PJ3 to PJ35, mapped to the SIII frame with the JRM33 model including the current sheet. We fit them using MCMC with the classical single-kappa and 4-kappa distributions. The mean distributions show a monotonic power-law decay with an energy cutoff beyond ~500 keV in most sub-regions, although some individual spectra depart from it at intermediate energies. Mean energies range from ~21 to ~119 keV, and energy fluxes from ~9.5 to ~28.7 mW/m$^2$. The classical single-kappa fit fails in all sub-regions, with $\kappa$ converging to the lower bound of its prior range. We therefore introduce the 4-kappa distribution, a linear combination of four classical single-kappa distributions modulated by an exponential high-energy cutoff, which accurately fits all six sub-regions. At equal energy flux and mean energy, transport simulations show that the 4-kappa distribution deposits energy at lower altitude than the classical one and distributes it differently along the vertical, with implications for the UV color ratio, atmospheric chemistry and thermal structure, and ionospheric conductances. This distribution provides an analytical framework for realistic modeling of electron precipitation and UV auroral emissions at Jupiter.
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All authors B. Benmahi, V. Hue, N. André, B. Bonfond, M. Blanc, Z.-Y. Liu, B. H. Mauk, F. Allegrini, G. Clark, M. Devinat, G. Gronoff, T. Le Liboux, M. Barthélémy, C. Lefour, T. Cavalié, B. Benne, T. Gautier, T. Briand, J. A. Noble, J. A. Sinclair

Earth and Planetary Astrophysics · Cross-listed from physics.space-ph

P2D - A Two-Dimensional Multi-Spacecraft Solar Wind Persistence Model

Daniel Milošić, Manuela Temmer, Stephan G. Heinemann et al. (+2 more)

The background solar wind is a key component in space weather forecasting, as it contains geoeffective high-speed streams and provides the medium through which coronal mass ejections propagate and evolve in interplanetary space. Due to the solar rotation and the slow evolution of large-scale solar wind structures, solar wind properties exhibit an autocorrelation with a period of roughly 27 days, particularly at solar minimum. We made use of this property to develop a solar wind persistence model with input from multiple spacecraft (Solar Orbiter, Parker Solar Probe, STEREO-A, STEREO-B and the OMNI database). The model ballistically propagates in-situ data from the position of their measurement radially away from the Sun, as well as longitudinally with the solar rotation rate, producing 2D maps of solar wind parameters. These can be extracted at any point in the heliosphere for a solar wind reconstruction. From Earth's perspective, the reconstruction performs with an MAE of 65.41 km/s and 3.51/cm^3 for speed and density, respectively. During high-speed streams, the peak hit rate is 50% and 48% for speed and density. It performs best during times when there are spacecraft located between Earth and Lagrange point L5. During these times, the mean absolute error of the predicted solar wind speed decreases by roughly 35% in comparison to the benchmark 27-day persistence model. Therefore, future L5 missions like Vigil are expected to provide a robust basis for reliable persistence forecasts.
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All authors Daniel Milošić, Manuela Temmer, Stephan G. Heinemann, Mathew Owens, Stefan J. Hofmeister

Earth and Planetary Astrophysics

Beyond gas dwarfs and water worlds: hybrid envelopes among the M-dwarf sub-Neptunes characterised with JWST

Juan F. Pagés Navarrete

Sub-Neptunes orbiting M dwarfs are commonly interpreted either as rocky cores beneath primordial H/He envelopes (gas dwarfs) or as volatile-rich bodies formed beyond the water-ice line (water worlds). Because the two are degenerate in mass and radius once envelope evolution is treated self-consistently, the atmospheric mean molecular weight $\mu$ is the more direct discriminant. We compile the eight M-dwarf sub-Neptunes with published JWST transmission spectra and a constraint on $\mu$, grade each constraint by the quality of the underlying evidence, and combine it with the restricted Jeans parameter and with energy-limited escape integrated over the system lifetime, using XUV histories from M-dwarf activity-age relations. Planets are classified by what their present composition implies about their origin. At the $\mu = 3.8$ amu threshold adopted in the gas-dwarf literature, four planets fit neither end-member: their envelopes ($3.8 < \mu \le 18$ amu) are too heavy for primordial H/He, yet neither their composition nor their escape history requires a volatile-rich origin. Two of these assignments rest on molecular detections (LP 791-18 c and TOI-270 d) and two on bounded or conditional metallicities. One planet, LHS 1140 b, requires a volatile-rich origin; one, TOI-776 c, is tentatively a gas dwarf; two remain ambiguous. We propose the term hybrid worlds for the intermediate class, whose envelopes can be produced by magma-ocean equilibration, supercritical miscibility, preferential hydrogen loss or accretion interior to the ice line. The count depends on the adopted threshold (three planets at 5 amu, one at 10 amu), but no threshold leaves both end-member classes physically consistent. The sample is set by JWST target selection, so these fractions are not occurrence rates; a homogeneous survey testing whether $\mu$ is bimodal would test the proposed class directly.
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Solar and Stellar Astrophysics

Power balance and anomalous exchange in post-AGB pulsations

Jan Zalewski

We develop a complex balance relation for stellar pulsations whose real and imaginary parts give paired relations for the excitation rate and oscillation frequency. The formulation includes thermodynamic exchange, boundary power, and the inertial, compression, horizontal-area, and gravitational-stratification terms, without assuming weak nonadiabaticity. Applied to portions of an envelope, it provides cumulative diagnostics evaluated using the eigenfrequency and eigenfunctions of the complete pulsation problem. We show that a negligible global boundary contribution can coexist with substantial internal boundary power, which may largely compensate the thermodynamic exchange within the envelope. Applications to radial pulsations of post-AGB envelopes illustrate this behaviour for ordinary, strange, and anomalous-exchange modes. The latter have a negative effective norm and opposite signs of net exchange power and excitation rate. For a selected excited anomalous mode, the principal exchange occurs between the He II ionization region and the Z-bump, with less participation from the outer ionization layers than in the comparison modes. Classification by the largest response norm reveals distinct domains across the examined pulsation spectrum. The selected anomalous branch retains horizontal-area dominance across its transition from damping to excitation.
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Astrophysics of Galaxies

KiDS-DR5: Exploring dust transport in dark matter halos of galaxies

Eray Genc, Angus H. Wright, Hendrik Hildebrandt et al. (+12 more)

We analyse a well-defined sample of galaxies from the final data release of the Kilo-Degree Survey (KiDS-DR5), selected using magnitude, photometric redshift, and stellar mass cuts, to measure their mean halo mass and circumgalactic dust content as a function of stellar mass. Our goal is to provide empirical constraints on dust transport mechanisms, such as stellar- and AGN-driven outflows, operating in galaxy halos. We develop and validate a new measurement and modelling framework using the MICE2 simulation, incorporating a realistic circumgalactic dust extinction scenario. Using this framework, we jointly model multiband ($ugriZYJHK_{\rm s}$) magnitude shifts and galaxy–galaxy lensing signals to infer the mean halo mass and dust mass of lens galaxies at $z_{\rm B} < 0.4$, analysed in five stellar-mass bins in KiDS-DR5. The modelling jointly describes the halo mass distribution and dust extinction, including dust associated with neighbouring halos. We demonstrate that the inclusion of a satellite fraction and dust extinction from neighbouring halos is required by the data. We find a linear relation between stellar mass and dust mass, consistent with previous observational studies, but flatter than predictions from the semi-analytic model Dusty-SAGE. This difference may indicate that current implementations of dust-related feedback in galaxy formation models require further refinement.
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All authors Eray Genc, Angus H. Wright, Hendrik Hildebrandt, Dian P. Triani, Dominik J. Bomans, Benjamin Stölzner, Marika Asgari, Henk Hoekstra, Benjamin Joachimi, Shahab Joudaki, Konrad Kuijken, Lauro Moscardini, Mario Radovich, Robert Reischke, Ziang Yan

High Energy Astrophysical Phenomena

Unexpected Gamma-ray Outburst from the CSS Radio Galaxy 3C 216

Stefano Ciprini and Federica Giacchino

While compact steep-spectrum (CSS) radio galaxies, genuine young/intermittent-jet or frustrated-jet radio galaxies trapped in gas-rich environments, are rarely detected in GeV gamma-ray energy bands, 3C 216 is an interesting exception. In 2023, the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope detected an unexpected, rapid, and powerful GeV gamma-ray outburst from this CSS radio galaxy, which was followed up by UV and X-ray observations from the Neil Gehrels Swift Space Observatory. During the outburst its spectral energy distribution is dominated by synchrotron and synchrotron self-Compton radiation, produced in the relativistic jet, suggesting a young quasar classification. Radio-band features, such as superluminal motion and a flat-spectrum core component, confirm that 3C 216 harbors a distinct blazar-like core, bent and viewed under a small angle to the line of sight. This is the unique large and energetic event from the source observed in 17 years of Fermi-LAT continuous all-sky and time-domain monitoring.
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Earth and Planetary Astrophysics

Resolved Structure and Orbital Motion of a Localized 1 au-scale Dust Accumulation in the Protoplanetary Disk around TW Hya

Takashi Tsukagoshi, Takayuki Muto, Hideko Nomura et al. (+6 more)

We present the results of high-resolution ($\sim1$~au) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the TW~Hya protoplanetary disk in the Band 6 dust continuum, as well as the \ce{^13CO} and \ce{C^18O} J=2–1 emission lines. The primary focus of this study is to investigate the kinematics, internal morphology, and local gas environment of the prominent dust blob at a radius of 52~au. By comparing our 2021 data with archival observations from 2017, we detect the proper motion of the blob. The measured azimuthal velocity of 3.3$\pm$0.9~km~s$^{-1}$ is fully consistent with local Keplerian rotation. Combined with the lack of significant radial migration over the four-year baseline, this confirms that the structure is robustly co-moving with the disk system. Crucially, our high-resolution continuum map resolves the blob into a distinct double-peaked morphology separated by $\sim$1.7~au azimuthally. We robustly validate this double-peaked substructure by reproducing it in the independent 2017 dataset using a sparse-modeling image reconstruction technique. We discuss potential physical origins for this double-peaked morphology, including an inclined circumplanetary disk with an inner dust cavity, the roots of planet-induced spiral arms, or alternative hydrodynamic scenarios that do not involve an actively accreting planet such as the U-turn trajectory of secondary dust or a short-lived hydrodynamic gas vortex. We detect no compact gas emission counterparts associated with the continuum blob. Since these CO lines likely trace optically thick upper atmospheric layers, the absence of localized vertical gas perturbations suggests that if an embedded planet is responsible for the dust structure, its mass must be exceptionally low.
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All authors Takashi Tsukagoshi, Takayuki Muto, Hideko Nomura, Ryohei Kawabe, Satoshi Okuzumi, Shigeru Ida, Jun Hashimoto, Taichi Uyama, Motohide Tamura

Cosmology and Nongalactic Astrophysics

Field-level inference of growth rate from DESI BGS galaxy and ZTF supernova simulations

Corentin Ravoux, Bastien Carreres, Julian Bautista et al. (+60 more)

Galaxy peculiar velocities are a powerful probe of the growth rate of structure $f$ at low redshifts ($z < 0.2$), measured through the combination $f\sigma_8$. These constraints are improved by combining peculiar velocities with redshift space distortion measurements from the galaxy density field. We create a dedicated simulation to test growth rate measurement from the combination of Type Ia supernova peculiar velocities from the Zwicky Transient Facility (ZTF) with the Bright Galaxy Survey (BGS) of the Dark Energy Spectroscopic Instrument (DESI), using projections for 6 years of ZTF data and the Data Release 3 (DR3) of DESI. We apply a wide-angle likelihood-based field-level inference to combine ZTF velocity and DESI BGS density fields simultaneously. This procedure is performed while varying the different density and velocity field configurations. Adding DESI galaxy density information to the ZTF supernovae improves the constraint on nuisance parameters and yields up to a 50 % reduction in the growth-rate uncertainty without introducing bias. If we consider the conservatively best DESI density configuration, the mean error bar achievable by a DESI ZTF measurement is $\sigma_{f\sigma_8} = {}^{+0.047}_{-0.048}$ corresponding to a 10 % error. These measurements will play a critical role for testing modified gravity theories.
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All authors Corentin Ravoux, Bastien Carreres, Julian Bautista, Damiano Rosselli, Jessica Aguilar, Steven Ahlen, Melissa Amenouche, Uendert Andrade, Eric Armengaud, Alejandro Aviles, Florian Beutler, Davide Bianchi, David Brooks, Umut Burgaz, Aurelio Carnero Rosell, Edmond Chaussidon, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Georgios Dimitriadis, Andreu Font-Ribera, Daniel Felipe Forero Sánchez, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Ariel Goobar, Gaston Gutierrez, Hiram K. Herrera-Alcantar, Cullan Howlett, Mustapha Ishak, Joel Johansson, Stephanie Juneau, Ofer Lahav, Martin Landriau, Laurent Le Guillou, Alexie Leauthaud, Marc Manera, Ramon Miquel, Seshadri Nadathur, Jakob Nordin, Hernan Enrique Noriega, Enrique Paillas, Nathalie Palanque-Delabrouille, Will Percival, Francisco Prada, Ignasi Pérez-Ràfols, Mickael Rigault, Antoine Rocher, Philippe Rosnet, Graziano Rossi, Rossana Ruggeri, Lado Samushia, Eusebio Sanchez, Christoph Saulder, David Schlegel, Michael Schubnell, Hee-Jong Seo, Joseph Silber, Małgorzata Siudek, Mathew Smith, Gregory Tarlé, Benjamin A. Weaver, Pauline Zarrouk

Astrophysics of Galaxies

Discovery of Kolmogorov-like turbulence in the inner shell of SNR HB 9

Li Xiao, Ming Zhu, Xiao-Hui Sun et al. (+2 more)

We investigated the scaling relation of the magnetohydrodynamic turbulence in the inner and outer shells of the supernova remnant HB 9 using multi-tracers. For the eastern inner shell section, one-dimensional structure function and power spectrum analyses of the radio total intensity, H-alpha emission, and polarized intensity consistently show a Kolmogorov-like scaling of l^2/3 over the inertial range. The two-dimensional power spectrum for the entire inner region follows k^-8/3 of all tracers, including the polarization gradient. It indicates that fully developed, trans-Alfvenic Kolmogorov turbulence is present in the inner shell of HB 9. We estimated the strength of random magnetic field therein from the low fractional polarization (5%), and obtained a upper limit delta B of 18 micro G. The turbulence in the inner shock shell is most likely driven by the Richtmyer-Meshkov instability.
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All authors Li Xiao, Ming Zhu, Xiao-Hui Sun, Wolfgang Reich, Patricia Reich