Earth and Planetary Astrophysics
Modeling the Impact of Starspot Inhomogeneity on Spectroscopic Retrievals of Directly-Imaged Planets
Alex R. Howe, Natasha Latouf, Christopher C. Stark et al. (+2 more)
Stellar activity is a major complication in the detection and characterization of
exoplanets by both radial velocities and transits, and the upcoming Habitable Worlds Observatory (HWO) invites us to also consider its effect on direct imaging. Spectra of directly-imaged
planets can vary with the activity of their host
stars because the face of the
star we see is not the same as the face reflected by the
planet. This discrepancy could potentially result in inaccurate measurements of the
planet's radius and unexpected, externally-caused variability in its contrast spectrum with the
star. To assess the scientific capabilities and requirements of HWO, it is important that the magnitude of these effects be quantified. We present results of model
retrievals of Earth-like
exoplanets observed with an HWO-style survey, as they would appear when affected by starspots, using the ExoVista code for spectrum generation and the BARBIE code for spectroscopic
retrieval. Both
Solar-type
stellar activity and highly active rapid rotators are considered and compared with an idealized quiescent host
star. In the quiescent case, ${\rm SNR}\approx5$ is needed to detect atmospheric water vapor at 0.9 microns and ${\rm SNR}\approx13$ at 0.74 microns. We find that for
Solar-type activity, the effect on
retrievals will be negligible, but it could present problems for certain highly-active
stars at limiting geometries. For an extreme case with a single large spot with 10% coverage not visible to the observer, the SNR required for water detection increases to ${\rm SNR}\approx8$ at 0.9 microns and ${\rm SNR}\approx18$ at 0.74 microns. It also decreases the accuracy of the retrieved albedo, resulting in a value $\sim2/3$ of the true value. In light of these results, we estimate the impact that
stellar variability and starspots may have on an HWO-style survey.
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All authors Alex R. Howe, Natasha Latouf, Christopher C. Stark, Avi M. Mandel, Veselin Kostov
Astrophysics of Galaxies
Saurabh Mittal, Thomas Siegert, Francesca Calore et al. (+12 more)
The origin of the 511 keV line signal in the Milky Way remains unresolved despite decades of observations. The measured flux of $\sim 3 \times 10^{-3}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$ suggests a steady-state positron injection rate of $\sim 10^{43}$-$10^{44}\,\mathrm{e^+\,s^{-1}}$. One proposed contributor to this signal is
stellar flaring activity since high energy
Solar flares are known to produce positrons and associated annihilation radiation. We estimate the quasi-persistent 511 keV luminosity expected from flaring
stellar populations and estimate the
Galactic contribution. We constrain the 511 keV fluxes for different sources in the
Galaxy, and in particular globular clusters. Using
Solar flare observations as a calibration baseline, we construct a hierarchical
Bayesian model to link
flare energy to 511 keV luminosity. We further use
flare frequency-energy distributions to estimate the time-averaged positron output of
stellar populations. The resulting predictions are compared with INTEGRAL/SPI observations using spatial and population-based models. We find that
stellar flares fall short by several orders of magnitude in explaining the
Galactic positron annihilation rate. Reproducing $\sim10\%$ of the observed luminosity in the
Galactic bulge would require unphysically large maximum
flare energies per
star reaching up to $E_\mathrm{{max}} \gtrsim 10^{37-39}\,\mathrm{erg}$. Spatial modeling further shows that
stellar flare scenarios cannot reproduce the observed 511 keV morphology.
Stellar flares cannot be the dominant source of
Galactic positrons. Although previous studies have shown that the measured 511 keV morphology is broadly consistent with old
stellar populations, our results exclude normal
stellar flaring activity as the underlying source for this emission.
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All authors Saurabh Mittal, Thomas Siegert, Francesca Calore, Fiona H. Panther, Pasquale D. Serpico, Hiroki Yoneda, Niklas C. Bauer, Tristan Bouchet, Laura Eisenberger, Mika A. Gelowicz, Tomohiko Oka, Rudi Reinhardt, Manuel R. H. W. Skalka, Dimitris Tsatsis, Manja L. Zimmerer
Astrophysics of Galaxies
JWST NIRCam and MIRI Reveal the Dust-Producing AGB Population of NGC 6822
Conor Nally, Olivia C. Jones, Laura Lenkić et al. (+9 more)
We present a photometric catalogue of the Local Group
dwarf galaxy NGC 6822 based on deep JWST observations obtained with the Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). Point-spread-function photometry and band matching were performed with StarbugII. The resulting catalogue contains 864,114 NIRCam point sources and 17,235 MIRI detections, with 10,079 detected in both instruments. Blackbody fitting yields effective temperatures and bolometric luminosities for 119,621
stars, providing a detailed view of the resolved
stellar content. Candidate evolved
stars were selected from NIRCam-MIRI colour-magnitude diagrams, with the sample refined by removing resolved contaminants and excluding young
stellar objects through spectral energy distribution (SED) fitting. The final sample of 1226 evolved
stars was analysed using the Grid of Red Supergiant and Asymptotic
Giant Branch Models (GRAMS), from which
dust-production rates were obtained and carbon-rich or oxygen-rich asymptotic
giant branch (AGB) classifications assigned via a likelihood-weighted comparison across the full model set. Across the JWST fields, evolved
stars return 5.6 x 10^-7 Msun yr^-1 of
dust to the interstellar medium, with oxygen-rich AGB
stars contributing 60% and carbon-rich AGB
stars 35%, despite the low
metallicity of NGC 6822. The unexpectedly high oxygen-rich contribution indicates the presence of intermediate-mass AGB
stars undergoing hot-bottom burning, in line with the recent
star-formation history of NGC 6822.
Dust-producing AGB
stars exhibit a centrally concentrated carbon-rich population and a more extended oxygen-rich population. We also identify JWST colour relations that provide robust photometric
estimators of
dust-production rates for evolved
stars.
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All authors Conor Nally, Olivia C. Jones, Laura Lenkić, Annette M. N. Ferguson, Nolan Habel, Alec S. Hirschauer, Margaret Meixner, P. J. Kavanagh, Martha L. Boyer, Omnarayani Nayak, B. Sargent, P. Scicluna
Earth and Planetary Astrophysics
Water gas discs in exo-asteroid belts
Paul Huet, Quentin Kral and Louis Manchon
Observations of tens of secondary CO gas discs associated with cold exo-Kuiper belts together with other arguments have led Kral et al (2024) to propose that water ice could also sublimate in exo-asteroid belts, suggesting a new pathway for the delivery of water to terrestrial
planets, including Earth. We aim to model such water vapour discs and to characterise their physical properties across a range of extrasolar systems with different host
stars. We further investigate the implications for the
accretion of this water by potential
planets located in the inner regions of these systems. We adapt and extend the model of Kral et al (2024) to follow the outgassing, photodissociation, and viscous
evolution of water vapour discs. We perform a suite of simulations exploring the parameter space, focusing on the
stellar mass, the mass of the parent belt, and its orbital location. We additionally include an inner
planet to estimate the mass of water accreted as a function of disc properties and system architecture. We find that systems hosting Sun's mass (and higher)
stars produce water vapour very efficiently, sublimating nearly all of the ice initially present in the belt. In most cases, the bulk of the gas mass is generated early, when the
stellar luminosity is highest. The amount of water accreted by inner
planets can approach the initial ice mass of the belt, leading to
planets with water inventories comparable to or exceeding those of Earth, potentially creating ocean
planets. We find that water outgassing occurs early after the protoplanetary disc dissipates in systems containing exo-asteroid belts. ALMA, JWST and ELT are capable of detecting this water vapour for several tens of millions of years, even in relatively low-mass water discs. Hence, if such water gas discs are present, they should be detectable with current facilities.
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Astrophysics of Galaxies
Up, Up, and Away? Quantifying ISM Fallback using Ram Pressure Stripping Simulations
Harrison J. Souchereau, Stephanie Tonnesen, Jingyao Zhu et al. (+1 more)
The
evolution of the cold interstellar medium (ISM) in satellite
galaxies orbiting through massive hosts is an important factor in how they evolve while experiencing ram pressure stripping (RPS), as cold molecular gas clouds are the most difficult ISM component to fully strip and serve as the sites of
star formation. We investigate ISM
evolution using a suite of hydrodynamical wind tunnel simulations with an intermediate mass ($M_* = 10^{9.7}$ M$_\odot$)
galaxy orbiting in a Coma cluster-like environment, varying the disk-wind angle. Even if the ultimate fate of a ram pressure stripped
galaxy is complete gas removal, we find that cold gas evolves through cycles of
outflow and inflow (fallback). We show that fallback can be identified at a wide range of wind angles, but is elevated for angles closer to edge-on and occurs predominantly in a specific quadrant (trailing side, rotating into the wind). Most inflow occurs in gas that never leaves an “inner tail" region that extends to $\sim20$ kpc. We discuss possible reasons for when and why fallback occurs using simple idealized simulations. For a highly inclined disk, offset rotational motion is a major driver of fallback, while disk shadowing and cloud growth can act at all wind angles. Lastly, we discuss the relative importance of each mechanism at different stages of a
galaxy's
evolution under ram pressure, and compare our findings with instances of ISM fallback detected in observed RPS
galaxies.
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All authors Harrison J. Souchereau, Stephanie Tonnesen, Jingyao Zhu, Jeffrey D. P. Kenney
Solar and Stellar Astrophysics
Unstable magnetospheric accretion on the T Tauri star TW Hya
J.-F. Donati, P.I. Cristofari, C. Moutou et al. (+9 more)
In this paper we present new spectropolarimetric and velocimetric observations of the prototypical classical T Tauri
star TW Hya obtained with SPIRou at the Canada-France-Hawaii
Telescope, expanding our previous monitoring over two new seasons (2024 and 2025). We confirm that the large-scale
magnetic field of TW Hya varied with time, and find that it showed fluctuations on a timescale of about a year in addition to the longer term variations outlined in the previous study. Using Zeeman-Doppler imaging, we obtain that the large-scale field of TW Hya mostly consisted of a poloidal dipole of mean polar strength 0.83 kG, inclined at an average 17degr to the rotation axis. We also find that the radial velocities of TW Hya, once fully filtered from telluric contamination, were dominated by rotational modulation induced by activity, with residuals of 32 m/s rms. No signal from a putative close-in
planet is found, with an upper limit on the
planet mass ranging from 0.33 to 0.98 Mjup for distances of 0.053 to 0.41 au from the central
star. Emission lines indicate that the mass
accretion rate was equal to $10^{-8.33\pm0.20}$ Msun/yr on average, with peak-to-peak fluctuations by a factor of ~5 from season to season. This confirms that
accretion onto TW Hya is unstable, with the magnetospheric gap carved by the large-scale field at the center of the disk extending on average no further than 33-40% of the corotation radius where the disk Keplerian angular velocity equals the rotation rate at the
stellar surface.
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All authors J.-F. Donati, P.I. Cristofari, C. Moutou, A. Carmona, A. Lavail, J. Bouvier, K. Perraut, S.H.P. Alencar, M. Audard, K. Grankin, F. Ménard, M. Takami
High Energy Astrophysical Phenomena
Extending the infrastructure of the BAM code towards resistive general-relativistic magnetohydrodynamics: tests and first applications
Matthew Beaudoin, Maximilano Ujevic, Ramon Jaeger et al. (+4 more)
Many astrophysical phenomena, including
pulsars and short gamma-ray bursts, are associated with the extremely strong
magnetic fields present in
neutron stars and
neutron star mergers. While the ideal magnetohydrodynamic approximation, which assumes infinite conductivity, provides an excellent description of the
neutron-
star interior, it cannot capture non-ideal processes such as Ohmic dissipation and
magnetic reconnection. To overcome this limitation, we present an extension of the numerical-relativity code BAM incorporating a resistive general-relativistic magnetohydrodynamic (GRMHD) description. We validate the new implementation through an extensive suite of special-relativistic magnetohydrodynamic
benchmark tests and by performing stable simulations of isolated and binary
neutron star systems. For the latter, we investigate the impact of finite conductivity on
magnetic-field amplification, mass ejection, and non-ideal GRMHD effects. In particular, we find that the component of the electric field parallel to the
magnetic field, which is zero in the ideal case, can reach up to 10% of the total electric field strength. This highlights the potential importance of non-ideal effects for accurately modeling the long-term
evolution of post-merger remnants, particularly in low-density regions. Although the present study is restricted to simplified piecewise-polytropic equations of state, it demonstrates the capabilities of the new resistive GRMHD framework and paves the way for future investigations employing more realistic microphysics.
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All authors Matthew Beaudoin, Maximilano Ujevic, Ramon Jaeger, Anna Neuweiler, Henrique Gieg, Kenta Kiuchi, Tim Dietrich
Solar and Stellar Astrophysics
Mapping Oscillatory Flows in a Giant Chromospheric Spiral
Yash.B.Saneshwar, Eamon Scullion and Gert J. J. Botha
The
solar chromosphere is permeated by complex
magnetic fields that guide
plasma flows and energy into the corona. This work presents a detailed analysis of a unique, high-resolution observation of a
giant chromospheric spiral structure that emerges due to a large
magnetic pore, captured by the Swedish 1-m
Solar Telescope (SST). A comprehensive data analysis pipeline is developed to automatically detect the edges of 2255
plasma flows (loops) that constitute the spiral, and these are used to extract the kinematics of flows propagating along the
magnetic field. The analysis reveals three primary insights into the spiral's physics. First,
magnetic curvature is correlated with oscillatory flow dynamics, i.e. regions of high loop
curvature exhibit a statistically significant excess of higher-order oscillation modes compared to straighter loops; it is also correlated with higher intensity and longer periods. Second, spatial distribution of oscillation period shows an inverse trend, decreasing from $\sim$3.5 minutes in the pore to $\sim$3 minutes in the outer spiral arms. This is interpreted as a signature of the overlying trans-equatorial quadrupolar coronal loop system compressing the pore's field lines into a near-horizontal orientation, producing a period gradient that challenges the standard expanding canopy model. Finally, the emission signature confirms that oscillating threads represent localised channels of brightness that lie within cooler, absorbing loop material. This study provides the first statistical analysis of oscillatory flows in a large-scale spiral, probing energy flow through the chromosphere through curved
magnetic structure.
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Astrophysics of Galaxies
New optical velocities for local galaxy candidates
Maksim Chazov, Igor Karachentsev and Serafim Kaisin
We used the 6-meter BTA
telescope to determine radial velocities for 46
galaxies, previously considered to be nearby objects. Twelve of them have kinematic distances within 13Mpc and are new probable companions to the bright Local Volume
galaxies: NGC1068, NGC2903, NGC4517, NGC4565, NGC4826. We also found a new tiny satellite of the nearby (10.38Mpc) SMC-like
dwarf galaxy DDO46. Two isolated dIrr
galaxies: dw1408-0802 and Dw1552-1027 are probably located inside the Local Void. The spectrum of the latter shows a rich set of emission lines. Using the radial velocities and projected separations of 13 NGC1068 satellites, we estimated the total mass of the group to be $M= (2.6\pm1.0)\times10^{12}\, M_\odot$.
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Earth and Planetary Astrophysics
Latitudinal chemical and cloud variations in the atmosphere of a brown dwarf
Benjamin Charnay, Sam de Regt, Matthieu Ravet et al. (+8 more)
Brown
dwarfs are massive analogues of extrasolar
giant planets. Compared to
exoplanets whose observations are generally limited by the presence of their bright host
star, brown
dwarfs are ideal targets for studying substellar atmospheric physics, chemistry and dynamics. Previous observations and simulations of their atmospheres suggest preferential cloud formation around the equator, associated with an equator-pole thermal gradient. Here we show that this atmospheric structure should induce latitudinal chemical variations detectable by the Doppler effect. We introduce a new method - Differential Molecular Rotational Broadening - which consists in comparing the apparent rotational broadening of individual molecules from high-resolution spectra. Application of this approach to VLT-CRIRES observations for different molecules (CO, H2O, CH4 and NH3) in the atmosphere of the brown
dwarf DENIS J0255-4700 confirms the existence of latitudinal chemical variations. Our data suggest a depletion of CH4 and NH3 at low latitudes, consistent with an equatorial cloud belt. Our method could be applied to multiple brown
dwarfs and
exoplanets to map their atmospheres and to study various atmospheric processes.
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All authors Benjamin Charnay, Sam de Regt, Matthieu Ravet, Lucas Teinturier, Flavien Kiefer, Gaël Chauvin, Allan Denis, Mickaël Bonnefoy, Paulina Palma-Bifani, Alice Radcliffe, Arthur Vigan
Earth and Planetary Astrophysics
Peering through the disc of HD 98800 BaBb. Precise timing predictions for the HD 98800 AaAb occultation
S. Zúñiga-Fernández, A. Bayo, J. Olofsson et al. (+2 more)
HD 98800 is a young hierarchical quadruple system composed of the tight binaries AaAb and BaBb on a wide, highly inclined outer orbit. The B subsystem hosts a circumbinary disc in a polar configuration, and the geometry of the system offers a rare opportunity to observe the passage of the disc around BaBb in front of AaAb. We aim to update the overall orbital solution to offer precise time windows of the main occultation features by combining the orbit with the state-of-the-art knowledge of the disc's structure. We combine new and published radial-velocity measurements and multi-wavelength astrometry for the outer AB orbit and both inner subsystems, AaAb and BaBb, in a joint orbital fit. The revised solution is consistent with previous dynamical masses and improved the outer orbit, reducing the uncertainties in the period and periastron epoch by about a factor of two. It also narrows the predicted crossing-phase windows to 5–15 days at the 1{\sigma} level, improving the timing of ingress, egress, and the first cavity-crossing predictions. These results provide a more accurate timing framework for future observations of the occultation, although the predicted epochs remain model-dependent because of uncertainties in the disc structure.
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All authors S. Zúñiga-Fernández, A. Bayo, J. Olofsson, J. Ehrhardt, Á. Ribas
Astrophysics of Galaxies
Can third- and fourth-order multipoles plus radial variation of iso-density ellipses explain the observed flux ratios in B1422$+$231? YES, and a lesson learned from a TNG100 lensing galaxy sample
Ruizhe Feng, Dandan Xu, Dominique Sluse et al. (+3 more)
Flux ratio anomalies in multiply-imaged
quasar lenses are a long-standing issue. Using a classical system B1422+231 as a case study, we investigate how typical non-clumpy perturbations beyond elliptical shapes – multipoles $m_3, m_4$ and radial variations in $q, \phi_q$ – can account for the observed image positions and flux ratios under different observational precisions. We extract these perturbations from a pre-selected strong-
lensing galaxy sample from the TNG100 simulation. Smooth macroscopic models (SIE+$\gamma$, EPL+$\gamma$) are then fitted to the observed image positions alone and to both positions and flux ratios, with and without including the extracted perturbations. With astrometric uncertainty of $\sigma_{p}=10$ mas, both macro-models alone can already successfully fit image positions within $3\sigma_{p}$. At $\sigma_{p}=2$ mas, however, 'astrometric anomalies' appear if smooth macro-models alone are adopted. In this case, adding the extracted perturbations can explain the anomalous image positions. When both positions and flux ratios are adopted, the SIE+$\gamma$ model family already shows 'flux ratio anomalies' at photometric uncertainty $\sigma_{f} \le 10\%$ (keeping $\sigma_{p}=10$ mas). When EPL+$\gamma$ is used, the smooth model alone can simultaneously fit both positions and flux ratios with $\sigma_{f}=10\%, 5\%$, but not with $\sigma_{f}=2\%$, where 'flux ratio anomalies' appear. Adding all four types of extracted perturbations can rescue the macro-models and explain the observed anomalous flux ratios. We present important lessons learned regarding model flexibility and degeneracy.
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All authors Ruizhe Feng, Dandan Xu, Dominique Sluse, Giulia Despali, Anowar Shajib, Cai-Na Hao
High Energy Astrophysical Phenomena
Radio and X-ray flux rebrightening six years after outburst in a partially-obscured extreme changing-look AGN
Tianyao Zhou, Xinwen Shu, Lei Yang et al. (+14 more)
SDSS J1548+2208 is a unique partially-obscured
nuclear transient that exhibits multiwavelength outbursts in mid-infrared, X-ray and
radio. We present the results from multiwavelength photometric and spectroscopic follow-up observations with a time span of ~2500 days since its discovery. We find that the mid-infrared and X-ray emission (with a hard X-ray spectrum) are still in a high flux level relative to the pre-
flare state, suggesting a sudden increased, and possibly long-sustained accreting activity from central black hole. This is supported by the slowly-evolving high-ionization coronal lines. The mid-infrared color turns blue slowly in the rising phase, which is distinct from
stellar tidal disruption events (TDEs). All these properties point to the origin of outbursts from an extreme changing-look AGN and the scenario with a normal TDE seems disfavored. The
radio spectral energy distribution (SED) in ~0.65-15 GHz is unusual, displaying a double-peak feature with distinct variability characteristics. In addition, we find evidence for the late-time
radio rebrightening more than six years since the initial outburst, as well as a possibly new X-ray
flare, though the significance for the latter is not high. The peculiar
radio flux and SED
evolution could be explained by a nascent
outflow expanding into and shocking circumnuclear diffuse medium filled by denser clouds. In this case, SDSS J1548+2208 represents a rare changing-look AGN which can launch
radio outflows. Continued multiwavelength observations are required to map the
dust and gas distribution on pc-scales, providing new insights into the environmental properties that could regulate AGN changing-look phenomenon.
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All authors Tianyao Zhou, Xinwen Shu, Lei Yang, Tao Wu, Luming Sun, Yibo Wang, Guobin Mou, Ning Jiang, Wenjie Zhang, Hucheng Ding, Fabao Zhang, Yujun Yao, Liming Dou, Yogesh Chandola, Ningyu Tang, Jianguo Wang, Tinggui Wang
High Energy Astrophysical Phenomena
AT2019ijn: a fast-rising, slow-decaying blue optical transient with exceptionally bright radio emission
Hucheng Ding, Xinwen Shu, Luming Sun et al. (+9 more)
We report the discovery of a peculiar optical transient, AT2019ijn, occurred in the
nuclear region of a
dwarf galaxy at z=0.273. It rises rapidly to peak at a luminosity of Mg=-21.1 in 5 days, followed by a slow decline over more than a month, during which the optical emission has a persistently high blackbody temperature of T_BB~1.5-1.6x10^4 K. The
radio emission is exceptional which peaks at 640 days after optical discovery with a high luminosity of 2x10^31 erg/s/Hz. The peak
radio luminosity is at least two orders of magnitude brighter than known
radio-bright fast blue optical transients and
supernova explosions at similar epochs, but comparable to jetted
tidal disruption events. The luminous and long-lasting
radio emission with a late-time peak can be explained by an off-axis relativistic jet with a viewing angle of ~40 deg. We discuss possible origins for AT2019ijn and favor a jetted
tidal disruption event involving an intermediate-mass black hole of ~10^5 Msun, although a jetted magnetar model cannot be fully ruled out. AT2019ijn represents a new class of relativistic optical transients that highlights the importance of
radio surveys for discovering off-axis jetted events.
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All authors Hucheng Ding, Xinwen Shu, Luming Sun, Liangduan Liu, Lei Yang, Yunwei Yu, Xueguang Zhang, Ying Gu, Fangkun Peng, Fabao Zhang, Zhumao Zhang, Ningyu Tang
High Energy Astrophysical Phenomena
Two Earliest Optical-UV Tidal Disruption Events Hidden in the SDSS DR7 Catalog Unveiled by the Transformer-Based Spectrum Classifier
Ranfang Zheng, Zheyu Lin, Xu Kong et al. (+3 more)
Optical spectroscopic features are decisive in the current identification of optical-UV
tidal disruption events (TDEs). Regarding that the TDE estimated occurrence rate is $10^{-5}-10^{-4}$
galaxy$^{-1}$ yr$^{-1}$ by both theoretical and observational methods, large optical spectroscopic catalogs with >10$^5$
galaxy spectra can include some serendipitous spectra with TDE spectroscopic features, which can be found after building a useful selection method. We hereby introduce a principal component analysis enhanced
Transformer TDE spectrum classifier which achieves a precision of 0.88 and a recall of 0.99 on our evaluation
dataset, and report its inspiring discoveries in the widely-used SDSS DR7 catalog: two newly discovered TDEs and one reported likely TDE. For SDSS J124225.39+642919.0, we confirm the presence of a UV transient in GALEX catalog when the spectrum was taken, and its occurrence time should be earlier than the spectrum observation time, MJD < 52316 (February 11, 2002), making it the earliest optical-UV TDE discovered by now. For SDSS J152459.70+045423.1, its spectrum matches all features of the TDE-H+He spectrum, and was taken during an optical outburst recorded by the Catalina Real-time Transient Survey. The start of this outburst lies in 54269 < MJD < 54476 (June 18, 2007 - January 11, 2008), making it one of the earliest among the reported optical TDEs. The discovery of two new TDEs highlights the power of machine-learning based classifiers in digging out buried treasures in large-volume catalogs, and marks a new method for discovering optical-UV TDEs.
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All authors Ranfang Zheng, Zheyu Lin, Xu Kong, Ran Song, Dezheng Meng, Lulu Fan
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
The petit four of color-superconducting phases in proto-neutron star evolution
Selina Kunkel, Ishfaq Ahmad Rather, Hosein Gholami et al. (+2 more)
At high densities and moderate temperatures, hadronic matter is expected to undergo a first-order phase transition into a color-superconducting (CSC) state. A proto-
neutron star describes the earliest evolutionary stages during the first seconds to minutes after core-collapse
supernovae and therefore has the potential to assess the appearance of CSC phases at such high densities and moderate temperatures. To address this, we incorporate proto-
neutron star conditions, considering
neutrino-trapped and
neutrino-transparent ones, into the equation of state including color-superconducting phases in a recently developed RG-consistent NJL model. Since the total
baryon number of a proto-
neutron star is conserved during its later
evolution, tracking
stellar configurations from an initial mass of the hot proto-
neutron star to the final cold
neutron star along isolines of
baryon number allows us to investigate whether color-superconducting phases can form at any point along this trajectory. By mapping this multidimensional transition in the hot furnace of a core-collapse
supernovae cooling from a
neutrino-trapped birth state to a cold,
neutrino-transparent final state, we reveal four distinct core
evolution scenarios-our "petit four" of proto-
neutron star evolution: a delayed collapse from the CSC phase to a black hole, a persistent CSC phase, a vanishing CSC phase, and a fleeting CSC phase. For our specific parameterization of the hadronic and the CSC equation of state, we find that a stable color-superconducting phase can only be sustained in the final cold
neutron star for a narrow, high-mass region.
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All authors Selina Kunkel, Ishfaq Ahmad Rather, Hosein Gholami, Marco Hofmann, Jürgen Schaffner-Bielich
Earth and Planetary Astrophysics
Evolution and Observable Properties of Rocky Planet Atmospheres
Marie-Luise Steinmeyer, Lena Noack, Philipp Baumeister et al. (+9 more)
The atmospheric composition of rocky
exoplanets offers an important tool for constraining the properties of the interior of this type of
planet, beyond what is possible from measurements of their mass and radius alone. However, the interpretation of these observations requires an understanding of the complex interplay of a larger number of coupled planetary and atmospheric processes. This review provides an overview of the current state of knowledge regarding rocky
exoplanet atmospheres, beginning with their formation and escape mechanisms. We specifically highlight the importance of long-term interaction between the atmosphere, the surface, and the interior on rocky
planets. Furthermore, this review addresses the influence of biological activity and photochemical reactions on the atmospheric compositions. Consequently, establishing how these different processes contribute to shaping the atmospheres of rocky
exoplanets during their
evolution is fundamental for the characterization of these
planets with future space missions and ground-based surveys.
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All authors Marie-Luise Steinmeyer, Lena Noack, Philipp Baumeister, Keiko Hamano, Michael J. Way, Doris Breuer, Kanako Seki, Caroline Brachmann, Fabrice Gaillard, Manuel Scherf, Svetlana V. Berdyugina, Brice-Olivier Demory
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Dynamics and observational signatures of warm Dirac-Born-Infeld inflation with nonminimal derivative coupling
Run-Qing Zhao, Xiao-Min Zhang, Peng-Cheng Chu et al. (+1 more)
This paper investigates a warm Dirac-Born-Infeld (DBI) inflationary model with nonminimal derivative coupling (NMDC) to
gravity, where the inflaton kinetic term interacts with the Einstein tensor, thereby improving the effective gravitational friction. This model seamlessly integrates the noncanonical DBI kinetic structure, the NMDC-induced gravitational friction, and thermal dissipation. We formulate the background
evolution equations along with the corresponding slow-roll stability conditions, leading to analytic results for the scalar spectral index $n_s$ and the tensor-to-scalar ratio $R$. By applying these results to power-law potentials with $n=2$ and $n=4$, the model parameter space is constrained using the Planck 2018 data. The findings indicate that the interaction between NMDC-induced gravitational friction and thermal dissipation effectively modulates $n_s$ and significantly expands the viable parameter space. In the $(n_s,R)$ plane, the predictions for $N=50$ fall within the 95% confidence-level region, while those for $N=60$ extend into the 68% confidence-level region and approach the observationally preferred central values. For the representative parameter choices examined, the tensor-to-scalar ratio is notably suppressed, generally within the range $10^{-8}\lesssim R\lesssim10^{-5}$. Moreover, the combined damping mechanism relaxes the slow-roll condition related to $\eta$ and limits the inflaton field excursion, thus addressing the $\eta$ problem without incurring super-Planckian field variations. These results indicate that warm DBI inflation with NMDC offers a theoretically coherent and observationally viable inflationary model, showcasing the complementary effects of thermal dissipation and enhanced gravitational friction in the context of modified
gravity.
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All authors Run-Qing Zhao, Xiao-Min Zhang, Peng-Cheng Chu, Yun-Cai Feng
Earth and Planetary Astrophysics
Discovering and Characterising Exoplanets and Ultracool Dwarfs with the Square Kilometre Array
Robert D. Kavanagh, Juan B. Climent, Philippe Zarka et al. (+14 more)
The majority of the
Solar System
planets are sources of bright
radio emission, driven by energetic electrons trapped within each
planet's
magnetic field. Detection of this emission from
exoplanets provides a unique opportunity to characterise their
magnetic fields, which is key to determining the atmospheric
evolution of
exoplanets. However, a conclusive detection of
radio emission from an
exoplanet remains at large, primarily due to a lack of sensitivity at low
radio frequencies. On the other hand,
planet-like
radio signatures have been detected on objects called ultracool
dwarfs (UCDs) for over two decades. UCDs are of comparable sizes to Jupiter, but are more massive. They also possess similar interior structures to Jupiter, the region where
magnetic fields are generated. Therefore, UCDs are ideal targets to study to advance our understanding of how
magnetic fields manifest at planetary scales. In this Chapter, we outline the revolutionary role that the Square Kilometre Array will play in the study of
exoplanets and UCDs. We anticipate that it will facilitate the first detection of
radio emission from
giant exoplanets with strong
magnetic fields, and will deliver thousands of detections of UCDs within a few hundred parsecs. Combined with very long baseline interferometry, we also expect that astrometric monitoring will enable the detection of
planets of a few Earth masses orbiting nearby
radio-emitting UCDs. These findings will open a new window into how
planets form and evolve in extrasolar systems.
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All authors Robert D. Kavanagh, Juan B. Climent, Philippe Zarka, Joseph R. Callingham, Yuka Fujii, Corentin K. Louis, Laurent Lamy, Mayank Narang, J. Sebastian Pineda, Harish K. Vedantham, Sanne Bloot, Jean-Mathias Grießmeier, Jose Carlos Guirado, Simranpreet Kaur, T. Joseph W. Lazio, Miguel Pérez-Torres, Alice Zurlo
High Energy Astrophysical Phenomena
Superdiffusion of cosmic rays in the vicinity of their accelerators and the resulting $\gamma$-ray emission
Zhaodong Shi, Guangwei Wang and Rui-zhi Yang
We study the distribution of
cosmic rays (CRs) in the vicinity of their accelerators, assuming that the transport of CRs in the interstellar medium surrounding the accelerators is described by the superdiffusion, beyond the normal
diffusion. We find that the superdiffusivity, which is characterized by the superdiffusion parameter $\alpha$, impacts significantly the distribution of CRs. For impulsive injection, the CR distribution behaves a constant radial profile, except with a power-law tail for $\alpha < 2$ or a Gaussian tail for $\alpha=2$ at large distance, $r$, from the accelerators. For stationary injection, the radial profile of CR
protons tends to being proportional to $r^{\alpha - 3}$, while that of CR electrons can deviate from the $r^{\alpha - 3}$ profile, due to their severe energy losses. We also compute the $\gamma$-ray emission, produced by the interactions of CRs with ambient gas and radiation fields, within 100 pc regions around the accelerators. We find that by investigating the $\gamma$-ray morphology, we can distinguish the superdiffusion from the normal
diffusion with present and next-generation imaging air Cherenkov
telescopes.
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High Energy Astrophysical Phenomena
Discovering Millisecond Pulsars in Globular Clusters with the GMRT (GCGPS)
Jyotirmoy Das, Jayanta Roy, Paulo C. C. Freire et al. (+6 more)
The Globular Clusters GMRT
Pulsar Search (GCGPS) project, launched in mid-May 2023, has emerged as one of the most successful
pulsar surveys conducted with the upgraded
Giant Metrewave
Radio Telescope (uGMRT), leading to the discovery of several new millisecond
pulsars (MSPs). The recently concluded Phase I of the survey resulted in the discovery of seven MSPs across four globular clusters (GCs), all of which previously had no known
pulsars. These discoveries have enabled the precise determination of the dispersion measures (DMs) for the respective clusters for the first time. Consistent timing follow-up revealed that out of the seven MSPs, three are confirmed binaries, while two are isolated. This paper summarises the design and the implementation of Phase I of the GCGPS project, presents the key scientific results obtained so far, and outlines the strategy and progress of the recently initiated Phase II observations.
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All authors Jyotirmoy Das, Jayanta Roy, Paulo C. C. Freire, Scott M Ransom, Bhaswati Bhattacharyya, Karel Adámek, Wes Armour, Sanjay Kudale, Mekhala V. Muley
Astrophysics of Galaxies
Mass–size evolution and the emerging passive–density relation revealed by JWST/NIRCam in the Spiderweb protocluster
J. Nadolny, J. M. Pérez-Martínez, H. Dannerbauer et al. (+8 more)
We investigate how the environment affects
galaxy structure in the Spiderweb protocluster at $z=2.16$ using JWST/NIRCam F115W, F182M, and F410M imaging (rest-frame $\sim 3500$Å to $1.4\,\mu$m). We perform homogeneous multi-wavelength parametric modelling of the single-Sérsic and bulge–disc decomposition for the Spiderweb member sample of 103
galaxies within the JWST field of view (up to $\sim 2\times R_{200}$).
Star-forming
galaxies follow a mass–size relation broadly consistent with the field, with a mildly steeper trend at the high-mass end within uncertainties. Passive
galaxies exhibit a flatter mass–size relation, and their typical size (intercept at fixed
stellar mass) lies between that of the coeval field and cluster passive populations, indicating an intermediate evolutionary stage. In both
star-forming and passive systems, bulges are systematically more compact than discs.
Galaxy sizes decrease slightly with increasing wavelength, whereas ALMA-detected dusty
star-forming
galaxies exhibit a much steeper wavelength dependence, consistent with centrally concentrated, obscured
star formation. The passive fraction depends primarily on local density: it resembles the field at $\Sigma \lesssim 100$–$200\,{\rm gal\,Mpc^{-2}}$ and rises to $\sim60\%$ at $\Sigma \gtrsim 1000\,{\rm gal\,Mpc^{-2}}$, although with relatively large uncertainties due to the small number of
galaxies in the highest-density bins, with no significant additional dependence on clustercentric distance. We also find a weak but significant correlation between local density and Sérsic index (strongest in F410M), but no clear correlation with effective radius or the
star-formation rate surface density $\Sigma_{\rm SFR}$. These results support a picture in which quenching and structural transformation are already advanced, while the size growth is still ongoing.
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All authors J. Nadolny, J. M. Pérez-Martínez, H. Dannerbauer, B. Haussler, M. Huertas-Company, K. Daikuhara, T. Kodama, Y. Koyama, A. Naufal, P. G. Pérez-González, Y. H. Zhang
Solar and Stellar Astrophysics
Pre-flare and active region plasma flows and structure seen by the short wavelength camera on SOLAR-C/EUVST
James McKevitt, Sarah Matthews, David H. Brooks et al. (+20 more)
The mechanisms triggering
solar flares and driving coronal heating occur across wide temperature ranges on small spatial scales and short timescales, making them difficult to observe with current instrumentation. The upcoming
SOLAR-C mission, launching in the late 2020s, will provide unprecedented
plasma diagnostic capability with its high-throughput extreme-ultraviolet (EUV) spectroscopic
telescope (EUVST), capable of ~0.2 arcsec/pix spatial sampling (~0.4 arcsec resolution), continuous temperature coverage from 0.02-15 MK, and exposure times down to 0.5 seconds. We present forward modelling of the spectrograph's short wavelength camera (170-210 Å;
SOLAR-C/EUVST-SW) and its response to log T~6.2 coronal
plasma in a three-dimensional MHD-simulated pre-
flare active region. We compare this performance to that of the previous-generation EUV Imaging Spectrometer (EIS) on Hinode (
SOLAR-B). Our results demonstrate that
SOLAR-C/EUVST can distinguish individual flux tubes in simulated active region loops which Hinode/EIS cannot resolve. In simulated pre-
flare plasma,
SOLAR-C/EUVST captures sharp velocity gradients between adjacent upflowing and downflowing
plasma which Hinode/EIS is unable to resolve. Doppler velocity measurement accuracy will reach better than 1 km/s in active regions. We show that this next-generation spectrograph can be expected to directly observe processes potentially related to
flare triggering, such as
plasma flows from low-altitude reconnection linked to emerging flux, and determine whether active region loops consist of a small number of strands or the hundreds predicted by
magnetic reconnection-induced nanoflare heating models.
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All authors James McKevitt, Sarah Matthews, David H. Brooks, Toshifumi Shimizu, Akiko Tei, Ignacio Ugarte-Urra, Shinsuke Imada, Shin Toriumi, Charles M. Brown, Ryohko Ishikawa, Yukio Katsukawa, Hirohisa Hara, Duncan Rust, David Walton, Berend Winter, Deborah Baker, Hamish Reid, Peter Young, Tiago M. D. Pereira, Louisa Bradley, Alexey Shitvov, Louise Harra, International SOLAR-C team
High Energy Astrophysical Phenomena
Probing radiation micro-physics in M 87 I. Total intensity and broad-band spectra
Christian M. Fromm, Yosuke Mizuno, Ziri Younsi et al. (+6 more)
Next generation Very Long Baseline Interferometers (VLBI) will provide dense sampling of the
Fourier space together with high signal to noise ratios allowing to reliably observe and image faint jet structure in M 87 at mm-wavelength. The proposed next generation Event Horizon
Telescope (ngEHT) and next generation Very Large Array (ngVLA) offers the unique capability to simultaneously resolve and image the
accretion flow around the supermassive black hole in M 87 together with the jet launching and acceleration zone. In order to explore these capabilities and to provide theoretical expectations we perform general relativistic magnetohydrodynamic simulations of
accretion on to black holes and jet launching. M 87 has been the target for multiple observations across the entire electromagnetic spectrum. Among these VLBI observations provide unique capability to resolve the jet structure down to several gravitational radii. In this work we provide possible observable signatures which will allow us to distinguish between different electron heating models and particle distributions. We use general relativistic magnetohydrodynamics and simulate the
accretion of the magnetised
plasma onto Kerr-black holes in 3D. The multi-frequency radiative signatures of these simulations are computed taking different electron heating and distribution functions into account. The results of our simulations show that with a dynamical range of $1\times 10^4$ and a frequency range from 86 GHz to 345 GHz observations with future VLBI arrays have the potential to tell turbulent and
magnetic reconnection electron heating and the electron distribution function apart.
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All authors Christian M. Fromm, Yosuke Mizuno, Ziri Younsi, Ainara Saiz-Perez, Hector Olivares, Antonios Nathanail, Alejandro Cruz-Osorio, Matthias Kadler, Karl Mannheim
Cosmology and Nongalactic Astrophysics
Direct Primary Beam Correction: Untangling Mutual Coupling in 21-cm Cosmological Experiments with the SKA-Low Radio Telescope
Oscar S.D. O'Hara, Quentin Gueuning, Eloy de Lera Acedo et al. (+7 more)
Mutual coupling between
antennas has emerged as the dominant direction-dependent corruption in dense aperture arrays, imprinting pronounced sub-MHz spatial and spectral structure that compromises the time-gating and foreground-separation strategies used to isolate the faint 21-cm signal. In this work, we introduce Direct Primary Beam Correction, a domain-agnostic framework for reconstructing the far-field radiation pattern relative to an arbitrary reference via a regularised, direction-weighted linear inversion of stacked Jones
matrices, thereby enabling the removal of direction-dependent distortions such as mutual coupling. Using full-wave electromagnetic simulations of SKA-Low, we demonstrate that this framework reconstructs the radiation pattern down to the numerical noise floor within a suitably conditioned field of view, with the reconstruction accuracy governed by the regularised inversion and the fidelity of the underlying beam model. Applying the framework to a simulated 4-hour observation of the EoR0 field in the $122$–$134$~MHz band, we identify two principal implications for 21-cm power-spectrum analysis. First, restricting the correction to the main lobe and near sidelobes is inadequate: chromatic grating lobe contributions, whether left insufficiently or entirely uncorrected, continue to contaminate the EoR window. Second, mutual-coupling-induced contamination is temporally coherent and, being anchored to the fixed array geometry, does not average down across snapshots as the EoR field is tracked. Direct primary beam correction, therefore, provides a computationally efficient means of mitigating mutual coupling; however, robust recovery of the EoR window necessitates either full-sky correction or explicit separation of main-beam and sidelobe contributions prior to power-spectrum estimation.
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All authors Oscar S.D. O'Hara, Quentin Gueuning, Eloy de Lera Acedo, John Cumner, Dominic Anstey, Anthony Brown, Fred Dulwich, Andrew Faulkner, Ashish Mhaske, Oskar Zetterstrom
Solar and Stellar Astrophysics
Potential Solar Precursors to Magnetic Switchbacks
Durgesh Tripathi, Maria S. Madjarska, Judy Karpen et al. (+9 more)
The origin of
magnetic switchbacks-large-amplitude, spherically polarized
magnetic-field fluctuations with local polarity inversions shown to be nearly ubiquitous in the inner heliosphere by Parker
Solar Probe-is presently one of the most outstanding open questions in
solar and heliospheric science. The occurrence of these structures in the young
solar wind is a topic of active research, focusing not only on their characteristics and
evolution but also on unraveling the puzzle of their origin. We first discuss the potential influence on switchback (SB) formation of large-scale coronal dynamics and restructuring processes that shape and regulate the extended
solar corona. Following that, we review the dynamics, physical properties, occurrence rate, and energetics of numerous possible precursor small-scale dynamic events that occur throughout the
solar atmosphere, emphasizing their possible roles in creating SBs. Finally, we discuss some recent studies attempting to connect in situ observations of SBs and SB patches with remote-sensing observations, and the related challenges in identifying
solar wind source regions precisely and linking in situ observations to transient
solar phenomena. We also clarify the terminology used by the
solar community to describe small-scale
solar phenomena.
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All authors Durgesh Tripathi, Maria S. Madjarska, Judy Karpen, Marco Velli, Clara Froment, Etienne Pariat, Spiros Patsourakos, Nour E. Raouafi, Alexis P. Rouillard, Alphonse C. Sterling, Kostas Tziotziou, Peter F. Wyper
Astrophysics of Galaxies
An HI+radio continuum study of local cluster galaxies: Intercepting the early stages of environmental processing with MeerKAT
Alessandro Ignesti, Paolo Serra, Alessandro Bianchetti et al. (+14 more)
The
evolution of
galaxies in clusters is driven by their interaction with the environment, which deeply affects and alters the properties of the multi-phase interstellar medium. Here we make use of MeerKAT observations to study the properties of the neutral and nonthermal interstellar medium, traced respectively by the HI 21 cm line and by the
radio continuum emission at 1.4 GHz, out to about twice the virial radius of three local ($z\simeq0.04$)
galaxy clusters, namely IIZW108, A4059 and A3558, with $M_{200}\simeq2-9\times10^{14}~M_\odot$. We assemble a sample of 61
galaxies, including the so-called jellyfish and unwinding
galaxies, detected in both HI and
radio continuum, and derive their optical properties from IR-to-UV photometry using ancillary data. We find that cluster
galaxies in our sample are on average $\sim2.7$ times more
star-forming than
galaxies with the same
stellar and HI mass in the field, indicating that the HI +
radio-continuum selection has intercepted
galaxies at the very early stages of their environmental processing when the external pressure has not yet removed the gas, but the resulting fast compression has enhanced both the
star formation and the
radio continuum luminosity. The study also reveals that
galaxies at the initial stage can features a
radio luminosity excess due to the old relativistic electrons permeating the interstellar medium. We show that unwinding
galaxies are characterized by high
stellar and HI masses, arguing that their peculiar morphology may results from their large baryonic mass. Finally, via the stacking analysis of 677 optically-selected cluster members we quantitatively show that cluster
galaxies are more HI-poor than in the field, and the deficiency steadily grows approaching the cluster center where
galaxies have, on average, a factor $\sim3\times$ less HI mass than those in the field.
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All authors Alessandro Ignesti, Paolo Serra, Alessandro Bianchetti, Antonino Marasco, Alessia Moretti, Francesca Loi, Bianca M. Poggianti, Benedetta Vulcani, Laura Bisigello, Myriam Gitti, Marco Gullieuszik, Augusto E. Lassen, Rosita Paladino, Christoph Pfrommer, Mpati Ramatsoku, Francesco Sinigaglia, Neven Tomičić
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ed-ph
Generative AI in Higher Education Laboratory Learning: A Qualitative Case Study of Epistemic Scaffolding and Assessment Boundaries
Matteo Tuveri and Alessandro Riggio
Advanced physics laboratories require students to integrate disciplinary knowledge, experimental practice and scientific argumentation across complex observational and analytical tasks. The increasing availability of generative artificial intelligence (GenAI) adds complexity to this coordination, since AI systems may function as conceptual explainers, operational assistants, artefact reviewers or apparently authoritative evaluators. This exploratory qualitative case study examines AstroTutor, a constrained GenAI tutor introduced as an optional support resource in a Master's-level advanced astrophysics laboratory. The study investigates how students framed the tutor within a broader GenAI-mediated learning ecology that included the instructor, peers, course materials, observations, measurements, data analysis and final assessed reports. Seven students attended the course, five used the tutor, and three groups produced a final report. The analysis combined content analysis, thematic analysis and frame analysis. Drawing on chat logs, final reports and limited post-use reflective responses, the results identify five principal GenAI functions: interface interpreter, warrant organiser, report scaffold, unstable authority and resource whose traces may appear in downstream reports. These findings extend previous research on GenAI in education to the context of advanced physics laboratories, showing that its use requires explicit design boundaries, guidance on legitimate and prohibited practices, verification routines, and assessment requirements that preserve students' epistemic responsibility. The educational implications of a GenAI-mediated learning ecology in advanced physics laboratories are also discussed.
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High Energy Astrophysical Phenomena
Cosmic-ray anisotropy: sensitivity of methods and implications for KASCADE data
M. Yu. Kuznetsov, N. A. Petrov and E. M. Shinkevich
We study the problem of measuring the anisotropy of high-energy
cosmic rays across all angular scales. The limited field of view and non-uniform exposure of ground-based
cosmic-ray experiments reduce their sensitivity to real anisotropy of
cosmic-ray arrival directions. A widely used signature of anisotropy – a dipole of the flux expansion over the right ascension – provides very limited understanding of the underlying physics of
cosmic-ray origin and propagation. In this study we test two other methods: the angular power spectrum and the autocorrelation function for sensitivity to possible medium- and small-scale anisotropies of
cosmic-ray flux. We find that the autocorrelation function is the most sensitive
estimator for an underlying physical anisotropy in most of the models tested, while the angular power spectrum can provide additional knowledge about
cosmic-ray flux properties, when the anisotropy is strong enough. As a test of our findings, we apply these methods to $10\%$ sample of the KASCADE experiment public data. Namely, we consider all-particle set of events and sets of individual mass groups classified by a convolutional neural network. We find an indication of anisotropy at $> 2.5 \sigma$ level at $\sim 10^\circ$ angular scale for the iron
nuclei mass group at $E \gtrsim 20$ PeV with both the angular power spectrum and the autocorrelation methods.
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High Energy Astrophysical Phenomena
Synchrotron radiation in nonuniform magnetic field
V.S. Beskin, A.Yu. Istomin, F.A. Kniazev et al. (+1 more)
The distortion of the spectrum of synchrotron radiation received by a distant observer due to
magnetic field inhomogeneity is discussed. It is shown that for single-particle radiation, a noticeable difference in the integrated spectrum from the case of a uniform
magnetic field occurs only for observation times significantly exceeding the observer's departure from the beam pattern, and only for subrelativistic particles, when the radiation arrives from regions with significantly different
magnetic fields during the observation time. For shorter observation times, field inhomogeneity leads only to small-scale distortions (smaller or comparable in frequency to the gyrofrequency) and does not manifest itself in the averaged spectrum. For the case of a particle ensemble, which is of interest for astrophysical applications, the difference in the integrated spectrum becomes negligible.
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All authors V.S. Beskin, A.Yu. Istomin, F.A. Kniazev, T.I. Khalilov