adsabs/SciX_UAT_keywords huggingface dataset:
Physics Beyond the Standard Model with Future X-Ray Observatories: Projected Constraints on Very-light Axion-like Particles with Athena and AXIS

Axion-like particles (ALPs) are well-motivated extensions of the Standard Model of Particle Physics and a generic prediction of some string theories. X-ray observations of bright active galactic nuclei (AGNs) hosted by rich clusters of galaxies are excellent probes of very-light ALPs, with masses $\mathrm{log}({m}_{{\rm{a}}}/\mathrm{eV})\lt -12.0$ . We evaluate the potential of future X-ray observatories, particularly Athena and the proposed AXIS, to constrain ALPs via observations of cluster-hosted AGNs, taking NGC 1275 in the Perseus cluster as our exemplar. Assuming perfect knowledge of the instrument calibration, we show that a modest exposure (200 ks) of NGC 1275 by Athena permits us to exclude all photon-ALP couplings g aγ > 6.3 × 10-14 GeV-1 at the 95% confidence level, as previously shown by Conlon et al., representing a factor of 10 improvement over current limits. We then proceed to assess the impact of realistic calibration uncertainties on the Athena projection by applying a standard Cash likelihood procedure, showing the projected constraints on g aγ weaken by a factor of 10 (back to the current most sensitive constraints). However, we show how the use of a deep neural network can disentangle the energy-dependent features induced by instrumental miscalibration and those induced by photon-ALP mixing, allowing us to recover most of the sensitivity to the ALP physics. In our explicit demonstration, the machine learning applied allows us to exclude g aγ > 2.0 × 10-13 GeV-1, complementing the projected constraints of next-generation ALP dark matter birefringent cavity searches for very-light ALPs. Finally, we show that a 200 ks AXIS/on-axis observation of NGC 1275 will tighten the current best constraints on very-light ALPs by a factor of 3.

Keywords: particle astrophysics; dark matter; x-ray active galactic nuclei; magnetic fields; x-ray telescopes; galaxy clusters
Spectral Features in Field-aligned Solar Wind Turbulence from Parker Solar Probe Observations

Parker Solar Probe (PSP) observed a large variety of Alfvénic fluctuations in the fast and slow solar wind flow during its two perihelia. The properties of Alfvénic solar wind turbulence have been studied for decades in the near-Earth environment. A spectral index of -5/3 or -2 for magnetic field fluctuations has been observed using spacecraft measurements, which can be explained by turbulence theories of nearly incompressible magnetohydrodynamics (NI MHD) or critical balance. In this study, a rigorous search of field-aligned solar wind is applied to PSP measurements for the first time, which yields two events in the apparently slow solar wind. The parallel spectra of the magnetic fluctuations in the inertial range show a ${k}_{\parallel }^{-5/3}$ power law. Probability distributions of the magnetic field show that these events are not contaminated by intermittent structures, which, according to previous studies, are known to modify spectral properties. The results presented here are consistent with spectral predictions from NI MHD theory and further deepen our understanding of the Alfvénic solar wind turbulence near the Sun.

Keywords: solar wind; interplanetary turbulence; spectral index
3D Hydrodynamics of Pre-supernova Outbursts in Convective Red Supergiant Envelopes

Eruptive mass loss likely produces the energetic outbursts observed from some massive stars before they become core-collapse supernovae (SNe). The resulting dense circumstellar medium may also cause the subsequent SNe to be observed as Type IIn events. The leading hypothesis of the cause of these outbursts is the response of the envelope of the red supergiant (RSG) progenitor to energy deposition in the months to years prior to collapse. Early theoretical studies of this phenomenon were limited to 1D, leaving the 3D convective RSG structure unaddressed. Using FLASH's hydrodynamic capabilities, we explore the 3D outcomes by constructing convective RSG envelope models and depositing energies less than the envelope binding energies on timescales shorter than the envelope dynamical time deep within them. We confirm the 1D prediction of an outward-moving acoustic pulse steepening into a shock, unbinding the outermost parts of the envelope. However, we find that the initial 2-4 km s-1 convective motions seed the intrinsic convective instability associated with the high-entropy material deep in the envelope, enabling gas from deep within the envelope to escape and increasing the amount of ejected mass compared to an initially "quiescent" envelope. The 3D models reveal a rich density structure, with column densities varying by ≈10× along different lines of sight. Our work highlights that the 3D convective nature of RSG envelopes impacts our ability to reliably predict the outburst dynamics, the amount, and the spatial distribution of the ejected mass associated with deep energy deposition.

Keywords: astrophysical fluid dynamics; stellar convection envelopes; late stellar evolution; stellar-interstellar interactions; supernova dynamics; time domain astronomy
Orbital Period Variations in HT Cas: Evidence for Additional Angular Momentum Loss and a High-eccentricity Giant Planet

We present a timing study of the short-period eclipsing cataclysmic variable (CV) HT Cas. Based on new eclipse times derived from our photometric monitoring and archival optical data, combined with historical timings, spanning ~42 yr, we detect a secular decrease in the orbital period at a rate of $\dot{P}=-1.32\times {10}^{-12}\,{\mathrm{ss}}^{-1}$ and a cyclic period wiggle with an amplitude of 79.3 s and a period of 30.28 yr. We find that neither gravitational radiation nor magnetic braking can explain the observed decrease rate, suggesting the presence of additional angular momentum loss (AML). The empirical consequential AML (eCAML) model developed by Schreiber et al. can well match the observed orbital decay in HT Cas, and the physical mechanism for eCAML is most likely attributable to the frictional AML following nova eruptions. As for the cyclic variation, the best explanation is the influence of an unseen companion in orbit around the binary. The derived orbital parameters reveal that the hypothetical third body could be a giant planet with mass of M 3 ≃ 14M Jup that is moving on a highly eccentric orbit (e = 0.82). Taken together the results of the present study suggest that HT Cas is a unique triple system containing a high-eccentricity giant planet and it has the potential to become an ideal laboratory in which to test models of CV evolution.

Keywords: close binary stars; eclipsing binary stars; cataclysmic variable stars; dwarf novae
Investigation of the Physical Origin of Overionized Recombining Plasma in the Supernova Remnant IC 443 with XMM-Newton

The physical origin of the overionized recombining plasmas (RPs) in supernova remnants (SNRs) has been attracting attention because its understanding provides new insight into SNR evolution. However, the process of the overionization, although it has been discussed in some RP-SNRs, is not yet fully understood. Here, we report on spatially resolved spectroscopy of X-ray emission from IC 443 with XMM-Newton. We find that RPs in regions interacting with dense molecular clouds tend to have lower electron temperature and lower recombination timescale. These tendencies indicate that RPs in these regions are cooler and more strongly overionized, which is naturally interpreted as a result of rapid cooling by the molecular clouds via thermal conduction. Our result on IC 443 is similar to that on W44 showing evidence for thermal conduction as the origin of RPs at least in older remnants. We suggest that evaporation of clumpy gas embedded in a hot plasma rapidly cools the plasma as was also found in the W44 case. We also discuss if ionization by protons accelerated in IC 443 is responsible for RPs. Based on the energetics of particle acceleration, we conclude that the proton bombardment is unlikely to explain the observed properties of RPs.

Keywords: supernova remnants; x-ray astronomy; plasma astrophysics; molecular clouds
Implications of a Fast Radio Burst from a Galactic Magnetar

A luminous radio burst was recently detected in temporal coincidence with a hard X-ray flare from the Galactic magnetar SGR 1935+2154 with a time and frequency structure consistent with cosmological fast radio bursts (FRBs) and a fluence within a factor of ≲10 of the least energetic extragalactic FRB previously detected. Although active magnetars are commonly invoked FRB sources, several distinct mechanisms have been proposed for generating the radio emission that make different predictions for the accompanying higher-frequency radiation. We show that the properties of the coincident radio and X-ray flares from SGR 1935+2154, including their approximate simultaneity and relative fluence ${E}_{\mathrm{radio}}/{E}_{{\rm{X}}}\sim {10}^{-5}$ , as well as the duration and spectrum of the X-ray emission, are consistent with extant predictions for the synchrotron maser shock model. Rather than arising from the inner magnetosphere, the X-rays are generated by (incoherent) synchrotron radiation from thermal electrons heated at the same internal shocks that produce the coherent maser emission as ultrarelativistic flare ejecta collides with a slower particle outflow (e.g., as generated by earlier flaring activity) on a radial scale of $\sim {10}^{11}$ cm. Although the rate of SGR 1935+2154-like bursts in the local universe is not sufficient to contribute appreciably to the extragalactic FRB rate, the inclusion of an additional population of more active magnetars with stronger magnetic fields than the Galactic population can explain both the FRB rate and the repeating fraction, but only if the population of active magnetars are born at a rate that is at least 2 orders of magnitude lower than that of the SGR 1935+2154-like magnetars. This may imply that the more active magnetar sources are not younger magnetars formed in a similar way to the Milky Way population (e.g., via ordinary supernovae) but are instead formed through more exotic channels, such as superluminous supernovae, accretion-induced collapse, or neutron star mergers.

Keywords: radio transient sources; magnetars; soft gamma-ray repeaters
Ion-scale Electromagnetic Waves in the Inner Heliosphere

Understanding the physical processes in the solar wind and corona that actively contribute to heating, acceleration, and dissipation is a primary objective of NASA's Parker Solar Probe (PSP) mission. Observations of circularly polarized electromagnetic waves at ion scales suggest that cyclotron resonance and wave-particle interactions are dynamically relevant in the inner heliosphere. A wavelet-based statistical study of circularly polarized events in the first perihelion encounter of PSP demonstrates that transverse electromagnetic waves at ion resonant scales are observed in 30-50% of radial field intervals. Average wave amplitudes of approximately 4 nT are measured, while the mean duration of wave events is on the order of 20 s; however, long-duration wave events can exist without interruption on hour-long timescales. Determination of wave vectors suggests propagation parallel/antiparallel to the mean magnetic field. Though ion-scale waves are preferentially observed during intervals with a radial mean magnetic field, we show that measurement constraints, associated with single spacecraft sampling of quasi-parallel waves superposed with anisotropic turbulence, render the measured coherent ion-wave spectrum unobservable when the mean magnetic field is oblique to the solar wind flow; these results imply that the occurrence of coherent ion-scale waves is not limited to a radial field configuration. The lack of radial scaling of characteristic wave amplitudes and duration suggests that the waves are generated in situ through plasma instabilities. Additionally, observations of proton distribution functions indicate that temperature anisotropy may drive the observed ion-scale waves.

Keywords: solar wind; space plasmas; solar coronal heating; interplanetary turbulence; plasma astrophysics
The Nature of γ-Ray Variability in Blazars

We present an in-depth and systematic variability study of a sample of 20 powerful blazars, including 12 BL Lacs and 8 flat-spectrum radio quasars, applying various analysis tools such as flux distribution, symmetry analysis, and time-series analysis on the decade-long Fermi/LAT observations. The results show that blazars with steeper γ-ray spectral indexes are found to be more variable, and the γ-ray flux distribution closely resembles a log-normal probability distribution function. The statistical variability properties of the sources as studied by power spectral density analysis are consistent with flicker noise (P(ν) ∝ 1/ν)—an indication of long-memory processes at work. Statistical analysis of the distribution of flux rise and decay rates in the light curves of the sources, aimed at distinguishing between particle acceleration and energy-dissipation timescales, counterintuitively suggests that both kinds of rates follow a similar distribution and the derived mean variability timescales are on the order of a few weeks. The corresponding emission region size is used to constrain the location of γ-ray production sites in the sources to be a few parsecs. Additionally, using Lomb-Scargle periodogram and weighted wavelet z-transform methods and extensive Monte Carlo simulations, we detected year-timescale quasi-periodic oscillations in the sources S5 0716+714, Mrk 421, ON +325, PKS 1424-418, and PKS 2155-304. The detection significance was computed taking proper account of the red noise and other artifacts inherent in the observations. We explain the results in light of current blazar models with relativistic shocks propagating down the jet viewed close to the line of sight.

Keywords: high energy astrophysics; blazars; relativistic jets
GRB 140423A: A Case of Stellar Wind to Interstellar Medium Transition in the Afterglow

We present very early ground-based optical follow-up observations of gamma-ray burst (GRB) 140423A, which was discovered by the Swift/Burst Alert Telescope (BAT) and by the Fermi/Gamma-Ray Burst Monitor. Its broadband afterglow was monitored by the Swift/X-Ray Telescope and ground-based optical telescopes from T0 + 70.96 s to 4.8 days after the Swift/BAT trigger. This is one more case of a prompt optical emission observation. The temporal and spectral joint fits of the multiwavelength light curves of GRB 140423A reveal that achromatic behavior is consistent with the external shock model, including a transition from a stellar wind to the interstellar medium (ISM) and energy injection. In terms of the optical light curves, there is an onset bump in the early afterglow with a rising index ${\alpha }_{{\rm{O}},{\rm{I}}}=-0.59\pm 0.04$ (peaking at ${t}_{\mathrm{peak}}-{T}_{0}\approx 206$ s). It then decays with a steep index ${\alpha }_{{\rm{O}},\mathrm{II}}=1.78\pm 0.03$ , and shows a steeper to flatter "transition" with ${\alpha }_{{\rm{O}},\mathrm{III}}=1.13\pm 0.03$ at around T0 + 5000 s. The observed X-ray afterglow reflects achromatic behavior, as does the optical light curve. There is no obvious evolution of the spectral energy distribution between the X-ray and optical afterglows, with an average value of the photon index ${\rm{\Gamma }}\approx 1.95$ . This "transition" is consistent with an external shock model having the circumburst medium transition from a wind to the ISM, by introducing a long-lasting energy injection with a Lorentz factor stratification of the ejecta. The best parameters from Monte Carlo Markov Chain fitting are ${E}_{{\rm{K}},\mathrm{iso}}\approx 2.14\times {10}^{55}$ erg, ${{\rm{\Gamma }}}_{0}\approx 162$ , ${\varepsilon }_{e}\approx 0.02$ , ${\varepsilon }_{B}\approx 1.7\times {10}^{-6}$ , ${A}_{* }\approx 1.0$ , ${R}_{t}\approx 4.1\times {10}^{17}$ cm, $n\approx 11.0\,\,{\mathrm{cm}}^{-3}$ , ${L}_{0}\approx 3.1\times {10}^{52}\,\mathrm{erg}\ {{\rm{s}}}^{-1}$ , $k\approx 1.98$ , $s\,\approx 1.54$ , and ${\theta }_{j}\gt 0.3\,\mathrm{rad}$ .

Keywords: gamma-ray bursts; non-thermal radiation sources
AGN Feedback and Star Formation of Quasar Host Galaxies: Insights from the Molecular Gas

Molecular gas serves as a key probe of the complex interplay between black hole accretion and star formation in the host galaxies of active galactic nuclei (AGNs). We use CO(2-1) observations from a new Atacama Large Millimeter/submillimeter Array survey, in conjunction with literature measurements, to investigate the molecular gas properties of a representative sample of 40 z < 0.3 Palomar-Green quasars, the largest and most sensitive study of molecular gas emission to date for nearby quasars. We find that the AGN luminosity correlates with both the CO luminosity and black hole mass, suggesting that AGN activity is loosely coupled to the cold gas reservoir of the host. The observed strong correlation between host galaxy total infrared luminosity and AGN luminosity arises from their common dependence on the molecular gas. We argue that the total infrared luminosity, at least for low-redshift quasars, can be used to derive reliable star formation rates for the host galaxy. The host galaxies of low-redshift quasars have a molecular gas content similar to that of star-forming galaxies of comparable stellar mass. Moreover, they share similar gas kinematics, as evidenced by their CO Tully-Fisher relation and the absence of detectable molecular outflows down to sensitive limits. There is no sign that AGN feedback quenches star formation for the quasars in our sample. On the contrary, the abundant gas supply forms stars prodigiously, at a rate that places most of them above the star-forming main sequence and with an efficiency that rivals that of starburst systems.

Keywords: interstellar medium; quasars; agn host galaxies; active galactic nuclei
Panchromatic HST/WFC3 Imaging Studies of Young, Rapidly Evolving Planetary Nebulae. I. NGC 6302

We present the results of a comprehensive, near-UV-to-near-IR Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging study of the young planetary nebula (PN) NGC 6302, the archetype of the class of extreme bilobed, pinched-waist PNe that are rich in dust and molecular gas. The new WFC3 emission-line image suite clearly defines the dusty toroidal equatorial structure that bisects NGC 6302's polar lobes, and the fine structures (clumps, knots, and filaments) within the lobes. The most striking aspect of the new WFC3 image suite is the bright, S-shaped 1.64 μm [Fe II] emission that traces the southern interior of the east lobe rim and the northern interior of the west lobe rim, in point-symmetric fashion. We interpret this [Fe II] emitting region as a zone of shocks caused by ongoing, fast (~100 km s-1), collimated, off-axis winds from NGC 6302's central star(s). The [Fe II] emission and a zone of dusty, N- and S-rich clumps near the nebular symmetry axis form wedge-shaped structures on opposite sides of the core, with boundaries marked by sharp azimuthal ionization gradients. Comparison of our new images with earlier HST/WFC3 imaging reveals that the object previously identified as NGC 6302's central star is a foreground field star. Shell-like inner lobe features may instead pinpoint the obscured central star's actual position within the nebula's dusty central torus. The juxtaposition of structures revealed in this HST/WFC3 imaging study of NGC 6302 presents a daunting challenge for models of the origin and evolution of bipolar PNe.

Keywords: planetary nebulae; stellar mass loss; jets; circumstellar matter
Pair Creation in Hot Electrosphere of Compact Astrophysical Objects

The mechanism of pair creation in the electrosphere of compact astrophysical objects such as quark stars or neutron stars is revisited, paying attention to evaporation of electrons and acceleration of electrons and positrons, which were previously not addressed in the literature. We perform a series of numerical simulations using the Vlasov–Maxwell equations. The rate of pair creation strongly depends on electric field strength in the electrosphere. Although Pauli blocking is explicitly taken into account, we find no exponential suppression of the pair creation rate at low temperatures. The luminosity in pairs increases with temperature and it may reach up to L ± ∼ 1052 erg s‑1, much larger than previously assumed.

Keywords: compact objects
Dust Production in a Thin Dense Shell in Supernovae with Early Circumstellar Interactions

In supernovae (SNe), where the light curves show evidence of strong and early interaction between the ejecta and the circumstellar matter (CSM), the formation of new dust is estimated to take place in a dense shell of gas between the forward shock (FS) and the reverse shock (RS). For the first time, in this study the mechanism of dust formation in this dense shell is modeled. A set of nine cases, considering variations of the ejecta mass and the pre-explosion mass-loss rates, is considered, accounting for the diverse nature of interactions reported in such SNe. For a single main-sequence mass, the variation of ejecta mass was manifested as a variation of the H-shell mass of the star, lost due to pre-explosion mass loss. We find that the dust masses in the dense shell range between 10-3 and 0.8 M ⊙, composed of O-rich and C-rich grains, whose relative proportions are determined by the nature of interaction. Dust formation in the post-shock gas is characterized by a gradual production rate, mostly ranging from 10-6 to 10-3 M ⊙ day-1, which may continue for a decade, post-explosion. A higher mass-loss rate leads to a larger mass of dust, while a smaller ejecta mass (smaller leftover H shell) increases the efficiency of dust production in such SNe. Dust formed behind the RS, as in our calculations, is not subject to destruction by either the FS or RS and is thus likely to survive in a larger proportion than dust formed in the ejecta.

Keywords: astrophysical dust processes; interstellar dust processes; core-collapse supernovae; type ii supernovae; shocks; circumstellar dust
TESS Observations of Be Stars: General Characteristics and the Impulsive Magnetic Rotator Model

Evidence of rotational light modulation in 30%-40% of normal B stars is presented, suggesting the presence of starspots and photospheric activity. On this basis, we propose that mass loss in Be stars is a result of magnetic reconnection coupled with rapid but not necessarily near-critical rotation. The ejected matter is trapped at two diametrically opposed locations where the magnetic and geometric equators intersect. Nonradial pulsation plays no role in the mass loss and in the short-period light and line profile variations, though Be stars may pulsate as SPB or β Cep variables. The model allows many of the major characteristics of Be stars to be understood, including the frequency pattern in the periodogram, allowing the approximate rotational frequency to be identified. From a large number of Be stars observed by TESS, it is shown that the resulting equatorial rotational velocities, v, are consistent with the projected rotational velocities, $v\sin i$ . Furthermore, it is shown that Be stars are rotating in a broad range of 30%-100% of the critical rotational velocity. This agrees with several statistical $v\sin i$ analyses, which all show that Be stars are very unlikely to be rotating at near-critical velocities.

Keywords: be stars; early-type emission stars; emission line stars; stellar rotation; stellar properties; starspots