adsabs/SciX_UAT_keywords huggingface dataset:
Significant Cocoon Emission and Photosphere Duration Stretching in GRB 211211A: A Burst from a Neutron Star‑Black Hole Merger

The radiation mechanism (thermal photosphere or magnetic synchrotron) and the progenitor of gamma-ray bursts (GRBs) are under hot debate. Recently discovered, the prompt long-duration (∼10 s, normally from the collapse of massive stars) property of GRB 211211A strongly conflicts with its association with a kilonova (normally from the merger of two compact objects, NS–NS, NS–BH, or NS–WD, duration ≲2 s). In this paper, we find that the probability photosphere model with a structured jet can satisfactorily explain this peculiar long duration, through the duration stretching effect (∼3 times) on the intrinsic longer (∼3 s) duration of an NS–BH merger, the observed empirical 2SBPL spectrum (with soft low-energy index α of ∼‑1), and its evolution. In addition, much evidence of the NS–BH merger origin is found, especially the good fit of the afterglow-subtracted optical‑near-IR light curves by the significant thermal cocoon emission and the sole thermal "red" kilonova component. Finally, a convincing new explanation for the X-ray afterglow plateau is revealed.

Keywords: gamma-ray bursts
Reanalysis of the X-Ray-burst-associated FRB 200428 with Insight-HXMT Observations

A double-peak X-ray burst from the Galactic magnetar SGR J1935+2154 was discovered to be associated with the two radio pulses of FRB 200428 separated by 28.97 ± 0.02 ms. Precise measurements of the timing and spectral properties of the X-ray bursts are helpful for understanding the physical origin of fast radio bursts. In this paper, we have reconstructed some information about the hard X-ray events, which were lost because the High Energy X-ray Telescope (HE) on board the Insight-HXMT mission was saturated by this extremely bright burst, and used the information to improve the temporal and spectral analyses of the X-ray burst. The arrival times of the two X-ray peaks by fitting the new Insight-HXMT/HE lightcurve with multi-Gaussian profiles are 2.77 ± 0.45 ms and 34.30 ± 0.56 ms after the first peak of FRB 200428, respectively, while these two parameters are 2.57 ± 0.52 ms and 32.5 ± 1.4 ms if the fitting profile is a fast-rise and exponential decay function. The spectrum of the two X-ray peaks could be described by a cutoff power law with cutoff energy ~60 keV and photon index ~1.4; the latter is softer than the result obtained in Li et al. when the two X-ray peaks appeared.

Keywords: magnetars; x-ray bursts; radio transient sources
Clumpy Star Formation and AGN Activity in the Dwarf-Dwarf Galaxy Merger Mrk 709

Nearby, low-metallicity dwarf starburst galaxies hosting active galactic nuclei (AGNs) offer the best local analogs to study the early evolution of galaxies and their supermassive black holes (BHs). Here we present a detailed multiwavelength investigation of star formation and BH activity in the low-metallicity dwarf-dwarf galaxy merger Mrk 709. Using Hubble Space Telescope Hα and continuum imaging combined with Keck spectroscopy, we determine that the two dwarf galaxies are likely in the early stages of a merger (i.e., their first pass) and discover a spectacular ∼10 kpc long string of young massive star clusters (t ≲ 10 Myr; M⋆ ≳ 105 M⊙) between the galaxies triggered by the interaction. We find that the southern galaxy, Mrk 709 S, is undergoing a clumpy mode of star formation resembling that seen in high-redshift galaxies, with multiple young clusters/clumps having stellar masses between 107 and 108 M⊙. Furthermore, we present additional evidence for a low-luminosity AGN in Mrk 709 S (first identified by Reines et al. using radio and X-ray observations), including the detection of the coronal [Fe X] optical emission line. The work presented here provides a unique glimpse into processes key to hierarchical galaxy formation and BH growth in the early universe.

Keywords: star clusters; young massive clusters; active galactic nuclei; galaxy mergers; dwarf irregular galaxies; dwarf galaxies; interacting galaxies; blue compact dwarf galaxies; low-luminosity active galactic nuclei
Unveiling the Mechanism for the Rapid Acceleration Phase in a Solar Eruption

Two major mechanisms have been proposed to drive the solar eruptions: the ideal magnetohydrodynamic instability and the resistive magnetic reconnection. Due to the close coupling and synchronicity of the two mechanisms, it is difficult to identify their respective contribution to solar eruptions, especially to the critical rapid acceleration phase. Here, to shed light on this problem, we conduct a data-driven numerical simulation for the flux rope eruption on 2011 August 4, and quantify the contributions of the upward exhaust of the magnetic reconnection along the flaring current sheet and the work done by the large-scale Lorentz force acting on the flux rope. Major simulation results of the eruption, such as the macroscopic morphology, early kinematics of the flux rope and flare ribbons, match well with the observations. We estimate the energy converted from the magnetic slingshot above the current sheet and the large-scale Lorentz force exerting on the flux rope during the rapid acceleration phase, and find that (1) the work done by the large-scale Lorentz force is about 4.6 times higher than the former, and (2) decreased strapping force generated by the overlying field facilitates the eruption. These results indicate that the large-scale Lorentz force plays a dominant role in the rapid acceleration phase for this eruption.

Keywords: solar coronal mass ejections; solar magnetic fields; solar active region magnetic fields; magnetohydrodynamical simulations
Observations of the 2024 May 14 X8.7 Solar Flare with the Goldstone-Apple Valley Radio Telescope (GAVRT)

The Goldstone-Apple Valley Radio Telescope (GAVRT) project conducts a regular monitoring program of the Sun. The GAVRT Solar Patrol project uses a 34 m diameter antenna to produce raster-scan maps of the Sun simultaneously at 4 frequencies ranging from approximately 3 to 14 GHz. On 2024 May 14, as part of regular GAVRT Solar Patrol observations, raster maps were produced when an X8.7 solar flare occurred in active region AR13664. Here we present the GAVRT maps of the May 14 flare along with microwave flux density spectra showing the non-thermal microwave burst emission from mildly relativistic electrons produced in this largest flare of Solar Cycle 25 to date. AR13664 reappeared as AR13697 and continued to be very active, producing X flares while GAVRT monitored its activity. GAVRT microwave data provide a powerful complement to the energetic electrons tracked by X-ray, millimeter-wave and γ-ray emissions.

Keywords: solar radio flares
A Luminous Red Supergiant and Dusty Long-period Variable Progenitor for SN 2023ixf

We analyze pre-explosion near- and mid-infrared (IR) imaging of the site of SN 2023ixf in the nearby spiral galaxy M101 and characterize the candidate progenitor star. The star displays compelling evidence of variability with a possible period of ≈1000 days and an amplitude of Δm ≈ 0.6 mag in extensive monitoring with the Spitzer Space Telescope since 2004, likely indicative of radial pulsations. Variability consistent with this period is also seen in the near-IR J and K s bands between 2010 and 2023, up to just 10 days before the explosion. Beyond the periodic variability, we do not find evidence for any IR-bright pre-supernova outbursts in this time period. The IR brightness ( ${M}_{{K}_{s}}=-10.7$ mag) and color (J - K s = 1.6 mag) of the star suggest a luminous and dusty red supergiant. Modeling of the phase-averaged spectral energy distribution (SED) yields constraints on the stellar temperature ( ${T}_{\mathrm{eff}}={3500}_{-1400}^{+800}$ K) and luminosity ( $\mathrm{log}L/{L}_{\odot }=5.1\pm 0.2$ ). This places the candidate among the most luminous Type II supernova progenitors with direct imaging constraints, with the caveat that many of these rely only on optical measurements. Comparison with stellar evolution models gives an initial mass of M init = 17 ± 4 M ⊙. We estimate the pre-supernova mass-loss rate of the star between 3 and 19 yr before explosion from the SED modeling at $\dot{M}\approx 3\times {10}^{-5}$ to 3 × 10-4 M ⊙ yr-1 for an assumed wind velocity of v w = 10 km s-1, perhaps pointing to enhanced mass loss in a pulsation-driven wind.

Keywords: supernovae; massive stars; stellar mass loss; evolved stars; circumstellar dust
CoLFI: Cosmological Likelihood-free Inference with Neural Density Estimators

In previous works, we proposed to estimate cosmological parameters with an artificial neural network (ANN) and a mixture density network (MDN). In this work, we propose an improved method called a mixture neural network (MNN) to achieve parameter estimation by combining ANN and MDN, which can overcome shortcomings of the ANN and MDN methods. Besides, we propose sampling parameters in a hyperellipsoid for the generation of the training set, which makes the parameter estimation more efficient. A high-fidelity posterior distribution can be obtained using ${ \mathcal O }({10}^{2})$ forward simulation samples. In addition, we develop a code named CoLFI for parameter estimation, which incorporates the advantages of MNN, ANN, and MDN, and is suitable for any parameter estimation of complicated models in a wide range of scientific fields. CoLFI provides a more efficient way for parameter estimation, especially for cases where the likelihood function is intractable or cosmological models are complex and resource-consuming. It can learn the conditional probability density p( θ ∣ d ) using samples generated by models, and the posterior distribution p( θ ∣ d 0) can be obtained for a given observational data d 0. We tested the MNN using power spectra of the cosmic microwave background and Type Ia supernovae and obtained almost the same result as the Markov Chain Monte Carlo method. The numerical difference only exists at the level of ${ \mathcal O }({10}^{-2}\sigma )$ . The method can be extended to higher-dimensional data.

Keywords: cosmological parameters from large-scale structure
Phase and Morphology of Water-ice Grains Formed in a Cryogenic Laboratory Plasma

Grains of ice are formed spontaneously when water vapor is injected into a weakly ionized laboratory plasma in which the background gas has been cooled to cryogenic temperatures comparable to those of deep space. These ice grains are levitated indefinitely within the plasma so that their time evolution can be observed under free-floating conditions. Using microscope imaging, ice grains are shown to have a spindle-like fractal structure and grow over time. Both crystalline and amorphous phases of ice are observed using Fourier transform infrared spectroscopy. A mix of crystalline and amorphous grains coexists under certain thermal conditions, and a linear mixing model is used on the ice absorption band surrounding 3.2 μm to examine the ice phase composition and its temporal stability. The extinction spectrum is also affected by inelastic scattering as grains grow, and characteristic grain radii are obtained from Mie scattering theory and compared to size measurements from direct imaging. Observations are used to compare possible ice nucleation mechanisms, and it is concluded that nucleation is likely catalyzed by ions, as ice does not nucleate in the absence of plasma and impurities are not detected. Ice grain properties and infrared extinction spectra show similarity to observations of some astrophysical ices observed in protoplanetary disks, implying that the fractal morphology of the ice and observed processes of homogeneous ice nucleation could occur as well in such astrophysical environments with weakly ionized conditions.

Keywords: laboratory astrophysics; astrophysical dust processes; ice formation; ice phases; ice spectroscopy; interstellar plasma; space plasmas; dust formation
A Catalog of AGN Host Galaxies Observed with HST/ACS: Correlations between Star Formation and AGN Activity

We present the Advanced Camera for Surveys Active Galactic Nuclei (ACS-AGN) Catalog, a catalog of 2585 active galactic nucleus (AGN) host galaxies that are at redshifts 0.2 < z < 2.5 and that were imaged with the Hubble Space Telescope’s Advanced Camera for Surveys (ACS). Using the ACS General Catalog (ACS-GC) as our initial sample, we select an AGN subsample using Spitzer and Chandra data along with their respective established AGN selection criteria. We then gather further multiwavelength photometric data in order to construct spectral energy distributions (SEDs). Using these SEDs, we are able to derive multiple AGN and host galaxy properties, such as star formation rate (SFR), AGN luminosity, stellar mass, and nuclear column density. From these data, we show that AGN host galaxies tend to lie below the star-forming main sequence, with X-ray-selected AGN host galaxies being more offset than IR-selected AGN host galaxies. This suggests that there is some process, possibly negative feedback, in AGN host galaxies causing decreased star formation. We also demonstrate that there is a positive trend between the SFR and AGN luminosity in AGN host galaxies, in individual redshift bins, and across all redshift bins, and that both are correlated with the stellar mass of their galaxies. This points toward an underlying link between the stellar mass, stellar growth, and supermassive black hole growth in a galaxy.

Keywords: agn host galaxies; active galactic nuclei; galaxy quenching; star formation; galaxy evolution
Error Analysis for Rotating-drift-scan Charge-coupled Device Observation of Near-Earth Asteroids

The apparent velocities of near-Earth asteroids (NEAs) are usually high when they pass by Earth. Observing these fast-moving objects with long exposure times would cause their images to streak and significantly decrease the precision of astronomical measurements. The rotating-drift-scan (RDS) charge-coupled device technique is a promising approach to observe fast-moving NEAs during their close approaches to Earth. By rotating the camera of a telescope, an NEA can be observed in the time delay integration mode. This allows the asteroid to be imaged as a point source, even with a long exposure time. Here, we thoroughly present the RDS follow-up observation and orbit determination of a newly discovered NEA 2023 BJ7. This technique makes an impactful contribution to improving the NEA's orbit accuracy by extending the observation arc. A detailed statistical analysis of the astrometric error was conducted, revealing that RDS observations can achieve a competitive accuracy with an rms error of 0.″24 in right ascension and 0.″32 in declination. The instability of the telescope is thought to be the main reason affecting the internal precision. Furthermore, the RDS technique excels at observing fast-moving NEAs, as well as newly discovered NEAs without accurate ephemerides. For NEAs with rates of motion exceeding 10 deg day‑1, the rms of RDS observation residuals is 0.″35 in the along-track direction and 0.″23 in the cross-track. With this technique, a network of small-aperture telescopes would substantially benefit our global NEAs monitoring system to ensure Earth's safety from any asteroid impacts.

Keywords: ccd observation; near-earth objects; astronomical techniques; orbit determination
Forecast of Major Solar X-Ray Flare Flux Profiles Using Novel Deep Learning Models

In this Letter, we present the application of a couple of novel deep learning models to the forecast of major solar X-ray flare flux profiles. These models are based on a sequence-to-sequence framework using long short-term memory cell and an attention mechanism. For this, we use Geostationary Operational Environmental Satellite 10 X-ray flux data from 1998 August to 2006 April. Seven hundred sixty events are used for training and 85 for testing. The models forecast 30 minutes of X-ray flux profiles during the rise phase of the solar flare with a minute time cadence. We evaluate the models using the 10-fold cross-validation and rms error (RMSE) based on flux profiles and RMSE based on its peak flux. For comparison we consider two simple deep learning models and four conventional regression models. Major results of this study are as follows. First, we successfully apply our deep learning models to the forecast of solar flare X-ray flux profiles, without any preprocessing to extract features from data. Second, our proposed models outperform the other models. Third, our models achieve better performance for forecasting X-ray flux profiles with low-peak fluxes than those with high-peak fluxes. Fourth, our models successfully predict flare duration with high correlations for both all cases and cases at peak times. Our study indicates that our deep learning models can be useful for forecasting time-series data in astronomy and space weather, even for impulsive events such as major flares.

Keywords: the sun; solar x-ray flares; time series analysis
Circumbinary Disks: Accretion and Torque as a Function of Mass Ratio and Disk Viscosity

Using numerical hydrodynamics calculations and a novel method for densely sampling parameter space, we measure the accretion and torque on a binary system from a circumbinary disk. In agreement with some earlier studies, we find that the net torque on the binary is positive for mass ratios close to unity, and that accretion always drives the binary toward equal mass. Accretion variability depends sensitively on the numerical sink prescription, but the torque and relative accretion onto each component do not depend on the sink timescale. Positive torque and highly variable accretion occurs only for mass ratios greater than around 0.05. This means that for mass ratios below 0.05, the binary would migrate inward until the secondary accreted sufficient mass, after which it would execute a U-turn and migrate outward. We explore a range of viscosities, from α = 0.03 to α = 0.15, and find that this outward torque is proportional to the viscous torque, so that torque per unit accreted mass is independent of α. Dependence of accretion and torque on mass ratio is explored in detail, densely sampling mass ratios between 0.01 and unity. For mass ratio q > 0.2, accretion variability is found to exhibit a distinct sawtooth pattern, typically with a five-orbit cycle that provides a smoking gun prediction for variable quasars observed over long periods, as a potential means to confirm the presence of a binary.

Keywords: galaxy mergers; quasars; supermassive black holes; black holes; circumstellar disks; galaxy accretion disks; binary stars; active galactic nuclei; wide binary stars; astrophysical fluid dynamics; close binary stars; shocks
SN 2018fif: The Explosion of a Large Red Supergiant Discovered in Its Infancy by the Zwicky Transient Facility

High-cadence transient surveys are able to capture supernovae closer to their first light than ever before. Applying analytical models to such early emission, we can constrain the progenitor stars' properties. In this paper, we present observations of SN 2018fif (ZTF 18abokyfk). The supernova was discovered close to first light and monitored by the Zwicky Transient Facility (ZTF) and the Neil Gehrels Swift Observatory. Early spectroscopic observations suggest that the progenitor of SN 2018fif was surrounded by relatively small amounts of circumstellar material compared to all previous cases. This particularity, coupled with the high-cadence multiple-band coverage, makes it a good candidate to investigate using shock-cooling models. We employ the SOPRANOS code, an implementation of the model by Sapir & Waxman and its extension to early times by Morag et al. Compared with previous implementations, SOPRANOS has the advantage of including a careful account of the limited temporal validity domain of the shock-cooling model as well as allowing usage of the entirety of the early UV data. We find that the progenitor of SN 2018fif was a large red supergiant with a radius of $R={744.0}_{-128.0}^{+183.0}\,{R}_{\odot }$ and an ejected mass of ${M}_{\mathrm{ej}}={9.3}_{-5.8}^{+0.4}\,{M}_{\odot }$ . Our model also gives information on the explosion epoch, the progenitor's inner structure, the shock velocity, and the extinction. The distribution of radii is double-peaked, with smaller radii corresponding to lower values of the extinction, earlier recombination times, and a better match to the early UV data. If these correlations persist in future objects, denser spectroscopic monitoring constraining the time of recombination, as well as accurate UV observations (e.g., with ULTRASAT), will help break the extinction/radius degeneracy and independently determine both.

Keywords: supernovae; type ii supernovae; astronomy data modeling; observational astronomy; ultraviolet transient sources; transient sources
A New Channel of Bulge Formation via the Destruction of Short Bars

Short (inner) bars of subkiloparsec radius have been hypothesized to be an important mechanism for driving gas inflows to small scales, thus feeding central black holes (BHs). Recent numerical simulations have shown that the growth of central BHs in galaxies can destroy short bars, when the BH reaches a mass of ∼0.1% of the total stellar mass of the galaxy. We study N-body simulations of galaxies with single and double bars to track the long-term evolution of the central stellar mass distribution. We find that the destruction of the short bar contributes significantly to the growth of the bulge. The final bulge mass is roughly equal to the sum of the masses of the initial pseudo bulge and short bar. The initially boxy/peanut-shaped bulge of Sérsic index n ≲ 1 is transformed into a more massive, compact structure that bears many similarities to a classical bulge, in terms of its morphology (n ≈ 2), kinematics (dispersion-dominated, isotropic), and location on standard scaling relations (Kormendy relation, mass-size relation, and correlations between BH mass and bulge stellar mass and velocity dispersion). Our proposed channel for forming classical bulges relies solely on the destruction of short bars without any reliance on mergers. We suggest that some of the less massive, less compact classical bulges were formed in this manner.

Keywords: galaxy dynamics; galaxy physics; galaxy bulges; black hole physics; galaxy structure
Return of 4U 1730-22 after 49 yr Silence: The Outburst Properties Observed by NICER and Insight-HXMT

After 49 yr of quiescence, 4U 1730-22 became active and had two outbursts in 2021 and 2022; the onset and tail of the outbursts were observed by NICER, which give us a peerless opportunity to study the state transition and its underlying mechanism. In this work, we take both the neutron star (NS) surface and accretion disk emission as the seed photons of the Comptonization and derive their spectral evolution in a bolometric luminosity range of 1%-15% L Edd. In the high/soft state, the inferred inner disk radius and the NS radius are well consistent, which implies that the accretion disk is close to the NS surface. For the decay stage, we report a steep change of the accretion disk emission within 1 day, i.e., the soft-to-hard transition, which could be due to the propeller effect, and the corresponding NS surface magnetic field is 1.8-2.2 × 108 G. Moreover, the inner disk radius is truncated at the corotation radius, which is similar to the propeller effect detected from 4U 1608-52. The absence of the propeller effect in the hard-to-soft state transition implies that the transition between the magnetospheric accretion and the disk accretion is not the sole cause of the state transitions.

Keywords: x-ray transient sources; low-mass x-ray binary stars