Newsfeeds
The Astrophysical Journal - latest papers
Latest articles for The Astrophysical Journal
-
Laboratory Studies on Absolute n-resolved Charge-exchange Cross Sections and Modeling X-Ray Emissions for Ne8+ Colliding with H2 and He
Charge exchange is a predominant process in inelastic collisions in astronomical plasmas, influencing the charge state balance and leading to X-ray emissions when solar wind ions interact with neutral gas in astrophysical environments. Accurate analysis of these dynamic properties to diagnose the solar wind composition and velocities, as well as the spatial distribution of the heliospheric neutral gas, can be hindered by the limited availability of relevant electron capture studies in the corresponding energy range. The absolute total and -resolved state-selective cross sections of single electron capture have been measured in the collisional energy range from 2.8 to 40 keV u−1, covering velocities corresponding to fast solar wind and coronal mass ejections. In comparison with existing atomic data, we observe good agreement with other results at overlapping energies. Based on the absolute -state electron capture cross sections, the absolute cross sections of photon emissions following charge exchange between Ne8+ and H2, as well as He gas, were determined for the potential applications in high-resolution X-ray spectra studies of solar wind charge exchange. This work serves as a benchmark for validating the theoretical calculations of charge exchange cross sections and astronomical plasma models, providing valuable insights into the investigation of soft X-ray emissions in solar wind plasma environments.
-
Testing the Bullet Dwarf Collision Scenario in the NGC 1052 Group through Morphologies and Stellar Populations
NGC 1052-DF2 and -DF4 are two ultradiffuse galaxies that have been reported as deficient in dark matter and associated with the same galaxy group. Recent findings suggest that DF2 and DF4 are part of a large linear substructure of dwarf galaxies that could have been formed from a high-velocity head-on encounter of two gas-rich galaxies, known as a “bullet dwarf” collision. Based on new observations from the Hubble Space Telescope, combined with existing imaging from the u band to mid-infrared, we test the bullet dwarf scenario by studying the morphologies and stellar populations of the trail dwarfs. We find no significant morphological differences between the trail dwarfs and other dwarfs in the group, while for both populations, their photometric major axes unexpectedly align parallel with the trail. We find that the trail dwarfs have significantly older ages and higher metallicities than the comparison sample, supporting the distinctiveness of the trail. These observations provide key constraints for any formation model, and we argue that they are currently best explained by the bullet dwarf collision scenario, with additional strong tests anticipated with future observations.
-
Detection of a Highly Ionized Outflow in the Quasiperiodically Erupting Source GSN 069
Quasiperiodic eruptions (QPEs) are high-amplitude, soft X-ray bursts recurring every few hours, associated with supermassive black holes. Many interpretations for QPEs were proposed since their recent discovery in 2019, including extreme mass ratio inspirals and accretion disk instabilities. But, as of today, their nature still remains debated. We perform the first high-resolution X-ray spectral study of a QPE source using the Reflection Grating Spectrometers' gratings on board XMM-Newton, leveraging nearly 2 Ms of exposure on GSN 069, the first discovered source of this class. We resolve several absorption and emission lines including a strong line pair near the N vii rest-frame energy, resembling the P-Cygni profile. We apply photoionization spectral models and identify the absorption lines as an outflow blueshifted by 1700−2900 km s−1, with a column density of about 1022 cm−2 and an ionization parameter /erg cm s−1) of 3.9−4.6. The emission lines are instead redshifted by up to 2900 km s−1, and likely originate from the same outflow that imprints the absorption features, and covers the full 4π sky from the point of view of GSN 069. The column density and ionization are comparable to the outflows detected in some tidal disruption events, but this outflow is significantly faster and has a strong emission component. The outflow is more highly ionized when the system is in the phase during which QPEs are present, and from the limits, we derive on its location, we conclude that the outflow is connected to the recent complex, transient activity of GSN 069, which began around 2010.
-
Combined Fit of Spectrum and Composition for FR0 Radio-galaxy-emitted Ultra–high energy Cosmic Rays with Resulting Secondary Photons and Neutrinos
This study comprehensively investigates the gamma-ray dim population of Fanaroff–Riley Type 0 (FR0) radio galaxies as potentially significant sources of ultra–high energy cosmic rays (UHECRs, E > 1018 eV) detected on Earth. While individual FR0 luminosities are relatively low compared to the more powerful Fanaroff–Riley Type 1 and Type 2 galaxies, FR0s are substantially more prevalent in the local universe, outnumbering the more energetic galaxies by a factor of ∼5 within a redshift of z ≤ 0.05. Employing CRPropa3 simulations, we estimate the mass composition and energy spectra of UHECRs originating from FR0 galaxies for energies above 1018.6 eV. This estimation fits data from the Pierre Auger Observatory (Auger) using three extensive air shower models; both constant and energy-dependent observed elemental fractions are considered. The simulation integrates an approximately isotropic distribution of FR0 galaxies, extrapolated from observed characteristics, with UHECR propagation in the intergalactic medium, incorporating various plausible configurations of extragalactic magnetic fields, both random and structured. We then compare the resulting emission spectral indices, rigidity cutoffs, and elemental fractions with recent Auger results. In total, 25 combined energy-spectrum and mass-composition fits are considered. Beyond the cosmic-ray fluxes emitted by FR0 galaxies, this study predicts the secondary photon and neutrino fluxes from UHECR interactions with intergalactic cosmic photon backgrounds. The multimessenger approach, encompassing observational data and theoretical models, helps elucidate the contribution of low-luminosity FR0 radio galaxies to the total cosmic-ray energy density.
-
Multiwavelength Study of Five Distant Transient Gamma-Ray AGNs with z > 1
The multiwavelength emissions, especially gamma-rays, of active galactic nuclei (AGNs) are essential for studying the physical properties of jets emanating from supermassive black holes at galaxy centers. However, for high-redshift AGNs, it is challenging to identify their gamma-ray emissions due to limited angular resolution of gamma-ray instruments. In this work, using the infrared light curves of the Wide-field Infrared Survey Explorer (WISE) and spectral measurements through Sloan Digital Sky Survey DR16 quasar observations, we assemble 64 mid-infrared flares with redshift z > 1 as the sample. Based on the Fermi-Large Area Telescope survey data, we search for gamma-ray emission from the 64 WISE sources. New quasi-simultaneous gamma-ray emissions are detected for five sample sources when their infrared emissions are at a flare state, and the infrared positions fall into the error bars of their best-fit gamma-ray positions, as well. We collect the optical data and historical data to perform a spectral energy distribution (SED) analysis. To investigate the multiband characteristics of these five gamma-ray AGNs at flare and quiescent states, a one-zone leptonic model is applied to reproduce their averaged SEDs.