Abstracts of Interest
Selected by:
Robert Christian Koenig
Abstract: 2505.06009
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Title:A Study of the Spectral Properties of Gamma-Ray Bursts with the Main and Second Bursts
View PDF HTML (experimental)Abstract:The origins of the main burst and second burst of gamma-ray bursts (GRBs) and the composition of their jets remain uncertain. To explore this complex subject more thoroughly, we conduct a spectral analysis on 18 GRBs with a main and a second burst observed by Fermi/GBM. First, we employ Bayesian time-resolved spectral analysis to compare the spectral components of the main and the second burst, finding that $83.3\%$ of the main and second bursts contain a thermal component. $67\%$ of the GRBs, the thermal component gradually decreased from the main to the second burst and the number of spectra exceeding the "Synchrotron line-of-death" is significantly higher in the main burst than in the second burst. Subsequently, we ascertain that for both the main and second bursts, $71.4\%$ of the low-energy spectral index $\alpha$ and $77.8\%$ of the peak energy $E_{p}$ evolve in a similar fashion. There are $50.0\%$ and $72.2\%$ of the GRBs exhibit comparable correlations for the $Flux-\alpha$ and $\alpha-E_{p}$, respectively. For $Flux-E_{p}$ both the main and second burst show a positive correlation. Moreover, from the perspective of the temporal evolution of characteristic radii, the transition from the main to the second burst appeared to be seamless. Finally, we find that both the main and the second burst follow the same Amati relation and Yonetoku relation. Our analysis strongly indicates that the second burst is a continuation of the main burst and is highly likely to share a common physical origin.
Abstract: 2505.07423
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Title:Origin of the Multi-Phase Interstellar Medium: the Effects of Turbulence and Magnetic Field
View PDF HTML (experimental)Abstract:The interstellar medium (ISM) consists of a multiphase gas, including the warm neutral medium (WNM), the unstable neutral medium (UNM), and the cold neutral medium (CNM). While significant attention has been devoted to understanding the WNM and CNM, the formation of a substantial fraction of the UNM, with temperatures ranging from a few hundred to a few thousand Kelvin, remains less well understood. In this study, we present three-dimensional hydrodynamical and magnetohydrodynamical simulations of turbulent multiphase ISM to investigate the roles of turbulence and magnetic fields in regulating the multiphase ISM. Our results confirm that turbulence is crucial in redistributing energy and producing the UNM. The turbulent mixing effect smooths the phase diagram, flattens the pressure-density relationship, and increases the fraction of gas in the UNM. We find that magnetic fields not only contribute to sustaining the UNM but also influence the dynamics and distribution of gas across all phases. Magnetic fields introduce anisotropy to the turbulent cascade, reducing the efficiency of turbulent mixing in the direction perpendicular to the magnetic field. We find the anisotropy results in a less flat phase diagram compared to hydrodynamical cases. Furthermore, the inclusion of magnetic fields shallowens the second-order velocity structure functions across multiple ISM phases, suggesting that more small-scale fluctuations are driven. These fluctuations contribute to the formation of the UNM by altering the energy cascade and thermodynamic properties of the gas. Our findings suggest that the combined effects of turbulence and magnetic fields are important in regulating the multiphase ISM.
Abstract: 2505.07422
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Title:Characterizing 3D Magnetic Fields and Turbulence in H I Clouds
View PDF HTML (experimental)Abstract:3D Galactic magnetic fields are critical for understanding the interstellar medium, Galactic foreground polarization, and the propagation of ultra-high-energy cosmic rays. Leveraging recent theoretical insights into anisotropic magnetohydrodynamic (MHD) turbulence, we introduce a deep learning framework to predict the full 3D magnetic field structure-including the plane-of-sky (POS) position angle, line-of-sight (LOS) inclination, magnetic field strength, sonic Mach number ($M_s$), and Alfvén Mach number ($M_A$)-from spectroscopic H~I observations. The deep learning model is trained on synthetic H~I emission data generated from multiphase 3D MHD simulations. We then apply the trained model to observational data from the Commensal Radio Astronomy FAST Survey, presenting maps of 3D magnetic field orientation, magnetic field strength, $M_s$, and $M_A$ for two H~I clouds, a low-velocity cloud (LVC) and an intermediate-velocity cloud (IVC), which overlap in the POS yet reside at different LOS distances. The deep-learning-predicted POS magnetic field position angles align closely with those determined using the velocity gradient technique, whose integrated results are consistent with independent measurements from Planck 353~GHz polarization data. This study demonstrates the potential of deep learning approaches as powerful tools for modeling the 3D distributions of 3D Galactic magnetic fields and turbulence properties throughout the Galaxy.
Abstract: 2505.06723
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Title:Mastering 3D-detection of Extensive Air Showers in Cherenkov Light
View PDF HTML (experimental)Abstract:A new SPHERE seires complex extensive air showers detector is under development. The main goal of its mission is to study the mass composition of cosmic ray nuclei in the 1-100 PeV energy range at a new level. The already well-established telescope of Cherenkov light reflected from the snow-covered ice surface of Lake Baikal from an altitude of 500-1000 m will be supported by a detector of direct light pointed upward. Since the two detectors will study the same shower at different stages of its development, it could be called a 3D detection, which is completely new for the EAS method. The development is based on an extensive MC modeling of the shower and the detection process using the Supercomputer Complex of the Lomonosov Moscow State University.
Abstract: 2505.06734
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Title:Searching for Dark Matter Annihilation in the Sun with the IceCube Upgrade
View PDF HTML (experimental)Abstract:The IceCube Upgrade will provide unprecedented sensitivity to dark matter particles annihilating in the core of the Sun. For dark matter candidates with spin-dependent couplings to nuclei and that annihilate significantly to tau leptons or neutrinos, we find that the IceCube Upgrade will be capable of testing parameter space that is beyond the reach of existing direct detection experiments. After calculating the sensitivity of the IceCube Upgrade to dark matter annihilation in the Sun, we explore dark matter models that could be tested by this experiment, identifying two classes of scenarios as promising targets for such searches.
Abstract: 2505.09510
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Title:A 70 pc-Diameter Nova Super-remnant Surrounding the Recurrent Nova RS Ophiuchi
View PDF HTML (experimental)Abstract:Recurrent novae undergo thermonuclear-powered eruptions separated by less than 100 years, enabled by subgiant or red giant donors transferring hydrogen-rich matter at very high rates onto their massive white dwarf companions. The most-rapidly moving parts of envelopes ejected in successive recurrent nova events are predicted to overtake and collide with the slowest ejecta of the previous eruption, leading to the buildup of vast (~ 10 - 100 parsec) super-remnants surrounding all recurrent novae; but only three examples are currently known. We report deep narrowband imaging and spectroscopy which has revealed a ~ 70-parsec-diameter shell surrounding the frequently recurring nova RS Ophiuchi. We estimate the super-remnant mass to be ~ 20 - 200 solar masses, expanding at a few tens of km/s, with an age of order 50-100 kyr. Its extremely low surface brightness and large angular size help explain the hitherto surprising absence of nova super-remnants. Our results support the prediction that ALL recurrent novae are surrounded by similar extended structures.
Abstract: 2505.09186
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Title:JWST & ALMA Joint Analysis with [OII]$λλ$3726,3729, [OIII]$λ$4363, [OIII]88$μ$m, and [OIII]52$μ$m: Multi-Zone Evolution of Electron Densities at $\mathbf{z\sim0-14}$ and Its Impact on Metallicity Measurements
View PDF HTML (experimental)Abstract:We present a JWST and ALMA detailed study of the ISM properties of high-redshift galaxies. Our JWST/NIRSpec IFU spectroscopy targeting three galaxies at $z=6-7$ detects key rest-frame optical emission lines, allowing us to derive [OII]$\lambda\lambda$3726,3729-based electron densities of $n_\mathrm{e,optical}\sim1000$ cm$^{-3}$ on average and [OIII]$\lambda$4363-based metallicities of $\mathrm{12+log(O/H)}=8.0-8.2$ in two galaxies. New ALMA Band 9/10 observations detect the [OIII]52$\mu$m line in one galaxy but do not in the others, resulting in FIR-based densities of $n_\mathrm{e,FIR}\lesssim500$ cm$^{-3}$ from the [OIII]52$\mu$m/[OIII]88$\mu$m ratios, systematically lower than the optical [OII]-based measurements. These low FIR-based densities are comparable to those at both $z\sim0$ and $z>6$ in the literature, including JADES-GS-z14-0 at $z=14.18$, suggesting little evolution up to $z\sim14$, in contrast to the increasing trend of optical-based densities with redshift. By conducting a JWST and ALMA joint analysis using emission lines detected with both telescopes, we find that the observed FIR [OIII]52,88$\mu$m luminosities are too high to be explained by the optical-based densities at which they would be significantly collisionally de-excited. Instead, a 2-zone model with distinct high- and low-density regions is required to reproduce all observed lines, indicating that FIR [OIII] emission arises predominantly from low-density gas, while optical [OIII] and [OII] lines trace both regions. We further demonstrate that the direct-$T_\mathrm{e}$ method can sometimes significantly underestimate metallicities up to 0.8 dex due to the presence of the low-density gas not fully traced by optical lines alone, highlighting the importance of combining optical and FIR lines to accurately determine gas-phase metallicities in the early universe.
Abstract: 2505.09042
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Title:The Mirya-m1 Cosmic Ray Detector: Features and First Year Observations
View PDF HTML (experimental)Abstract:We introduce the Mirya-m1 Cosmic Ray Detector, the largest and only cosmic ray detector in Turkiye designed for space weather research. Mirya-m1, modeled and built after the Muon Impact Tracer and Observer (MITO) (Ayuso et al. 2021), is located at the Eastern Anatolia Observatory (DAG) site of the Turkiye National Observatories in Erzurum, Turkiye, at an altitude of 3099 meters. This elevation positions Mirya-m1 among the highest-altitude cosmic ray detectors globally. The detector consists of two stacked scintillator counters, each measuring 1x1 meters, separated by a vertical distance of 1.36 meters. Each scintillator is monitored by four H1411 Hamamatsu photomultiplier tubes, enabling precise detection and measurement of light by incident cosmic rays. In this study, we present the data collected throughout 2024, which includes the detection of two Forbush decrease events in March and May 2024. These significant detections demonstrate the capability of Mirya-m1 to contribute valuable data for space weather research, establishing its potential as a critical instrument for cosmic ray studies in the region.
Abstract: 2505.08920
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Title:Uncertainties in the Estimation of Air Shower Observables from Monte Carlo Simulation of Radio Emission
View PDF HTML (experimental)Abstract:The detection of extensive air showers (EAS) induced by cosmic rays via radio signals has undergone significant advancements in the last two decades. Numerous ultra-high energy cosmic ray experiments routinely capture radio pulses in the MHz to GHz frequency range emitted by EAS. The Monte Carlo simulation of these radio pulses is crucial to enable an accurate reconstruction of the primary cosmic ray energy and to infer the composition of the primary particles. In this work, a comprehensive comparison of the predicted electric field in EAS simulated with CoREAS and ZHAireS was conducted to estimate the systematic uncertainties arising from the use of different simulation packages in the determination of two key shower observables namely, the electromagnetic energy of the EAS and the depth of maximum development ($X_{\rm max}$). For this comparison, input parameters and settings as similar as possible were used in both simulations, along with the same realistic atmospheric refractive index depending on altitude, which is crucial for the prediction of radio emission properties of EAS. In addition, simulated EAS with very similar values of depth of maximum development were selected. Good agreement was found between CoREAS and ZHAireS, with discrepancies in the dominant electric field components generally remaining below $10\%$ across the frequency range of a few MHz to hundreds of MHz, relevant for most radio detection experiments, translating into uncertainties in the determination of energy below $5\%$ and $\simeq 10\,\mathrm{g/cm^2}$ in $X_{\rm max}$.
Abstract: 2505.09111
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Title:Measuring the Cosmic Ray Spectrum with Next Generation Neutrino Detectors
View PDF HTML (experimental)Abstract:We investigate the capabilities of upcoming kiloton-scale neutrino detectors, such as Hyper-Kamiokande, in determining the primary cosmic ray spectrum. These detectors provide full-sky coverage and long-term monitoring, unlike traditional satellite and balloon experiments that measure cosmic ray flux at specific altitudes and locations. By analyzing the atmospheric neutrino flux generated by cosmic ray interactions, we demonstrate that future detectors can differentiate between various cosmic ray models with high statistical significance, even when accounting for uncertainties in neutrino cross sections and hadronic interactions. We introduce a technique for reconstructing the primary cosmic ray spectrum using neutrino measurements, which reduces the flux uncertainty from approximately 20\% to about 7\%. We then show that Hyper-K has the potential to increase sensitivity to neutrino oscillation parameters, such as $\sin^2\theta_{23}$, by a factor of 2. Our results highlight the complementary role of neutrino detectors in cosmic ray physics and their critical importance for precision measurements in particle astrophysics.
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