Abstracts of Interest
Selected by:
Jemma Pilossof
Abstract: 2504.00098
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:The Optical to X-ray Luminosity and Spectrum of Supernova Wind Breakouts
View PDF HTML (experimental)Abstract:Observations indicate that optically thick circum-stellar medium (CSM) at radii of $10^{14}-10^{15}$ cm around core-collapse supernovae (SN) progenitors is common. The breakout of the SN radiation-mediated shock (RMS) through such CSM leads to the formation of a collisionless shock (CLS). We analyze the evolution of the shock structure and associated radiation field during and after the RMS-CLS transition for non-relativistic breakouts (breakout shock velocity $v_{\rm bo}=10^9v_9~{\rm cm/s}<0.1c$) through a hydrogen-rich CSM "wind" density profile, $\rho\propto r^{-2}$, with breakout radius $R_{\rm bo}=10^{14}R_{14}$ cm much larger than the progenitor radius. An analytic description of the key properties of the emitted optical to X-ray radiation is provided, supported by numeric radiation-hydrodynamics calculations that self-consistently describe the time-dependent spatial distribution of the plasma and radiation, governed by the interplay between Bremsstrahlung emission/absorption and inelastic Compton scattering. We show that the characteristic energy of the photons carrying most of the luminosity, $\approx10^{43}R_{14}v_9^2$ erg/s, shifts from UV to X-ray, reaching 1 keV as the shock reaches $\approx3R_{\rm bo}$. The X-ray signal is not suppressed by propagation through the upstream wind, and its absence may suggest that the dense CSM does not extend much beyond $R_{\rm bo}$. Our results provide the basis for a quantitative calculation of the high energy $\gamma$-ray and neutrino emission that is expected from particles accelerated at the CLS, and will allow using data from upcoming surveys that will systematically detect large numbers of young SNe, particularly ULTRASAT, to infer the pre-explosion mass loss history of the SN progenitor population.
Abstract: 2503.24384
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:High Energy Emission from the Intrabinary Shocks in Redback Pulsars
View PDF HTML (experimental)Abstract:The intrabinary shocks (IBS) of spider pulsars emit non-thermal synchrotron X-rays from accelerated electrons and positrons in the shocked pulsar wind, likely energized by magnetic reconnection. In redback spider pulsars, the IBS typically wraps around the pulsar, leading to a near-normal IBS shock with relatively bright X-ray emission. The characteristic energies of radiating particles and the magnetic fields in the IBS suggest spectral features in the hard X-ray band. Here we perform joint soft-hard X-ray analyses of three redback pulsars, J1723-2837, J2215+5135, and J2339-0533, including new J2215 NuSTAR data. We identify a significant cooling break in J1723-2837 and a marginal break in J2215+5135, while placing constraints on the break energy in J2339-0533. Interpreting these as synchrotron cooling features allows us to estimate the IBS magnetic field $B_{\rm IBS} \sim 40-100$ G and place lower bounds on the maximum radiating electron energy. Our results constrain the magnetization of the pulsar wind as well as pair-production in millisecond pulsar magnetospheres.
Abstract: 2503.22891
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:High-Energy Neutrino Emission from a Radiatively Inefficient Accretion Flow with a three-dimensional GRMHD Simulation
View PDF HTML (experimental)Abstract:The high-energy particle production in the accretion flow onto black holes can be a key physics to explain the high-energy neutrino background. While the single-zone approximation has been commonly adopted in studies of the high-energy neutrino emission around black holes, the effects of the global plasma structure may be non-negligible. We carry out the first computations of cosmic-ray acceleration and high-energy neutrino emission via the hadronuclear ($pp$) interaction in global radiatively inefficient accretion flows and outflows around a supermassive black hole, using three-dimensional general relativistic magnetohydrodynamic simulation data. The Fokker-Planck equation for cosmic-ray protons is solved with a phenomenological model for the energy diffusion coefficient to express the turbulent acceleration in the sub-grid scale. The inhomogeneous and time variable structure of the accretion flow leads to a variety of particle energy distribution. The spectral energy distributions (SEDs) of neutrinos emitted from the entire region are flatter than those calculated under the single-zone approximation. In our model, the neutrino emission originating from cosmic rays advected with the outflow rather than the inflow predominates the SEDs. Such galactic nuclei can be significant sources of cosmic rays in those galaxies.
Abstract: 2504.03543
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Clustering analysis of Fermi-LAT unidentified point sources
View PDF HTML (experimental)Abstract:The Fermi Large Area Telescope (LAT) has detected thousands of sources since its launch in 2008, with many remaining unidentified. Some of these point sources may arise from source confusion. Specifically, there could be extended sources erroneously described as groups of point sources. Using the DBSCAN clustering algorithm, we analyze unidentified Fermi-LAT sources alongside some classified objects from the 4FGL-DR4 catalog. We identified 44 distinct clusters containing 106 sources, each including at least one unidentified source. Detailed modeling of selected clusters reveals some cases where extended source models are statistically preferred over multiple point sources. The work is motivated by prior observations of extended TeV gamma-ray sources, such as HESS J1813-178, and their GeV counterparts. In the case of HESS J1813-178, two unidentified Fermi-LAT point sources were detected in the region. Subsequent multiwavelength analysis combining TeV and GeV data showed that a single extended source is a better description of the emission in this region than two point-like sources.
Abstract: 2504.02677
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Monte Carlo evaluations of gamma-ray and radio pulsar populations
View PDF HTML (experimental)Abstract:Based on well-grounded Galactic neutron star populations formed from radio pulsar population syntheses of canonical pulsars (CPs) and millisecond pulsars (MSPs), we use the latest Fermi-LAT catalog (4FGL-DR4) to investigate the implications of proposed $\gamma-$ray luminosity models. Using Monte Carlo techniques, we calculate the number of CPs and MSPs that would comprise the sample of pulsar-like unidentified sources (PLUIDs) in 4FGL-DR4. While radio beaming fractions were used to scale the sizes of the populations, when forming the mock 4FGL-DR4 samples, we make the simplifying assumption that all $\gamma-$ray pulsars are beaming towards the Earth. We then explore the observable outcomes of seven different $\gamma-$ray luminosity models. Four of the models provide a good match to the observed number of PLUIDs, while three others significantly over-predict the number of PLUIDs. For these latter models, either the average beaming fraction of $\gamma-$ray pulsars is more like 25--50\%, or a revision in the luminosity scaling is required. Most of the radio detectable MSPs that our models predict as part of the PLUIDs within 4FGL-DR4 are, unsurprisingly, fainter than the currently observed sample and at larger dispersion measures. For CPs, in spite of an excellent match to the observed radio population, none of the $\gamma-$ray models we investigated could replicate the observed sample of 150 $\gamma-$ray CPs. Further work is required to understand this discrepancy. For both MSPs and CPs, we provide encouraging forecasts for targeted radio searches of PLUIDs from 4FGL-DR4 to elucidate the issues raised in this study.
Abstract: 2504.02185
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Multiwavelength observation of a candidate pulsar halo LHAASO J0621+3755 and the first X-ray detection of PSR J0622+3749
View PDF HTML (experimental)Abstract:Pulsar halos are regions around middle-aged pulsars extending out to tens of parsecs. The large extent of the halos and well-defined central cosmic-ray accelerators make this new class of Galactic sources an ideal laboratory for studying cosmic-ray transport. LHAASO J0621+3755 is a candidate pulsar halo associated with the middle-aged gamma-ray pulsar PSR J0622+3749. We observed LHAASO J0621+3755 with VERITAS and XMM-Newton in the TeV and X-ray bands, respectively. For this work, we developed a novel background estimation technique for imaging atmospheric Cherenkov telescope observations of such extended sources. No halo emission was detected with VERITAS (0.3--10 TeV) or XMM-Newton (2--7 keV) within 1 degree and 10 arcmin around PSR J0622+3749, respectively. Combined with the LHAASO-KM2A and Fermi-LAT data, VERITAS flux upper limits establish a spectral break at ~1--10 TeV, a unique feature compared with Geminga, the most studied pulsar halo. We model the gamma-ray spectrum and LHAASO-KM2A surface brightness as inverse Compton emission and find suppressed diffusion around the pulsar, similar to Geminga. A smaller diffusion suppression zone and harder electron injection spectrum than Geminga are necessary to reproduce the spectral cutoff. A magnetic field <= 1 uG is required by our XMM-Newton observation and synchrotron spectral modeling, consistent with Geminga. Our findings support slower diffusion and lower magnetic field around pulsar halos than the Galactic averages, hinting at magnetohydrodynamic turbulence around pulsars. Additionally, we report the detection of an X-ray point source spatially coincident with PSR J0622+3749, whose periodicity is consistent with the gamma-ray spin period of 333.2 ms. The soft spectrum of this source suggests a thermal origin.
Abstract: 2504.02043
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Transient gamma rays from the 2021 outburst of the recurrent nova RS Ophiuchi: the effect of gamma-ray absorption
View PDF HTML (experimental)Abstract:In 2021, RS Ophiuchi was the first nova to be detected in the very-high-energy (TeV) gamma-ray domain, directly testifying of efficient acceleration of charged particles up to at least the TeV range at the nova shock. Surprisingly, the TeV gamma-ray signal peaks $\sim 2$ days after the GeV signal and the origin of this delay has still not been clearly understood. We investigate the possibility that this delay is due to the effect of gamma-ray absorption resulted from interactions between gamma rays and optical photons copiously emitted during the outburst. We model particle acceleration at a nova shock to obtain the gamma-ray emission produced in interactions between the accelerated particles and the shocked gas. The effect of gamma-ray absorption is then included in details using the radiative transfer equation. We find that this can naturally account for the delay between the peaks of GeV and TeV gamma-ray lightcurves. This result emphasizes the importance of gamma-ray absorption for interpreting gamma-ray observations of novae in the TeV range which, in turn, demonstrates the necessity of a multi-wavelength view for unraveling the underlying physics of particle acceleration in these systems.
Abstract: 2504.01892
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Synchro-curvature description of γ-ray light curves and spectra of pulsars: concurrent fitting
View PDF HTML (experimental)Abstract:We present a concurrent fitting of spectra and light curves of the whole population of detected gamma-ray pulsars. Using a synchro-curvature model we compare our theoretical output with the observational data published in the Third Fermi Pulsar Catalog, which has significantly increased the number of known gamma-ray pulsars. Our model properly fits all the spectra and reproduces well a considerable fraction of light curves. Light curve fitting is carried out with two different techniques, whose strong points and caveats are discussed. We use a weighted reduced \{chi}^2 of light curves in time domain, and the Euclidean distance of the Fourier transform of the light curves, i.e. transforming the light curves to the frequency domain. The performance of both methods is found to be qualitatively similar, but individual best-fit solutions may differ. We also show that, in our model based on few effective parameters, the light curve fitting is basically insensitive to the timing and spectral parameters of the pulsar. Finally, we look for correlations between model and physical parameters, and recover trends found in previous studies but without any significant correlation involving geometrical parameters.
Abstract: 2504.01799
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:A discussion on the origin of the sub-PeV Galactic gamma-ray emission
View PDF HTML (experimental)Abstract:Galactic diffuse gamma-ray flux measured by the Tibet AS{\gamma} experiment and the total Galactic gamma-ray flux measured by Large High Altitude Air Shower Observatory (LHAASO) are found to be consistent, within the statistical and systematic uncertainties, for the inner Galactic Plane region in the sub-PeV energy range (E > 10^14 eV). The result suggests that the sub-PeV Galactic gamma-ray flux is dominated by the diffuse emission. On the other hand, the LHAASO observations suggest that the sub-PeV gamma-ray sources presented in the first LHAASO catalog possibly give a significant contribution to the total sub-PeV Galactic gamma-ray emission ($\approx$ 60%). However, the estimate must be regarded as a conservative upper limit. In fact, current gamma-ray observations imply that many of the sub-PeV gamma-ray sources detected by LHAASO have a cutoff or significant softening in their energy spectra in the several tens of TeV energy range, and the resolved-source contribution to the total sub-PeV Galactic gamma-ray emission should be much lower than the above estimate. More sophisticated discussion about the origin of the sub-PeV Galactic gamma-ray emission requires detailed spectral studies of the individual gamma-ray sources and an accurate estimate of the contamination of the source fluxes from the diffuse emission.
Abstract: 2504.01569
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:An advanced pulse-avalanche stochastic model of long gamma-ray burst light curves
View PDF HTML (experimental)Abstract:A unified explanation of the variety of long-duration gamma-ray burst (GRB) light curves (LCs) is essential for identifying the dissipation mechanism and possibly the nature of their central engines. In the past, a model was proposed to describe GRB LCs as the outcome of a stochastic pulse avalanche process, possibly originating from a turbulent regime, and it was tested by comparing average temporal properties of simulated and real LCs. Recently, we revived this model and optimised its parameters using a genetic algorithm (GA), a machine-learning-based approach. Our findings suggested that GRB inner engines may operate near a critical regime. Here we present an advanced version of the model, which allows us to constrain the peak flux distribution of individual pulses, and evaluate its performance on a new dataset of GRBs observed by the Fermi Gamma-ray Burst Monitor (GBM). After introducing new model parameters and a further comparison metric, that is the observed signal-to-noise (S/N) distribution, we test the new model on three complementary datasets: CGRO/BATSE, Swift/BAT, and Fermi/GBM. As in our previous work, the model parameters are optimised using a GA. The updated sets of parameters achieve a further reduction in loss compared to both the original model and our earlier optimisation. The different values of the parameters across the datasets are shown to originate from the different energy passbands, effective areas, trigger algorithms, and, ultimately, different GRB populations of the three experiments. Our results further underpin the stochastic and avalanche character of the dissipation process behind long GRB prompt emission, with an emphasis on the near-critical behaviour, and establish this new model as a reliable tool for generating realistic GRB LCs as they would be seen with future experiments.
Abstract: 2504.00601
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Study of Ultra-High-Energy Gamma-Ray Source 1LHAASO J0056+6346u and Its Possible Origins
View PDF HTML (experimental)Abstract:We report a dedicated study of the newly discovered extended UHE $\gamma$-ray source 1LHAASO J0056+6346u. Analyzing 979 days of LHAASO-WCDA data and 1389 days of LHAASO-KM2A data, we observed a significant excess of $\gamma$-ray events with both WCDA and KM2A. Assuming a point power-law source with a fixed spectral index, the significance maps reveal excesses of ${\sim}12.65\,\sigma$, ${\sim}22.18\,\sigma$, and ${\sim}10.24\,\sigma$ in the energy ranges of 1--25 TeV, 25--100 TeV, and $> 100$ TeV, respectively. We use a 3D likelihood algorithm to derive the morphological and spectral parameters, and the source is detected with significances of $12.65\,\sigma$ by WCDA and $25.27\,\sigma$ by KM2A. The best-fit positions derived from WCDA and KM2A data are (R.A. = $13.96^\circ\pm0.09^\circ$, Decl. = $63.92^\circ\pm0.05^\circ$) and (R.A. = $14.00^\circ\pm0.05^\circ$, Decl. = $63.79^\circ\pm0.02^\circ$), respectively. The angular size ($r_{39}$) of 1LHAASO J0056+6346u is $0.34^\circ\pm0.04^\circ$ at 1--25 TeV and $0.24^\circ\pm0.02^\circ$ at $> 25$ TeV. The differential flux of this UHE $\gamma$-ray source can be described by an exponential cutoff power-law function: $(2.67\pm0.25) \times 10^{-15} (E/20\,\text{TeV})^{-1.97\pm0.10} e^{-E/(55.1\pm7.2)\,\text{TeV}} \,\text{TeV}^{-1}\,\text{cm}^{-2}\,\text{s}^{-1}$. To explore potential sources of $\gamma$-ray emission, we investigated the gas distribution around 1LHAASO J0056+6346u. 1LHAASO J0056+6346u is likely to be a TeV PWN powered by an unknown pulsar, which would naturally explain both its spatial and spectral properties. Another explanation is that this UHE $\gamma$-ray source might be associated with gas content illuminated by a nearby CR accelerator, possibly the SNR candidate G124.0+1.4.
Abstract: 2504.00290
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Cosmic-ray propagation features in gamma-ray measurements
View PDF HTML (experimental)Abstract:Gamma-ray measurements from GeV to PeV energies have provided us with a wealth of information on diffuse emission and sources in the Universe lately. With improved spatial and temporal resolutions together with real-time multimessenger astronomy, the modeling of 3D cosmic-ray transport becomes more and more important to explain the data. Here, we will give a compact summary of how cosmic-ray propagation in very different astrophysical environments like the Sun, Milky Way, and active galaxies can be constrained by combining 3D modeling with the propagation software CRPropa with gamma-ray measurements.
Abstract: 2504.01660
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:STRAUSS: Sonification Tools & Resources for Analysis Using Sound Synthesis
View PDF HTML (experimental)Abstract:Sonification, or conveying data using non-verbal audio, is a relatively niche but growing approach for presenting data across multiple specialist domains including astronomy, climate science, and beyond. The STRAUSS Python package aims to provide such a tool, which builds upon previous approaches to provide a powerful means to explore different ways of expressing data, with fine control over the output audio and its format. STRAUSS is a free, open source (FOSS) package, designed to allow flexible and effective sonification to be integrated into data workflows, in analogy to widely used visualisation packages. The remit of STRAUSS is broad; it is intended to be able to bridge between ad-hoc solutions for sonifying very particular datasets, and highly technical compositional and sound-design tools that are not optimised for sonification, or may have a steep learning curve. The code offers a range of approaches to sonification for a variety of contexts (e.g. science education, science communication, technical data analysis, etc). To this end, STRAUSS is packaged with a number of examples of different sonification approaches, and preset configurations to support "low-barrier, high-ceiling" approach. STRAUSS has been used to produce both educational resources and analysis tools.
Abstract: 2504.01161
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:3D printing for teaching and exploration in astronomy for individuals with blindness/visual impairment: textured representations of imagery
View PDFAbstract:Astronomy, a captivating field that draws upon science, mathematics, and engineering, has traditionally relied on visual representations to convey the wonders of the cosmos. While this approach effectively engages the sighted population, the use of imagery can exclude individuals with blindness or visual impairment (B/VI). Astronomical research is incorporated into press releases, media, outreach efforts, and educational systems aimed at enhancing public interest and often skill in science, but visual materials can hamper a population with B/VI. This paper explores the potential of 3D printing as an assistive technology providing an alternative to imagery. We produced textured 3D prints of astronomical research data from the Hubble Space Telescope (HST). Useability assessment of materials is an important phase of production before integration into structured programs, and we used a multi-phased approach in our prior research to create and test appropriate textures for 3D astronomical prints. This paper describes the last step of reviewing our 3D prints through informal useability sessions with diverse individuals. The assessment indicated our 3D prints provide reliable, informative representations of astronomical data appropriate for public use especially for public information, outreach programs, and science education for individuals with BVI.
This page created: Wed Apr 9 11:38:42 ACST 2025 by jpilosso
For details on generating this page see the instructions. If there are problems with this page contact Violet.
For previous lists of abstracts of interest click Previous abstracts of interest