Abstracts of Interest
Selected by:
Imogen
Abstract: 2311.01834
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Title:Fermi-LAT detection of the supernova remnant G312.4-0.4 in the vicinity of 4FGL J1409.1-6121e
Download PDFAbstract:Gamma-ray emission provides constraints on the non-thermal radiation processes at play in astrophysical particle accelerators. This allows both the nature of accelerated particles and the maximum energy that they can reach to be determined. Notably, it remains an open question to what extent supernova remnants (SNRs) contribute to the sea of Galactic cosmic rays. In the Galactic plane, at around 312° of Galactic longitude, Fermi-LAT observations show an extended source (4FGL J1409.1-6121e) around five powerful pulsars. This source is described by one large disk of 0.7° radius with a high significance of 45 sigma in the 4FGL-DR3 catalog. Using 14 years of Fermi-LAT observations, we revisited this region with a detailed spectro-morphological analysis in order to disentangle its underlying structure. Three sources have been distinguished, including the supernova remnant G312.4-0.4 whose gamma-ray emission correlates well with the shell observed at radio energies. The hard spectrum detected by the LAT, extending up to 100 GeV without any sign of cut-off, is well reproduced by a purely hadronic model.
Abstract: 2311.03085
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Title:Inefficient acceleration of electrons in the shocked wind of the massive star $Θ^1$ Ori C within the Trapezium cluster
Download PDFAbstract:Shocked winds of massive stars in young stellar clusters have been proposed as possible sites in which relativistic particles are accelerated. Electrons, accelerated in such an environment, are expected to efficiently comptonize optical radiation (from massive stars) and the infra-red radiation (re-scattered by the dust within the cluster) producing GeV-TeV gamma-rays. We investigate the time dependent process of acceleration, propagation and radiation of electrons in the stellar wind of the massive star $\Theta^1$ Ori C within the Trapezium cluster. This cluster is located within the nearby Orion Nebula (M 42). We show that the gamma-ray emission expected from the Trapezium cluster is consistent with the present observations of the Orion Molecular Cloud by the Fermi-LAT telescope provided that the efficiency of energy conversion from the stellar wind to relativistic electrons is very low, i.e. $\chi < 10^{-4}$. For such low efficiencies, the gamma-ray emission from electrons accelerated in the stellar wind of $\Theta^1$ Ori C can be only barely observed by the future Cherenkov telescopes, e.g. the Cherenkov Telescope Array (CTA).
Abstract: 2311.03048
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Title:Modelling cross-correlations of ultra-high-energy cosmic rays and galaxies
Download PDFAbstract:The astrophysical engines that power ultra-high-energy cosmic rays (UHECRs) remain to date unknown. Since the propagation horizon of UHECRs is limited to the local, anisotropic Universe, the distribution of UHECR arrival directions should be anisotropic. In this paper we expand the analysis of the potential for the angular, harmonic cross-correlation between UHECRs and galaxies to detect such anisotropies. We do so by studying proton, oxygen and silicium injection models, as well as by extending the analytic treatment of the magnetic deflections. Quantitatively, we find that, while the correlations for each given multipole are generally weak, (1) the total harmonic power summed over multipoles is detectable with signal-to-noise ratios well above~5 for both the auto-correlation and the cross-correlation (once optimal weights are applied) in most cases studied here, with peaks of signal-to-noise ratio around between~8 and~10 at the highest energies; (2) if we combine the UHECR auto-correlation and the cross-correlation we are able to reach detection levels of \(3\sigma\) and above for individual multipoles at the largest scales, especially for heavy composition. In particular, we predict that the combined-analysis quadrupole could be detected already with existing data.
Abstract: 2311.02979
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Title:Modeling blazar broadband emission with convolutional neural networks -- I. Synchrotron self-Compton model
Download PDFAbstract:Modeling the multiwavelength spectral energy distributions (SEDs) of blazars provides key insights into the underlying physical processes responsible for the emission. While SED modeling with self-consistent models is computationally demanding, it is essential for a comprehensive understanding of these astrophysical objects. We introduce a novel, efficient method for modeling the SEDs of blazars by the mean of a convolutional neural network (CNN). In this paper, we trained the CNN on a leptonic model that incorporates synchrotron and inverse Compton emissions, as well as self-consistent electron cooling and pair creation-annihilation processes. The CNN is capable of reproducing the radiative signatures of blazars with high accuracy. This approach significantly reduces computational time, thereby enabling real-time fitting to multi-wavelength datasets. As a demonstration, we used the trained CNN with MultiNest to fit the broadband SEDs of Mrk 421 and 1ES 1959+650, successfully obtaining their parameter posterior distributions. This novel framework for fitting the SEDs of blazars will be further extended to incorporate more sophisticated models based on external Compton and hadronic scenarios, allowing for multi-messenger constraints in the analysis. The models will be made publicly available via a web interface, the Markarian Multiwavelength Datacenter, to facilitate self-consistent modeling of multi-messenger data from blazar observations.
Abstract: 2311.02753
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Title:On Why the 10-TeV Cosmic Ray Bump Originates in the Local Interstellar Medium
Download PDFAbstract:Recent measurements of primary and secondary CR spectra, their arrival directions, and our improved knowledge of the magnetic field geometry around the heliosphere allow us to set a bound on the distance beyond which a puzzling 10-TeV "bump" cannot originate. The sharpness of the spectral breaks associated with the bump, the abrupt change of the CR intensity across the local magnetic equator ($90^{\circ}$ pitch angle), and the similarity between the primary and secondary CR spectral patterns point to a local reacceleration of the bump particles out of the background CRs. We argue that a nearby shock may generate such a bump by increasing the rigidity of the preexisting CRs below 50 TV by a mere factor of ~1.5. Reaccelerated particles below ~0.5 TV are convected with the interstellar medium flow and do not reach the Sun, thus creating the bump. This single universal process is responsible for the observed spectra of all CR species in the rigidity range below 100 TV. We propose that one viable candidate is the system of shocks associated with Epsilon Eridani star at 3.2 pc of the Sun, which is well aligned with the direction of the local magnetic field. Other shocks, such as old supernova shells, may produce a similar effect. We provide a simple formula that reproduces the spectra of all CR species with only three parameters uniquely derived from the CR proton data. We show how our formalism predicts helium and carbon spectra and the B/C ratio.
Abstract: 2311.02320
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Title:The Hubble Diagram: Jump from Supernovae to Gamma-Ray Bursts
Download PDFAbstract:The Hubble diagram (HD) is a plot that contains luminous distance modulus presented with respect to the redshift. The distance modulus--redshift relation of the most well-known ``standard candles'', the type Ia supernovae (SN), is a crucial tool in cosmological model testing. In this work, we use the SN Ia data from the Pantheon catalogue to calibrate the Swift long gamma-ray bursts (LGRBs) as ``standard candles'' via the Amati relation. Thus, we expand the HD from supernovae to the area of the Swift LGRBs up to $z\sim8$. To improve the quality of estimation of the parameters and their errors, we implement the Monte-Carlo uncertainty propagation method. We also compare the results of estimation of the Amati parameters calibrated by the SN Ia, and by the standard $\Lambda$CDM model and find no statistically significant distinguish between them. Although the size of our LGRB sample is relatively small and the errors are high, we find this approach of expanding the cosmological distance scale perspective for future cosmological tests.
Abstract: 2311.02184
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Title:All People, One Sky: A Foundation for IAU CPS Community Engagement
Download PDFAbstract:This report first describes the status quo regarding the emerging deployment of very large groups of low-Earth-orbit satellites in the late 2010s, the concerns raised by the international astronomy community, and steps the community took to address the issue. We then describe the results of a series of four conferences held in 2020-21 that considered the impacts of large satellite constellations as it impacted a number of stakeholders, and how those outcomes resulted in the establishment of both the IAU Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS) and its Community Engagement (CE) Hub. We finish with a brief description of CE Hub's initial plans and activities, flowing from the recommendations of those conferences.
Abstract: 2311.03678
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Title:Classifications of Fermi-LAT unassociated sources in multiple machine learning methods
Download PDFAbstract:The classifications of Fermi-LAT unassociated sources are studied using multiple machine learning (ML) methods. The update data from 4FGL-DR3 are divided into high Galactic latitude (HGL, Galactic latitude $|b|>10^\circ$) and low Galactic latitude (LGL, $|b|\le10^\circ$) regions. In the HGL region, a voting ensemble of four binary ML classifiers achieves a 91$\%$ balanced accuracy. In the LGL region, an additional Bayesian-Gaussian (BG) model with three parameters is introduced to eliminate abnormal soft spectrum AGNs from the training set and ML-identified AGN candidates, a voting ensemble of four ternary ML algorithms reach an 81$\%$ balanced accuracy. And then, a catalog of Fermi-LAT all-sky unassociated sources is constructed. Our classification results show that (i) there are 1037 AGN candidates and 88 pulsar candidates with a balanced accuracy of $0.918 \pm 0.029$ in HGL region, which are consistent with those given in previous all-sky ML approaches; and (ii) there are 290 AGN-like candidates, 135 pulsar-like candidates, and 742 other-like candidates with a balanced accuracy of $0.815 \pm 0.027$ in the LGL region, which are different from those in previous all-sky ML approaches. Additionally, different training sets and class weights were tested for their impact on classifier accuracy and predicted results. The findings suggest that while different training approaches can yield similar model accuracy, the predicted numbers across different categories can vary significantly. Thus, reliable evaluation of the predicted results is deemed crucial in the ML approach for Fermi-LAT unassociated sources.
Abstract: 2311.02180
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Title:ALMA Observations of Supernova Remnant N49 in the Large Magellanic Cloud. II. Non-LTE Analysis of Shock-heated Molecular Clouds
Download PDFAbstract:We present the first compelling evidence of shock-heated molecular clouds associated with the supernova remnant (SNR) N49 in the Large Magellanic Cloud (LMC). Using $^{12}$CO($J$ = 2-1, 3-2) and $^{13}$CO($J$ = 2-1) line emission data taken with the Atacama Large Millimeter/Submillimeter Array, we derived the H$_2$ number density and kinetic temperature of eight $^{13}$CO-detected clouds using the large velocity gradient approximation at a resolution of 3.5$''$ (~0.8 pc at the LMC distance). The physical properties of the clouds are divided into two categories: three of them near the shock front show the highest temperatures of ~50 K with densities of ~500-700 cm$^{-3}$, while other clouds slightly distant from the SNR have moderate temperatures of ~20 K with densities of ~800-1300 cm$^{-3}$. The former clouds were heated by supernova shocks, but the latter were dominantly affected by the cosmic-ray heating. These findings are consistent with the efficient production of X-ray recombining plasma in N49 due to thermal conduction between the cold clouds and hot plasma. We also find that the gas pressure is roughly constant except for the three shock-engulfed clouds inside or on the SNR shell, suggesting that almost no clouds have evaporated within the short SNR age of ~4800 yr. This result is compatible with the shock-interaction model with dense and clumpy clouds inside a low-density wind bubble.
Abstract: 2311.03804
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Title:Searches for neutrino counterparts of gravitational waves from the LIGO/Virgo third observing run with KM3NeT
Download PDFAbstract:The KM3NeT neutrino telescope is currently being deployed at two different sites in the Mediterranean Sea. First searches for astrophysical neutrinos have been performed using data taken with the partial detector configuration already in operation. The paper presents the results of two independent searches for neutrinos from compact binary mergers detected during the third observing run of the LIGO and Virgo gravitational wave interferometers. The first search looks for a global increase in the detector counting rates that could be associated with inverse beta decay events generated by MeV-scale electron anti-neutrinos. The second one focuses on upgoing track-like events mainly induced by muon (anti-)neutrinos in the GeV--TeV energy range. Both searches yield no significant excess for the sources in the gravitational wave catalogs. For each source, upper limits on the neutrino flux and on the total energy emitted in neutrinos in the respective energy ranges have been set. Stacking analyses of binary black hole mergers and neutron star-black hole mergers have also been performed to constrain the characteristic neutrino emission from these categories.
Abstract: 2311.03577
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Title:The Potential of Water-Cherenkov Air Shower Arrays for detecting transient sources of high-energy astrophysical neutrinos
Download PDFAbstract:In this study, we highlight the capacity of current and forthcoming air shower arrays utilizing water-Cherenkov stations to detect neutrino events spanning energies from $10\,$GeV to $100\,$TeV. This detection approach leverages individual stations equipped with both bottom and top photosensors, making use of features of the signal time trace and machine learning techniques. Our findings demonstrate the competitiveness of this method compared to established and future neutrino-detection experiments, including IceCube and the upcoming Hyper-Kamiokande experiment.
Abstract: 2311.04851
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Title:The High Energy X-ray Probe (HEX-P): Galactic PeVatrons, star clusters, superbubbles, microquasar jets, and gamma-ray binaries
Download PDFAbstract:HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10" FWHM) and broad spectral coverage (0.2-80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. With the recent discoveries of over 40 ultra-high-energy gamma-ray sources (detected above 100 TeV) and neutrino emission in the Galactic Plane, we have entered a new era of multi-messenger astrophysics facing the exciting reality of Galactic PeVatrons. In the next decade, as more Galactic PeVatrons and TeV gamma-ray sources are expected to be discovered, the identification of their acceleration and emission mechanisms will be the most pressing issue in both particle and high-energy astrophysics. In this paper, along with its companion papers (Reynolds et al. 2023, Mori et al. 2023), we will present that HEX-P is uniquely suited to address important problems in various cosmic-ray accelerators, including Galactic PeVatrons, through investigating synchrotron X-ray emission of TeV-PeV electrons produced by both leptonic and hadronic processes.
Abstract: 2311.04273
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Title:Constraining the astrophysical origin of intergalactic magnetic fields
Download PDFAbstract:High-energy photons can produce electron-positron pairs upon interacting with the extragalactic background light (EBL). These pairs will in turn be deflected by the intergalactic magnetic field (IGMF), before possibly up-scattering photons of the cosmic microwave background (CMB), thereby initiating an electromagnetic cascade. The non-observation of an excess of GeV photons and an extended halo around individual blazars due to this electromagnetic cascade can be used to constrain the properties of the IGMF. In this work, we use publicly available data of 1ES 0229+200 by Fermi LAT and H.E.S.S. to constrain cosmological MHD simulations of various magnetogenesis scenarios, and find that all models without a strong space-filling primordial component or over-optimistic dynamo amplifications can be excluded at 95% confidence level. In fact, we find that the fraction of space filled by a strong IGMF has to be at least $f\gtrsim 0.67$, thus excluding most astrophysical production scenarios. Moreover, we set the lower limits $B_0>5.1\times 10^{-15}$ G ($B_0>1.0\times 10^{-14}$ G) of a space-filling primordial IGMF for a blazar activity time of $\Delta t = 10^4$ yr ($\Delta t = 10^7$ yr).
Abstract: 2311.04983
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Title:Two Watts is All You Need: Enabling In-Detector Real-Time Machine Learning for Neutrino Telescopes Via Edge Computing
Download PDFAbstract:The use of machine learning techniques has significantly increased the physics discovery potential of neutrino telescopes. In the upcoming years, we are expecting upgrade of currently existing detectors and new telescopes with novel experimental hardware, yielding more statistics as well as more complicated data signals. This calls out for an upgrade on the software side needed to handle this more complex data in a more efficient way. Specifically, we seek low power and fast software methods to achieve real-time signal processing, where current machine learning methods are too expensive to be deployed in the resource-constrained regions where these experiments are located. We present the first attempt at and a proof-of-concept for enabling machine learning methods to be deployed in-detector for water/ice neutrino telescopes via quantization and deployment on Google Edge Tensor Processing Units (TPUs). We design a recursive neural network with a residual convolutional embedding, and adapt a quantization process to deploy the algorithm on a Google Edge TPU. This algorithm can achieve similar reconstruction accuracy compared with traditional GPU-based machine learning solutions while requiring the same amount of power compared with CPU-based regression solutions, combining the high accuracy and low power advantages and enabling real-time in-detector machine learning in even the most power-restricted environments.
This page created: Mon Nov 13 15:05:35 ACDT 2023 by Imogen
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