Abstracts of Interest
Selected by:
Adila Abdul Halim
Abstract: 2311.05916
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Title:Direct Measurement of the Spectral Structure of Cosmic-Ray Electrons+Positrons in the TeV Region with CALET on the International Space Station
Download PDFAbstract:Detailed measurements of the spectral structure of cosmic-ray electrons and positrons from 10.6 GeV to 7.5 TeV are presented from over 7 years of observations with the CALorimetric Electron Telescope (CALET) on the International Space Station. Because of the excellent energy resolution (a few percent above 10 GeV) and the outstanding e/p separation (10$^5$), CALET provides optimal performance for a detailed search of structures in the energy spectrum. The analysis uses data up to the end of 2022, and the statistics of observed electron candidates has increased more than 3 times since the last publication in 2018. By adopting an updated boosted decision tree analysis, a sufficient proton rejection power up to 7.5 TeV is achieved, with a residual proton contamination less than 10%. The observed energy spectrum becomes gradually harder in the lower energy region from around 30 GeV, consistently with AMS-02, but from 300 to 600 GeV it is considerably softer than the spectra measured by DAMPE and Fermi-LAT. At high energies, the spectrum presents a sharp break around 1 TeV, with a spectral index change from -3.15 to -3.91, and a broken power law fitting the data in the energy range from 30 GeV to 4.8 TeV better than a single power law with 6.9 sigma significance, which is compatible with the DAMPE results. The break is consistent with the expected effects of radiation loss during the propagation from distant sources (except the highest energy bin). We have fitted the spectrum with a model consistent with the positron flux measured by AMS-02 below 1 TeV and interpreted the electron + positron spectrum with possible contributions from pulsars and nearby sources. Above 4.8 TeV, a possible contribution from known nearby supernova remnants, including Vela, is addressed by an event-by-event analysis providing a higher proton-rejection power than a purely statistical analysis.
Abstract: 2311.05942
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Title:Limits on the Primordial Black Holes Dark Matter with current and future missions
Download PDFAbstract:In this proceeding we consider primordial black holes (PBHs) as a dark matter candidate. We discuss the existing limits on the fraction $f_{pbh}$ of the dark matter constituting of PBHs as a function of PBHs mass. The discussed limits cover almost all possible mass range with the currently only open window in $3\cdot 10^{16}-10^{18}$ g in which the PBHs can make up to 100% of the dark matter content of the universe. We present the estimates of the capabilities of the near-future instruments (Einstein Probe/WXT, SVOM/MXT) and discuss the potential of next-generation missions(Athena, THESEUS, eXTP) to probe this mass range. We discuss the targets most suitable for the PBH dark matter searches with these missions and the potential limiting factor of the systematics on the derived results.
Abstract: 2311.06181
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Title:Application of neural networks to synchro-Compton blazar emission models
Download PDFAbstract:Jets from supermassive black holes in the centers of active galaxies are the most powerful persistent sources of electromagnetic radiation in the Universe. To infer the physical conditions in the otherwise out-of-reach regions of extragalactic jets we usually rely on fitting of their spectral energy distribution (SED). The calculation of radiative models for the jet non-thermal emission usually relies on numerical solvers of coupled partial differential equations. In this work machine learning is used to tackle the problem of high computational complexity in order to significantly reduce the SED model evaluation time, which is needed for SED fitting with Bayesian inference methods. We compute SEDs based on the synchrotron self-Compton model for blazar emission using the radiation code ATHE${\nu}$A, and use them to train Neural Networks exploring whether these can replace the original computational expensive code. We find that a Neural Network with Gated Recurrent Unit neurons can effectively replace the ATHE${\nu}$A leptonic code for this application, while it can be efficiently coupled with MCMC and nested sampling algorithms for fitting purposes. We demonstrate this through an application to simulated data sets and with an application to observational data. We offer this tool in the community through a public repository. We present a proof-of-concept application of neural networks to blazar science. This is the first step in a list of future applications involving hadronic processes and even larger parameter spaces.
Abstract: 2311.06644
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Title:The shape of the electron and muon lateral distribution functions of extensive air showers
Download PDFAbstract:The lateral density data obtained for different secondaries of an extensive air shower (EAS) from an array of detectors are usually described by some suitable lateral density functions (LDFs). Analyzing non-vertical simulated EASs generated with the CORSIKA code, it is found that the lateral and polar density distributions of electrons and muons are asymmetric in the ground plane. It means that typical expressions for symmetric lateral density functions (SLDFs) (\emph{e.g.} the Nishimura-Kamata-Greisen function) are inadequate to reconstruct the lateral and polar dependencies of such asymmetric electron or muon densities accurately. In order to provide a more consistent LDF for non-vertical shower reconstruction in the ground plane, the paper considers the issue of the modification of the SLDF analytically. The asymmetry arising from additional attenuation and correction of the positional coordinates (radial and polar) of cascade particles causes a gap length between the center of concentric equidensity ellipses and the EAS core. A toy function is introduced as a basic LDF to describe the asymmetric lateral and polar density distributions of electrons or muons of EASs, thereby predicting the gap length parameter. Consequently, the desired LDF describing the asymmetric density distributions of electrons and muons of EASs has emerged. We compare results from detailed simulations with the predictions of the analytical parametrization. The LDF derived in this work is found to be well-suited to reconstruct EASs in the ground plane directly.
Abstract: 2311.07318
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Title:Detector development for the CRESST experiment
Download PDFAbstract:Recently low-mass dark matter direct searches have been hindered by a low energy background, drastically reducing the physics reach of the experiments. In the CRESST-III experiment, this signal is characterised by a significant increase of events below 200 eV. As the origin of this background is still unknown, it became necessary to develop new detector designs to reach a better understanding of the observations. Within the CRESST collaboration, three new different detector layouts have been developed and they are presented in this contribution.
Abstract: 2311.07481
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Title:HESS J1809-193: Gamma-Ray Emission by Cosmic Rays from Past Explosion
Download PDFAbstract:The very high energy gamma-ray source HESS J1809-193 has been detected by the LHAASO and HAWC observatory beyond 100 TeV energy. It is an interesting candidate for exploring the underlying mechanisms of gamma-ray production due to the presence of supernova remnants, pulsar and molecular clouds close to it. We have considered the injection of the energetic cosmic rays from a past explosion, whose reminiscent may be SNR G011.0-00.0, which is located within the extended gamma-ray source HESS J1809-193. We explain the multi-wavelength data from the region of HESS J1809-193 with synchrotron, inverse Compton, bremsstrahlung emission of cosmic ray electrons and secondary gamma-ray production in interactions of cosmic ray protons with the cold protons in the local molecular clouds within a time-dependent framework including the diffusion loss of cosmic rays. The observational data has been modelled with the secondary photons produced by the time-evolved cosmic ray spectrum, assuming the age of the explosion is 4500 years.
Abstract: 2311.08459
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Title:Fermi-bubble bulk and edge analysis reveals dust, cooling breaks, and cosmic-ray diffusion, facilitating a self-consistent model
Download PDFAbstract:The full, radio to $\gamma$-ray spectrum of the Fermi bubbles is shown to be consistent with standard strong-shock electron acceleration at the bubble edge, without ad-hoc energy cutoffs, if the ambient interstellar radiation is strong; the $\gamma$-ray cooling break should then have a microwave counterpart, undetected until now. Indeed, a broadband bubble-edge analysis uncovers a pronounced downstream dust component, which masked the anticipated $\sim35$ GHz spectral break, and the same overall radio softening consistent with Kraichnan diffusion previously reported in $\gamma$-rays.
Abstract: 2311.08749
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Title:Multi-wavelength variability and broadband SED modeling of BL Lac during a bright flaring period MJD 59000-59943
Download PDFAbstract:We carried a detailed temporal and spectral study of the BL\,Lac by using the long-term \emph{Fermi}-LAT and \emph{Swift}-XRT/UVOT observations, during the period MJD\,59000-59943. The daily-binned $\gamma$-ray light curve displays a maximum flux of $1.74\pm 0.09\times 10^{-5} \rm ph\,cm^{-2}\,s^{-1}$ on MJD\,59868, which is the highest daily $\gamma$-ray flux observed from BL\,Lac. The $\gamma$-ray variability is characterised by power-spectral-density (PSD), r.m.s-flux relation and flux-distribution study. We find that power-law model fits the PSD with index $\sim 1$, which suggest for long memory process at work. The observed r.m.s.-flux relation exhibits a linear trend, which indicates that the $\gamma$-ray flux distribution follows a log-normal distribution. The skewness/Anderson-Darling test and histogram-fit reject the normality of flux distribution, and instead suggest that the flux distribution is log-normal distribution. The fractional-variability amplitude shows that source is more variable in X-ray band than in optical/UV/$\gamma$-ray bands. In order to obtain an insight into the underlying physical process, we extracted broadband spectra from different time periods of the lightcurve. The broadband spectra are statistically fitted with the convolved one-zone leptonic model with different forms of the particle energy distribution. We found that spectral energy distribution during different flux states can be reproduced well with the synchrotron, synchrotron-self-Compton and external-Compton emissions from a broken power-law electron distribution, ensuring equipartition condition. A comparison between the best fit physical parameters show that the variation in different flux-states are mostly related to increase in the bulk-Lorentz factor and spectral hardening of the particle distribution.
Abstract: 2311.08898
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Title:Prospects for the Detection of the Standing Accretion Shock Instability in IceCube-Gen2
Download PDFAbstract:Core-collapse supernovae (CCSNe) are among the most energetic processes in our Universe and are crucial for the understanding of the formation and chemical composition of the Universe. The precise measurement of the neutrino light curve from CCSNe is crucial to understanding the hydrodynamics and fundamental processes that drive CCSNe. The IceCube Neutrino Observatory has mass-independent sensitivity within the Milky Way and some sensitivity to the higher mass CCSNe in the Large and Small Magellanic clouds. The envisaged large-scale extension of the IceCube detector, IceCube-Gen2, opens the possibility for new sensor design and trigger concepts that could increase the number of neutrinos detected from a CCSNe burst compared to IceCube. In this contribution, we study how wavelength-shifting technology can be used in IceCube-Gen2 to measure the fast modulations of the neutrino signal due to standing accretion shock instabilities (SASI).
Abstract: 2311.07332
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Title:Multi-wavelength observations of the lensed quasar PKS 1830$-$211 during the 2019 $γ$-ray flare
Download PDFAbstract:PKS 1830$-$211 is a $\gamma$-ray emitting, high-redshift (z $= 2.507 \pm 0.002$), lensed flat-spectrum radio quasar. During the period mid-February to mid-April 2019, this source underwent a series of strong $\gamma$-ray flares that were detected by both AGILE-GRID and Fermi-LAT, reaching a maximum $\gamma$-ray flux of $F_{\rm E>100 MeV}\approx 2.3\times10^{-5}$ ph cm$^{-2}$ s$^{-1}$. Here we report on a coordinated campaign from both on-ground (Medicina, OVRO, REM, SRT) and orbiting facilities (AGILE, Fermi, INTEGRAL, NuSTAR, Swift, Chandra), with the aim of investigating the multi-wavelength properties of PKS 1830$-$211 through nearly simultaneous observations presented here for the first time. We find a possible break in the radio spectra in different epochs above 15 GHz, and a clear maximum of the 15 GHz data approximately 110 days after the $\gamma$-ray main activity periods. The spectral energy distribution shows a very pronounced Compton dominance (> 200) which challenges the canonical one-component emission model. Therefore we propose that the cooled electrons of the first component are re-accelerated to a second component by, e.g., kink or tearing instability during the $\gamma$-ray flaring periods. We also note that PKS 1830$-$211 could be a promising candidate for future observations with both Compton satellites (e.g., e-ASTROGAM) and Cherenkov arrays (CTAO) which will help, thanks to their improved sensitivity, in extending the data availability in energy bands currently uncovered.
Abstract: 2311.07205
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Title:Testing Millisecond Pulsars as the Source of the Galactic Center Excess Gamma-Ray emission
Download PDFAbstract:The Galactic Center Excess (GCE) $\gamma$-ray emission detected with the Large Area Telescope onboard the {\it Fermi Gamma-ray Space Telescope} has been considered as a possible sign for dark matter (DM) annihilation, but other possibilities such as the millisecond pulsar (MSP) origin have also been suggested. As a spectral fitting method, constructed based on properties of $\gamma$-ray MSPs, has been developed, we apply this method to the study of the GCE emission for the purpose of probing the MSP origin for the GCE. A number of $\sim$1660 MSPs can provide a fit to the spectrum of the GCE emission upto $\sim$10\,GeV, but the higher energy part of the spectrum requires additional emission components. We further carry out a stacking analysis of 30--500\,GeV data for relatively nearby $\gamma$-ray MSPs, and the resulting flux upper limits are still lower than those of the GCE emission. We consider the single DM annihilation channel $\tau^{+}\tau^{-}$ or channel $b\bar{b}$,or the combination of the two for comparison, and find they generally can provide better fits than MSPs. Combination of MSPs plus a DM channel are also tested, and MSPs plus the DM channel $b\bar{b}$ can always provide better fits. Comparing this combination case to the pure DM channel $b\bar{b}$, the MSP contribution is found to be marginally needed.
Abstract: 2311.08693
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Title:Discovery of Diffuse Radio Source in Abell 1060
Download PDFAbstract:Non-thermal components in the intra-cluster medium (ICM) such as turbulence, magnetic field, and cosmic rays imprint the past and current energetic activities of jets from active galactic neuclie (AGN) of member galaxies as well as disturbance caused by galaxy cluster mergers. Meter- and centimeter-radio observations of synchrotron radiation allow us to diagnose the nonthermal component. Here we report on our discovery of an unidentified diffuse radio source, named the Flying Fox, near the center of the Abell 1060 field. The Flying Fox has an elongated ring-like structure and a central bar shape, but there is no obvious host galaxy. The average spectral index of the Flying Fox is -1.4, which is steeper than those for radio sources seen at meter wavelength. We discussed the possibilities of radio lobes, phoenixes, radio halos and relics, and Odd Radio Circle (ORC). In conclusion, the Flying Fox is not clearly explained by known radio sources.
Abstract: 2311.09504
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Title:Astronomy, Doughnuts, and Carrying Capacity
Download PDFAbstract:I examine the applicability of ecological concepts in discussing issues related to space environmentalism. Terms such as "ecosystem"", "carrying capacity"", and "tipping point" are either ambiguous or well defined but not applicable to orbital space and its contents; using such terms uncritically may cause more confusion than enlightenment. On the other hand, it may well be fruitful to adopt the approach of the Planetary Boundaries Framework, defining trackable metrics that capture the damage to the space environment. I argue that the key metric is simply the number of Anthropogenic Space Objects (ASOs), rather than for example their reflectivity, which is currently doubling every 1.7 years; we are heading towards degree scale separation. Overcrowding of the sky is a problem astronomers and satellite operators have in common.
This page created: Mon Nov 20 13:08:03 ACDT 2023 by Adila Abdul Halim
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