Abstracts of Interest
Selected by:
Adila Abdul Halim
Abstract: 2302.14137
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Title:Detailed Analysis of the TeV γ-Ray Sources 3HWC J1928+178, 3HWC J1930+188, and the New Source HAWC J1932+192
Download PDFAbstract: The latest High Altitude Water Cherenkov (HAWC) point-like source catalog up to 56 TeV reported the detection of two sources in the region of the Galactic plane at galactic longitude 52°< l < 55°, 3HWC J1930+188 and 3HWC J1928+178. The first one is associated with a known TeV source, the supernova remnant SNR G054.1+00.3. It was discovered by one of the currently operating Imaging Atmospheric Cherenkov Telescope (IACT), the Very Energetic Radiation Imaging Telescope Array System (VERITAS), detected by the High Energy Stereoscopic System (H.E.S.S.), and identified as a composite SNR. However, the source 3HWC J1928+178, discovered by HAWC and coincident with the pulsar PSR J1928+1746, was not detected by any IACT despite their long exposure on the region, until a recent new analysis of H.E.S.S. data was able to confirm it. Moreover, no X-ray counterpart has been detected from this pulsar. We present a multicomponent fit of this region using the latest HAWC data. This reveals an additional new source, HAWC J1932+192, which is potentially associated with the pulsar PSR J1932+1916, whose gamma-ray emission could come from the acceleration of particles in its pulsar wind nebula. In the case of 3HWC J1928+178, several possible explanations are explored, in a attempt to unveil the origins of the very-high-energy gamma-ray emission.
Abstract: 2303.00183
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Title:Pulsars as candidates of LHAASO sources J2226+6057, J1908+0621 and J1825-1326: The leptonic origin
Download PDFAbstract: Recently, from 12 $\gamma$-ray Galactic sources, the LHAASO has detected ultrahigh-energy photons up to 1.4PeV. The $\gamma$-ray spectra of the sources J2226+6057, J1908+0621, J1825-1326 and the suggested origin pulsars near the sources have been published. In our previous work, we studied the hadronic $\gamma$-ray spectra of the sources J2226+6057, J1908+0621, J1825-1326 in terms of the Hertzian dipole model of pulsar. In this paper, we investigate the possibility of the leptonic origin of the $\gamma$-ray. We use the Hertzian dipole model to describe the pulsars around the sources. The electrons around the pulsars can be accelerated to PeV by the electromagnetic fields of pulsars. Under the assumption that the initial electrons are uniform distributed in a spherical shell between $10^{7}$ to $10^{9}$m around the pulsar, we obtain the energy distribution of electrons. The leptonic $\gamma$-ray spectra can be calculated through inverse Compton scattering processes. It finds that the leptonic $\gamma$-ray spectra can fit the observations of LHAASO very well.
Abstract: 2303.00898
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Title:Synchrotron Radiation Dominates the Extremely Bright GRB 221009A
Download PDFAbstract: The brightest Gamma-ray burst, GRB 221009A, has spurred numerous theoretical investigations, with particular attention paid to the origins of ultra-high energy TeV photons during the prompt phase. However, analyzing the mechanism of radiation of photons in the $\sim$MeV range has been difficult because the high flux causes pile-up and saturation effects in most GRB detectors. In this letter, we present systematic modeling of the time-resolved spectra of the GRB using unsaturated data obtained from Fermi/GBM (precursor) and SATech-01/GECAM-C (main emission and flare). Our approach incorporates the synchrotron radiation model, which assumes an expanding emission region with relativistic speed and a global magnetic field that decays with radius, and successfully fits such a model to the observational data. Our results indicate that the spectra of the burst are fully in accordance with a synchrotron origin from relativistic electrons accelerated at a large emission radius. The lack of thermal emission in the prompt emission spectra supports a Poynting-flux-dominated jet composition.
Abstract: 2303.02172
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Title:Observable signatures of stellar-mass black holes in active galactic nuclei
Download PDFAbstract: Stellar-mass black holes (BHs) are predicted to be embedded in the disks of active galactic nuclei (AGN) due to gravitational drag and in-situ star formation. However, clear evidence for AGN disk-embedded BHs is currently lacking. Here, as possible electromagnetic signatures of these BHs, we investigate breakout emission from shocks emerging around Blandford-Znajek jets launched from accreting BHs in AGN disks. We assume that the majority of the highly super-Eddington flow reaches the BH, produces a strong jet, and the jet produces feedback that shuts off accretion and thus leads to episodic flaring. While these assumptions are highly uncertain at present, they predict a breakout emission characterized by luminous thermal emission in the X-ray bands, and bright, broadband non-thermal emission from the infrared to the gamma-ray bands. The flare duration depends on the BH's distance $r$ from the central supermassive BH, varying between $10^3-10^6$ s for $r \sim 0.01-1$ pc. This emission can be discovered by current and future infrared, optical, and X-ray wide-field surveys and monitoring campaigns of nearby AGNs.
Abstract: 2303.02248
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Title:Successful Kinetic Impact into an Asteroid for Planetary Defense
Download PDFAbstract: While no known asteroid poses a threat to Earth for at least the next century, the catalog of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid. A test of kinetic impact technology was identified as the highest priority space mission related to asteroid mitigation. NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by DART's impact. While past missions have utilized impactors to investigate the properties of small bodies those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in Dimorphos's orbit demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary.
Abstract: 2303.02792
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Title:Pythia 8 as hadronic interaction model in air shower simulations
Download PDFAbstract: Hadronic interaction models are a core ingredient of simulations of extensive air showers and pose the major source of uncertainties of predictions of air shower observables. Recently, Pythia~8, a hadronic interaction model popular in accelerator-based high-energy physics, became usable in air shower simulations as well. We have integrated Pythia~8 with its new capabilities into the air shower simulation framework CORSIKA~8. First results show significantly shallower shower development, which we attribute to higher cross-section predictions by the new simplified nuclear model of Pythia.
Abstract: 2303.03021
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Title:Probing the origin of cosmic rays in Cygnus Cocoon using ultrahigh-energy gamma-ray and neutrino observations
Download PDFAbstract: Recent ultrahigh energy gamma-ray observations by the HAWC up to 100 TeV and LHAASO observatories up to 1.4 PeV energies from the direction of Fermi-LAT 4FGL source 4FGL J2028.6+4110e (Cygnus Cocoon), are indicative of a hadronic origin over a leptonic process for their creation. The IceCube Neutrino Observatory has reported IceCube-201120A, a neutrino event coming from the same direction, suggesting that the Cygnus Cocoon may correspond to one of the most plausible sources of high-energy cosmic rays. The apparent relationship of the neutrino event with the observed ultra high energy gamma-rays from Cygnus Cocoon is investigated in this work to study if it can be explained consistently in hadronic interactions of accelerated cosmic rays with ambient matter. Our findings reveal that leptonic mechanisms, together with pure hadronic mechanisms, make a considerable contribution to the understanding of the total electromagnetic spectrum as well as the observed neutrino event. The estimate of expected muon neutrino events from the Cygnus cocoon agrees with the one muon neutrino event detected so far in IceCube multi-year observations. Thus, our results are indicative of the potential of the Cygnus Cocoon to be a galactic cosmic ray source capable of accelerating at least up to PeV energies.
Abstract: 2303.03039
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Title:Gamma-ray flares and broadband spectral study of PKS 0402-362
Download PDFAbstract: We study the long-term behavior of the bright gamma-ray blazar PKS 0402-362. We collected approximately 13 years of Fermi-LAT data between Aug 2008 to Jan 2021 and identified three bright $\gamma$-ray activity epochs. The second was found to be the brightest epoch ever seen in this source. We observed most of the $\gamma$-ray flare peaks to be asymmetric in profile suggesting a slow cooling time of particles or the varying Doppler factor as the main cause of these flares. The $\gamma$-ray spectrum is fitted with PL and LP spectral models, and in both cases, the spectral index is very steep. The $\gamma$-ray spectrum does not extend beyond 10 GeV energy suggesting the emission is produced within the BLR. The absence of time lags between optical-IR and $\gamma$-ray suggest one zone emission model. Using the above information, we have modeled the broadband SED with a simple one-zone emission model using the publicly available code `GAMERA'. The particle distribution index is found to be the same as expected in diffusive shock acceleration suggesting it as the main mechanism of particle acceleration to very high energy up to 4 - 6 GeV. Throughout the various flux phases, we noticed that the optical emission is dominated by the thermal disk, suggesting it to be a good source to examine the disk-jet coupling. We postulate that the observed broadband flares could be linked with perturbation produced in the disk, which propagates to the jet and interacts with the standing shock. However, a more detailed examination is required.
Abstract: 2303.03298
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Title:Gamma-ray emission from the Seyfert galaxy NGC 4151 and multimessenger implications for ultra-fast outflows
Download PDFAbstract: The enhanced activity typical of the core of Seyfert galaxies can drive powerful winds where high-energy phenomena can occur. In spite of their high power content, the number of such non-jetted active galactic nuclei detected in gamma-ray is very limited. In this Letter, we report the detection of a gamma-ray flux from NGC 4151, a Seyfert galaxy located at about 15.8 Mpc. The source is known for hosting ultra-fast outflows (UFOs) in its innermost core through X-ray spectroscopic observations, thereby becoming the first UFO host ever detected in gamma rays. UFOs are mildly relativistic, wide opening angle winds detected in the innermost parsecs of active galaxies where strong shocks can develop. We interpret the gamma-ray flux as a result of diffusive shock acceleration at the wind termination shock of the UFO and inelastic hadronic collisions in its environment. Interestingly, NGC 4151 is also spatially coincident with a weak excess of neutrino events identified by the IceCube neutrino observatory. We discuss the contribution of the UFO to such a neutrino excess.
Abstract: 2303.03316
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Title:Constraining High-Energy Neutrino Emission from Supernovae with IceCube
Download PDFAbstract: Core-collapse supernovae are a promising potential high-energy neutrino source class. We test for correlation between seven years of IceCube neutrino data and a catalog containing more than 1000 core-collapse supernovae of types IIn and IIP and a sample of stripped-envelope supernovae. We search both for neutrino emission from individual supernovae, and for combined emission from the whole supernova sample through a stacking analysis. No significant spatial or temporal correlation of neutrinos with the cataloged supernovae was found. The overall deviation of all tested scenarios from the background expectation yields a p-value of 93% which is fully compatible with background. The derived upper limits on the total energy emitted in neutrinos are $1.7\times 10^{48}$ erg for stripped-envelope supernovae, $2.8\times 10^{48}$ erg for type IIP, and $1.3\times 10^{49}$ erg for type IIn SNe, the latter disfavouring models with optimistic assumptions for neutrino production in interacting supernovae. We conclude that strippe-envelope supernovae and supernovae of type IIn do not contribute more than $14.6\%$ and $33.9\%$ respectively to the diffuse neutrino flux in the energy range of about $10^3-10^5$ GeV, assuming that the neutrino energy spectrum follows a power-law with an index of $-2.5$. Under the same assumption, we can only constrain the contribution of type IIP SNe to no more than $59.9\%$. Thus core-collapse supernovae of types IIn and stripped-envelope supernovae can both be ruled out as the dominant source of the diffuse neutrino flux under the given assumptions.
Abstract: 2303.03407
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Title:Identification of tidal features in deep optical galaxy images with Convolutional Neural Networks
Download PDFAbstract: Interactions between galaxies leave distinguishable imprints in the form of tidal features which hold important clues about their mass assembly. Unfortunately, these structures are difficult to detect because they are low surface brightness features so deep observations are needed. Upcoming surveys promise several orders of magnitude increase in depth and sky coverage, for which automated methods for tidal feature detection will become mandatory. We test the ability of a convolutional neural network to reproduce human visual classifications for tidal detections. We use as training $\sim$6000 simulated images classified by professional astronomers. The mock Hyper Suprime Cam Subaru (HSC) images include variations with redshift, projection angle and surface brightness ($\mu_{lim}$ =26-35 mag arcsec$^{-2}$). We obtain satisfactory results with accuracy, precision and recall values of Acc=0.84, P=0.72 and R=0.85, respectively, for the test sample. While the accuracy and precision values are roughly constant for all surface brightness, the recall (completeness) is significantly affected by image depth. The recovery rate shows strong dependence on the type of tidal features: we recover all the images showing shell features and 87% of the tidal streams; these fractions are below 75% for mergers, tidal tails and bridges. When applied to real HSC images, the performance of the model worsens significantly. We speculate that this is due to the lack of realism of the simulations and take it as a warning on applying deep learning models to different data domains without prior testing on the actual data.
Abstract: 2303.03416
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Title:Dark Matter Annihilation Inside Large Volume Neutrino Detectors
Download PDFAbstract: New stable particles are generic predictions of theories beyond the Standard Model and can manifest as relics that interact strongly with visible matter and make up a small fraction of the total dark matter abundance. Such particles represent an interesting physics target since they can evade existing bounds from direct detection due to their rapid thermalization in high-density environments. In this work we point out that their annihilation to visible matter inside large-volume neutrino telescopes can provide a new way to constrain or discover such particles. The signal is the most pronounced for relic masses in the GeV range, and can be efficiently constrained by existing Super-Kamiokande searches for di-nucleon annihilation. We also provide an explicit realization of this scenario in the form of secluded dark matter coupled to a dark photon, and we show that the present method implies novel and stringent bounds on the model that are complementary to direct constraints from beam dumps, colliders, and direct detection experiments.
This page created: Thu Mar 9 01:27:04 ACDT 2023 by Adila Abdul Halim
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