Abstracts of Interest
Selected by:
Adnaan Thakur
Abstract: 2411.02270
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Title:Connecting dust and outflows in AGN: the intriguing case of NGC 6860
View PDF HTML (experimental)Abstract:Cosmic dust plays a crucial role in the evolution of galaxies, significantly influencing star formation and the interstellar medium. However, in active galactic nuclei (AGN), the role and origin of dust remain poorly understood. High-resolution X-ray spectroscopy is a powerful tool for probing the properties of dust in AGN. NGC 6860, an X-ray bright type-1 quasar, is an ideal target for investigating the connection between dust and winds in AGN. It exhibits reddening and X-ray absorption by both dust and winds. By modeling high-resolution X-ray spectra from XMM-Newton and Chandra observations, we determine the properties of dust and outflows in this AGN. Our analysis finds four photoionized components, outflowing with velocities of 50-300 km/s. The first two are relatively highly ionized with logxi = 3.4 and logxi = 2.9. The results of our photoionization modeling suggest that these two components are thermally unstable. The third component is ionized, with logxi = 2.3 and is located further away from the central black hole. The fourth component is less ionized, and is possibly located in the host galaxy. The application of dust models enables us to probe the abundance and location of the dust in NGC 6860. Our findings suggest that dust absorption and reddening originates from the extended narrow-line region and its host galaxy.
Abstract: 2502.04626
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Title:The Gas-to-Dust Ratio Investigation in the Massive Star-Forming region M17
View PDF HTML (experimental)Abstract:M17 is a well-known massive star-forming region, and its Gas-to-Dust Ratio (GDR) may vary significantly compared to the other areas. The mass of gas can be traced by the ${\rm CO}$ emission observed in the \emph{Milky Way Imaging Scroll Painting (MWISP) project}. The dust mass can be traced by analyzing the interstellar extinction magnitude obtained from the \emph{United Kingdom Infrared Telescope (UKIRT)}. We computed the ratio ${W({\rm CO})/A_V}$: for ${A_V \le }$ 10 mag, ${{ W(^{12}{\rm CO})/ A_V}= (6.27 \pm 0.19)}$ ${\mathrm{{K \cdot km/s} \cdot mag^{-1}}}$ and ${{ W(^{13}{\rm CO})/ A_V} = (0.75 \pm 0.72)}$ ${ \mathrm{{K \cdot km/s} \cdot mag^{-1}}}$; whereas for ${{A_V} \ge 10}$ mag, ${{ W(^{12}{\rm CO})/ A_V} = (15.8 \pm 0.06) }$ ${\mathrm{{K \cdot km/s} \cdot mag^{-1}}}$ and ${{ W(^{13}{\rm CO})/ A_V} = (3.11 \pm 0.25)}$ ${ \mathrm{{K \cdot km/s} \cdot mag^{-1}}}$. Then, we converted the ${W({\rm CO})/A_V}$ into ${N(\rm H)/A_V}$. Using the WD01 model, we derived the GDR: for ${A_V \le }$ 10 mag, the GDRs were ${118 \pm 9}$ for ${^{12}{\rm CO}}$ and ${83 \pm 62}$ for ${^{13}{\rm CO}}$, comparable to those of the Milky Way; however, for ${A_V \ge }$ 10 mag, the GDRs increased significantly to ${296 \pm 3}$ for ${^{12}{\rm CO}}$ and ${387 \pm 40}$ for ${^{13}{\rm CO}}$, approximately three times higher than those of the Milky Way. In the discussion, we compared the results of this work with previous studies and provided a detailed discussion of the influence of massive stars and other factors on GDR.
Abstract: 2502.04513
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Title:A search for the anomalous events detected by ANITA using the Pierre Auger Observatory
View PDF HTML (experimental)Abstract:A dedicated search for upward-going air showers at zenith angles exceeding $110^\circ$ and energies $E>0.1$ EeV has been performed using the Fluorescence Detector of the Pierre Auger Observatory. The search is motivated by two "anomalous" radio pulses observed by the ANITA flights I and III which appear inconsistent with the Standard Model of particle physics. Using simulations of both regular cosmic ray showers and upward-going events, a selection procedure has been defined to separate potential upward-going candidate events and the corresponding exposure has been calculated in the energy range [0.1-33] EeV. One event has been found in the search period between 1 Jan 2004 and 31 Dec 2018, consistent with an expected background of $0.27 \pm 0.12$ events from mis-reconstructed cosmic ray showers. This translates to an upper bound on the integral flux of $(7.2 \pm 0.2) \times 10^{-21}$ cm$^{-2}$ sr$^{-1}$ y$^{-1}$ and $(3.6 \pm 0.2) \times 10^{-20}$ cm$^{-2}$ sr$^{-1}$ y$^{-1}$ for an $E^{-1}$ and $E^{-2}$ spectrum, respectively. An upward-going flux of showers normalized to the ANITA observations is shown to predict over 34 events for an $E^{-3}$ spectrum and over 8.1 events for a conservative $E^{-5}$ spectrum, in strong disagreement with the interpretation of the anomalous events as upward-going showers.
Abstract: 2502.04508
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Title:Clash of the Titans: ultra-high energy KM3NeT event versus IceCube data
View PDF HTML (experimental)Abstract:KM3NET has reported the detection of a remarkably high-energy through-going muon. Lighting up about a third of the detector, this muon could originate from a neutrino exceeding 10 PeV energy. The crucial question we need to answer is where this event comes from and what its source is. Intriguingly, IceCube has been running with a much larger effective area for a much longer time, and yet it has not reported neutrinos above 10 PeV. We quantify the tension between the KM3NeT event with the absence of similar high-energy events in IceCube. Through a detailed analysis, we determine the most likely neutrino energy to be in the range 23-2400 PeV. We find a $3.8\sigma$ tension between the two experiments assuming the neutrino to be from the diffuse isotropic neutrino background. Alternatively, assuming the event is of cosmogenic origin and considering three representative models, this tension still falls within 3.2-3.9$\sigma$. The least disfavored scenario is a steady or transient point source, though still leading to $2.9\sigma$ and $2.1\sigma$ tensions, respectively. The lack of observation of high-energy events in IceCube seriously challenges the explanation of this event coming from any known diffuse fluxes. Our results indicate the KM3NeT event is likely the first observation of a new astrophysical source.
Abstract: 2409.09109
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Title:Neutrino flux sensitivity to the next galactic core-collapse supernova in COSINUS
View PDF HTML (experimental)Abstract:While neutrinos are often treated as a background for many dark matter experiments, these particles offer a new avenue for physics: the detection of core-collapse supernovae. Supernovae are extremely energetic, violent and complex events that mark the death of massive stars. During their collapse stars emit a large number of neutrinos in a short burst. These neutrinos carry 99\% of the emitted energy which makes their detection fundamental in understanding supernovae. This paper illustrates how COSINUS (Cryogenic Observatory for SIgnatures seen in Next-generation Underground Searches), a sodium iodide (NaI) based dark matter search, will be sensitive to the next galactic core-collapse supernova. The experiment is composed of two separate detectors which will be sensitive to far and nearby supernovae. The inner core of the experiment will consist of NaI crystals operating as scintillating calorimeters, mainly sensitive to the Coherent Elastic Scattering of Neutrinos (CE$\nu$NS) against the Na and I nuclei. The low mass of the cryogenic detectors gives the experiment a sensitivity to close supernovae below 1kpc without pileup. They will see up to hundreds of CE$\nu$NS events from a supernova happening at 200pc. The crystals reside at the center of a cylindrical 230T water tank, instrumented with 30 photomultipliers. This tank acts as a passive and active shield able to detect the Cherenkov radiation induced by impinging charged particles from ambient and cosmogenic radioactivity. A supernova near the Milky Way Center (10kpc) will be easily detected inducing $\sim$60 measurable events, and the water tank will have a 3$\sigma$ sensitivity to supernovae up to 22kpc, seeing $\sim$10 events. This paper shows how, even without dedicated optimization, modern dark matter experiments will also play their part in the multi-messenger effort to detect the next galactic core-collapse supernova.
Abstract: 2406.06319
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Title:Measurement of the Depth of Maximum of Air-Shower Profiles with energies between $\mathbf{10^{18.5}}$ and $\mathbf{10^{20}}$ eV using the Surface Detector of the Pierre Auger Observatory and Deep Learning
View PDF HTML (experimental)Abstract:We report an investigation of the mass composition of cosmic rays with energies from 3 to 100 EeV (1 EeV=$10^{18}$ eV) using the distributions of the depth of shower maximum $X_\mathrm{max}$. The analysis relies on ${\sim}50,000$ events recorded by the Surface Detector of the Pierre Auger Observatory and a deep-learning-based reconstruction algorithm. Above energies of 5 EeV, the data set offers a 10-fold increase in statistics with respect to fluorescence measurements at the Observatory. After cross-calibration using the Fluorescence Detector, this enables the first measurement of the evolution of the mean and the standard deviation of the $X_\mathrm{max}$ distributions up to 100 EeV. Our findings are threefold:
(1.) The evolution of the mean logarithmic mass towards a heavier composition with increasing energy can be confirmed and is extended to 100 EeV.
(2.) The evolution of the fluctuations of $X_\mathrm{max}$ towards a heavier and purer composition with increasing energy can be confirmed with high statistics. We report a rather heavy composition and small fluctuations in $X_\mathrm{max}$ at the highest energies.
(3.) We find indications for a characteristic structure beyond a constant change in the mean logarithmic mass, featuring three breaks that are observed in proximity to the ankle, instep, and suppression features in the energy spectrum.
Abstract: 2501.07283
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Title:Theoretical Modelling of Gamma-Ray Burst 090510
View PDF HTML (experimental)Abstract:Gamma-ray bursts detected at high energies provide valuable insights into the emission mechanisms behind these still puzzling enigmatic events. In this study, we focus on GRB 090510, which is an unusual short GRB exhibiting plateau emission observed by the Fermi-LAT. Using the general relativistic magnetohydrodynamic code (HARM), we aim to infer the key properties of this GRB, such as the jet opening angle, the energetics, the Lorentz Gamma factor, the jet structure and its variability, and the progenitor parameters of the compact binary system. We explored both the 2D and 3D models and estimated the variability timescales. Our findings show that the predicted jet opening angle is within $88\%$ of the observed upper limit from observations, and the energetics are in general agreement with observed values when accounting for the evolution of jet opening angle with redshift. This work establishes the foundation for ongoing exploration, which will further align the theoretical model simulations with observational data.
Abstract: 2502.03995
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Title:Modeling fast X-ray variability around an accreting black hole
View PDF HTML (experimental)Abstract:X-ray inter-band time lags are observed during the outbursts of black hole X-ray binaries (BHXRBs). Timing analysis of fast variability in low Fourier frequency bands shows that high-energy photons lag behind low-energy photons, a phenomenon referred to as hard lag. Conversely, in high Fourier frequency bands, low-energy photons lag behind high-energy photons, known as soft lag. This frequency-dependent lag spectrum suggests that the lags arise from different physical processes. Notably, a trend has been observed wherein the lags shift towards shorter timescales during the rising hard state, indicating an evolution in the inner accretion flow. In this study, we simulate these inter-band lags by conducting Monte Carlo simulations of the rapid variability within the geometry of a jet base corona. We consider both inward propagating accretion rate fluctuations and reverberation (light crossing) delays in our simulations. We successfully reproduce both low-frequency hard lags and high-frequency soft lags in a self-consistent manner. We replicate the observed evolution of the frequency-dependent lag spectra by varying the geometrical scale of the corona and the viscous frequency of the disc. Finally, we discuss the potential of a spherical corona and emphasize that polarization observations from the Imaging X-ray Polarimetry Explorer (IXPE) and the enhanced X-ray Timing and Polarimetry mission (eXTP) will be crucial for distinguishing the corona's geometry in future studies.
Abstract: 2502.03913
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Title:ALMA observations of massive clouds in the central molecular zone: slim filaments tracing parsec-scale shocks
View PDF HTML (experimental)Abstract:The central molecular zone (CMZ) of our Galaxy exhibits widespread emission from SiO and various complex organic molecules (COMs), yet the exact origin of such emission is uncertain. Here we report the discovery of a unique class of long ($>$0.5 pc) and narrow ($<$0.03 pc) filaments in the emission of SiO 5$-$4 and eight additional molecular lines, including several COMs, in our ALMA 1.3 mm spectral line observations toward two massive molecular clouds in the CMZ, which we name as slim filaments. However, these filaments are not detected in the 1.3 mm continuum at the 5$\sigma$ level. Their line-of-sight velocities are coherent and inconsistent with being outflows. The column densities and relative abundances of the detected molecules are statistically similar to those in protostellar outflows but different from those in dense cores within the same clouds. Turbulent pressure in these filaments dominates over self gravity and leads to hydrostatic inequilibrium, indicating that they are a different class of objects than the dense gas filaments in dynamical equilibrium ubiquitously found in nearby molecular clouds. We argue that these newly detected slim filaments are associated with parsec-scale shocks, likely arising from dynamic interactions between shock waves and molecular clouds. The dissipation of the slim filaments may replenish SiO and COMs in the interstellar medium and lead to their widespread emission in the CMZ.
Abstract: 2502.03794
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Title:The GeV $γ$-ray emission from the composite SNR CTB 87
View PDF HTML (experimental)Abstract:We report the GeV $\gamma$-ray emission around the composite supernova remnant (SNR) CTB 87 with more than 16 yrs PASS 8 data recorded by the Fermi Large Area Telescope. Two separate point sources with the different GeV spectra are identified in this region: one has a soft $\gamma$-ray spectrum, likely due to interactions between the SNR shock and molecular clouds (MCs); and another source with a hard GeV $\gamma$-ray spectrum aligns with the TeV spectrum of VER J2016+371, suggesting it as the GeV counterpart. Considering the observations of CTB 87 in the radio and X-ray bands, VER J2016+371 is proposed to originate from the pulsar wind nebula (PWN) associated with PSR J2016+3711. A leptonic model with a broken power-law electron distribution could explain the multi-wavelength data of VER J2016+371, with fitted parameters matching typical $\gamma$-ray PWNe. Deeper searching for the SNR shock of CTB 87 in other bands and the future TeV observations by LHAASO and CTA are crucial to reveal the nature of CTB 87.
Abstract: 2502.03453
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Title:Gamma Ray Burst GRB 221009A: two distinct hints at once at new physics
View PDF HTML (experimental)Abstract:The brightest ever observed gamma ray burst GRB 221009A at redshift $z = 0.151$ was detected on October 9, 2022. Its highest energy photons have been recorded by the LHAASO collaboration up to above $12 \, \rm TeV$, and one of the at ${\cal E} = 251 \, \rm TeV$ by the Carpet-2 collaboration. Very recently, the Carpet-3 collaboration has completed the data analysis, showing that the evidence of the $251 \, {\rm TeV}$ photon is quite robust. Still, according to conventional physics photons with ${\cal E} \gtrsim 10 \, \rm TeV$ cannot be observed owing to the absorption by the extragalactic background light (EBL). Previously it has been demonstrated that an axion-like particle (ALP) with allowed parameters ensures the observability of the LHAASO photons. Here we show that the Lorentz invariance violation allows the ${\cal E} = 251 \, {\rm TeV}$ (now around 300 TeV) Carpet photon to be detected.
Abstract: 2502.03138
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Title:Detection of the Extended $γ$-ray Emission around TeV source 1LHAASO J0249+6022 with Fermi-LAT
View PDF HTML (experimental)Abstract:1LHAASO J0249+6022 is an extended very-high-energy gamma-ray source discovered by the Large High-Altitude Air Shower Observatory. Based on nearly 16.1 years of data from the Fermi Large Area Telescope, we report the probable gamma-ray emission from 1LHAASO J0249+6022 in the 0.03-1 TeV energy range. The results show that its gamma-ray spectrum can be well fitted by a single power law with an index of 1.54 $\pm$ 0.17, and integral photon flux is (4.28 $\pm$ 1.03) $\times$ 10$^{-11}$ photons cm$^{-2}$ s$^{-1}$. We also considered theoretically whether the non-thermal emission could originate from a pulsar wind nebula (PWN) scenario. Assuming that the particles injected into the nebula have a power-law distribution, the resulting spectrum from the inverse Compton scattering is consistent with the detected GeV and TeV gamma-ray fluxes. Our study shows that the PWN scenario is reasonable for 1LHAASO J0249+6022.
Abstract: 2410.11884
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Title:Impact of chaotic magnetic field on physical properties of rotating neutron stars
View PDF HTML (experimental)Abstract:Observations reveal that magnetic fields on neutron stars (NSs) are in the range of $10^{8-15}$ G. Apart from being celestial bodies, NSs are normally rotating. In this work, we study the impact of a chaotic magnetic field on the physical properties of the rotating NSs. i.e. mass, radius, Kepler frequency, and moment of inertia. We employ an equation of state of NSs with the nuclei in the crust and hyperons in the core. Hartle-Thorne formalism as an approximation of the rotating NSs is utilized. For the magnetic field ansatz, we use the one coupled to the energy density. We find that the magnetic field can decrease radius of NS. NSs formed with higher central magnetic field strength and higher-order surface magnetic field strength exhibit a lower maximum mass compared to those formed with lower central magnetic field strength and lower-order surface magnetic field strength. In contrast, the increment of the magnetic field can increase the compactness and deformation of rotating NSs. As the magnetic field strength increases, the mass-radius curve begins to resemble that of quark stars. The presence of chaotic magnetic field enhances the Kepler frequency of rotating NSs, whereas it simultaneously tend to decreases their moment of inertia. The moment of inertia of rotating NSs with chaotic magnetic fields at $\Omega=1000$ s$^{-1}$ and $\Omega=3000$ s$^{-1}$ is consistent with the constraint range obtained from pulsar mass measurements, gravitational wave event data, and X-ray observations of emissions from hotspots on NS surfaces measured by NICER.
Abstract: 2502.02425
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Title:Carpet-3 detection of a photon-like air shower with estimated primary energy above 100 TeV in a spatial and temporal coincidence with GRB 221009A
View PDF HTML (experimental)Abstract:The brightest cosmic gamma-ray burst (GRB) ever detected, GRB 221009A, was accompanied by photons of very high energies. These gamma rays may be used to test both the astrophysical models of the burst and our understanding of long-distance propagation of energetic photons, including potential new-physics effects. Here we present the observation of a photon-like air shower with the estimated primary energy of $300^{+43}_{-38}$ TeV, coincident (with the chance probability of $\sim 9\cdot 10^{-3}$) with the GRB in its arrival direction and time. Making use of the upgraded Carpet-3 muon detector and new machine learning analysis, we estimate the probability that the primary was hadronic as $\sim 3 \cdot 10^{-4}$. This is the highest-energy event ever associated with any GRB.
Abstract: 2407.15076
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Title:Fast radio bursts as precursor radio emission from monster shocks
View PDF HTML (experimental)Abstract:It has been proposed recently that the breaking of MHD waves in the inner magnetosphere of strongly magnetized neutron stars can power different types of high-energy transients. Motivated by these considerations, we study the steepening and dissipation of a strongly magnetized fast magnetosonic wave propagating in a declining background magnetic field, by means of particle-in-cell simulations that encompass MHD scales. Our analysis confirms the formation of a monster shock as $B^2-E^2 \to 0$, that dissipates about half of the fast magnetosonic wave energy. It also reveals, for the first time, the generation of a high-frequency precursor wave by a synchrotron maser instability at the monster shock front, carrying a fraction of $\sim 10^{-3}$ of the total energy dissipated at the shock. The spectrum of the precursor wave exhibits several sharp harmonic peaks, with frequencies in the GHz band under conditions anticipated in magnetars. Such signals may appear as fast radio bursts.
Abstract: 2502.02381
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Title:Search for a diffuse flux of photons with energies above tens of PeV at the Pierre Auger Observatory
View PDF HTML (experimental)Abstract:Diffuse photons of energy above 0.1 PeV, produced through the interactions between cosmic rays and either interstellar matter or background radiation fields, are powerful tracers of the distribution of cosmic rays in the Galaxy. Furthermore, the measurement of a diffuse photon flux would be an important probe to test models of super-heavy dark matter decaying into gamma-rays. In this work, we search for a diffuse photon flux in the energy range between 50 PeV and 200 PeV using data from the Pierre Auger Observatory. For the first time, we combine the air-shower measurements from a 2 km$^2$ surface array consisting of 19 water-Cherenkov surface detectors, spaced at 433 m, with the muon measurements from an array of buried scintillators placed in the same area. Using 15 months of data, collected while the array was still under construction, we derive upper limits to the integral photon flux ranging from 13.3 to 13.8 km$^{-2}$ sr$^{-1}$ yr$^{-1}$ above tens of PeV. We extend the Pierre Auger Observatory photon search program towards lower energies, covering more than three decades of cosmic-ray energy. This work lays the foundation for future diffuse photon searches: with the data from the next 10 years of operation of the Observatory, this limit is expected to improve by a factor of $\sim$20.
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