Abstracts of Interest
Selected by:
Jemma Pilossof
Abstract: 2312.14192
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Title:iDMEu: An initiative for Dark Matter in Europe and beyond
Download PDF HTML (experimental)Abstract:We introduce the initiative for Dark Matter in Europe and beyond (iDMEu), a collective effort by a group of particle and astroparticle physicists to set up an online resource meta-repository, a common discussion platform and a series of meetings on everything concerning Dark Matter. This document serves as a status report as well as a citable item concerning iDMEu.
Abstract: 2312.14352
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Title:The Propagation of Fast Radio Bursts in the Magnetosphere Shapes Their Waiting-time and Flux Distributions
Download PDF HTML (experimental)Abstract:The field of fast radio bursts (FRBs) has entered the age of fine characterization as observational results from different radio telescopes become more and more abundant. The large FRB sample is suitable for a statistical study. There is an interesting finding that the waiting-time distributions of very active repeating FRBs show a universal double-peaked feature, with left peaks lower than right ones. Assuming these two peaks are independent and initially comparable, we show that the observed asymmetric shape can be ascribed to the propagational effect in the magnetosphere. An FRB passing through the magnetized plasma will induce the circular motion of charged particles to form a current loop. This further leads to an induced magnetic field with opposite direction respect to the background field. As the effective field strength changes, the scattering absorption probability of the following FRB will be influenced. The absorption can be important under certain physical conditions and bursts with smaller time-lags are easier to be absorbed. Also there will be an imprint on the flux distribution as the scattering optical depth depends on burst luminosity as well.
Abstract: 2312.14431
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Title:Disc Novae: Thermodynamics of Gas Assisted Binary Black Hole Formation in AGN Discs
Download PDF HTML (experimental)Abstract:We investigate the thermodynamics of close encounters between stellar mass black holes (BHs) in the gaseous discs of active galactic nuclei (AGN), during which binary black holes (BBHs) may form. We consider a suite of 2D viscous hydrodynamical simulations within a shearing box prescription using the Eulerian grid code Athena++. We study formation scenarios where the fluid is either an isothermal gas or an adiabatic mixture of gas and radiation in local thermal equilibrium. We include the effects of viscous and shock heating, as well as optically thick cooling. We co-evolve the embedded BHs with the gas, keeping track of the energetic dissipation and torquing of the BBH by gas and inertial forces. We find that compared to the isothermal case, the minidiscs formed around each BH are significantly hotter and more diffuse, though BBH formation is still efficient. We observe massive blast waves arising from collisions between the radiative minidiscs during both the initial close encounter, and subsequent periapsis periods for successfully bound BBHs. These "disc novae" have a profound effect, depleting the BBH Hill sphere of gas and injecting energy into the surrounding medium. In analysing the thermal emission from these events, we observe periodic peaks in local luminosity associated with close encounters/periapses, with emission peaking in the optical/near-IR. In the AGN outskirts, these outbursts can reach 4% of the AGN luminosity in the IR band, with flares rising over 0.5-1year. Collisions in different disc regions, or when treated in 3D with magnetism, may produce more prominent flares.
Abstract: 2312.14645
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Title:A magnetar giant flare in the nearby starburst galaxy M82
Download PDF HTML (experimental)Abstract:Giant flares, short explosive events releasing up to 10$^{47}$ erg of energy in the gamma-ray band in less than one second, are the most spectacular manifestation of magnetars, young neutron stars powered by a very strong magnetic field, 10$^{14-15}$ G in the magnetosphere and possibly higher in the star interior. The rate of occurrence of these rare flares is poorly constrained, as only three have been seen from three different magnetars in the Milky Way and in the Large Magellanic Cloud in about 50 years since the beginning of gamma-ray astronomy. This sample can be enlarged by the discovery of extragalactic events, since for a fraction of a second giant flares reach peak luminosities above 10$^{46}$ erg/s, which makes them visible by current instruments up to a few tens of Mpc. However, at these distances they appear similar to, and difficult to distinguish from, regular short gamma-ray bursts (GRBs). The latter are much more energetic events, 10$^{50-53}$ erg, produced by compact binary mergers and originating at much larger distances. Indeed, only a few short GRBs have been proposed, with different levels of confidence, as magnetar giant flare candidates in nearby galaxies. Here we report the discovery of a short GRB positionally coincident with the central region of the starburst galaxy M82. Its spectral and timing properties, together with the limits on its X-ray and optical counterparts obtained a few hours after the event and the lack of an associated gravitational wave signal, qualify with high confidence this event as a giant flare from a magnetar in M82.
Abstract: 2312.14673
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Title:Highlights from the Pierre Auger Observatory
Download PDF HTML (experimental)Abstract:The Pierre Auger Observatory is a unique facility designed to study ultra-high energy cosmic rays, with energies up to 10$^{20}$ eV and beyond. The Observatory is located in Argentina and comprises more than 1600 water Cherenkov detectors spread over an area of 3000 square kilometers overlooked by Fluorescence detectors. The first phase of the Observatory's data-taking began in 2004 and continued until the end of 2021. In this contribution, the results from the Phase~I data analysis of the Pierre Auger Observatory are presented. They include, among others, measurements of the cosmic-ray energy spectrum, composition, and arrival direction anisotropy. The Phase~I results from the Pierre Auger Observatory provide major advances in the understanding of the ultra-high energy cosmic ray phenomena and lay the foundation for second-phase studies with the upgraded AugerPrime detector. The status of the AugerPrime upgrade and its performance will be also discussed.
Abstract: 2312.14772
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Title:Very high-energy gamma rays from GRB 180720B and GRB 190829A with external Compton emission
Download PDF HTML (experimental)Abstract:Gamma-ray bursts (GRBs) comprise of short, bright, energetic flashes of emission from extragalactic sources followed by a longer afterglow phase of decreased brightness. Recent discoveries of very-high-energy (VHE, $\gtrsim 100$ GeV) afterglow emission from GRB 180720B and GRB 190829A by H.E.S.S. have raised questions regarding the emission mechanism responsible. We interpret these observed late-time emission to be the result of inverse Compton emission of ultra-relativistic electrons in the GRB blastwave in an external radiation field, i.e., external Compton (EC), considering both the wind and interstellar medium scenarios. We present predictions of multiwavelength light curves and energy spectra, ranging from optical to VHE, and include the synchrotron and synchrotron self-Compton (SSC) radiation mechanisms as well. We corrected the EC and SSC model for the $\gamma$-ray attenuation by absorption of photons through their interaction with the extragalactic background light (EBL). We compared our results to multiwavelength data and found that EC gives a satisfactory fit for a given set of fixed model parameters for GRB 180720B, whereas SSC result in a better fit for GRB 190829A. For both GRBs a wind environment is preferred over constant density inter-stellar medium, and the Cosmic Microwave Background as the external radiation field. However, with more data and an effective optimisation tool we can find a more robust fit of the model, implying better constraints on the GRB environment and the particle energy requirements for the emission observed at late times. This has consequences for future observations of GRBs at these extreme energies.
Abstract: 2312.14857
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Title:Investigation of the correlation between optical and $γ$-ray flux variation in the blazar Ton 599
Download PDF HTML (experimental)Abstract:The correlation between optical and $\gamma$-ray flux variations in blazars reveals a complex behaviour. In this study, we present our analysis of the connection between changes in optical and $\gamma$-ray emissions in the blazar Ton 599 over a span of approximately 15 years, from August 2008 to March 2023. Ton 599 reached its highest flux state across the entire electromagnetic spectrum during the second week of January 2023. To investigate the connection between changes in optical and $\gamma$-ray flux, we have designated five specific time periods, labeled as epochs A, B, C, D, and E. During periods B, C, D, and E, the source exhibited optical flares, while it was in its quiescent state during period A. The $\gamma$-ray counterparts to these optical flares are present during periods B, C, and E, however during period D, the $\gamma$-ray counterpart is either weak or absent. We conducted a broadband spectral energy distribution (SED) fitting by employing a one-zone leptonic emission model for these epochs. The SED analysis unveiled that the optical-UV emission primarily emanated from the accretion disk in quiescent period A, whereas synchrotron radiation from the jet dominated during periods B, C, D, and E. Diverse correlated patterns in the variations of optical and $\gamma$-ray emissions, like correlated optical and $\gamma$-ray flares, could be accounted for by changes in factors such as the magnetic field, bulk Lorentz factor, and electron density. On the other hand, an orphan optical flare could result from increased magnetic field and bulk Lorentz factor.
Abstract: 2312.15057
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Title:The S-PLUS Transient Extension Program: Imaging Pipeline, Transient Identification, and Survey Optimization for Multi-Messenger Astronomy
Download PDF HTML (experimental)Abstract:We present the S-PLUS Transient Extension Program (STEP): a supernova and fast transient survey conducted in the southern hemisphere using data from the Southern Photometric Local Universe Survey (S-PLUS) Main Survey and the T80-South telescope. Transient astrophysical phenomena have a range of interest that goes through different fields of astrophysics and cosmology. With the detection of an electromagnetic counterpart to the gravitational wave (GW) event GW170817 from a binary neutron stars merger, new techniques and resources to study fast astrophysical transients in the multi-messenger context have increased. In this paper, we present the STEP overview, the SN follow-up data obtained, data reduction, analysis of new transients and deep learning algorithms to optimize transient candidate selection. Additionally, we present prospects and optimized strategy for the search of Gravitational Wave counterparts in the current LIGO/Virgo/Kagra observational run (O4) in the context of T80-South telescope.
Abstract: 2312.15125
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Title:Are There Correlations in the HAWC and IceCube High Energy Skymaps Outside the Galactic Plane?
Download PDF HTML (experimental)Abstract:We use publicly-available data to perform a search for correlations of high energy neutrino candidate events detected by IceCube and high-energy photons seen by the HAWC collaboration. Our search is focused on unveiling such correlations outside of the Galactic plane. This search is sensitive to correlations in the neutrino candidate and photon skymaps which would arise from a population of unidentified point sources. We find no evidence for such a correlation, but suggest strategies for improvements with new data sets.
Abstract: 2312.15206
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Title:Impact of anisotropic cosmic-ray transport on the gamma-ray signatures in the Galactic Center
Download PDF HTML (experimental)Abstract:The very high energy (VHE) emission of the Central Molecular Zone (CMZ) is rarely modelled in 3D. Most approaches describe the morphology in 1D or simplify the diffusion to the isotropic case. In this work we show the impact of a realistic 3D magnetic field configuration and gas distribution on the VHE gamma-ray distribution of the CMZ. We solve the 3D cosmic-ray transport equation with an anisotropic diffusion tensor using the approach of stochastic differential equations as implemented in the CRPropa framework. We test two different source distributions for five different anisotropies of the diffusion tensor, covering the range of effectively fieldline-parallel diffusion to isotropic diffusion. Within the tested magnetic field configuration the anisotropy of the diffusion tensor is close to the isotropic case and three point sources within the CMZ are favoured. Future missions like the upcoming CTA will reveal more small-scale structures which are not jet included in the model. Therefor a more detailed 3D gas distribution and magnetic field structure will be needed.
Abstract: 2312.15415
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Title:Evolution of Tidal Disruption Event Disks with Magnetically Driven Winds
Download PDF HTML (experimental)Abstract:We present a time-dependent, one-dimensional magnetically driven disk-wind model based on magnetohydrodynamical (MHD) equations in the context of tidal disruption events (TDEs). We assume that the disk is geometrically thin and gas-pressure dominant and explicitly take into account magnetic braking as well as turbulent viscosity by an extended alpha viscosity prescription. We find a particular wind solution for a set of basic equations that satisfies the necessary and sufficient conditions for vertically unbound MHD flows. The solution demonstrates that the disk evolves with losing mass due to wind and accretion from the initial Gaussian density distribution. We confirm that the mass accretion rate follows the power law of time $t^{-19/16}$ at late times if the wind is absent, which corresponds to the classical solution of Cannizzo et al. (1990). We find that the mass accretion rate is steeper than the $t^{-19/16}$ curve if the disk wind is present. This is because the wind removes a significant fraction of the mass and angular momentum. Mass accretion is further induced by magnetic braking, known as a wind-driven accretion mechanism, resulting in more rapid decay with time in both the mass accretion and loss rates. The ultraviolet (UV) luminosity is the highest among the optical, UV, and X-ray luminosities from early to late evolutionary phases, suggesting optical and X-ray emissions from the disk are observationally insignificant due to magnetically driven winds in TDEs. Our model predicts that late-time bolometric light curves steeper than $t^{-19/16}$ in UV-bright TDEs potentially serve as compelling indicators for magnetically driven winds.
Abstract: 2312.15797
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Title:Popular astronomy and other science articles in glossy magazines -- outreaching to those who do not care to be reached
Download PDF HTML (experimental)Abstract:The target auditory of scientific outreach efforts is often limited to the small enthusiastic subset of the society that value science and actively seeks knowledge. However, the vast majority is usually indifferent or in some cases may even be opposed to sciences. To bring these people around to support sciences, we have to double and triple our efforts. I describe my personal experience how I reach out to them by means of popular articles in glossy magazines - not the most common outreach venue, at least in Bulgaria. Four years of writing have though me that the key for success is to turn the science into and engaging human story that will keep the readers curious until the revelation of the riddle at the end of the last paragraph. Next, come the spectacular visuals - for the modern reader, spoiled by eye candies of Internet and Hollywood they are almost as important as the written words. The final requirement is accessibility - an article should explain well only two or three concepts; I am not calling for simplicity but for measuring and structuring of the information content - it is better to give the readers two understandable pieces that they would enjoy instead one impenetrable article that would turn them away from popular science for good.
Abstract: 2312.16089
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Title:Sub-GeV Gamma Rays from Nearby Seyfert Galaxies and Implications for Coronal Neutrino Emission
Download PDF HTML (experimental)Abstract:Recent observations of high-energy neutrinos by IceCube and gamma rays by the Fermi Large Area Telescope (LAT) and the MAGIC telescope have suggested that neutrinos are produced in gamma-ray opaque environments in the vicinity of supermassive black holes. In this work, we present 20 MeV - 1 TeV spectra of three Seyfert galaxies whose nuclei are predicted to be active in neutrinos, NGC 4151, NGC 4945 and the Circinus Galaxy, using 14.4 years of the Fermi LAT data. In particular, we find evidence of sub-GeV excess emission that can be attributed to gamma rays from NGC 4945, as was also seen in NGC 1068. These spectral features are consistent with predictions of the magnetically-powered corona model, and we argue that NGC 4945 is among the brightest neutrino active galaxies detectable for KM3Net and Baikal-GVD. On the other hand, in contrast to other reported results, we do not detect gamma rays from NGC 4151, which constrains neutrino emission from the accretion shock model. Future neutrino detectors such as IceCube-Gen2 and MeV gamma-ray telescopes such as AMEGO-X will be crucial for discriminating among the theoretical models.
Abstract: 2312.16254
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Title:Through the eyes of a reader and science communicator: science in the mainstream and in the genre literature of yesterday and today
Download PDF HTML (experimental)Abstract:For most writers the science is either an exotic setting or a source of thrilling conflict that would drive the story forward. For a communicator it is the other way around - the science is neatly wrapped in a package of literary tools that make it "invisible" while it remains tangible and most importantly - it can be conveyed to the reader in understandable terms. There are many examples showing how these seemingly contradicting goals can complement each other successfully. I will review how the science was communicated by mainstream and genre writers of yesterday and today, and in different (not necessarily anglophone) cultures. I will bring forward the best and the worst examples that illuminate various astronomical concepts. Finally, I will discuss how we can use them both in outreach and education. Contrary to many similar summaries I will concentrate on some often overlooked mainstream literary examples, including the plays The Physisists by Friedrich Dürrenmatt and Copenhagen by Michael Frayn, the novel White Garments by Vl. Dudintsev and even an episode of the Inspector Morse TV show, featuring scientists. I will also mention in passing a few less well known genre books.
Abstract: 2312.17151
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Title:Imprints of light dark matter on the evolution of cosmic neutrinos
Download PDF HTML (experimental)Abstract:Neutrinos are often considered as a portal to new physics beyond the Standard Model (SM) and might possess phenomenologically interesting interactions with dark matter (DM). This paper examines the cosmological imprints of DM that interacts with and is produced from SM neutrinos at temperatures below the MeV scale. We take a model-independent approach to compute the evolution of DM in this framework and present analytic results which agree well with numerical ones. Both freeze-in and freeze-out regimes are included in our analysis. Furthermore, we demonstrate that the thermal evolution of neutrinos might be substantially affected by their interaction with DM. We highlight two distinctive imprints of such DM on neutrinos: (i) a large, negative contribution to $N_{\rm eff}$, which is close to the current experimental limits and will readily be probed by future experiments; (ii) spectral distortion of the cosmic neutrino background (C$\nu$B) due to DM annihilating into neutrinos, a potentially important effect for the ongoing experimental efforts to detect C$\nu$B.
Abstract: 2312.17239
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Title:Interacting supernovae as high-energy multimessenger transients
Download PDF HTML (experimental)Abstract:Multiwavelength observations have revealed that dense, confined circumstellar material (CCSM) commonly exists in the vicinity of supernova (SN) progenitors, suggesting enhanced mass losses years to centuries before their core collapse. Interacting SNe, which are powered or aided by interaction with the CCSM, are considered to be promising high-energy multimessenger transient sources. We present detailed results of broadband electromagnetic emission, following the time-dependent model proposed in the previous work on high-energy SN neutrinos [Murase, Phys. Rev. D 97, 081301(R) (2018)]. We investigate electromagnetic cascades in the presence of Coulomb losses, including inverse-Compton and synchrotron components that significantly contribute to MeV and high-frequency radio bands, respectively. We also discuss the application to SN 2023ixf.
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