Abstracts of Interest
Selected by:
Teddy
Abstract: 2412.06883
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Title:Dark Astronomy with Dark Matter Detectors
View PDF HTML (experimental)Abstract:We present a novel way of probing non-gravitational dark matter interactions: dark astronomy, which leverages the dark radiation emitted by dissipative dark sectors. If the mediator of the dark matter self interactions is a dark photon with a small mass that kinetically mixes with the visible photon, the dark radiation flux becomes accessible to underground experiments. We argue that the emission may be dominantly longitudinally polarized, thereby enhancing the sensitivity of direct detection experiments such as XENON and SENSEI to this signal. We introduce a new detection mechanism based on resonant dark-photon-to-photon conversion at the surface of conducting materials, which offers unique directional sensitivity to dark radiation. This mechanism facilitates the development of experiments that combine dark matter detection techniques with methods of traditional astronomy, opening the possibility to map dark radiation sources within our galaxy.
Abstract: 2412.06898
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Title:On the kinematic and thermodynamic state of clouds in complex wind-multi-cloud environments using a Friends-of-Friends analysis
View PDF HTML (experimental)Abstract:We investigate the interaction between a shock-driven hot wind and a cold multi-cloud layer, for conditions commonly found in interstellar and circumgalactic gas. We present a method for identifying distinct clouds using a Friends-of-Friends algorithm. This approach unveils novel detailed information about individual clouds and their collective behaviour. By tracing the evolution of individual clouds, our method provides comprehensive descriptions of cloud morphology, including measures of the elongation and fractal dimension. Combining the kinematics and morphology of clouds, we refine previous models for drag and entrainment processes. Our by-cloud analysis allows to discern the dominant entrainment processes at different times. We find that after the initial shock passage, momentum transfer due to condensation becomes increasingly important, compared to ram pressure, which dominates at early times. We also find that internal motions within clouds act as an effective dynamic pressure that exceeds the thermal pressure by an order of magnitude. Our analysis shows how the highly efficient cooling of the warm mixed gas at temperatures $\sim 10^{5}$ K is effectively balanced by the kinetic energy injected by the hot wind into the warm and cold phases via shocks and shear motions. Compression-driven condensation and turbulence dissipation maintain a multi-phase outflow and can help explain the presence of dense gas in galaxy-scale winds. Finally, we show that applying our Friends-of-Friends analysis to $\rm{H}_\rm{I}$-emitting gas and correcting for beam size and telescope sensitivity can explain two populations of $\rm{H}_\rm{I}$ clouds within the Milky-Way nuclear wind as structures pertaining to the same outflow.
Abstract: 2412.07595
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Title:On volume density and star formation in nearby molecular clouds
View PDF HTML (experimental)Abstract:Volume density is a key physical quantity controlling the evolution of the interstellar medium (ISM) and star formation, but it cannot be accessed directly by observations of molecular clouds. We aim at estimating the volume density distribution in nearby molecular clouds, to measure the relation between column and volume densities and to determine their roles as predictors of star formation. We develop an inverse modelling method to estimate the volume density distributions of molecular clouds. We apply this method to 24 nearby molecular clouds for which column densities have been derived using Herschel observations and for which star formation efficiencies (SFE) have been derived using observations with the Spitzer space telescope. We then compare the relationships of several column- and volume-density based descriptors of dense gas with the SFE of the clouds. We derive volume density distributions for 24 nearby molecular clouds, which represents the most complete sample of such distributions to date. The relationship between column densities and peak volume densities in these clouds is a piece-wise power-law relation that changes its slope at a column density of $5-10\times 10^{22}$ H$_2$cm$^{-2}$. We interpret this as a signature of hierarchical fragmentation in the dense ISM. We find that the volume-density based dense gas fraction is the best predictor of star formation in the clouds, and in particular, it is as anticipated a better predictor than the column-density based dense gas fraction. We also derive a volume density threshold density for star formation of $2\times 10^4$ H$_2$cm$^{-3}$.
Abstract: 2412.07861
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Title:Did IceCube discover Dark Matter around Blazars?
View PDF HTML (experimental)Abstract:Models of blazar jets, that explain observations of their photon spectra, typically predict too few neutrinos to be possibly seen by existing telescopes. In particular, they fall short in reproducing the first neutrino ever detected from a blazar, TXS 0506+056, by IceCube in 2017. We predict larger neutrino fluxes by using the same jet models, extended to include deep inelastic scatterings between protons within the jet and sub-GeV dark matter (DM) around the central black holes of blazars. In this way we succeed in explaining neutrino observations of TXS 0506+056, for DM parameters allowed by all laboratory, direct and indirect searches. Our proposal will be tested by DM searches as well as by the observation of more neutrinos from blazars. Our findings motivate to implement DM-nuclei interactions in jet models and to improve our knowledge of DM spikes around active galactic nuclei.
Abstract: 2412.07973
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Title:The Benefits of the Virtual Observatory to Underserved Communities
View PDF HTML (experimental)Abstract:The Virtual Observatory (VO) is a global ecosystem of interoperating services that connect worldwide data archives. The VO is implemented in all major astronomy archives through common interfaces developed by the 22 members of the International Virtual Observatory Alliance (IVOA). It was founded in 2002, and the newest members, the SKA Observatory and the Kazakhstan Virtual Observatory, joined in 2022. The VO offers access to data on FAIR principles and from its inception has supported Open Science. The VO acts as a democratizing influence in astronomy: it provides equal access to worldwide public data sets to underserved communities as well as to large data centers, and it enables international participation in scientific research and education. Thus, astronomers from many different communities are positioned to participate in the big science questions emerging in astronomy in the 2020s, such as interpreting transient sources that will be measured in forthcoming missions such as Rubin. In addition, the IVOA has signed an MoU with the IAU Office of Astronomy for Development (OAD). Under this MoU, IVOA members participated in "Astronomy from Archival Data," which involved educational activities for undergraduate and post-graduate students organized by Dr. Priya Hasan. The IVOA plans to participate in future such educational events. The presentation describes how new communities may participate in Virtual Observatory science and educational activities, including practices for developing VO-compliant data centers and archives and education and training for developers and end users.
Abstract: 2412.08089
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Title:Detection of extended X-ray emission around the PeVatron microquasar V4641 Sgr with XRISM
View PDF HTML (experimental)Abstract:A recent report on the detection of very-high-energy gamma rays from V4641 Sagittarii (V4641 Sgr) up to ~0.8 peta-electronvolt has made it the second confirmed "PeVatron" microquasar. Here we report on the observation of V4641 Sgr with X-Ray Imaging and Spectroscopy Mission (XRISM) in September 2024. Thanks to the large field of view and low background, the CCD imager Xtend successfully detected for the first time X-ray extended emission around V4641 Sgr with a significance of > 4.5 sigma and > 10 sigma based on our imaging and spectral analysis, respectively. The spatial extent is estimated to have a radius of $7 \pm 3$ arcmin ($13 \pm 5$ pc at a distance of 6.2 kpc) assuming a Gaussian-like radial distribution, which suggests that the particle acceleration site is within ~10 pc of the microquasar. If the X-ray morphology traces the diffusion of accelerated electrons, this spatial extent can be explained by either an enhanced magnetic field (~80 uG) or a suppressed diffusion coefficient (~$10^{27}$ cm$^2$ s$^{-1}$ at 100 TeV). The integrated X-ray flux, (4-6)$\times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$ (2-10 keV), would require a magnetic field strength higher than the galactic mean (> 8 uG) if the diffuse X-ray emission originates from synchrotron radiation and the gamma-ray emission is predominantly hadronic. If the X-rays are of thermal origin, the measured extension, temperature, and plasma density can be explained by a jet with a luminosity of ~$2\times 10^{39}$ erg s$^{-1}$, which is comparable to the Eddington luminosity of this system.
Abstract: 2412.08136
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Title:Isolated Black Holes as Potential PeVatrons and Ultrahigh-energy Gamma-ray Sources
View PDF HTML (experimental)Abstract:The origin of PeV cosmic rays is a long-standing mystery, and ultrahigh-energy gamma-ray observations would play a crucial role in identifying it. Recently, LHAASO reported the discovery of ``dark'' gamma-ray sources that were detected above 100 TeV without any GeV--TeV gamma-ray counterparts. The origins of these dark gamma-ray sources are unknown. We propose isolated black holes (IBHs) wandering in molecular clouds as the origins of PeV cosmic rays and LHAASO dark sources. An IBH accretes surrounding dense gas, which forms a magnetically arrested disk (MAD) around the IBH. Magnetic reconnection in the MAD can accelerate cosmic-ray protons up to PeV energies. Cosmic-ray protons of GeV-TeV energies fall to the IBH, whereas cosmic-ray protons at sub-PeV energies can escape from the MAD, providing PeV CRs into the interstellar medium. The sub-PeV cosmic-ray protons interact with the surrounding molecular clouds, producing TeV-PeV gamma rays without emitting GeV-TeV gamma rays. This scenario can explain the dark sources detected by LHAASO. Taking into account the IBH and molecular cloud distributions in our Galaxy, we demonstrate that IBHs can provide a significant contribution to the PeV cosmic rays observed on Earth. Future gamma-ray detectors in the southern sky and neutrino detectors would provide a concrete test to our scenario.
Abstract: 2412.08190
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Title:Hadronic particle acceleration in the supernova remnant SN 1006 as traced by Fermi-LAT observations
View PDF HTML (experimental)Abstract:The supernova remnant SN 1006 is a source of high-energy particles detected at radio, X-rays, and tera-electronvolt gamma rays. It was also announced as a source of gamma rays by Fermi-LAT but only the north-east (NE) limb was detected at more than $5\sigma$ significance level. Using 15 years of Fermi-LAT observation and a thorough morphological analysis above 1 GeV, we report the detection of the NE rim at the $6\sigma$ level and the south-west (SW) rim at the $5.5\sigma$ level using radio templates from the GLEAM survey. The spectral analysis performed between 100 MeV and 1 TeV allows the detection of a hard spectral index for the NE limb of $1.7 \pm 0.1 \pm 0.1$ while the emission detected in the SW is well reproduced with a steeper spectral index of $2.2 \pm 0.1 \pm 0.1$. A marginal detection (~$3\sigma$) of emission coincident with the bright north-west (NW) H$\alpha$ filament is also described with a similar spectral index of ~2.1. We successfully characterized the non-thermal multi-wavelength emission of the NE and SW limbs with a model in which inverse-Compton emission dominates in the NE while proton-proton interactions becomes significant in the SW due to the enhanced density of the medium.
Abstract: 2412.08349
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Title:Hypothetical Lorentz invariance violation and the muon content of extensive air showers
View PDF HTML (experimental)Abstract:Extensive air showers (EAS), produced by cosmic rays in the atmosphere, serve as probes of particle interactions, providing access to energies and kinematical regimes beyond the reach of laboratory experiments. Measurements from multiple cosmic-ray detectors indicate a significant, yet unexplained, discrepancy between the observed muon content in EAS and that predicted by state-of-the-art interaction models, suggesting a need for refinements in our understanding of fundamental physics. Here we show that a tiny, experimentally allowed, violation of the Lorentz invariance (LIV) may result in the suppression of the number of electrons in EAS, leaving the muon number intact and explaining both the ''muon excess'' and its energy dependence. On the other hand, we use the lack of a much stronger discrepancy between EAS data and simulations to obtain strict constraints on the LIV scale. Future experimental tests of this LIV scenario are outlined.
Abstract: 2412.08861
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Title:Resolved and unresolved Galactic gamma-ray sources
View PDF HTML (experimental)Abstract:The Galactic gamma-ray flux can be described as the sum of two components: the first is due to the emission from an ensemble of discrete sources, and the second is formed by the photons produced by cosmic rays propagating in interstellar space and interacting with gas or radiation fields. The source component is partially resolved as the contributions from individual sources, but a fraction is unresolved and appears as a diffuse flux. Both the unresolved source flux and the interstellar emission flux encode information of great significance for high energy astrophysics, and therefore the separation of these two contributions is very important. In this work we use the distributions in celestial coordinates of the objects contained in the catalogs obtained by the Extensive Air Showers telescopes HAWC and LHAASO to estimate the total luminosity of the Galactic gamma--ray sources and the contribution of unresolved sources to the diffuse gamma--ray flux. This analysis suggests that while the flux from unresolved sources is measurable and important, the dominant contribution to the diffuse flux over most of the celestial sphere is interstellar emission.
Abstract: 2412.09699
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Title:Neutrinos from explosive transients at the dawn of multi-messenger astronomy
View PDF HTML (experimental)Abstract:With the advent of time-domain astronomy and the game-changing next generation of telescopes, we have unprecedented opportunities to explore the most energetic events in our Universe through electromagnetic radiation, gravitational waves, and neutrinos. These are elementary particles, which exist in three different flavors and change the latter as they propagate in the dense core of astrophysical sources as well as en route to Earth. To capitalize on existing and upcoming multi-messenger opportunities, it is crucial to understand: 1. the role of neutrinos in explosive transient sources as well as in the synthesis of the elements heavier than iron; 2. the impact of neutrino physics on the multi-messenger observables; 3. the information on the source physics carried by the detectable neutrino signal. In this review, the status of this exciting and fast-moving field is outlined, focusing on astrophysical sources linked to collapsing massive stars and neutron-star mergers. In light of the upcoming plethora of multi-messenger data, outstanding open issues concerning the optimization of multi-messenger detection strategies are discussed.
Abstract: 2412.06372
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Title:Numerical simulations of internal shocks in spherical geometry: hydrodynamics and prompt emission
View PDF HTML (experimental)Abstract:Among the models used to explain the prompt emission of gamma-ray bursts (GRBs), internal shocks is a leading one. Its most basic ingredient is a collision between two cold shells of different Lorentz factors in an ultra-relativistic outflow, which forms a pair of shock fronts that accelerate electrons in their wake. The optically-thin synchrotron emission from the high-energy electrons at both shock fronts explains key features of the prompt GRB emission and their diversity without fine-tuning of the physical conditions. We investigate the internal shocks model as mechanism for prompt emission based on a full hydrodynamical analytic derivation in planar geometry by Rahaman et al. (2024a,b), extending this approach to spherical geometry using hydrodynamic simulations. We used the moving mesh relativistic hydrodynamics code GAMMA to study the collision of two ultra-relativistic cold shells of equal kinetic energy (and power). Using the built-in shock detection, we calculate the corresponding synchrotron emission by the relativistic electrons accelerated into a power-law energy distribution behind the shock, in the fast cooling regime. During the first dynamical time after the collision, the spherical effects cause the shock strength to decrease with radius. The observed peak frequency decreases faster than expected by other models in the rising part of the pulse, and the peak flux saturates even for moderately short pulses. This is likely caused by the very sharp edges of the shells in our model, while smoother edges will probably mitigate this effect. Our model traces the evolution of the peak frequency back to the source activity time scales.
Abstract: 2412.06675
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Title:Overview of Indigenous rights and outer space for the IAU-CPS Policy Hub
View PDF HTML (experimental)Abstract:As part of the mission of the International Astronomical Union Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU-CPS) Policy Hub to consider national and international regulations about the usage and sustainability in outer space, we also included discussion specific to the rights of Indigenous peoples with respect to outer space under the context of the United Nations Declaration for the Rights of Indigenous Peoples (UNDRIP). In this work, we review how some of the articles of UNDRIP require various actors in the use and exploitation of outer space including satellite companies, nation states, and professional/academic astronomy to consult and support Indigenous peoples/nations and respect Indigenous sovereignties. This work is concluded with recommendations for consulting and collaborating with Indigenous peoples and recommendations for moving from the traditional colonial exploitation of outer space and building an anti-colonial future in relationship with outer space.
Abstract: 2412.06669
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Title:Indigenous knowledges and kinship as a model for our future in outer space
View PDF HTML (experimental)Abstract:Commercial endeavours have already compromised our relationship with space. The Artemis Accords are creating a framework that will commercialize the Moon and further impact that relation. To confront that impact, a number of organizations have begun to develop new principles of sustainability in space, many of which are borne out of the capitalist and colonial frameworks that have harmed water, nature, peoples and more on Earth. Indigenous methodologies and ways of knowing offer different paths for living in relationship with space and the Moon. While Indigenous knowledges are not homogeneous, there are lessons we can use from some of common methods. In this talk we will review some Indigenous methodologies, including the concept of kinship and discuss how kinship can inform our actions both on Earth and in space.
Abstract: 2412.08244
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Title:Call to Protect the Dark and Quiet Sky from Harmful Interference by Satellite Constellations
View PDFAbstract:The growing number of satellite constellations in low Earth orbit (LEO) enhances global communications and Earth observation, and support of space commerce is a high priority of many governments. At the same time, the proliferation of satellites in LEO has negative effects on astronomical observations and research, and the preservation of the dark and quiet sky. These satellite constellations reflect sunlight onto optical telescopes, and their radio emission impacts radio observatories, jeopardising our access to essential scientific discoveries through astronomy. The changing visual appearance of the sky also impacts our cultural heritage and environment. Both ground-based observatories and space-based telescopes in LEO are affected, and there are no places on Earth that can escape the effects of satellite constellations given their global nature. The minimally disturbed dark and radio-quiet sky is crucial for conducting fundamental research in astronomy and important public services such as planetary defence, technology development, and high-precision geolocation. Some aspects of satellite deployment and operation are regulated by States and intergovernmental organisations. While regulatory agencies in some States have started to require operators to coordinate with their national astronomy agencies over impacts, mitigation of the impact of space objects on astronomical activities is not sufficiently regulated. To address this issue, the CPS urges States and the international community to take steps to protect the dark and quiet sky as specified in this paper.
This page created: Wed Dec 18 12:13:35 ACDT 2024 by Teddy
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