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Dark matter search in dwarf irregular galaxies with the Fermi Large Area Telescope
Viviana Gammaldi, Judit Pérez Romero, Javier Coronado-Blázquez, Mattia di Mauro, Ekaterina Karukes, Miguel Sánchez-Conde, Paolo Salucci, 2021, original scientific article

Abstract: We analyze 11 years of Fermi-Large Area Telescope (LAT) data corresponding to the sky regions of seven dwarf irregular (dIrr) galaxies. DIrrs are dark matter (DM)-dominated systems, proposed as interesting targets for the indirect search of DM with gamma rays. The galaxies represent interesting cases with a strong disagreement between the density profiles (core versus cusp) inferred from observations and numerical simulations. In this work, we addressed the problem by considering two different DM profiles, based on both the fit to the rotation curve (in this case, a Burkert cored profile) and results from N-body cosmological simulations (i.e., Navarro-Frenk-White cuspy profile). We also include halo substructure in our analysis, which is expected to boost the DM signal by a factor of 10 in halos such as those of dIrrs. For each DM model and dIrr, we create a spatial template of the expected DM-induced gamma-ray signal to be used in the analysis of Fermi-LAT data. No significant emission is detected from any of the targets in our sample. Thus, we compute upper limits on the DM annihilation cross section versus mass parameter space. Among the seven dIrrs, we find IC10 and NGC6822 to yield the most stringent individual constraints, independently of the adopted DM profile. We also produce combined DM limits for all objects in the sample, which turn out to be dominated by IC10 for all DM models and annihilation channels, i.e., b¯b, τ+τ−, and W+W−. The strongest constraints are obtained for b¯b and are at the level of <σv>∼7×10−26 cm3 s−1 at mχ ∼ 6 GeV. Though these limits are a factor of ∼3 higher than the thermal relic cross section at low weakly interacting massive particles masses, they are independent from and complementary to those obtained by means of other targets.
Keywords: Dark matter, gamma-ray astronomy, galaxies, astronomical masses and mass distributions
Published in RUNG: 26.01.2023; Views: 1065; Downloads: 0
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Photopyroelectric spectroscopy and calorimetry
D Dadarlat, C Tripon, Iain R. White, Dorota Korte, 2022, review article

Abstract: In this tutorial, we present an overview of the development of the photopyroelectric (PPE) technique, from its beginnings in 1984, through to the present day. The tutorial is organized in five sections, exploring both theoretical and experimental aspects of PPE detection, as well as some important spectroscopic and calorimetric applications. In the “Introduction” section we present the fundamental basics of photothermal phenomena and the state-of-the-art of the photopyroelectric technique. In the “Theoretical aspects” section we describe some specific cases of experimental interest, with examples in both back and front detection configurations. Several mathematical expressions for the PPE signal in specific detection modes (combined back-front configurations and PPE-IRT methods) are also deduced. The “Instrumentation and experiment” section contains two sub-sections. The first describes several examples of set-ups used for both room temperature and temperature-controlled experiments. The second sub-section is dedicated to the configuration of detection cells and to the various sensor/sample assemblies that are currently used in spectroscopic and calorimetric experiments for both liquid and solid samples. The “Applications” section is in fact a collection of experimental results dedicated to the thermal characterization of a wide range of solid and liquid samples. At the end of this section we present some examples that have been selected to convey that the PPE technique is not only useful in the investigation of optical and thermal properties of a variety of condensed matter samples, but also to study physical and chemical processes such as molecular associations, food adulteration or phase transitions. In “Concluding remarks” we summarize the advantages of this technique in spectroscopic and calorimetric applications.
Keywords: photopyroelectric spectroscopy, photopyroelectric calorimetry, phase transitions, condensed matter samples, thermal parameters
Published in RUNG: 16.11.2022; Views: 1228; Downloads: 22
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Tuning the thermal diffusivity of the seed matter for enhanced biosynthesis: A thermal lens study
Mohanachandran Nair Sindhu Swapna, Sankararaman S, 2020, original scientific article

Abstract: The thermodynamics of the seed matter after imbibition is highly significant as the growth and germination involve complex biochemical exergonic process. The germination of seed and compositional variation of the seed matter has always been a fascinating field of research. The present work unveils the thermodynamics associated with the changing thermal diffusivity of the seed matter through the green technology-based single-beam thermal lens technique. Investigations are carried out in Vigna radiata seeds, germinating in media with and without carbon allotropes, through various spectroscopic techniques. The morphology of the soot and carbon allotropes is understood from the field emission scanning electron microscope images. The thermal lens study throws light into the energy trapping nature of the seed matter of the seed growing in carbon allotropic media which facilitates biosynthesis. The observed increased rate of growth of the seed is substantiated through the ultraviolet–visible–near-infrared (NIR), Fourier transform infrared, and photoluminescence (PL) spectroscopic analyses. The NIR and PL studies also reveal the formation of chlorophyll molecule during germination. Thus, the study suggests a mechanism for tuning the thermal diffusivity of the seed matter as to trap the biochemical energy to facilitate the further biosynthesis and thereby to enhance the growth rate.
Keywords: seed matter, thermal diffusivity, thermal lens, carbon nanoparticle, soot
Published in RUNG: 04.07.2022; Views: 1252; Downloads: 0
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Tidal Disruption Events seen through the eyes of Vera C. Rubin Observatory
Katja Bučar Bricman, 2021, doctoral dissertation

Abstract: Tidal Disruption Events (TDEs) are rare transients, which are considered to be promising tools in probing supermassive black holes (SMBHs) and their environments in quiescent galaxies, accretion physics, and jet formation mechanisms. The majority of $\approx$ 60 detected TDEs has been discovered with large field of view time-domain surveys in the last two decades. Currently, about 10 TDEs are discovered per year, and we expect this number will increase largely once the Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory begins its observations. In this work we demonstrate and explore the capabilities of the LSST to study TDEs. To begin with, we simulate LSST observations of TDEs over $10$ years of survey duration by including realistic SED models from MOSFiT into the simulation framework of the LSST. SEDs are then converted into observed fluxes and light curves are simulated with the LSST observing strategy minion_1016. Simulated observations are used to estimate the number of TDEs the LSST is expected to observe and to assess the possibility of probing the SMBH mass distribution in the Universe with the observed TDE sample. We find that the LSST has a potential of observing ~1000 TDEs per year, the exact number depending on the SMBH mass distribution and the adopted observing strategy. In spite of this large number, we find that probing the SMBH mass distribution with LSST observed TDEs will not be straightforward, especially at the low-mass end. This is largely attributed to the fact that TDEs caused by low-mass black holes ($\le 10^6 M_\odot$) are less luminous and shorter than TDEs by heavier SMBHs ($> 10^6 M_\odot$), and the probability of observationally missing them with LSST is higher. Second, we built a MAF TDE metric for photometric identification of TDEs based on LSST data. We use the metric to evaluate the performance of different proposed survey strategies in identifying TDEs with pre-defined identification requirements. Since TDEs are blue in color for months after peak light, which separates them well from SNe and AGN, we include u-band observations as one of the criteria for a positive identification. We find that the number of identified TDEs strongly depends of the observing strategy and the number of u-band visits to a given field in the sky. Observing strategies with a larger number of u-band observations perform significantly better. For these strategies up to 10% of LSST observed TDEs satisfy the identification requirements.
Keywords: Ground-based ultraviolet, optical and infrared telescopes Astronomical catalogs, atlases, sky surveys, databases, retrieval systems, archives, Black holes, Galactic nuclei (including black holes), circumnuclear matter, and bulges, Infall, accretion, and accretion disks
Published in RUNG: 03.01.2022; Views: 2780; Downloads: 62
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Testing the predictions of axisymmetric distribution functions of galactic dark matter with hydrodynamical simulations
Mihael Petač, Julien Lavalle, Arturo Núñez-Castiñeyra, Emmanuel Nezri, 2021, original scientific article

Abstract: Signal predictions for galactic dark matter (DM) searches often rely on assumptions regarding the DM phase-space distribution function (DF) in halos. This applies to both particle (e.g. p-wave suppressed or Sommerfeld-enhanced annihilation, scattering off atoms, etc.) and macroscopic DM candidates (e.g. microlensing of primordial black holes). As experiments and observations improve in precision, better assessing theoretical uncertainties becomes pressing in the prospect of deriving reliable constraints on DM candidates or trustworthy hints for detection. Most reliable predictions of DFs in halos are based on solving the steady-state collisionless Boltzmann equation (e.g. Eddington-like inversions, action-angle methods, etc.) consistently with observational constraints. One can do so starting from maximal symmetries and a minimal set of degrees of freedom, and then increasing complexity. Key issues are then whether adding complexity, which is computationally costy, improves predictions, and if so where to stop. Clues can be obtained by making predictions for zoomed-in hydrodynamical cosmological simulations in which one can access the true (coarse-grained) phase-space information. Here, we test an axisymmetric extension of the Eddington inversion to predict the full DM DF from its density profile and the total gravitational potential of the system. This permits to go beyond spherical symmetry, and is a priori well suited for spiral galaxies. We show that axisymmetry does not necessarily improve over spherical symmetry because the (observationally unconstrained) angular momentum of the DM halo is not generically aligned with the baryonic one. Theoretical errors are similar to those of the Eddington inversion though, at the 10-20% level for velocity-dependent predictions related to particle DM searches in spiral galaxies. We extensively describe the approach and comment on the results.
Keywords: galaxy dynamics, dark matter experiments, dark matter simulations, dark matter theory, cosmology, nongalactic astrophysics, astrophysics of galaxies, high energy physics
Published in RUNG: 01.10.2021; Views: 2054; Downloads: 65
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Two-integral distribution functions in axisymmetric galaxies: Implications for dark matter searches
Mihael Petač, Piero Ullio, 2019, original scientific article

Abstract: We address the problem of reconstructing the phase-space distribution function for an extended collisionless system, with known density profile and in equilibrium within an axisymmetric gravitational potential. Assuming that it depends on only two integrals of motion, namely the energy and the component of the angular momentum along the axis of symmetry Lz , there is a one-to-one correspondence between the density profile and the component of the distribution function that is even in Lz, as well as between the weighted azimuthal velocity profile and the odd component. This inversion procedure was originally proposed by Lynden-Bell and later refined in its numerical implementation by Hunter and Qian; after overcoming a technical difficulty, we apply it here for the first time in presence of a strongly flattened component, as a novel approach of extracting the phase-space distribution function for dark matter particles in the halo of spiral galaxies. We compare results obtained for realistic axisymmetric models to those in the spherical symmetric limit as assumed in previous analyses, showing the rather severe shortcomings in the latter. We then apply the scheme to the Milky Way and discuss the implications for the direct dark matter searches. In particular, we reinterpret the null results of the Xenon1T experiment for spin-(in)dependent interactions and make predictions for the annual modulation of the signal for a set of axisymmetric models, including a self-consistently defined corotating halo.
Keywords: dark matter, astrophysics of galaxies, high energy physics, phenomenology
Published in RUNG: 01.10.2021; Views: 1904; Downloads: 0
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Equilibrium axisymmetric halo model for the Milky Way and its implications for direct and indirect dark matter searches
Mihael Petač, 2020, original scientific article

Abstract: We for the first time provide self-consistent axisymmetric phase-space distribution models for the Milky Way's dark matter (DM) halo which are carefully matched against the latest kinematic measurements through Bayesian analysis. By using broad priors on the individual galactic components, we derive conservative estimates for the astrophysical factors entering the interpretation of direct and indirect DM searches. While the resulting DM density profiles are in good agreement with previous studies, implying ρ⊙≈10-2 M⊙/pc3, the presence of baryonic disc leads to significant differences in the local DM velocity distribution in comparison with the standard halo model. For direct detection, this implies roughly 30% stronger cross section limits at DM masses near detectors maximum sensitivity and up to an order of magnitude weaker limits at the lower end of the mass range. Furthermore, by performing Monte Carlo simulations for the upcoming DARWIN and DarkSide-20k experiments, we demonstrate that upon successful detection of heavy DM with coupling just below the current limits, the carefully constructed axisymmetric models can eliminate bias and reduce uncertainties by more then 50% in the reconstructed DM coupling and mass, but also help in a more reliable determination of the scattering operator. Furthermore, the velocity anisotropies induced by the baryonic disc can lead to significantly larger annual modulation amplitude and sizable differences in the directional distribution of the expected DM-induced events. For indirect searches, we provide the differential J factors and compute several moments of the relative velocity distribution that are needed for predicting the rate of velocity-dependent annihilations. However, we find that accurate predictions are still hindered by large uncertainties regarding the DM distribution near the galactic center.
Keywords: dark matter, astrophysics, galaxies, high energy physics, experiments, phenomenology
Published in RUNG: 01.10.2021; Views: 1898; Downloads: 41
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On velocity-dependent dark matter annihilations in dwarf satellites
Mihael Petač, Piero Ullio, Mauro Valli, 2018, original scientific article

Abstract: Milky Way dwarf spheroidal satellites are a prime target for Dark Matter (DM) indirect searches. There have been recent reassessments of the expected DM gamma-ray signals in case of long-range interactions, commonly known as Sommerfeld enhancement. Since details of the underlying DM phase-space distribution function become critical, there are potentially large uncertainties in the final result. We provide here a first attempt towards a comprehensive investigation of these systematics, addressing the impact on the expected DM flux from Milky Way dwarfs via Bayesian inference on the available stellar kinematic datasets. After reconsidering the study case of ergodic systems, we investigate for the first time scenarios where DM particle orbits may have a radial or tangential bias. We consider both cuspy and cored parametric DM density profiles, together with the case of a non-parametric halo modelling directly connected to line-of-sight observable quantities. The main findings of our work highlight the relevance of the assumed phase-space distribution: Referring to a generalized J-factor, namely the line-of-sight convolution of the spatial part in case of velocity-dependent annihilation rate, an enhancement (suppression) with respect to the limit of isotropic phase-space distributions is obtained for the case of tangentially (radially) biased DM particle orbits. We provide new estimates for J-factors for the eight brightest Milky Way dwarfs also in the limit of velocity-independent DM annihilation, in good agreement with previous results in literature, and derive data-driven lower-bounds based on the non-parametric modelling of the halo density. The outcome of our broad study stands out as a representative of the state-of-the-art in the field, and falls within the interest of current and future experimental collaborations involved in DM indirect detection programs.
Keywords: dark matter, indirect detection, dwarf satellites, sommerfeld enhancement, gamma-rays
Published in RUNG: 01.10.2021; Views: 1678; Downloads: 43  (1 vote)
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