#### 003.05. Energetic Cosmos Laboratory

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Item Open Access BLACK HOLE HOOKEAN LAW AND THERMODYNAMIC FRAGMENTATION: INSIGHTS FROM THE MAXIMUM FORCE CONJECTURE AND RUPPEINER GEOMETRY(PHYSICAL REVIEW RESEARCH, 2022) Gennaro, Sofia Di; Good, Michael R. R.; Ong, Yen ChinShow more We show that the notion of “Hookean law” F = kx, suitably defined in asymptotically flat singly spinning Myers-Perry black hole space-times in dimensions d 5, is related to the Emparan-Myers fragmentation (splitting of a black hole into two becomes thermodynamically preferable). Specifically, the values of black hole parameters when fragmentation occurs correspond to the maximal value of F. Furthermore this always happens before F reaches 1/4 in Planck units. These results suggest that a version of “maximum force conjecture” may be relevant for black hole thermodynamics. We also relate these findings to the Ruppeiner thermodynamic geometry of these black holes and speculate on the implications for the underlying microstructures of black hole horizons.Show more Item Open Access CHARACTERIZATION OF A HIGH EFFICIENCY SILICON PHOTOMULTIPLIER FOR MILLISECOND TO SUB-MICROSECOND ASTROPHYSICAL TRANSIENT(arxiv, 2020) Li, Siyang; Smoot, George F.Show more We characterized the S14160-3050HS Multi-Pixel Photon Counter (MPPC), a high efficiency, single channel silicon photomultiplier manufactured by Hamamatsu Photonics K.K. All measurements were performed at a room temperature of (23.0 ± 0.3) °C. We obtained an I-V curve and used relative derivatives to find a breakdown voltage of 38.88 V. At a 3 V over voltage, we find a dark count rate of 1.08 MHz, crosstalk probability of 21 %, photon detection efficiency of 55 % at 450 nm, and saturation at 1.0x1011 photons per second. The S14160- 3050HS MPPC is a candidate detector for the Ultra-Fast Astronomy (UFA) telescope which will characterize the optical (320 nm - 650 nm) sky in the millisecond to sub-microsecond timescales using two photon counting arrays operated in coincidence on the 0.7 meter Nazarbayev University Transient Telescope at the Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) located near Almaty, Kazakhstan. We discuss advantages and disadvantages of using the S14160-3050HS MPPC for the UFA telescope and future ground-based telescopes in sub-second time domain astrophysics.Show more Item Open Access COMPLEMENTARITY OF PECULIAR VELOCITY SURVEYS AND REDSHIFT SPACE DISTORTIONS FOR TESTING GRAVITY(PHYSICAL REVIEW D, 2020) Kim, Alex G.; Linder, Eric V.Show more Peculiar-velocity surveys of the low-redshift universe have significant leverage to constrain the growth rate of cosmic structure and test gravity. Wide-field imaging surveys combined with multiobject spectrographs [e.g., ZTF2, Large Synoptic Survey Telescope (LSST), DESI, and 4MOST] can use type Ia supernovae as informative tracers of the velocity field, reaching few percent constraints on the growth rate fσ8 at z ≲ 0.2 where density tracers cannot do better than ∼10%. Combining the high-redshift DESI survey mapping redshift space distortions with a low-redshift supernova peculiar velocity survey using LSST and DESI can determine the gravitational growth index to σðγÞ ≈ 0.02, testing general relativity. We study the characteristics needed for the peculiar velocity survey, and how its complementarity with clustering surveys improves when going from a ΛCDM model assumption to a w0–wa cosmologyShow more Item Open Access CONSTRAINING SCALE DEPENDENT GROWTH WITH REDSHIFT SURVEYS(Journal of Cosmology and Astroparticle Physics, 2022) Denissenya, Mikhail; Linder, Eric V.Show more Ongoing and future redshift surveys have the capability to measure the growth rate of large scale structure at the percent level over a broad range of redshifts, tightly constraining cosmological parameters. Beyond general relativity, however, the growth rate in the linear density perturbation regime can be not only redshift dependent but scale dependent, revealing important clues to modified gravity. We demonstrate that a fully model independent approach of binning the gravitational strength Geff (k,z) matches scalar-tensor results for the growth rate fσ8(k,z) to 0.02%–0.27% rms accuracy. For data of the quality of the Dark Energy Spectroscopic Instrument (DESI) we find the bin values can be constrained to 1.4%–28%. We also explore the general scalar-tensor form, constraining the amplitude and past and future scalaron mass/shape parameters. Perhaps most interesting is the strong complementarity of low redshift peculiar velocity data with DESI-like redshift space distortion measurements, enabling improvements up to a factor 6–7 on 2D joint confidence contour areas. Finally, we quantify some issues with gravity parametrizations that do not include all the key physics.Show more Item Open Access DEEP LEARNING UNRESOLVED LENSED LIGHT CURVES(Monthly Notices of the Royal Astronomical Society, 2022) Denissenya, Mikhail; Linder, Eric VShow more Gravitationally lensed sources may have unresolved or blended multiple images, and for time varying sources, the light curves from individual images can overlap. We use convolutional neural nets to both classify the light curves as due to unlensed, double, or quad lensed sources and fit for the time delays. Focusing on lensed supernova systems with time delays Δt ≳ 6 d, we achieve 100 per cent precision and recall in identifying the number of images and then estimating the time delays to σΔt ≈ 1 d, with a 1000× speedup relative to our previous Monte Carlo technique. This also succeeds for flux noise levels ∼10 per cent . For Δt ∈ [2, 6] d, we obtain 94–98 per cent accuracy, depending on image configuration. We also explore using partial light curves where observations only start near maximum light, without the rise time data, and quantify the success.Show more Item Open Access DETECTING HELIUM REIONIZATION WITH FAST RADIO BURSTS(PHYSICAL REVIEW D, 2020) Linder, Eric V.Show more Fast radio bursts (FRBs) probe the electron density of the universe along the path of propagation, making high redshift FRB sensitive to the helium reionization epoch. We analyze the signal to noise with which a detection of the amplitude of reionization can be made, and its redshift, for various cases of future FRB survey samples, assessing survey characteristics including total number, redshift distribution, peak redshift, redshift depth, and number above the reionization redshift, as well as dependence on reionization redshift. We take into account scatter in the dispersion measure due to an inhomogeneous intergalactic medium (IGM) and uncertainty in the FRB host and environment dispersion measure, as well as cosmology. For a future survey with 7000 FRBs extending out to z ¼ 5, and a sudden reionization, the detection of helium reionization can approach the 5σ level and the reionization redshift be determined to σðzrÞ ≈ 0.24 in an optimistic scenario, or 2σ and σðzrÞ ≈ 0.34 taking into account further uncertainties on IGM fraction evolution and redshift uncertaintiesShow more Item Open Access DETERMINING MODEL-INDEPENDENT H0 AND CONSISTENCY TESTS(arxiv, 2020) Liao, Kai; Shafieloo, Arman; Keeley, Ryan E.; Linder, Eric V.Show more We determine the Hubble constant H0 precisely (2.3% uncertainty) in a manner independent of cosmological model through Gaussian process regression, using strong lensing and supernova data. Strong gravitational lensing of a variable source can provide a time-delay distance D∆t and angular diameter distance to the lens Dd. These absolute distances can anchor Type Ia supernovae, which give an excellent constraint on the shape of the distance-redshift relation. Updating our previous results to use the H0LiCOW program’s milestone dataset consisting of six lenses, four of which have both D∆t and Dd measurements, we obtain H0 = 72.8 +1.6 −1.7 km/s/Mpc for a flat universe and H0 = 77.3 +2.2 −3.0 km/s/Mpc for a non-flat universe. We carry out several consistency checks on the data and find no statistically significant tensions, though a noticeable redshift dependence persists in a particular systematic manner that we investigate. Speculating on the possibility that this trend of derived Hubble constant with lens distance is physical, we show how this can arise through modified gravity light propagation, which would also impact the weak lensing σ8 tensionShow more Item Open Access DOUBLE SOURCE LENSING PROBING HIGH REDSHIFT COSMOLOGY(Journal of Cosmology and Astroparticle Physics, 2022) Sharma, Divij; Linder, Eric V.Show more Double source lensing, with two sources lensed by the same foreground galaxy, involves the distance between each source and the lens and hence is a probe of the universe away from the observer. The double source distance ratio also reduces sensitivity to the lens model and has good complementarity with standard distance probes. We show that using this technique at high redshifts z > 1, to be enabled by data from the Euclid satellite and other surveys, can give insights on dark energy, both in terms of w0–wa and redshift binned density. We find a dark energy figure of merit of 245 from combination of 256 double source systems with moderate quality cosmic microwave background and supernova data. Using instead five redshift bins between z = 1.1–5, we could detect the dark energy density out to z ≈ 5, or make measurements ranging between 31σ and 2.5σ of its values in the bins.Show more Item Open Access EXPLORING EARLY AND LATE COSMOLOGY WITH NEXT GENERATION SURVEYS(PHYSICAL REVIEW D, 2020) Brando, Guilherme; Linder, Eric V.Show more Perturbations from inflation evolve into large scale structure of the late universe, and encode abundant cosmic structure formation physics. We allow freedom in the primordial power spectrum, rather than assuming a power law scale dependence, to study its impact on cosmological parameter determination. Combining various generations of cosmic microwave background (CMB) data and galaxy redshift survey data, we investigate the constraints on reconstruction of the primordial curvature perturbation power spectrum and the late time cosmology, especially the sum of neutrino masses. We quantify how each successive generation, in CMB and galaxy surveys, provides significant improvements, often by factors of several. By using CMB polarization information over a broad range of angular scales, and galaxy redshift data in many bins of redshift, one can allow inflationary freedom and still constrain parameters comparably to assuming power law dependence. The primordial power spectrum can be reconstructed at the subpercent level in a dozen wave number bins, while simultaneously fitting the sum of neutrino masses to 14 meVShow more Item Open Access EXTREME ELECTRON ACCELERATION WITH FIXED RADIATION ENERGY(Entropy, 2022) Good, Michael R. R.; Singha, Chiranjeeb; Zarikas, VasiliosShow more We examine the extreme situation of radiation from an electron that is asymptotically accelerated to the speed of light, resulting in finite emission energy. The analytic solution explicitly demonstrates the difference between radiation power loss and kinetic power loss (null).Show more Item Open Access EXTREME HAWKING RADIATION(arxiv, 2020) Good, Michael R.R.Show more Modeling the collapse of an extreme Reissner-Nordstr¨om (ERN) black hole by solving the corre sponding moving mirror model for the trajectory that asymptotically approaches uniform accelera tion, we obtain the non-zero beta coefficients for all times. Finite energy is emitted, the radiation spectra is non-thermal (non-steady / not Planck), soft particles characterize the evaporation, and particle production at ultra-late times is damped. Entanglement entropy diverges with no Page curve turn-over, demonstrating non-thermal information loss. The radiation obeys time-reversal symmetryShow more Item Open Access THE MIRROR AT THE EDGE OF THE UNIVERSE: REFLECTIONS ON AN ACCELERATED BOUNDARY CORRESPONDENCE WITH DE SITTER COSMOLOGY(arxiv, 2020) Zhakenuly, Abay; Good, Michael R.R.; Linder, Eric V.Show more An accelerated boundary correspondence (ABC) is solved for the de Sitter moving mirror cos mology. The beta Bogoliubov coefficients reveal the particle spectrum is a Planck distribution with temperature inversely proportional to horizon radius. The quantum stress-tensor indicates a con stant emission of energy flux consistent with eternal equilibrium, while the total energy carried by the particles remains finite. The curved spacetime transformation to flat spacetime with an accelerated boundary is illustrated, and also shown for Anti-de Sitter (AdS) spacetimeShow more Item Open Access NGC 6240 SUPERMASSIVE BLACK HOLE BINARY DYNAMICAL EVOLUTION BASED ON CHANDRA DATA(Monthly Notices of the Royal Astronomical Society, 2022) Sobolenko, M; Kompaniiets, O; Berczik, P; Marchenko, V; Vasylenko, A; Fedorova, E; Shukirgaliyev, BShow more The main idea of our research is to estimate the physical coalescence time of the double supermassive black hole (SMBH) system in the centre of NGC 6240 based on the X-ray observations from the Chandra space observatory. The spectra of the northern and southern nuclei were fitted by spectral models from Sherpa and both presented the narrow component of the Fe Kα emission line. It enabled us to apply the spectral model to these lines and to find relative offset ≈0.02 keV. The enclosed dynamical mass of the central region of NGC 6240 with radius 1 kpc was estimated ≈2.04×1011M⊙ . These data allowed us to carry on the high-resolution direct N-body simulations with Newtonian and post-Newtonian (up to 2.5PN correction) dynamics for this particular double SMBH system. As a result, from our numerical models, we approximated the central SMBH binary merging time for the different binary eccentricities. In our numerical parameters range, the upper limit for the merging time, even for the very small eccentricities, is still below ≈70 Myr. Gravitational waveforms and amplitude-frequency pictures from such events can be detected using pulsar timing array projects at the last merging phase.Show more Item Open Access A NUMERICAL STUDY OF STELLAR DISCS IN GALACTIC NUCLEI(Monthly Notices of the Royal Astronomical Society, 2022) Panamarev, Taras; Kocsis, BenceShow more We explore the dynamics of stellar discs in the close vicinity of a supermassive black hole (SMBH) by means of direct N-body simulations. We show that an isolated nuclear stellar disc exhibits anisotropic mass segregation meaning that massive stars settle to lower orbital inclinations and more circular orbits than the light stars. However, in systems in which the stellar disc is embedded in a much more massive isotropic stellar cluster, anisotropic mass segregation tends to be suppressed. In both cases, an initially thin stellar disc becomes thicker, especially in the inner parts due to the fluctuating anisotropy in the spherical component. We find that vector resonant relaxation is quenched in the disc by nodal precession, but it is still the most efficient relaxation process around SMBHs of mass 106M⊙ and above. Two-body relaxation may dominate for less massive SMBHs found in dwarf galaxies. Stellar discs embedded in massive isotropic stellar clusters ultimately tend to become isotropic on the local two-body relaxation time-scale. Our simulations show that the dynamics of young stars at the centre of the Milky Way is mostly driven by vector resonant relaxation leading to an anticorrelation between the scatter of orbital inclinations and distance from the SMBH. If the S-stars formed in a disc less than 10 Myr ago, they may coexist with a cusp of stellar mass black holes or an intermediate mass black hole with mass up to 1000M⊙ to reproduce the observed scatter of angular momenta.Show more Item Open Access ON THE DUALITY OF SCHWARZSCHILD-DE SITTER SPACETIME AND MOVING MIRROR(Classical and Quantum Gravity, 2022) Fernandez-Silvestre, Diego; Foo, Joshua; Good, Michael R.R.Show more The Schwarzschild-de Sitter (SdS) metric is the simplest spacetime solution in general relativity with both a black hole event horizon and a cosmological event horizon. Since the Schwarzschild metric is the most simple solution of Einstein’s equations with spherical symmetry and the de Sitter metric is the most simple solution of Einstein’s equations with a positive cosmological constant, the combination in the SdS metric defines an appropriate background geometry for semi-classical investigation of Hawking radiation with respect to past and future horizons. Generally, the black hole temperature is larger than that of the cosmological horizon, so there is heat flow from the smaller black hole horizon to the larger cosmological horizon, despite questions concerning the definition of the relative temperature of the black hole without a measurement by an observer sitting in an asymptotically flat spacetime. Here we investigate the accelerating boundary correspondence (ABC) of the radiation in SdS spacetime without such a problem. We have solved for the boundary dynamics, energy flux and asymptotic particle spectrum. The distribution of particles is globally non-thermal while asymptotically the radiation reaches equilibriumShow more Item Open Access ON-SKY SILICON PHOTOMULTIPLIER DETECTOR PERFORMANCE MEASUREMENTS FOR MILLISECOND TO SUB-MICROSECOND OPTICAL SOURCE VARIABILITY STUDIES(arxiv, 2020) Lau, Albert Wai Kit; Shafiee, Mehdi; Smoot, George F.; Grossan, Bruce; Li, Siyang; Maksut, ZhanatShow more In our Ultra-Fast Astronomy (UFA) program, we aim to improve measurements of variability of astro nomical targets on millisecond and shorter time scales. In this work, we present initial on-sky measurements of the performance of silicon photomultiplier detectors (SiPMs) for UFA. We mounted two different SiPMs at the focal plane of the 0.7-meter aperture Nazarbayev University Transient Telescope at the Assy-Turgen Astrophysical Observatory (NUTTelA-TAO), with no filter in front of the detector. The 3mm × 3mm SiPM single-channel detectors have a field of view of 2.27160 × 2.27160 . During the nights of 2019 October 28-29, we measured sky background, bright stars, and an artificial source with a 100Hz flashing frequency. We compared detected SiPM counts with Gaia satellite G-band flux values to show that our SiPMs have a linear response. With our two SiPMs (models S14520-3050VS and S14160-3050HS), we measured a dark current of ∼130 and ∼85 kilo counts per second (kcps), and a sky background of ∼201 and ∼203 kcps, respectively. We measured an intrinsic crosstalk of 10.34% and 10.52% and derived a 5σ sensitivity of 13.9 and 14.0 Gaia G-band magnitude for 200ms exposures, for the two detectors respectively. For a 10 µs window, and allowing a false alarm rate of once per 100 nights, we derived a sensitivity of 22 detected photons, or 6 Gaia G-band magnitudes. For nanosecond timescales, our detection is limited by crosstalk to 12 detected photons, which corresponds to a fluence of ∼155 photons per square meterShow more Item Open Access OUT OF ONE, MANY: DISTINGUISHING TIME DELAYS FROM LENSED SUPERNOVAE(Monthly Notices of the Royal Astronomical Society, 2022) Denissenya, Mikhail; Bag, Satadru; Kim, Alex G; Linder, Eric V; Shafieloo, ArmanShow more Gravitationally lensed Type Ia supernovae are an emerging probe with great potential for constraining dark energy, spatial curvature, and the Hubble constant. The multiple images and their time delayed and magnified fluxes may be unresolved, however, blended into a single light curve. We demonstrate methods without a fixed source template matching for extracting the individual images, determining whether there are one (no lensing) or two or four (lensed) images, and measuring the time delays between them that are valuable cosmological probes. We find 100 per cent success for determining the number of images for time delays greater than ∼10 d.Show more Item Open Access UNDERSTANDING THE ‘FEEBLE GIANT’ CRATER II WITH TIDALLY STRETCHED WAVE DARK MATTER(Monthly Notices of the Royal Astronomical Society, 2022) Pozo, Alvaro; Broadhurst, Tom; Emami, Razieh; Smoot, GeorgeShow more The unusually large ‘dwarf’ galaxy Crater II, with its small velocity dispersion, ≃3 km s−1, defies expectations that low-mass galaxies should be small and dense. We combine the latest stellar and velocity dispersion profiles finding Crater II has a prominent dark core of radius ≃0.71+0.09−0.08 kpc, surrounded by a low density halo, with a transition visible between the core and the halo. We show that this profile matches the distinctive core-halo profile predicted by ‘Wave Dark Matter’ as a Bose-Einstein condensate, ψDM, where the ground state soliton core is surrounded by a tenuous halo of interfering waves, with a marked density transition predicted between the core and halo. Similar core-halo structure is seen in most dwarf spheroidal galaxies (dSphs), but with smaller cores, ≃0.25 kpc and higher velocity dispersions, ≃9 km s−1, and we argue here that Crater II may have been a typical dSph that has lost most of its halo mass to tidal stripping, so its velocity dispersion is lower by a factor of 3 and the soliton is wider by a factor of 3, following the inverse scaling required by the Uncertainty Principle. This tidal solution for Crater II in the context of ψDM is supported by its small pericenter of ≃20 kpc established by Gaia, implying significant tidal stripping of Crater II by the Milky Way is expected.Show more