scholarly journals The high energy Universe at ultra-high resolution: the power and promise of X-ray interferometry

2021 ◽  
Author(s):  
Phil Uttley ◽  
Roland den Hartog ◽  
Cosimo Bambi ◽  
Didier Barret ◽  
Stefano Bianchi ◽  
...  
Keyword(s):  
Strong Field ◽  
Imaging Spectroscopy ◽  
Hubble Constant ◽  
High Energy ◽  
Observable Universe ◽  
X Ray ◽  
Accretion Flows ◽  
High Energies ◽  
Light Echoes ◽  
The Universe

AbstractWe propose the development of X-ray interferometry (XRI), to reveal the Universe at high energies with ultra-high spatial resolution. With baselines which can be accommodated on a single spacecraft, XRI can reach 100 μ as resolution at 10 Å (1.2 keV) and 20 μ as at 2 Å (6 keV), enabling imaging and imaging-spectroscopy of (for example) X-ray coronae of nearby accreting supermassive black holes (SMBH) and the SMBH ‘shadow’; SMBH accretion flows and outflows; X-ray binary winds and orbits; stellar coronae within $\sim $ ∼ 100 pc and many exoplanets which transit across them. For sufficiently luminous sources XRI will resolve sub-pc scales across the entire observable Universe, revealing accreting binary SMBHs and enabling trigonometric measurements of the Hubble constant with X-ray light echoes from quasars or explosive transients. A multi-spacecraft ‘constellation’ interferometer would resolve well below 1 μ as, enabling SMBH event horizons to be resolved in many active galaxies and the detailed study of the effects of strong field gravity on the dynamics and emission from accreting gas close to the black hole.

OBSERVATIONAL CONSTRAINTS ON STRONG GRAVITY

2011 ◽  
Vol 20 (14) ◽  
pp. 2755-2760
Author(s):  
CHRIS DONE
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Strong Field ◽  
Field Tests ◽  
High Energy ◽  
Observational Constraints ◽  
Tests Of General Relativity ◽  
Strong Gravity ◽  
Accretion Flows ◽  
Spacetime Curvature

Accretion onto a black hole transforms the darkest objects in the universe to the brightest. The high energy radiation emitted from the accretion flow before it disappears forever below the event horizon lights up the regions of strong spacetime curvature close to the black hole, enabling strong field tests of General Relativity. I review the observational constraints on strong gravity from such accretion flows, and show how the data strongly support the existence of such fundamental General Relativistic features of a last stable orbit and the event horizon. However, these successes also imply that gravity does not differ significantly from Einstein's predictions above the event horizon, so any new theory of quantum gravity will be very difficult to test.

scholarly journals Multimessenger observations of counterparts to IceCube-190331A

2020 ◽  
Vol 497 (3) ◽  
pp. 2553-2561
Author(s):  
Felicia Krauß ◽  
Emily Calamari ◽  
Azadeh Keivani ◽  
Alexis Coleiro ◽  
Phil A Evans ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
High Energy ◽  
Spectral Energy ◽  
Ultra High Energy ◽  
X Ray ◽  
High Energy Cosmic Rays ◽  
High Energies ◽  
Neutrino Event ◽  
Promising Tool ◽  
Localization Region

ABSTRACT High-energy neutrinos are a promising tool for identifying astrophysical sources of high and ultra-high energy cosmic rays (UHECRs). Prospects of detecting neutrinos at high energies (≳TeV) from blazars have been boosted after the recent association of IceCube-170922A and TXS 0506+056. We investigate the high-energy neutrino, IceCube-190331A, a high-energy starting event (HESE) with a high likelihood of being astrophysical in origin. We initiated a Swift/XRT and UVOT tiling mosaic of the neutrino localization and followed up with ATCA radio observations, compiling a multiwavelength spectral energy distribution (SED) for the most likely source of origin. NuSTAR observations of the neutrino location and a nearby X-ray source were also performed. We find two promising counterpart in the 90 per cent confidence localization region and identify the brightest as the most likely counterpart. However, no Fermi/LAT γ-ray source and no prompt Swift/BAT source is consistent with the neutrino event. At this point, it is unclear whether any of the counterparts produced IceCube-190331A. We note that the Helix Nebula is also consistent with the position of the neutrino event and we calculate that associated particle acceleration processes cannot produce the required energies to generate a high-energy HESE neutrino.

scholarly journals A NuSTAR view of powerful γ-ray loud blazars

2019 ◽  
Vol 627 ◽  
pp. A72 ◽  
Author(s):  
G. Ghisellini ◽  
M. Perri ◽  
L. Costamante ◽  
G. Tagliaferri ◽  
T. Sbarrato ◽  
...  
Keyword(s):  
Energy Distribution ◽  
Spectral Energy Distribution ◽  
Peak Frequency ◽  
High Energy ◽  
Spectral Energy ◽  
X Rays ◽  
X Ray ◽  
Γ Ray ◽  
The Universe ◽  
Jet Power

We observed three blazars at z >  2 with the NuSTAR satellite. These were detected in the γ-rays by Fermi/LAT and in the soft X-rays, but have not yet been observed above 10 keV. The flux and slope of their X-ray continuum, together with Fermi/LAT data allows us to estimate their total electromagnetic output and peak frequency. For some of them we were able to study the source in different states, and investigate the main cause of the different observed spectral energy distribution. We then collected all blazars at redshifts greater than 2 observed by NuSTAR, and confirm that these hard and luminous X-ray blazars are among the most powerful persistent sources in the Universe. We confirm the relation between the jet power and the disk luminosity, extending it at the high-energy end.

scholarly journals Soft gamma rays from low accreting supermassive black holes and connection to energetic neutrinos

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shigeo S. Kimura ◽  
Kohta Murase ◽  
Péter Mészáros
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Hadronic Interactions ◽  
Neutrino Detectors ◽  
Accretion Flows ◽  
Diffuse Background ◽  
The Universe

AbstractThe Universe is filled with a diffuse background of MeV gamma-rays and PeV neutrinos, whose origins are unknown. Here, we propose a scenario that can account for both backgrounds simultaneously. Low-luminosity active galactic nuclei have hot accretion flows where thermal electrons naturally emit soft gamma rays via Comptonization of their synchrotron photons. Protons there can be accelerated via turbulence or reconnection, producing high-energy neutrinos via hadronic interactions. We demonstrate that our model can reproduce the gamma-ray and neutrino data. Combined with a contribution by hot coronae in luminous active galactic nuclei, these accretion flows can explain the keV – MeV photon and TeV – PeV neutrino backgrounds. This scenario can account for the MeV background without non-thermal electrons, suggesting a higher transition energy from the thermal to nonthermal Universe than expected. Our model is consistent with X-ray data of nearby objects, and testable by future MeV gamma-ray and high-energy neutrino detectors.

scholarly journals The high-energy Sun - probing the origins of particle acceleration on our nearest star

2021 ◽  
Author(s):  
S. A Matthews ◽  
H. A. S. Reid ◽  
D. Baker ◽  
D. S. Bloomfield ◽  
P. K. Browning ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Electric Fields ◽  
Temporal Resolution ◽  
Imaging Spectroscopy ◽  
High Energy ◽  
Particle Accelerator ◽  
Energy Budgets ◽  
X Ray ◽  
Γ Ray ◽  
Photon Spectra

AbstractAs a frequent and energetic particle accelerator, our Sun provides us with an excellent astrophysical laboratory for understanding the fundamental process of particle acceleration. The exploitation of radiative diagnostics from electrons has shown that acceleration operates on sub-second time scales in a complex magnetic environment, where direct electric fields, wave turbulence, and shock waves all must contribute, although precise details are severely lacking. Ions were assumed to be accelerated in a similar manner to electrons, but γ-ray imaging confirmed that emission sources are spatially separated from X-ray sources, suggesting distinctly different acceleration mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic understanding of accelerated particle spectra and the total energy budgets are therefore poorly constrained. Additionally, the recent detection of relativistic ion signatures lasting many hours, without an electron counterpart, is an enigma. We propose a single platform to directly measure the physical conditions present in the energy release sites and the environment in which the particles propagate and deposit their energy. To address this fundamental issue, we set out a suite of dedicated instruments that will probe both electrons and ions simultaneously to observe; high (seconds) temporal resolution photon spectra (4 keV – 150 MeV) with simultaneous imaging (1 keV – 30 MeV), polarization measurements (5–1000 keV) and high spatial and temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray) regimes. These instruments will observe the broad range of radiative signatures produced in the solar atmosphere by accelerated particles.

Young radio sources at high-energies and the γ-ray CSO PKS 1718–649

2018 ◽  
Vol 14 (S342) ◽  
pp. 176-179
Author(s):  
Giulia Migliori
Keyword(s):  
Radio Galaxy ◽  
Radio Galaxies ◽  
High Energy ◽  
Radio Sources ◽  
Host Galaxies ◽  
X Ray ◽  
High Energies ◽  
Γ Rays ◽  
Γ Ray ◽  
High Energy Emission

AbstractObservations at high-energies are important to define the first stages of the evolution of extragalactic radio sources and to characterize the interstellar medium of their host galaxies. In some of the X-ray-observed Compact Symmetric Objects (CSOs, among the youngest and most compact radio galaxies), we measured values of the total hydrogen column densities large enough to slow or prevent the radio source growth. The γ-ray window has the potential to constrain the non-thermal contribution of jets and lobes to the total high-energy emission. However, so far, young radio sources remain elusive in γ-rays, with only a handful of detections (or candidates) reported by Fermi. I present our γ-ray study of the CSO PKS 1718–649, and draw comparison with the restarted, γ-ray detected, radio galaxy 3C 84.

scholarly journals X-Ray Studies of Quasars and Active Galaxies with the Einstein Observatory

1980 ◽  
Vol 5 ◽  
pp. 677-687 ◽  
Author(s):  
William H.-M. Ku
Keyword(s):  
Statistical Tests ◽  
Cosmological Parameters ◽  
High Energy ◽  
Active Galaxies ◽  
X Ray ◽  
Upper Limits ◽  
Extensive Program ◽  
The Universe ◽  
Bl Lacs ◽  
Einstein Observatory

The launch of the Einstein Observatory has added a new and exciting dimension to the study of active galaxies. Not only have a large number of optical and radio active galaxies been detected, but many new examples of high energy activity have been found. The ease with which a large number of quasars may now be studied in the X-ray regime out to a redshift of at least four promises to improve our understanding of the nature of these tremendous powerhouses and the evolution of the universe.The Columbia Astrophysics Laboratory (CAL) is carrying out an extensive program to study active galaxies with the imaging proportional counter (IPC) on board the Einstein Observatory (Giacconi et al. 1979). These observations have already yielded a large number of positive detections including four Seyferts, five N galaxies, seven BL Lacs, and 17 quasars. Upper limits were obtained for eight additional quasars. Six new Seyfert I and/or quasars have been identified from X-ray observations (Chanan 1979). Preliminary results from the first six months of the CAL survey of active galaxies will be presented below. A few representative objects of interest will be discussed briefly. Simple statistical tests will be applied to determine whether X-ray properties can be used to understand the differences and similarities between the various classes of active galaxies. Particular emphasis will be placed on the quasars in our sample. Our results for the quasar survey will be compared with those discussed by Tananbaum et al. (1979). Finally, the implications of the discovery of a large number of quasars will be briefly discussed. (Cosmological parameters of qo = 0 and Ho = 50 km (s Mpc)-1 are used throughout.)

scholarly journals The Gravothermal Instability at All Scales: From Turnaround Radius to Supernovae

Universe ◽  
2019 ◽  
Vol 5 (1) ◽  
pp. 12 ◽  
Author(s):  
Zacharias Roupas
Keyword(s):  
Thermal Energy ◽  
Gravitational Instability ◽  
Spatial Scales ◽  
High Energy ◽  
Core Collapse ◽  
Zero Temperature ◽  
High Energies ◽  
Ideal Quantum ◽  
Self Gravity ◽  
The Universe

The gravitational instability, responsible for the formation of the structure of the Universe, occurs below energy thresholds and above spatial scales of a self-gravitating expanding region, when thermal energy can no longer counterbalance self-gravity. I argue that at sufficiently-large scales, dark energy may restore thermal stability. This stability re-entrance of an isothermal sphere defines a turnaround radius, which dictates the maximum allowed size of any structure generated by gravitational instability. On the opposite limit of high energies and small scales, I will show that an ideal, quantum or classical, self-gravitating gas is subject to a high-energy relativistic gravothermal instability. It occurs at sufficiently-high energy and small radii, when thermal energy cannot support its own gravitational attraction. Applications of the phenomenon include neutron stars and core-collapse supernovae. I also extend the original Oppenheimer–Volkov calculation of the maximum mass limit of ideal neutron cores to the non-zero temperature regime, relevant to the whole cooling stage from a hot proto-neutron star down to the final cold state.

Matrix effects in white-beam X-ray fluorescence holography

2015 ◽  
Vol 48 (2) ◽  
pp. 542-549 ◽  
Author(s):  
D. T. Dul ◽  
P. Korecki
Keyword(s):  
Local Structure ◽  
Matrix Effects ◽  
High Energy ◽  
Sensitive Information ◽  
Pure Element ◽  
Model Calculations ◽  
X Ray ◽  
High Energies ◽  
Beam Attenuation ◽  
White Beam

Recently, it has been shown that atomic structure determination with X-ray fluorescence holography (XFH) can be hindered by matrix effects,i.e.beam attenuation and indirect excitation. The analysis was limited to the monochromatic regime. In this work, the description of matrix effects is extended to the polychromatic case. It is shown that matrix effects affect the element sensitivity of white-beam XFH by introducing distortions in the holographic signal which may lead to spurious maxima in the reconstructed image. For high energies of the X-ray beam it is found that the effect of beam attenuation is very weak and indirect excitation mainly contributes to the distortions. A correction for matrix effects is proposed in the high-energy range, which allows one to remove the distortions and retrieve pure element-sensitive information. Numerical model calculations are performed to visualize the reduction of element sensitivity and its implications on local structure imaging.

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