After more than two years of scanning the sky the eROSITA X-ray telescope aboard SRG orbital observatory produced the best ever X-ray maps of the sky and discovered more than three million X-ray sources, of which about 20% are stars with active coronas in the Milky Way, and most of the rest are galaxies with active nuclei, quasars and clusters of galaxies. eROSITA detected over 10^3 sources...
Sw 1644 was one of the most surprising tidal disruption events (TDEs). Its prompt emission in soft gamma-rays triggered Swift. Later this was followed by X-ray and Radio afterglows. The energy implied by the radio afterglow increased by a factor of 10 over a period of a few hundred days, reaching an ultimate value of a few times $10^{52}$ erg. This is much higher than in other TDEs. Recently...
The Imaging X-ray Polarimetry Explorer (IXPE) is a NASA-ASI Small Explorer mission selected on January 2017 and launched on 9$^{th}$ December 2021. Three X-ray mirrors are coupled to three Detector Units clocked at 120$^\circ$ each one hosting a Gas Pixel Detector, sensitive to X-ray polarization designed, built tested, and calibrated by INAF and INFN institutes. Some dozens of celestial...
The polarized X-ray radiation emitted from an accreting low mass X-ray binary (LMXB) is expected to give information about the geometry of the region where the Comptonization occurs and about the spin of the accreting BH. Actually, first results obtained from IXPE seem to reveal that the scenario for LMXBs is more complicated than expected: the polarization properties seem to differ from what...
online talk
If a rotation-powered (non-accreting) pulsar is in a binary with a high-mass star, then the collision of the relativistic pulsar wind with the stellar wind creates an intrabinary shock, generating high-energy radiation. In addition, the shocked pulsar and stellar winds can leave the binary and form a nebula whose properties should vary with the orbital phase. To search for such a nebula, we...
We address i) the point-particle assumption inherent to non-quantum physics. It is singular and entails divergences. ii) In quantum mechanics (QM) EM plays an asymmetric role. It acts on QM fields, but the latter does not react back. We suggest a mutual action-reaction partnership between the two. By so doing, QM fields share their analyticity with EM fields and remove the singularities. iii)...
Observations support the idea that supermassive black holes (SMBHs) power the emission at the center of active galaxies. However, contrary to stellar-mass BHs, there is a poor understanding of their origin and physical formation channel. In this article, we propose a new process of SMBH formation in the early Universe that is not associated with baryonic matter (massive stars) or primordial...
The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has been in operation since early 2020. Largely motivated by the great Arecibo observatory, FAST now perches on the apex of sensitivity among centimeter-band radio instruments and will stay there until the advent of SKA. In a little three years, FAST data has facilitated more than 150 journal papers, including at least 7 on...
In the local universe have been observed enhancements of star formation due to relativistic jets from accreting black holes (BHs). These BH “positive feedbacks” take place by the interaction of BH-jets with high-density molecular clouds, which leads to compression of the gas and subsequent enhancement of star formation. This BH-jet triggering mechanism of star formation must have been more...
MAGIC is a ground-based Imaging Atmospheric Cherenkov Telescope (IACT) for very high energy gamma-ray measurements that has pioneered high-sensitivity measurements down to a few tens of GeV. It includes a system of double telescopes with a diameter of 17 m, separated by a distance of 85 m, operating in coincidence mode (stereo). The telescopes are located at an altitude of 2200 m above sea...
The Extreme Universe is the most powerful and fastest explosions in the Universe associated with the formation and transformation of relativistic stars.
For localization of gravitational-wave, neutrino and gamma-ray events, first of all, optical instruments of the 21st century are needed, which have outstanding technical characteristics: fast response, full robotization and high angular...
The advent of the Cerenkov Telescope Array (CTA) will increase dramatically the number of detected very-high energy transients and will improve the accuracy of their variability timescale sampling. A number of facilities at lower energies are being designed and developed to guarantee accurate follow-up, identification, and monitoring of the counterparts to the TeV emitters. Within this...
In the course of the last decade, the IceCube Neutrino Observatory has marked the first milestones of neutrino astronomy, starting with the discovery and characterisation of the astrophysical neutrino flux. Astrophysical neutrinos are unique tracers of hadronic particle acceleration and could be the key to unveil the origin of high-energy cosmic rays. IceCube has been hunting for the sources...
The progress in the construction and operation of the Baikal Gigaton Volume Detector in Lake Baikal is reported. The detector is designed for search for high energy neutrinos whose sources are not yet reliably identified. It currently includes over 3500 optical modules arranged on 98 strings, providing an effective volume of 0.6 km3 for cascades with energy above 1 PeV. We review the...
25 years after the discovery of the first GRB/SN, SN1998bw remains the best observed example of this extraordinary class of events. Several other GRB/SNe have been discovered, allowing progress in determining their overall properties.
I will review some of the advances and outline the outstanding problems in this field.
One of the problems in the modern cosmology is a so-called Hubble tension (HT), which is the difference between values of the present Hubble constant H0, measured by observation of the universe at redshift z ≤1, and the same value measured by observations of a distant universe by observations of CMB fluctuations corresponding to z ≌1100. We suggest that this Tension may be explained by...
Among astrophysical objects whose emission originates from relativistic shocks are active galactic nuclei, gamma-ray bursts, and pulsar winds. Their exceptionally broad spectra are due to synchrotron and inverse Compton emission of accelerated leptons. Although these radiation processes are common in space, the relativistic shocks and shear flows possess an efficient feedback mechanism that...
I will briefly describe the James Webb Space Telescope and its status. I will provide an overview of its major science results, or planned observations, in areas that will impact cosmology and fundamental physics.
Insight-HXMT (hxmt.cn) is China’s first X-ray astronomy satellite and was successfully launched on June 15th, 2017. It carries three sets of collimated X-ray instruments with large effective areas, covering energy ranges of 1-15 keV, 5-30 keV, and 20-250 keV, respectively. In addition, it can also serve as an all-sky monitor for high energy sources between 0.2 to 3 MeV, such as bright pulsars...
LHAASO is a muti-purpose ground-based array of gamma-ray and cosmic-ray detectors in China, consisting of three detector arrays, the Water Cherenkov Detector Array (WCDA), the Kilo-meter squre Array ( KM2A) and the Wide Field of view Cherenkov Telescope Array (WFCTA). In this talk the observations of the brightest GRB 221009A by LHAASO including SEDs and light curves are to be presented.
It has been thought for decades that rotating black holes (BHs) power the energetic gamma-ray bursts (GRBs) and active galactic nuclei (AGNs), but the mechanism that extracts the BH energy has remained elusive. This problem might be solved when the BH is immersed in an external magnetic field and ionized low-density matter. For a magnetic field parallel to the BH spin, the induced electric...
Due to the technical time delay, greater than $\sim 40$ s, of the XRT instrument on board the Neil Gehrels Swift Observatory satellite, we are not able to observe the x-ray emission occurring less than $\sim 40$ s after a gamma-ray burst (GRB) trigger time. A new strategy is indicated here of using the cosmological dilatation of time in the observer rest frame measured in high redshift GRBs to...
We propose that the progenitor of the Crab Nebula and the Crab pulsar shares similarities with binary-driven hypernovae. The understanding of binary-driven hypernovae has revealed the crucial role played by the explosion of the supernova, as well as the hypercritical accretion of the supernova ejecta onto the binary companion neutron star (NS) and the newborn NS (νNS) in determining the...
The collapse of the CO star forms a newborn neutron star (νNS) and triggers a supernova (SN) explosion. Mass and angular momentum are transferred to the νNS through fallback accretion. The energy from this accretion powers the gamma-ray burst prompt emission, while the synchrotron radiation fueled by the spinning νNS, explains the afterglow. Taking GRB 171205A as an example, we calculate the...
We present recent observations of gamma-ray bursts using the GRB IKI Follow up Network. In particular, we are discussing observations of the long duration GRB 221009A.The burst is the brightest one which registered almost all space-born gamma-ray detectors and saturated most of them. Besides of brightness it is usual GRB at low redshift of z=0.151 and due to its near vicinity both highest...
Due to their strong beaming, relativistic jets are overwhelmingly more likely to be detected from viewing angles close to their jet axis. This makes the angular structure of the jets (and in particular the under-energetic `wings’ of the jet) difficult to explore in the majority of jet powered transient events. Nonetheless, jets viewed mildly off-axis should be commonly detected and the...
Multimessenger studies of blazars combine electromagnetic emission from radio to gamma wavelengths, and neutrino detections up to petaelectronvolts. We demonstrate the synergy of the highest-resolution observations in the radio band and hard X-ray observations, and how they help us study sources of IceCube neutrinos. The radio VLBI technique is uniquely positioned in this space, as its...
We demonstrate an extraordinary effect of energy gain by a single radiating charged particle inside the ergosphere of a Kerr black hole in presence of magnetic field. We solve numerically the covariant form of the Lorentz-Dirac equation reduced from the DeWitt-Brehme equation and analyze energy evolution of the radiating charged particle inside the ergosphere, where the energy of emitted...
A compact supermassive source SgrA* located at the center of our Galaxy has been observed at different wavelengths across the electromagnetic spectrum. It is the closest and largest in projection supermassive black hole candidate. At the same time, its particle acceleration capability related to the cosmic ray and neutrino messengers were not yet experimentally probed despite indirect...
Over the past decade, substantial evidence has emerged supporting the presence of diverse progenitor channels leading to Type Ia Supernovae (SNe Ia). Among these channels, there are SNe Ia originating from carbon-oxygen white dwarfs with sub-Chandrasekhar masses. These white dwarfs undergo detonation and explosion triggered by primary detonation in the helium shell, which has been accreted...
We consider interaction between strong uniform electric field and electron-positron plasma. Depending on initial pair distirbution in momentum space pairs are either created or annihilated in external field. Accounding for back reaction of pairs on the electric field leads in the former case to damped plasma oscillations, while in the latter case to energy transfer from rest mass into internal...
Many Galactic black holes and neutron stars sources in Low-Mass X-Ray Binaries (LMXBs) exhibit quasi-periodic oscillations (QPOs) in the observed X-ray fluxes in their peaks. There are models of high frequency QPOs (HF QPOs) that relate this oscillatory motion to the properties of accretion disk formed in the vicinity of a compact object. Our interest is the study this phenomena in the black...
Bimodal distribution of duration of gamma-ray bursts (GRBs) has led to two progenitors; compact star mergers (two neutron stars, NSs or a NS and a black hole), for short GRBs (SGRBs),
and collapsars for long GRBs (LGRBs). It is expected that formation rate (FR) of LGRBs should be similar to the cosmic SFR, while that of SGRBs to be delayed relative to the SFR.
The localization of some...
As has been emphasized in the talk of Hansjoerg Dittus, the second quantum revolution enables new technologies which are not accessible through classical physics. These technologies are characterized by the engineering and manipulating of quantum states. In this talk the interface between these new technologies and the gravitational interaction is highlighted by considering a few topics: (i) a...
Progress in physics always has been stimulated by unexplained observations or experiments. Expressions like “dark matter” or “dark energy” might help to apply the present standard physical theories, but cannot explain their origin sufficiently. The situation of fundamental physics today still causes a lot of open questions, e.g. the theoretical inconsistency of quantum mechanics and General...
Black holes represent ideal laboratories to test Einstein's theory of general relativity and alternative theories of gravity. Alternative theories of gravity typically introduce additional degrees of freedom, among them most prominently a scalar field. Depending on the theory, the resulting black holes may then differ significantly from their counterparts in General Relativity. Possessing...
Numerical simulations are the driving force behind much of the theoretical
progress in our understanding of the formation of structure in the
universe. Cosmological simulations must cover a large dynamical and mass
range. A representative volume of the universe should be large, but this
comes at the expense of the resolution. To overcome this problem we developed a new approach over the...
Impressive progress has been achieved recently in studies addressing fundamental physical processes near the event horizon scale of putative cosmic black holes. The detection of gravitational waves, the near infrared interferometry measurements of relativistic stellar orbits and accretion disk hot spot motion in the Galactic Centre, and the millimetre interferometry imaging of the strong...
Local properties of scalar, fermionic and electromagnetic vacua are discussed in the presence of cosmic string type topological defects. As important characteristics of the vacuum state we consider the expectation values of the squared fields, of the energy-momentum tensor and of the current density in the case of charged fields. The topological contributions are extracted from the vacuum...
General relativity (GR) and quantum theory form the basis of the modern physical picture of the universe. However, attempts to unify them inevitably lead to violations of the Einstein Equivalence Principle (EEP) which is the basis of GR. A promising kind of experiments to test the domain of validity of EEP is based on measuring the gravitational redshift. Recent progress in the stability and...
We consider the gravity assist maneuver, that is, a correction of spacecraft motion at its passing near a planet, as a tool for evaluating the Eddington post-Newtonian parameters $\beta$ and $\gamma$, characterizing vacuum spherically symmetric gravitation fields in metric theories of gravity. We estimate the effect of variation in $\beta$ and $\gamma$ on a particular trajectory of a probe...
We consider the generalized Tolman solution of general relativity, describing the evolution of a spherical dust cloud in the presence of an external electric or magnetic field. In such models, we study the possible existence of wormhole throats defined as spheres of minimum radius at a fixed time instant, and prove the existence of throats in the elliptic branch under certain conditions...
We study the quantum-gravitational corrections to the power spectrum of a gauge-invariant inflationary scalar perturbations in a closed model of a universe. We consider canonical quantum gravity as an approach to quantizing gravity. This leads to the Wheeler-DeWitt equation, which has been studied by applying a semiclassical Born–Oppenheimer type of approximation. At the corresponding orders...
The knowledge of electromagnetic field of charged particles in the vicinity of a black hole is important for the study of many astrophysical phenomena, in particular of gamma-ray bursts and jets of supermassive black holes. In the present work we determine multipole coefficients of electromagnetic field for charged particle, radially falling into Schwarzschild black hole and consider the limit...
Due to the high-density nuclear matter equation of state (EOS) being as yet unknown, neutron stars (NSs) do not have a confirmed limiting “Chandrasekhar” type maximum mass. However,observations of NSs (PSR J1614-2230, PSR J0348+0432, PSR J0740+6620, PSR J0952–0607) indicate that NS’s limiting mass, if there is any, could be well over $2M⊙$. On the other hand, there exists an observational mass...
We consider general radially moving frames realized in the background of nonextremal black holes having causal structure similar to that of the Schwarzschild metric. In doing so, we generalize the Lemaître approach, constructing free-falling frames which are built from the reference particles with an arbitrary specific energy $e_0$ including $e_0<0$ and a special case $e_0=0$. The general...
We consider a family of 4-dimensional black hole solutions
governed by natural number $q= 1, 2, 3 , \dots$, which appear in the model with anisotropic fluid and the equations of state: $p_r = -\rho (2q-1)^{-1}$, $p_t = - p_r$, where $p_r$ and $p_t$ are pressures in radial and transverse directions, respectively, and $\rho > 0$ is the density. These equations of state obey weak,...
We consider the motion of charged particles in Gutsunaev--Manko spacetime, which is the exact solution of the Einstein--Maxwell field equations for a massive dipole. In the present work we study periodic orbits symmetric with respect to the equatorial plane. The spacetime is static and axially symmetric, therefore the problem is reduced to the motion in two-dimentional effective potential. We...
The present upper limit on the amount of tensor perturbations (primordial gravitational waves) generated during inflation, the tensor-to-scalar ratio r < 0.03, excludes many inflationary models popular in the past, like those with a power-law inflaton potential (‘chaotic inflation’). However, a number of viable inflationary models still remain including the three one-parametric models: the...
The huge luminosity, the redshift distribution extending at least up to z∼10 and the association with the explosive death of very massive stars make long GRBs (i.e., those lasting up to a few minutes) potentially extremely powerful probes for shedding light on main open issues in our understanding of the early Universe: star formation rate evolution up to the first generation of stars...
Interest to astrophysical evidence for primordial black holes formed in the early Universe from initial cosmological perturbation has increased after the discovery of coalescing binary black holes with masses more than dozen solar ones by gravitational-wave observatories. I will discuss the formation channels of merging binary black holes with a special focus on the possibility that some...
Titarchuk, Lev (University of Ferrara, Italy and Seifina, Elena (GAISH, MSU, Russia
In 2017 the work on the Comptonization (Sunyaev-Titarchuk) seen in the X-ray spectra of astrophysical sources was a candidate for the Nobel Prize in Physics. In this talk I provide all the details of the exciting prehistory of this topic and precise details of this discovery. The solution of this...
Strong electromagnetic fields polarize the vacuum and electric fields produce charged pairs, the so-called Schwinger effect. The critical strength of electromagnetic fields, whose energy density equals to the rest mass of the charge, cannot be achieved in present laboratories. The critical electric fields enormously produce electron-positron pairs and the critical magnetic field has the lowest...
We consider the decay of a particle with some energy E_0 > 0 inside the ergosphere of a black hole. After the first decay, one of particles with the energy E_1 < 0 falls towards a black hole while the second one with E_2 > E_0 moves in the outward direction. It bounces back from a reflecting shell and, afterwards, the process repeats. For radial motion of charged particles in the...
We analyze the “ballistic method” of rotational energy extraction from an Kerr black hole (BH) by massive particle decay in the BH ergosphere pioneered by Roger Penrose. We focus on the negative energy counterrotating particles in-going to the horizon and evaluate the feedback on the BH irreducible mass (∆Mirr > |E1|). The change in irreducible mass is a function of the ratio of...
In the context of reversible vs. irreversible transformations of a black hole, Christodoulou and Ruffini introduced the notion of irreducible mass, which is related to the event horizon area. The area of the event horizon was subsequently interpreted as the black hole entropy by Hawking and Bekenstein. Furthermore, Penrose conjectured the Weyl curvature hypothesis: the Weyl curvature is a...
Gamma-ray bursts (GRB) are the most energetic explosions that occur naturally in distant galaxies [1]. Their analysis facilitates the probing of early Universe and its expansion, the understanding of stellar evolution, the analysis of high energy phenomena and of the matter under extreme conditions [2, 3, 4]. GRBs constitute excellent natural laboratory settings to test the fundamental physics...
We represent a numerical method for the simulation of 3D differentially rotating astrophysical MHD flows in cylindrical and spherical geometries. This approach belongs to the class of mixed Euler-Lagrange methods. The grid consists of rings which are rotating in a quasi-Lagrangian manner together with the background (differential and solid state) large-scale rotation, significantly reducing...
An optically thin advective accretion disk appears to be indispensable to explain hard-state
of black hole sources. Any transport of matter therein is assumed to be led by (modified) α-viscosity when the magnetic field is weak. We explore how large scale stronger magnetic
field helps in transporting angular momentum, over α-viscosity based transport, depending
on the field geometry....
We use certain compatibility conditions in the formalism of geometrothermodynamics and the non-extensivity property of black holes to argue that the corresponding fundamental equations should be given in terms of quasi-homogeneous functions. As a result, coupling constants in alternative theories of gravity, such as the cosmological constant, the Born-Infeld constant, etc., turn out to be...
Within the precanonical quantization, which we will outline, the dynamics of quantum fields is controlled by the operator of the De Donder-Weyl Hamiltonian (DWH) whose classical version is derived from the Lagrangian. The operator ordering in the DWH operators of GR and its teleparallel equivalent, which is consistent with the diffeomorphism-invariant measure in the scalar product and the...
Calculations of gravitational waves (GWs), both analytical and numerical, assume that they propagate from source to a detector on Earth in a vacuum spacetime. Whilst the average cosmological density of baryonic plus dark matter is small, a detected GW event may be a considerable distance away from its source, up to order 1 Gpc, and the quantity of intervening matter may not be negligible....
In the past decades, several neutron stars (NSs), particularly pulsars, with mass $M>2M_\odot$, have been observed. Hence, there is a generic question of the origin of massive compact objects. Here we explore the existence of massive, magnetized, rotating NSs by solving axisymmetric stationary stellar equilibria in general relativity using the Einstein equation solver for stellar structure XNS...
This paper revives the Descartes-Leibniz debate on the constant quantity of motion. This idea is based on keeping the total energy E=mc2 as a constant where the energy and the mass are independent of the form and speed even when the latter converges to the speed of light. With the increase of the speed, the object transforms the rest energy denoted here as the unexposed energy. The energy...
We aim to study warm inflation via irreversible thermodynamics of open systems with matter creation/decay within Rastall theory of gravity. Interacting scalar field and radiation are assumed to be the components of cosmological fluid in a spatially flat FRW universe model. Considering the early universe as an open system and implementing the thermodynamics on the interacting cosmological fluid...
By using the gravitational decoupling method to create an exact solution to the field equations, this talk discusses the formulation of a charged anisotropic spherically symmetric strange star model. The initial decoupled system is split into Einstein-Maxwell and quasi-Einstein systems using minimal geometric modification. By employing the complexity factor to solve quasi-Einstein field...
General theory and quantum mechanics are fundamentally very different theories with distinct formulations. Nevertheless, both of them claim to predict how Nature works! The everlasting battle for exploring and understanding the Universe and for privileging a consistent perception of reality is therefore awaiting a consolidator rather than a conqueror. This should be capable of either unifying...
