I will briefly review what X-ray surveys and their multiwavelength follow-up have revealed about the sources constituting the cosmic X-ray background (CXRB), focusing on results from the past 25 years from missions including Chandra, Einstein Probe, INTEGRAL, NuSTAR, SRG, Swift, and XMM-Newton. I will first detail the identification, classification, and basic nature of the extragalactic...
Surveys of the radio sky have a long history, dating back to the very early days of radio astronomy. These early surveys provided crucial input to our understanding of both cosmology and the AGN/quasar population. As the field of radio astronomy has evolved so to have survey techniques, resulting in the current "Golden Age" of radio surveys. Wide-field surveys today cover frequency ranges from...
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...
5 years after the launch from the Russian Baikonur Cosmodrome, all systems and instruments of the Spektr-RG (SRG) observatory are working perfectly. With eROSITA, the German contribution to this mission, half of all 8 sky surveys have been completed so far. Millions of X-ray sources, mostly of an extragalactic nature, have been discovered. This has confirmed what we had hoped for before the...
An overview of highlights and discoveries from Mikhail Pavlinsky ART-XC telescope on board the SRG observatory is presented. Since 2019 SRG/ART-XC has conducted several full all sky surveys as well as a deep survey of our Galaxy. As a result, we obtained the catalogue of hard X-ray sources detected at the all sky, which includes more than one and a half thousand objects, most of them are...
During the 2.5 years in 2019-2022 the eROSITA telescope onboard the SRG space observatory produced a deep all-sky survey in soft X-rays. The competitive analysis of this unique data requires: firstly, massive usage of publicly available sky surveys (photometric, spectroscopic, astrometric) in the broad spectral range from Radio to UV; secondly - intensive application of modern machine learning...
SRG/eROSITA and microwave observations of clusters of galaxies
The Einstein Probe mission is a dedicated satellite for time-domain astrophysics collaborated with ESA, MPE as well as CNES, which was launched on Jan. 9, 2024. There are two payloads onboard EP, the Wide-Field X-ray telescope (WXT) and the Follow-up X-ray telescope (FXT). WXT employ the Lobster-Eye Optics with FOV of about 3830 square degrees by 12 modules. FXT employ traditional Wolter-I...
Wide Field Survey Telescope (WFST) is the largest time-domain survey facility in the northern hemisphere. The telescope is a dedicated photometric surveying facility being built jointly by the University of Science and Technology of China (USTC) and the Purple Mountain Observatory(PMO). It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera...
As China's first X-ray astronomy satellite, Insight-HXMT has been successfully operating in orbit for over seven years since its launch in 2017, producing substantial findings in the study of compact objects. As a next-generation space mission, CATCH will utilize the collaborative capabilities of a multi-satellite constellation, presenting significant scientific potential in exploring the...
The INTEGRAL hard X-ray surveys have proven to be of fundamental importance. In more than twenty years of operation, the INTEGRAL observatory has given us a sharper view of the hard X-ray sky, and provided the triggers for many follow-up campaigns from radio frequencies to gamma-rays. In addition to conducting a census of hard X-ray sources across the entire sky, INTEGRAL has carried out...
The Pierre Auger Observatory is conceived to study ultra-high energy cosmic rays from about 10^17 eV to beyond 10^20 eV. It is a multi-hybrid Observatory comprising 1660 surface detector stations spread over an area of 3000 km2 over-looked by 27 imaging Fluorescence telescopes erected at four sites at its periphery. Each of the detector stations consists of a 10 m2 water Cherenkov detector...
We discuss propagation of heavy nuclei at energies higher than 10 19 eV from their sources to the Earth, assuming them to be of extragalactic origin. In extragalactic space nuclei interact with background emission and inevitably decay. Analyzing the content of heavy nuclei arriving the Earth we reveal their energy at the Earth as a function of the source-Earth distance. It is found that the...
The integration of Artificial Intelligence (AI) into astronomy and astrophysics marks a transformative era in the exploration of the Universe, enhancing the analysis of vast data sets with unparalleled efficiency and precision. AI is revolutionizing the usability of observational data, expanding our understanding of various cosmic phenomena. Blazar research particularly benefits from the...
The cosmic environments of accreting supermassive black holes provide powerful insights on the intertwined histories of structure growth, black hole growth, and galaxy evolution. One way to probe these environments is via the spatial clustering of active galactic nuclei (AGN). Using new data from the BASS and HETDEX wide-field surveys, I will present recent AGN clustering measurements as a...
We were quite fortunate with John Wheeler introducing the concept of Black Hole (BH) and more important using the Kerrr mathematical solution to find the BH mass energy formula with Christodoulou and Hawking. We have been equally fortunate to participate in developing the largest observational effort extending to the earliest million years from the Big Bang and observing BH in all range of...
We search for reflection-dominated Compton-thick active galactic nuclei (CT AGN) candidates in the Lockman Hole region using the SRG/eROSITA Lockman Hole survey data. To this end, we selected sources with anomalously hard photon indexes in the 0.3 $-$ 8.0 keV band, untypical for type I AGN. In particular, we required that the upper end of the 90% error interval did not exceed a fudicial...
We present a comprehensive multi-wavelength analysis of NGC 1275/Perseus A, focusing on its X-ray and gamma-ray emission over a 24-year period (2000-2024). Our study utilizes data from multiple space-based observatories, including SUZAKU, XMM-Newton, SWIFT, and INTEGRAL. The X-ray data observed by Suzaku/XIS were treated using a model-independent method for separating the spectral components...
We will discuss pair creation by electrically neutral compact astrophysical objects, having sufficiently sharp positively charged surface boundary to create an electrosphere with overcritical electric field. Two types of energy sources will be considered: heat and radial electromagnetic perturbation. Implications for astrophysical observations will be outlined.
In this report we would like to discuss recent developments in ground-based gamma-ray astrophysics. Since the 1990s, very high energy gamma rays have been studied with the Imaging Atmospheric Cherenkov Telescopes (IACT), which measure the Cherenkov light component of air showers. These have high sensitivity in a field of view of several degrees and can provide angular resolution on the order...
The Cherenkov Telescope Array will bring an entirely new view on high-energy transients. This opportunity will be enhanced by the coming on line of various large field-of-view ground-based and orbiting facilities that will paint a multi-wavelength picture of the variable sky. I will discuss some of the exploration areas and projects development, including the VST Polarimetric camera (VSTPol).
Extragalactic TeV astronomy with Cherenkov telescopes is synergistic with multi-frequency and multi-messenger observations, conducted through observational campaigns or triggers (target of opportunities).
We will outline these two main directions by presenting recent results from multifrequency observations of blazars, such as the quasi-periodic PG1553+113, and by discussing the prospects...
The acceleration of charged particles to very high energies in powerful astrophysical sources such as pulsar winds, active galactic nuclei, gamma-ray bursts etc., represents a central question in modern high-energy astrophysics, astroparticle physics and nowadays, multi-messenger astronomy. Accelerated particles can interact with and radiate in ambient fields to produce secondary photon or...
The modern radio sky surveys have shown that compact radio sources, so named FR0 radio galaxies, are the majority among radio loud active galactic nuclei of the local Universe. The numerous FR0 population have to make a significant contribution to cosmic background emissions. These sources have mildly relativistic jets at parsec scales despite lack of prominent extended kpc radio structures....
Supermassive black holes are ubiquitous in the nearby Universe. AGN feedback is thought to be a key mechanism that regulates the growth of supermassive black holes and their joint evolution with their host galaxies. How and when did these mysterious objects form? How did they grow quickly enough to power high-redshift quasars? I will summarize recent discoveries made with the JWST that offer...
Supernovae are among the most energetic and luminous events in the universe, providing unique opportunities to study stellar evolution, nucleosynthesis, the dynamics of interstellar matter, and the physics of stellar remnants such as neutron stars and black holes. The next galactic supernova could offer unprecedented insights if we are adequately prepared to discover it. This paper briefly...
Wide-field time-domain surveys across the multi-wavelength spectrum have revealed a complex array of transient and variable phenomena from SMBH populations, including flares from tidal disruption events (TDEs), ‘changing-look’ events when AGN broad lines appear or disappear following an optical flare, and other classes of extreme AGN variability. These events provide important insights into...
Almost all galaxies contain a supermassive black hole (masses > 100,000 solar masses) residing at their center. In the last decade or so a subsample of these black holes are found to exhibit repeating X-ray modulations with timescales ranging from a few minutes to up to a month. The nature of these recurring signals is currently debated but most ideas can be put into two categories: they are...
Galactic nuclei are extreme environments where stars are densely packed around a supermassive black hole (SMBH). Occasionally, dynamical interactions in the galactic center cause stars to interact violently at short distances with each other or with the SMBH, resulting in the formation of nuclear transients. In this talk, I will discuss two types of extreme nuclear transients: extreme tidal...
Extragalactic Fast X-ray Transients (FXTs) are X-ray flashes lasting minutes to hours. Their nature is unclear, but the most remarkable scenarios related to them are shock breakout supernovae, tidal disruption events involving white dwarf stars and intermediate massive black holes, and binary neutron star mergers. Observing them using different wavelength facilities in the coming hours and...
The four completed SRG Observatory half-year all-sky surveys have yielded a significant number of variable X-ray sources.
The SRG/eROSITA telescope has discovered a rich population of tidal disruption events (TDE) that exhibit strong X-ray variability.
Searching for TDE in the X-ray band offers certain advantages over a selection in the optical range.
In X-rays, the background flux of the...
The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a mission conceptdeveloped by a large European collaboration under study by ESA since2018 and currently one of the three candidate M7 mission for a launch in mid '30s. THESEUS aims at fully exploiting Gamma-Ray Bursts for investigating the early Universe and as keyphenomena for multi-messenger astrophysics. By providing an...
The Iranian National Observatory (INO) is poised to become a significant contributor to the global effort in monitoring and following up on transient astronomical events. With its 3.4-meter optical telescope strategically located in a low-density region of telescopes on Mount Gargash at 3600 m above sea level in central Iran, the INO offers a unique opportunity to fill critical gaps in the...
The discovery of high-energy cosmic neutrinos opened a new window of astroparticle physics. Their origin is a new mystery in the field, which is tightly connected to the long-standing puzzle about the origin of cosmic rays. I will discuss theoretical implications of the latest results on high-energy neutrino observations, and demonstrate the power of multimessenger approaches. In particular, I...
While most of neutrinos can traverse the Earth, the sensitivity of high-energy neutrino telescopes varies significantly depending on whether the neutrinos are detected from above or below the horizon. The deployment of large-scale detectors in both hemispheres, such as Baikal-GVD and KM3NeT in addition to IceCube, is essential for full-sky studies of neutrinos across a wide energy range. I...
I will briefly review the current status of the NewAthena mission, with particular emphasis on its NewScience Performances for surveys and spectroscopic follow-ups
The field of X-ray astronomy has entered an era of spatially-resolved high-resolution spectroscopy, as driven by the technology of microcalorimeters. Through sounding-rocket experiments and the (brief) Hitomi mission in the past, the scientific potential of a microcalorimeter-based X-ray spectrometer is well illustrated and is highly exciting. All eyes are now on XRISM, with the expectation of...
The National Academies’ 2020 Decadal Survey in Astronomy and Astrophysics, Pathways to Discovery in Astronomy and Astrophysics for the 2020s recommended probe missions to be competed to accomplish the survey’s scientific goals. In particular, a far-infrared or an X-ray probe was recommended. In response to this, NASA posted the Astrophysics Probe Explorer Announcement of Opportunity (AO), to...
The LIGO-Virgo-KAGRA detectors have so far registered only 2 mergers of binary neutron stars GW170817 and GW190425. Based on the experience of searching and observing electromagnetic components of these mergers (GRB 170817 and GRB 190425), we consider the properties of these components in the gamma-range and discuss the possibility of registering electromagnetic components in the future.
In this work, we studied X-ray source SRGe J021932.4-040154, that we associated with a single X-ray active star of spectral class G2V-G4V and the rotational period $P_{\rm rot} = 3.2 \pm 0.5$ days. The SRGe J021932 was observed with the SRG/eRROSITA during eUDS survey in 2019 in much dimmer state compared to the XMM-Newton catalogue 4XMM-DR12. Detailed analysis revealed that the archival...
The Nuclear Stellar Disk (NSD), along with the Nuclear Stellar Cluster (NSC) and the supermassive black hole Sgr A*, forms the central region of the Milky Way. Observations have well established that the Galaxy's X-ray emission is associated with the stellar population and predominantly arises from the integrated emission of accreting white dwarfs. This study focuses on the NSD emission in the...
Gamma-ray bursts (GRBs) are among the most explosive and brightest transient phenomena in the universe, occurring at cosmological distances. After decades of investigation, the origin of the jet composition, the radiation, and energy dissipation mechanisms of GRBs are among the most important open questions regarding the nature of the GRB central engine.
Here, we consider the evolution of a...
The origins of supermassive black holes (SMBHs) at the centers of massive galaxies are a topic of intense investigation. One way to address this subject is to identify the seeds of SMBH as intermediate-mass black holes (IMBHs; $100M_\odot < M_{BH} < 10^6M_\odot$). Given the observed relationship between the mass of a black hole and the mass of its host galaxy, IMBHs are expected to be found at...
For nearly 30 years, Konus-Wind has been a tireless workhorse for high-energy astrophysics.In this talk, we provide an overview and recent results from Konus-Wind observations of short, long, and ultra-long gamma-ray busts, Galactic and extragalactic magnetars, and solar flares. The recent results include the detection of giant flares from extragalactic magnetars, the famous SGR/FRB 200428...
Recent observations of TeV emission from Gamma-Ray Bursts (GRBs)
demonstrated with certainty that it belongs to the afterglow phase. Afterglows' emission from radio frequencies to GeV gamma-rays is of synchrotron origin, whereas the TeV component is produced via distinct physical process (inverse Compton). Thus, TeV observations open an entirely new window into physics of relativistic shocks....
A gamma-ray burst (GRB) afterglow is considered an orphan when it is detected without a targeted search triggered by the prompt GRB emission. This can occur when the GRB jet points away from us or if the prompt emission along our line of sight is dim (e.g. a ``dirty fireball''). We present a semi-analytic model for the afterglow lightcurves based on and calibrated with numerical simulations....
We show that Compton scattering by electrons of the hot intergalactic gas in galaxy clusters should lead to peculiar distortions of the cosmic background X-ray and soft gamma-ray radiation - an increase in its brightness at energies smaller than 60-100 keV and a drop at higher energies. In the cluster frame the maximum of the background decrease occurs at ~500-600 keV due to the recoil effect....
We describe the survey of the Galactic Bulge, performed by the Mikhail Pavlinsky ART-XC telescope on board the SRG observatory. In order to obtain the maximal sensitivity the special source detection algorithm was developed, which helped to reduce unusable areas around bright sources, populating the region. Using this algorithm a total of 172 point sources were detected. Of these, 153 are...
We report the study and characterization of two new eclipsing CVs (SRGeJ045359.9+622444 (SRGeJ0453) and SRGeJ041130.3+685350 (SRGeJ0411)) discovered from a joint SRG/eROSITA and ZTF program. These objects were identified as CV candidates in a crossmatch of a 1200 $\rm deg^2$ patch of sky of SRG/eROSITA X-ray data with Gaia proper motion data and the optical ZTF database. SRGeJ0453 and...
We present a study of the radio properties of distant quasars at z$>$3. The complete sample consists of 101 objects with a flux density level greater than 100 mJy at 1.4 GHz selected in a declination range from -35° to +49°. The study based on simultaneous RATAN-600 observations at frequencies of 1.2, 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2017-2020. The flux density measurements uncertainties...
Constraining the mass and spin of black holes is among the holy grails of contemporary research into accreting sources. Any image of a sufficiently optically thin source near a black hole exhibits contributions of extremely lensed light rays, which orbit the black hole due to its inexorable pull before travelling to the observer. In interferometric images like those produced by the Event...
Temperature of the hot gas in galaxy clusters is known to be a reliable proxy for the their total gravitating mass, allowing one to use spectroscopic X-ray observations for halo mass function measurements. Data of shallow wide area surveys, however, often precludes direct fitting of the X-ray spectra, given possible biases arising due to unresolved (multitemperature) inner structure of the...
In this talk we discuss constraints on the parameters of decaying sterile neutrinos as candidates for dark matter particles from the data of telescopes ART-XC and NuSTAR. We also discuss constraints that can be obtained from the data of these telescopes for annihilating dark matter.
The GRAVITY instrument made a remarkable observation during the Near-Infrared flares of 2018, detecting a fast-moving hot spot in what seemed to be a circular orbit around SgrA, the supermassive black hole in our Galactic Center. The Gravity Collaboration attempted to fit the observed flaring behavior with a circular Keplerian orbit, a few gravitational radii from the supermassive black hole....
We investigate accretion flows around rotating black holes (BHs) and obtain self-consistent transonic solutions in full general relativistic prescription. The flow is assumed to be viscous and radiative. Viscosity helps in the removal of angular momentum outwards, allowing matter to get accreted inwards. In addition, viscous heat dissipated makes the matter hotter. On the other hand, radiation...
The new generation of galaxy surveys will provide unprecedented data allowing us to test gravity at cosmological scales. A robust cosmological analysis of the large-scale structure demands exploiting the nonlinear information encoded in the cosmic web. This study delves into the meticulous task of mapping modified gravity (MG) signatures within cosmic volumes by employing a large...
Core-collapse supernovae are powerful explosions marking the end of massive star's lives. These events give birth to neutron stars and, in some cases, black holes. Despite extensive research, the intricate details of these explosions remain elusive. Strong gravitational waves (GWs) emitted during these events carry vital information about their origins. Detecting these waves could...
AGN jets are detected via their radio and/or gamma-ray emissions while the accretion disks by their X-ray to IR radiation. The relation between these two mechanism can be investigated using broad band spectra of bright sources or through population studies, in particular the luminosity-luminosity (L-L) correlation at different wavelength for large samples of AGNs. In general, there is a large...
In this work we will scrutinize the universality of the well-known non-linear relation between the UV and X-ray luminosity of AGNs. The LX-LUV correlation provides insights on the energy generating mechanisms and structural characteristics of AGNs, but it has also been proposed as a cosmological probe, under the assumption that it is redshift independent. However, recent works on the subject...
