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A semi-analytic approximation is derived for the time-dependent fraction |$f_\gamma (t)$| of the energy deposited by radioactive decay |$\gamma$| -rays in a homologously expanding plasma of general structure. An analytic approximation is given for spherically symmetric plasma distributions. Applied to Kilonovae (KNe) associated with neutron stars mergers and Type Ia supernovae, our semi-analytic and analytic approximations reproduce, with a few per cent and 10 per cent accuracy, respectively, the energy deposition rates, |$\dot{Q}_{\rm dep}$|⁠ , obtained in numeric Monte Carlo calculations. The time |$t_\gamma$| beyond which |$\gamma$| -ray deposition is inefficient is determined by an effective frequency-independent |$\gamma$| -ray opacity |$\kappa _{\gamma ,\text{eff}}$|⁠ , |$t_\gamma = \sqrt{\kappa _{\gamma ,\text{eff}}\langle \Sigma \rangle t^2}$|⁠ , where |$\langle \Sigma \rangle \propto t^{-2}$| is the average plasma column density. For |$\beta$| -decay dominated energy release, |$\kappa _{\gamma ,\text{eff}}$| is typically close to the effective Compton scattering opacity, |$\kappa _{\gamma ,\text{eff}} \approx 0.025$| cm |$^{2}$|  g |$^{-1}$| with a weak dependence on composition. For KNe, |$\kappa _{\gamma ,\text{eff}}$| depends mainly on the initial electron fraction |$Y_e$|⁠ , |$\kappa _{\gamma ,\text{eff}} \approx 0.03(0.05)$| cm |$^{2}$|  g |$^{-1}$| for |$Y_e \gtrsim (\lesssim) 0.25$| (in contrast with earlier work that found |$\kappa _{\gamma ,\text{eff}}$| larger by 1–2 orders of magnitude for low |$Y_e$|⁠), and is insensitive to the (large) nuclear physics uncertainties. Determining |$t_\gamma$| from observations will therefore measure the ejecta |$\langle \Sigma \rangle t^2$|⁠ , providing a stringent test of models. For |$\langle \Sigma \rangle t^2=2\times 10^{11}~{\rm g\, {cm}^{-2}\, s^2}$|⁠ , a typical value expected for KNe, |$t_\gamma \approx 1$| d. [ABSTRACT FROM AUTHOR]

The soft X-ray excess in the spectra of active galactic nuclei is characterized by similar electron temperatures of 0.1–0.3 keV and similar photon indices around 2.2–3, if fitted with inverse Comptonization. It remains a puzzle why both values are not sensitive to the black hole mass nor the accretion rate. Supposing that the scattering-dominated surface layer of an accretion disk can act as a warm corona, we construct a vertical one-zone model to understand what determines its temperature. By solving the equations of (1) the condition for the effective optical depth, (2) the energy balance, and (3) the dominance of the Compton cooling over the bound–free cooling, we could reproduce the basic observational features of the soft excess, provided that anomalous heating (excess heating other than what is expected by local energy dissipation) takes place in the warm corona in agreement with similar studies done so far. The similar temperatures can be understood, since both the anomalous heating and Compton cooling rates are proportional to the dissipation rate of the accretion energy, while similar photon indices are a natural consequence of the fact that observed photons are finally emitted from the layer of Compton y ∼ 1. The soft excess is not observed in black hole binaries, since disk temperatures are too high for the Compton scattering to work as cooling. The derived temperatures are somewhat of an underestimation, however. This may indicate a necessity of multi-zone corona structure. The stability of the warm corona and its consequences are briefly discussed. [ABSTRACT FROM AUTHOR]

Gamma-ray bursts (GRBs) comprise short, bright, energetic flashes of emission from extragalactic sources followed by a longer afterglow phase of decreased brightness. Recent discoveries of very high energy (VHE, ≳100 GeV) afterglow emission from GRB 180720B and GRB 190829A by the High Energy Stereoscopic System have raised questions regarding the emission mechanism responsible. We interpret this observed late-time emission to be the result of inverse Compton emission of ultrarelativistic electrons in the GRB blast wave in an external radiation field, i.e. external Compton (EC), considering both the wind and interstellar medium scenarios. We present predictions of multiwavelength light curves and energy spectra, ranging from optical to VHE, and include the synchrotron and synchrotron self-Compton (SSC) radiation mechanisms as well. We corrected the EC and SSC models for the gamma-ray attenuation by absorption of photons through their interaction with the extragalactic background light. We compared our results to multiwavelength data and found that EC gives a satisfactory fit for a given set of fixed model parameters for GRB 180720B, whereas SSC results in a better fit for GRB 190829A. For both GRBs, a wind environment is preferred over constant-density interstellar medium, and the cosmic microwave background as the external radiation field. However, with more data and an effective optimization tool we can find a more robust fit of the model, implying better constraints on the GRB environment and the particle energy requirements for the emission observed at late times. This has consequences for future observations of GRBs at these extreme energies. [ABSTRACT FROM AUTHOR]

Low-luminosity active galactic nuclei are strong sources of X-ray emission produced by Compton scattering originating from the accretion flows surrounding their supermassive black holes. The shape and energy of the resulting spectrum depend on the shape of the underlying electron distribution function (DF). In this work, we present an extended version of the grmonty code, called κmonty. The grmonty code previously only included a thermal Maxwell–Jütner electron DF. We extend the grmonty code with non-thermal electron DFs, namely the κ and power-law DFs, implement Cartesian Kerr–Schild coordinates, accelerate the code with mpi , and couple the code to the non-uniform adaptive mesh refinement grid data from the general relativistic magnetohydrodynamics code bhac. For the Compton scattering process, we derive two sampling kernels for both DFs. Finally, we present a series of code tests to verify the accuracy of our schemes. The implementation of non-thermal DFs opens the possibility of studying the effect of non-thermal emission on previously developed black hole accretion models. [ABSTRACT FROM AUTHOR]

Radiation hydrodynamical equations with Compton scattering are presented in a convenient way; equations are available in the subrelativistic regime of |$k_{\rm B}T/(m_{\rm e}c^2) \lesssim 0.1$|⁠ , |$h\nu /(m_{\rm e}c^2) \lesssim 0.1$| (or |$k_{\rm B}T_{\rm rad}/(m_{\rm e}c^2) \lesssim 0.1$|⁠), and |$v/c \lesssim 0.1$|⁠ , where T is the electron temperature, ν the photon frequency, T rad the photon temperature, and v the fluid bulk velocity. Several basic concepts and radiation hydrodynamical phenomena under Compton scattering are briefly discussed; e.g. electron-scattering opacity and the Eddington luminosity, optical depth and a static atmosphere, the photon trapping radius, the magic terminal speed, the pseudo-photosphere of radiative winds, the explicit form of basic equations for steady flows, radiation acoustic wave, and so on. [ABSTRACT FROM AUTHOR]

We present analyses of an Intermediate Polar, IGR J15094-6649, based on the archival optical data obtained from the Transiting Exoplanet Survey Satellite (TESS) and X-ray data obtained from the Suzaku, NuSTAR , and Neil Gehrels Swift Observatory (Swift). Present analysis confirms and refines the previously reported spin period of IGR J15094-6649 as 809.49584 ± 0.00075 s. Clear evidence of a beat period of 841.67376 ± 0.00082 s is found during the long-term TESS optical observations, which was not evident in the earlier studies. The dominance of X-ray and optical spin pulse unveils the disc-fed dominance accretion, however, the presence of an additional beat frequency indicates that part of the accreting material also flows along the magnetic field lines. The energy-dependent spin pulsations in the low (<10 keV) energy band are due to the photoelectric absorption in the accretion flow. However, the complex absorbers may be responsible to produce low amplitude spin modulations via Compton scattering in the hard (>10 keV) energy band and indicate that the height of the X-ray emitting region may be negligible. The observed double-humped X-ray profiles with a pronounced dip are indicative of the photoelectric absorption in the intervening accretion stream. Analysis of the X-ray spectra reveals the complexity of the X-ray emission, being composed of multitemperature plasma components with a soft excess, reflection, and suffers from strong absorption. [ABSTRACT FROM AUTHOR]

Magnetar giant flares (MGFs) have been long proposed to contribute at least a subsample of the observed short gamma-ray bursts (GRBs). The recent discovery of the short GRB 200415A in the nearby galaxy NGC 253 established a textbook-version connection between these two phenomena. Unlike previous observations of the Galactic MGFs, the unsaturated instrument spectra of GRB 200415A provide for the first time an opportunity to test the theoretical models with the observed γ-ray photons. This paper proposed a new readily fit-able model for the MGFs, which invokes an expanding fireball Comptonized by the relativistic magnetar wind at photosphere radius. In this model, a large amount of energy is released from the magnetar crust due to the magnetic reconnection or the starquakes of the star surface and is injected into confined field lines, forming a trapped fireball bubble. After breaking through the shackles and expanding to the photospheric radius, the thermal photons of the fireball are eventually Comptonized by the relativistic e ± pairs in the magnetar wind region, which produces additional higher-energy gamma-ray emission. The model predicts a modified thermal-like spectrum characterized by a low-energy component in the Rayleigh-Jeans regime, a smooth component affected by coherent Compton scattering in the intermediate energy range, and a high-energy tail due to the inverse Compton process. By performing a Monte-Carlo fit to the observational spectra of GRB 200415A, we found that the observation of the burst is entirely consistent with our model predictions. [ABSTRACT FROM AUTHOR]

We study the Fourier time lags due to the Comptonization of disc-emitted photons in a spherical, uniform, and stationary X-ray corona, which located on the rotational axis of the black hole. We use monk , a general relativistic Monte Carlo radiative transfer code, to calculate Compton scattering of photons emitted by a thin disc with a Novikov–Thorne temperature profile. We find that the model time lags due to Comptonization remain constant up to a characteristic frequency and then rapidly decrease to zero at higher frequencies. We provide equations that can be used to determine the time lags and cross-spectra for a wide range of values for the corona radius, temperature, optical depth, height, and for various accretion rates and black hole masses. We also provide an equation for the X-ray luminosity of a single corona, as a function of its characteristics and location above the disc. Remarkably, the observed X-ray time lags of nearby, bright active galaxies can be successfully reproduced by inverse Comptonization process of multiple dynamic coronae. [ABSTRACT FROM AUTHOR]

The CZTI (Cadmium Zinc Telluride Imager) onboard AstroSat is a high energy coded mask imager and spectrometer in the energy range of 20–100 keV. Above 100 keV, the dominance of Compton scattering cross-section in CZTI results in a significant number of 2-pixel Compton events and these have been successfully utilized for polarization analysis of Crab pulsar and nebula (and transients like Gamma-ray bursts) in 100–380 keV. These 2-pixel Compton events can also be used to extend the spectroscopic energy range of CZTI up to 380 keV for bright sources. However, unlike the spectroscopy in primary energy range, where simultaneous background measurement is available from masked pixels, Compton spectroscopy requires blank sky observation for background measurement. Background subtraction, in this case, is non-trivial because of the presence of both short-term and long-term temporal variations in the data, which depend on multiple factors like earth rotation and the effect of South Atlantic Anomaly (SAA) regions etc. We have developed a methodology of background selection and subtraction that takes into account for these effects. Here, we describe these background selection and subtraction techniques and validate them using spectroscopy of Crab in the extended energy range of 30–380 keV region, and compare the obtained spectral parameters with the INTEGRAL results. This new capability allows for the extension of the energy range of AstroSat spectroscopy and will also enable the simultaneous spectropolarimetric study of other bright sources like Cygnus X-1. [ABSTRACT FROM AUTHOR]

Accurate computations of spectral distortions of the cosmic microwave background (CMB) are required for constraining energy release scenarios at redshifts z ≳ 103. The existing literature focuses on distortions that are small perturbations to the background blackbody spectrum. At high redshifts (z ≳ 106), this assumption can be violated, and the CMB spectrum can be significantly distorted at least during part of its cosmic evolution. In this paper, we carry out accurate thermalization computations, evolving the distorted CMB spectrum in a general, fully non-linear way, consistently accounting for the time-dependence of the injection process, modifications to the Hubble expansion rate and relativistic Compton scattering. Specifically, we study single energy injection and decaying particle scenarios, discussing constraints on these cases. We solve the thermalization problem using two independent numerical approaches that are now available in CosmoTherm as dedicated setups for computing CMB spectral distortions in the large distortion regime. New non-linear effects at low frequencies are furthermore highlighted, showing that these warrant a more rigorous study. This work eliminates one of the long-standing simplifications in CMB spectral distortion computations, which also opens the way to more rigorous treatments of distortions induced by high-energy particle cascade, soft photon injection, and in the vicinity of primordial black holes. [ABSTRACT FROM AUTHOR]

We present a temporal and spectral study of the blazar PKS 0208−512, using recent flaring activity from 2019 November to 2020 May, as detected by the Fermi Large Area Telescope. The contemporaneous X-ray and optical/ultraviolet observations from the Swift X-Ray Telescope and UltraViolet and Optical Telescope are also used. During the activity state, the 2-d binned γ-ray light curve shows multiple peaks indicating subflares. To understand the possible physical mechanisms behind flux enhancement, we divided the activity state of the source into several flux states and carried out detailed temporal and spectral studies. The timing analysis of light curves suggests that peaks of subflares have rise and decay times of the order of days, with the flux doubling time ∼ 2 d. The 2-d binned γ-ray light curve shows double-lognormal flux distribution. The broad-band spectral energy distribution (SED) for three selected flux states can be well fitted under synchrotron, synchrotron self-Compton and external Compton emission mechanisms. We obtained the physical parameters of the jet by SED modelling and their confidence intervals through χ2-statistics. Our SED modelling results suggest that during the quiescent state, the γ-ray spectrum can be explained by considering the external Compton scattering of infrared photons from the dusty torus. However, γ-ray spectra corresponding to flares demand additional target photons from the broad-line region (BLR) along with infrared. These suggest that, during flares, the emission region is close to the edge of the BLR, while for the quiescent state, the emission region is away from the BLR. The best-fitting results suggest that a marginal increase in the magnetic field during the flaring episode can result in flux enhancement. This is possibly associated with the efficiency of particle acceleration during flaring states compared with the quiescent state. [ABSTRACT FROM AUTHOR]

Relativistic Fe K emission lines from accretion discs and from disc winds encode key information about black holes, and their accretion and feedback mechanisms. We show that these two processes can in principle produce indistinguishable line profiles, such that they cannot be disentangled spectrally. We argue that it is likely that in many cases both processes contribute to the net line profile, and their relative contributions cannot be constrained purely by Fe K spectroscopy. In almost all studies of Fe K emission to date, a single process (either disc reflection or wind Compton scattering) is assumed to dominate the total line profile. We demonstrate that fitting a single process emission model (pure reflection or pure wind) to a hybrid line profile results in large systematic biases in the estimates of key parameters, such as mass outflow rate and spin. We discuss various strategies to mitigate this effect, such as including high-energy data covering the Compton hump, and the implications for future X-ray missions. [ABSTRACT FROM AUTHOR]

Irradiation of the accretion disc causes reflection signatures in the observed X-ray spectrum, encoding important information about the disc structure and density. A Type I X-ray burst will strongly irradiate the accretion disc and alter its properties. Previous numerical simulations predicted the evolution of the accretion disc due to an X-ray burst. Here, we process time-averaged simulation data of six time intervals to track changes in the reflection spectrum from the burst onset to just past its peak. We divide the reflecting region of the disc within r ≲ 50 km into six to seven radial zones for every time interval and compute the reflection spectra for each zone. We integrate these reflection spectra to obtain a total reflection spectrum per time interval. The burst ionizes and heats the disc, which gradually weakens all emission lines. Compton scattering and bremsstrahlung rates increase in the disc during the burst rise, and the soft excess at <3 keV rises from ≈4 to ≈38 per cent of the total emission at the burst peak. A soft excess is expected to be ubiquitous in the reflection spectra of X-ray bursts. Structural disc changes such as inflation because of heating or drainage of the inner disc due to Poynting–Robertson drag affect the strength of the soft excess. Further studies on the dependence of the reflection spectrum characteristics to changes in the accretion disc during an X-ray burst may lead to probes of the disc geometry. [ABSTRACT FROM AUTHOR]

Repeated Compton scattering of photons with thermal electrons is one of the fundamental processes at work in many astrophysical plasma. Solving the exact evolution equations is hard and one common simplification is based on Fokker–Planck (FP) approximations of the Compton collision term. Here we carry out a detailed numerical comparison of several FP approaches with the exact scattering kernel solution for a range of test problems assuming isotropic media and thermal electrons at various temperatures. The Kompaneets equation, being one of the most widely used FP approximations, fails to account for Klein–Nishina corrections and enhanced Doppler boosts and recoil at high energies. These can be accounted for with an alternative FP approach based on the exact first and second moments of the scattering kernel. As demonstrated here, the latter approach works very well in dilute media, but inherently fails to reproduce the correct equilibrium solution in the limit of many scattering. Conditions for the applicability of the FP approximations are clarified, overall showing that the Kompaneets equation provides the most robust approximation to the full problem, even if inaccurate in many cases. We close our numerical analysis by briefly illustrating the solutions for the spectral distortions of the cosmic microwave background (CMB) after photon injection at redshift z  ≲ 105, when double Compton and Bremsstrahlung emission can be omitted. We demonstrate that the exact treatment using the scattering kernel computed with cspack is often needed. This work should provide an important step towards accurate computations of the CMB spectral distortions from high-energy particle cascades. [ABSTRACT FROM AUTHOR]

The choice of the material base to which the material decomposition is performed in dual-energy computed tomography may affect the quality of reconstructed images. The aim of this work is to investigate how the commonly used bases (water, bone), (water, iodine) and (photoelectric effect, Compton scattering) affect the reconstructed linear attenuation coefficient in the case of the Alvarez–Macovski method. The performance of this method is also compared with the performance of the Dual-energy Iterative Reconstruction Algorithm (DIRA). In both cases, the study is performed using simulations. The results show that the Alvarez–Macovski method produced artefacts when iodine was present in the phantom together with human tissues since this method can only work with one doublet. It was shown that these artefacts could be avoided with DIRA using the (water, bone) doublet for tissues and the (water, iodine) doublet for the iodine solution. [ABSTRACT FROM AUTHOR]

We present the long-term X-ray spectral and temporal analysis of a 'bare-type AGN' Ark 120. We consider the observations from XMM–Newton, Suzaku, Swift , and NuSTAR from 2003 to 2018. The spectral properties of this source are studied using various phenomenological and physical models present in the literature. We report (a) the variations of several physical parameters, such as the temperature and the optical depth of the electron cloud, the size of the Compton cloud, and the accretion properties for the last 15 yr. The spectral variations are explained from the changes in the accretion dynamics; (b) the X-ray time delay between 0.2–2 and 3–10 keV light-curves exhibited zero-delay in 2003, positive delay of 4.71 ± 2.1 ks in 2013, and negative delay of 2.90 ± 1.26 ks in 2014. The delays are explained considering Comptonization, reflection, and light-crossing time; (c) the long-term intrinsic luminosities, obtained using nthcomp , of the soft-excess and the primary continuum show a correlation with a Pearson correlation coefficient of 0.90. This indicates that the soft-excess and the primary continuum originate from the same physical process. From a physical model fitting, we infer that the soft excess for Ark 120 could be due to a small number of scatterings in the Compton cloud. Using Monte Carlo simulations, we show that indeed the spectra corresponding to fewer scatterings could provide a steeper soft-excess power law in the 0.2–3 keV range. Simulated luminosities are found to be in agreement with the observed values. [ABSTRACT FROM AUTHOR]

We analytically study the dynamical and thermal properties of the optically thin gases at the parsec-scale when they are spherically accreted on to low luminous active galactic nuclei. The falling gases are irradiated by the central X-ray radiation with the Compton temperature of 5–15 × 107 K. The radiative heating/cooling and the bulge stellar potential in galaxies are taken into account. We analyse the effect of accretion rate, luminosity, gas temperature, and Compton temperature on steady solutions of dynamical and thermal properties. The steady solutions are obviously different from Bondi solution. Compared to our models, the Bondi model underestimates the accretion rate. We give the boundary between thermal stability and instability. The boundary is significantly affected by Compton temperature. When Compton temperature is higher, the falling gases tend to become thermally unstable. When thermal instability takes place in the irradiated gases, the gases become two phases (i.e. hot gases and cool gases) and the hot gases may become outflows. This effect may reduce the accretion rates. [ABSTRACT FROM AUTHOR]

The synchrotron mechanism has the radiation limit of about 160 MeV, and it is not possible to explain the very high energy (VHE) photons that are emitted by high-energy objects. Inverse Compton scattering as a traditional process is applied for the explanation of the VHE emission. In this paper, jitter radiation, the relativistic electron radiation in the random and small-scale magnetic field, is proposed to be a possible mechanism to produce VHE photons. The jitter radiation frequency is associated with the perturbation field. The spectral index of the jitter radiation is dominated by the kinetic turbulence. We utilize the jitter radiation to explain the gamma-ray burst (GRB 190114C and GRB 180720B) VHE emissions that were recently detected by the Imaging Atmospheric Cherenkov Telescopes. We suggest that this mechanism can be applied to other kinds of VHE sources. [ABSTRACT FROM AUTHOR]

We present X-ray spectral and long-term variability analyses of an unbiased sample of 361 optically selected radio-loud quasars (RLQs) utilizing sensitive serendipitous X-ray data from the Chandra and XMM-Newton archives. The spectral and temporal properties of RLQs are compared with those of radio-quiet quasars (RQQs) matched in L 2500Å and z. The median power-law photon index (Γ) of RLQs is |$1.84_{-0.01}^{+0.01}$|⁠ , which is close to that of matched RQQs (⁠|$1.90_{-0.01}^{+0.02}$|⁠). No significant correlations between Γ and radio-loudness, L x/ L x, rqq (the X-ray luminosity over that expected from the L x– L uv relation for RQQs), redshift, or Eddington ratio are found for our RLQs. The stacked X-ray spectra of our RLQs show strong iron-line emission and a possible Compton-reflection hump. The intrinsic X-ray variability amplitude is ≈40 per cent for RLQs on time-scales of months-to-years in the rest frame, which is somewhat smaller than for the matched RQQs (≈60 per cent) on similar time-scales, perhaps due to the larger black hole masses and lower Eddington ratios in our RLQ sample. The X-ray spectral and variability results for our RLQs generally support the idea that the X-ray emission of typical RLQs is dominated by the disc/corona, as is also indicated by a recent luminosity correlation study. [ABSTRACT FROM AUTHOR]

Synchrotron radiation from a decelerating blastwave is a widely accepted model of radio to X-ray afterglow emission from gamma-ray bursts (GRBs). GeV gamma-ray emission detected by the Fermi Large Area Telescope (LAT) and the duration of which extends beyond the prompt gamma-ray emission phase is also compatible with broad features of afterglow emission. We revisit the synchrotron self-Compton (SSC) emission model from a decelerating blastwave to fit multiwavelength data from three bright GRBs, namely GRB 190114C, GRB 130427A, and GRB 090510. We constrain the afterglow model parameters using the simultaneous fit of the spectral energy distributions at different times and light curves at different frequencies for these bursts. We find that a constant density interstellar medium is favoured for the short GRB 090510, while a wind-type environment is favoured for the long GRB 130427A and GRB 190114C. The sub-TeV component in GRB 190114C detected by MAGIC is the SSC emission in our modelling. Furthermore, we find that the SSC emission in the Thomson regime is adequate to fit the spectra and light curves of GRB 190114C. For the other two GRBs, lacking sub-TeV detection, the SSC emissions are also modelled in the Thomson regime. For the model parameters we have used, the γγ attenuation in the blastwave is negligible in the sub-TeV range compared to the redshift-dependent γγ attenuation in the extragalactic background light. [ABSTRACT FROM AUTHOR]

The Electron-Tracking Compton Camera (ETCC), which is a complete Compton camera that tracks Compton scattering electrons with a gas micro time projection chamber, is expected to open up MeV gamma-ray astronomy. The technical challenge for achieving several degrees of the point-spread function is precise determination of the electron recoil direction and the scattering position from track images. We attempted to reconstruct these parameters using convolutional neural networks. Two network models were designed to predict the recoil direction and the scattering position. These models marked 41 |$^\circ$| of angular resolution and 2.1 mm of position resolution for 75 keV electron simulation data in argon-based gas at 2 atm pressure. In addition, the point-spread function of the ETCC was improved to 15 |$^\circ$| from 22 |$^\circ$| for experimental data from a 662 keV gamma-ray source. The performance greatly surpassed that using traditional analysis. [ABSTRACT FROM AUTHOR]

We present a definitive assessment of the role of inverse Compton scattering of cosmic microwave background photons (IC/CMB) in the context of radio galaxies. Owing to the steep increase of the CMB radiation energy density, IC/CMB is supposed to become progressively more important with respect to radio synchrotron cooling as the redshift increases. For typical energies at play, this process will up-scatter the CMB photons into the X-ray band, and is thus expected to yield a redshift-dependent, concurrent X-ray brightening and radio dimming of the jet-powered structures. Here, we show how a conclusive proof of this effect hinges on high-resolution imaging data in which the extended lobes can be distinguished from the compact hotspots where synchrotron self-Compton dominates the X-ray emission regardless of redshift. We analyse Chandra and Very Large Array data of 11 radio galaxies between |$1.3 \lesssim z \lesssim 4.3$|⁠ , and demonstrate that the emission from their lobes is fully consistent with the expectations from IC/CMB in equipartition. Once the dependence on size and radio luminosity are properly accounted for, the measured lobe X-ray luminosities bear the characteristic ∝(1 + z)4 proportionality expected of a CMB seed radiation field. Whereas this effect can effectively quench the (rest-frame) GHz radio emission from |$z \gtrsim 3$| radio galaxies below |${\lesssim}$| 1 mJy, IC/CMB alone cannot be responsible for a deficit in high- z , radio-loud active galactic nuclei (AGNs) if – as we argue – such AGNs typically have bright, compact hotspots. [ABSTRACT FROM AUTHOR]

The detailed study of nuclear regions of galaxies is important because it can help understanding the active galactic nucleus (AGN) feedback mechanisms, the connections between the nuclei and their host galaxies, and ultimately the galaxy formation processes. We present the analysis of an optical data cube of the central region of the galaxy NGC 2442, obtained with the integral field unit (IFU) of the Gemini Multi-Object Spectrograph (GMOS). We also performed a multiwavelength analysis, with Chandra data, XMM–Newton and NuSTAR spectra, and Hubble Space Telescope (HST) images. The analysis revealed that the nuclear emission is consistent with a Low Ionization Nuclear Emission-line Region (LINER) associated with a highly obscured compact hard X-ray source, indicating a Compton-thick AGN. The HST image in the F658N filter (H  α) reveals an arched structure corresponding to the walls of the ionization cone of the AGN. The gas kinematic pattern and the high gas velocity dispersion values in the same region of the ionization cone suggest an outflow emission. The stellar archaeology results indicate the presence of only old stellar populations (∼ 10 Gyr), with high metallicity (z = 0.02 and 0.05), and the absence of recent star formation in the central region of NGC 2442, which is possibly a consequence of the AGN feedback, associated with the detected outflow, shutting off star formation. NGC 2442 is a late-type galaxy similar to the Milky Way, and comparisons show that the main difference between them is the presence of a low-luminosity AGN. [ABSTRACT FROM AUTHOR]

We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC 3516 carried out in 2018 to 2020 covering the wavelength range from the X-ray to the optical. The facilities included the telescopes of the CMO SAI MSU, the 2.3-m WIRO telescope, and the XRT and UVOT of Swift. We found that NGC 3516 brightened to a high state and could be classified as Sy1.5 during the late spring of 2020. We have measured time delays in the responses of the Balmer and He  ii λ4686 lines to continuum variations. In the case of the best-characterized broad H β line, the delay to continuum variability is about 17 d in the blue wing and is clearly shorter, 9 d, in the red, which is suggestive of inflow. As the broad lines strengthened, the blue side came to dominate the Balmer lines, resulting in very asymmetric profiles with blueshifted peaks during this high state. During the outburst the X-ray flux reached its maximum on 2020 April 1 and it was the highest value ever observed for NGC 3516 by the Swift observatory. The X-ray hard photon index became softer, ∼1.8 in the maximum on 2020 April 21 compared to the mean ∼0.7 during earlier epochs before 2020. We have found that the UV and optical variations correlated well (with a small time delay of 1–2 d) with the X-ray until the beginning of 2020 April, but later, until the end of 2020 June, these variations were not correlated. We suggest that this fact may be a consequence of partial obscuration by Compton-thick clouds crossing the line of sight. [ABSTRACT FROM AUTHOR]

Recently, ground-based Imaging Atmospheric Cherenkov Telescopes have reported the detection of very-high-energy (VHE) gamma-rays from some gamma-ray bursts (GRBs). One of them, GRB 190829A, was triggered by the Swift satellite, and about 2 × 104 s after the burst onset the VHE gamma-ray emission was detected by H.E.S.S. with ∼5σ significance. This event had unusual features of having much smaller isotropic equivalent gamma-ray energy than typical long GRBs and achromatic peaks in X-ray and optical afterglow at about 1.4 × 103 s. Here, we propose an off-axis jet scenario that explains these observational results. In this model, the relativistic beaming effect is responsible for the apparently small isotropic gamma-ray energy and spectral peak energy. Using a jetted afterglow model, we find that the narrow jet, which has the initial Lorentz factor of 350 and the initial jet opening half-angle of 0.015 rad, viewed off-axis can describe the observed achromatic behaviour in the X-ray and optical afterglow. Another wide, baryon-loaded jet is necessary for the later-epoch X-ray and radio emissions. According to our model, the VHE gamma rays observed by H.E.S.S. at 2 × 104 s may come from the narrow jet through the synchrotron self-Compton process. [ABSTRACT FROM AUTHOR]

We develop a model describing the dynamical and observed properties of disc-dominated tidal disruption events (TDEs) around black holes with the lowest masses (M ≲ few × 106M⊙). TDEs around black holes with the lowest masses are most likely to reach super-Eddington luminosities at early times in their evolution. By assuming that the amount of stellar debris that can form into a compact accretion disc is set dynamically by the Eddington luminosity, we make a number of interesting and testable predictions about the observed properties of bright soft-state X-ray TDEs and optically bright, X-ray dim TDEs. We argue that TDEs around black holes of the lowest masses will expel the vast majority of their gravitationally bound debris into a radiatively driven outflow. A large-mass outflow will obscure the innermost X-ray producing regions, leading to a population of low black hole mass TDEs that are only observed at optical and UV energies. TDE discs evolving with bolometric luminosities comparable to their Eddington luminosity will have near constant (i.e. black hole mass independent) X-ray luminosities, of order L X, max ≡ LM ∼ 1043 − 1044 erg s−1. The range of luminosity values stems primarily from the range of allowed black hole spins. A similar X-ray luminosity limit exists for X-ray TDEs in the hard (Compton scattering dominated) state, and we therefore predict that the X-ray luminosity of the brightest X-ray TDEs will be at the scale LM (a) ∼ 1043 − 1044 erg s−1, independent of black hole mass and accretion state. These predictions are in strong agreement with the properties of the existing population (∼40 sources) of observed TDEs. [ABSTRACT FROM AUTHOR]

We extend the relativistic time-dependent thin-disc TDE model to describe non-thermal (2−10 keV) X-ray emission produced by the Compton up-scattering of thermal disc photons by a compact electron corona, developing analytical and numerical models of the evolving non-thermal X-ray light curves. In the simplest cases, these X-ray light curves follow power-law profiles in time. We suggest that TDE discs act in many respects as scaled-up versions of XRB discs, and that such discs should undergo state transitions into harder accretion states. XRB state transitions typically occur when the disc luminosity becomes roughly one per cent of its Eddington value. We show that if the same is true for TDE discs then this, in turn, implies that TDEs with non-thermal X-ray spectra should come preferentially from large-mass black holes. The characteristic hard-state transition mass is M HS ≃ 2 × 107M⊙. Hence, subpopulations of thermal and non-thermal X-ray TDEs should come from systematically different black hole masses. We demonstrate that the known populations of thermal and non-thermal X-ray TDEs do indeed come from different distributions of black hole masses. The null-hypothesis of identical black hole mass distributions is rejected by a two-sample Anderson-Darling test with a p -value <0.01. Finally, we present a model for the X-ray rebrightening of TDEs at late times as they transition into the hard state. These models of evolving TDE light curves are the first to join both thermal and non-thermal X-ray components in a unified scenario. [ABSTRACT FROM AUTHOR]

The results of a long-term multiwavelength study of the powerful flat spectrum radio quasar 3C 454.3 using Fermi -LAT and Swift XRT/UVOT data are reported. In the γ -ray band, Fermi -LAT observations show several major flares when the source flux was |$\gt 10^{-5}\, {\rm photon\, cm^{-2}\, s^{-1}}$|⁠ ; the peak γ -ray flux above 141.6 MeV, |$(9.22\pm 1.96)\times 10^{-5}\, {\rm photon\, cm^{-2}\, s^{-1}}$| observed on MJD 55519.33, corresponds to |$2.15\times 10^{50}\, {\rm erg\, s^{-1}}$| isotropic γ -ray luminosity. The analysis of Swift XRT and UVOT data revealed a flux increase, although with smaller amplitudes, also in the X-ray and optical/UV bands. The X-ray emission of 3C 454.3 is with a hard spectral index of ΓX = 1.16–1.75, and the flux in the flaring states increased up to |$(1.80\pm 0.18)\times 10^{-10}\, {\rm erg\, cm^{-2}\, s^{-1}}$|⁠. Through combining the analysed data, it was possible to assemble 362 high-quality and quasi-simultaneous spectral energy distributions of 3C 454.3 in 2008–2018, which all were modelled within a one-zone leptonic scenario assuming the emission region is within the broad-line region, involving synchrotron, synchrotron self-Compton, and external Compton mechanisms. Such an extensive modelling is the key for constraining the underlying emission mechanisms in the 3C 454.3 jet and allows to derive the physical parameters of the jet and investigate their evolution in time. The modelling suggests that during the flares, along with the variation of emitting electron parameters, the Doppler boosting factor increased substantially, implying that the emission in these periods has most likely originated in a faster moving region. [ABSTRACT FROM AUTHOR]

Although more than a half-century since pulsar discovery, the field of pulsar astronomy has attained an unprecedented level of success and has opened several windows in astronomy, very few theories have been put forwarded to investigate the nature of power spectra and emission properties of radio pulsars. There has been a copious amount of observation dedicated to investigating the nature and shape of radio pulsar's power spectra. In this paper, I have suggested some alternative plasma processes in the frame of general parametric instability, such as Stimulated Raman Scattering (SRS) and Stimulated Compton Scattering (SCS) as a potential probe to generate power spectra theoretically. There are basically three prominent processes in which electromagnetic waves can undergo scattering in an ambient plasma medium. First, one is very well-known Compton scattering; it is when the scattering of radiation occurs by a single electron. The second and third ones are SRS and SCS, which are the relatively less known plasma phenomena. By definition, SRS is a process where the scattering of radiation occurs by longitudinal electron plasma mode, whereas SCS occurs by highly damped electron plasma mode. I have explored the possibility of explaining the radio power spectra of pulsar under different circumstances of plasma. I have computed the growth rates of SRS and SCS instabilities numerically. Thereafter, I have produced full radio power spectra of the pulsars PSRB 2111+46, PSRB 0329+54 theoretically by assuming typical pulsar parameters, dispersion relation associated with the plasma of three-wave interacting parametric instability process and the spatial variation associated with different plasma parameters like plasma density, Lorentz factor of electrons, frequency, and input flux of the pump wave. [ABSTRACT FROM AUTHOR]

We consider the Compton scattering in the optically thick uniform spherical corona around a neutron star in an X-ray binary. In the scattering, the low energy seed photons (0.1 ∼ 2.5 keV) are scattered in low energy electrons (2.5 ∼ 10 keV) in the corona in two conditions, i.e. initial seed photons are scattered in a whole corona and scattered in every layer of the corona that are supposed to be divided into many layers. When the same number of input seed photons, the same corona parameters, and the same energy distribution of all photons in the two conditions are considered, the approximately same number of output photons can be obtained, which means that there is approximately a transform invariance of layering the Comptonized corona. Thus the scattering in the layers of a multilayered corona is approximately equal to the scattering in the whole corona by dividing the whole corona into several layers. It means that Compton scattering for the initial seed photons scattered in a whole optically thick spherical corona with uniformly distributed electrons also can be considered as that the multiple Compton scatterings take place in the layers of a multilayered corona in order approximately, which can be used to explore some physical process in one part of a corona. [ABSTRACT FROM AUTHOR]

We report here results of the analysis of correlated flux variations between the optical and GeV γ-ray bands in three bright BL Lac objects, namely AO 0235+164, OJ 287, and PKS 2155−304. This was based on the analysis of about 10 yr of data from the Fermi Gamma-ray Space Telescope covering the period between 2008 August 8 and 2018 August 8 along with optical data covering the same period. For all the sources, during the flares analysed in this work, the optical and γ-ray flux variations are found to be closely correlated. From broad-band spectral energy distribution modelling of different epochs in these sources using the one-zone leptonic emission model, we found that the optical–ultraviolet emission is dominated by synchrotron emission from the jet. The γ-ray emission in the low synchrotron peaked sources AO 0235+164 and OJ 287 is found to be well fitted with external Compton (EC) component, while the γ-ray emission in the high synchrotron peaked source PKS 2155−304 is well fitted with synchrotron self-Compton component. Further, we note that the γ-ray emission during the high-flux state of AO 0235+164 (epochs A and B) requires seed photons from both the dusty torus and broad-line region, while the γ-ray emission in OJ 287 and during epochs C and D of AO 0235+164 can be modelled by EC scattering of infrared photons from the torus. [ABSTRACT FROM AUTHOR]

The dominant radiation mechanism that produces the prompt emission in gamma-ray bursts (GRBs) remains a major open question. Spectral information alone has proven insufficient in elucidating its nature. Time-resolved linear polarization has the potential to distinguish between popular emission mechanisms, e.g. synchrotron radiation from electrons with a power-law energy distribution or inverse Compton scattering of soft seed thermal photons, which can yield the typical GRB spectrum but produce different levels of polarization. Furthermore, it can be used to learn about the outflow's composition (i.e. whether it is kinetic-energy-dominated or Poynting-flux-dominated) and angular structure. For synchrotron emission, it is a powerful probe of the magnetic field geometry. Here, we consider synchrotron emission from a thin ultrarelativistic outflow, with bulk Lorentz factor Γ(R) = Γ0(R / R 0)− m /2 ≫ 1, that radiates a Band-function spectrum in a single (multiple) pulse(s) over a range of radii, R 0 ≤ R ≤ R 0 + Δ R. Pulse profiles and polarization evolution at a given energy are presented for a coasting (m = 0) and accelerating (m = −2/3) thin spherical shell and for different viewing angles for a top-hat jet with sharp as well as smooth edges in emissivity. Four different magnetic field configurations are considered, such as a locally ordered field coherent over angular scales θ B ≳ 1/Γ, a tangled field (B ⊥) in the plane transverse to the radial direction, an ordered field (B ∥) aligned in the radial direction, and a globally ordered toroidal field (B tor). All field configurations produce distinct polarization evolution with single (for B ⊥ and B ∥) and double (for B tor) 90○ changes in the polarization position angle. [ABSTRACT FROM AUTHOR]

The regular monitoring of flat-spectrum radio quasars (FSRQs) in γ-rays by Fermi -LAT (Large Area Telescope) since past 12 yr indicated six sources who exhibited extreme γ-ray outbursts crossing daily flux of 10−5 photons cm−2 s−1. We obtained nearly simultaneous multiwavelength data of these sources in radio to γ-ray waveband from OVRO (Owens Valley Radio Observatory), Steward Observatory, SMARTS (Small and Moderate Aperture Research Telescope System), Swift -UVOT (UV/Optical Telescope), Swift -XRT (X-ray Telescope), and Fermi -LAT. The time-averaged broad-band spectral energy distributions (SEDs) of these sources in quiescent states were studied to get an idea about the underlying baseline radiation processes. We modelled the SEDs using one-zone leptonic synchrotron and inverse Compton emission scenario from broken power-law electron energy distribution inside a spherical plasma blob, relativistically moving down a conical jet. The model takes into account inverse Compton scattering of externally and locally originated seed photons in the jet. The big blue bumps visible in quiescent state SEDs helped to estimate the accretion disc luminosities and central black hole masses. We found a correlation between the magnetic field inside the emission region and the ratio of emission region distance to disc luminosity, which implies that the magnetic field decreases with an increase in emission region distance and decrease in disc luminosity, suggesting a disc–jet connection. The high-energy index of the electron distribution was also found to be correlated with observed γ-ray luminosity as γ-rays are produced by high-energy particles. In most cases, kinetic power carried by electrons can account for jet radiation power as jets become radiatively inefficient during quiescent states. [ABSTRACT FROM AUTHOR]

We present an implementation of a self-consistent way of modelling synchrotron self-Compton (SSC) effects in gamma-ray burst afterglows, with and without approximated Klein–Nishina suppressed scattering for the afterglow modelling code boxfit , which is currently based on pure synchrotron emission. We discuss the changes in spectral shape and evolution due to SSC effects, and comment on how these changes affect physical parameters derived from broad-band modelling. We show that SSC effects can have a profound impact on the shape of the X-ray light curve using simulations including these effects. This leads to data that cannot be simultaneously fit well in both the X-ray and radio bands when considering synchrotron-only fits, and an inability to recover the correct physical parameters, with some fitted parameters deviating orders of magnitude from the simulated input parameters. This may have a significant impact on the physical parameter distributions based on previous broad-band modelling efforts. [ABSTRACT FROM AUTHOR]

While theory and simulations indicate that galaxy mergers play an important role in the cosmological evolution of accreting black holes and their host galaxies, samples of active galactic nuclei (AGNs) in galaxies at close separations are still small. In order to increase the sample of AGN pairs, we undertook an archival project to investigate the X-ray properties of an SDSS-selected sample of 32 galaxy pairs with separations ≤150 kpc containing one optically identified AGN, which were serendipitously observed by XMM–Newton. We discovered only one X-ray counterpart among the optically classified non-active galaxies, with a weak X-ray luminosity (≃ 5 × 1041 erg s−1). 59 per cent (19 out of 32) of the AGNs in our galaxy pair sample exhibit an X-ray counterpart, covering a wide range in absorption-corrected X-ray luminosity (5 × 1041–2 × 1044 erg s−1). More than 79 per cent of these AGNs are obscured (column density N H > 1022 cm−2), with more than half thereof (i.e. about 47 per cent of the total AGN sample) being Compton-thick. AGN/no-AGN pairs are therefore more frequently X-ray obscured (by a factor ≃1.5) than isolated AGNs. When compared to a luminosity and redshift-matched sample of bona fide dual AGN, AGN/no-AGN pairs exhibit one order-of-magnitude lower X-ray column density in the same separation range (>10 kpc). A small sample (4 objects) of AGN/no-AGN pairs with sub-pc separation is all heavily obscured, driving a formal anticorrelation between the X-ray column density and the galaxy pair separation in these systems. These findings suggest that the galactic environment has a key influence on the triggering of nuclear activity in merging galaxies. [ABSTRACT FROM AUTHOR]

We present results from a 20 ks XMM–Newton director's discretionary time observation of the radio-loud quasar CFHQS J142952 + 544717 at z  = 6.18, whose extreme X-ray luminosity was recently revealed by the SRG / eROSITA telescope in the course of its first all-sky survey. The quasar has been confidently detected with a total of ∼1400 net counts in the 0.2–10 keV energy band (1.4–72 keV in the object's rest frame). Its measured spectrum is unusually soft and can be described by an absorbed power-law model with a photon index of Γ = 2.5 ± 0.2. There are no signs of a high-energy cut-off or reflected component, with a 90 per cent upper limit on the fluorescence iron K α equivalent width of ≈290 eV and the corresponding upper limit on the iron K-edge absorption depth of 0.6. We have detected, at the >95 per cent confidence level, an excess absorption above the Galactic value, corresponding to a column density N H = 3 ± 2 × 1022 cm−2 of material located at z  = 6.18. The intrinsic luminosity of CFHQS J142952 + 544717 in the 1.4–72 keV energy band is found to be |$5.5_{-0.6}^{+0.8} \times 10^{46}$|  erg s−1. We did not detect statistically significant flux changes between two SRG scans and the XMM–Newton observation, spanning over ∼7.5 months, implying that the quasar remained at this extremely high-luminosity level for at least a month in its rest frame. We put forward the hypothesis that the extreme X-ray properties of CFHQS J142952 + 544717 are associated with inverse Compton scattering of cosmic microwave background photons (at z  = 6.18) in its relativistic jets. [ABSTRACT FROM AUTHOR]

The Sunyaev–Zeldovich (SZ) effect provides a powerful cosmological probe, which traditionally is approached independently as cluster number count (CNC) or power spectrum (PS) analysis. Here, we devise a new method for analysing the y -map by introducing the survey completeness function, conventionally only used in the CNC analysis, in the yy -PS modelling. This provides a systematic method, based mainly on SZ observables, for obtaining two complementary y -maps, one incorporating detected/resolved clusters and the other relying only on diffuse/unresolved SZ contributions. We use the catalogue of clusters obtained in the Planck CNC analysis to define the completeness function linking these two y -maps. The split depends on the chosen signal-to-noise detection threshold, which we vary in our discussion. We carefully propagate the effect of completeness cuts on the non-Gaussian error contributions in the yy -PS analysis, highlighting the benefits of masking massive clusters. Our analysis of the Planck yy -PS for the unresolved component yields a mass bias of b  = 0.15 ± 0.04, consistent with the standard value (b ≈ 0.2), in comparison to b  = 0.4 ± 0.05 for the total yy -PS. We find indications for this drift being driven by the CIB-tSZ cross-correlation, which dominantly originates from clusters in the resolved component of the y -map. Another possible explanation is the presence of a mass-dependent bias, which has been theoretically motivated and can be quantified with our novel method. We furthermore find first hints for the presence of the 2-halo terms in the yy -PS. Finally, the proposed method provides a new framework for combining the complementary information of the CNC and PS analyses in upcoming SZ surveys. [ABSTRACT FROM AUTHOR]

The knowledge of the dynamical state of galaxy clusters allows to alleviate systematics when observational data from these objects are applied in cosmological studies. Evidence of correlation between the state and the morphology of the clusters is well studied. The morphology can be inferred by images of the surface brightness in the X-ray band and of the thermal component of the Sunyaev–Zel'dovich (tSZ) effect in the millimetre range. For this purpose, we apply, for the first time, the Zernike polynomial decomposition, a common analytical approach mostly used in adaptive optics to recover aberrated radiation wavefronts at the telescopes pupil plane. With this novel way, we expect to correctly infer the morphology of clusters and so possibly their dynamical state. To verify the reliability of this new approach, we use more than 300 synthetic clusters selected in the three hundred project at different redshifts ranging from 0 up to 1.03. Mock maps of the tSZ, quantified with the Compton parameter, y -maps, are modelled with Zernike polynomials inside R 500, the cluster reference radius. We verify that it is possible to discriminate the morphology of each cluster by estimating the contribution of the different polynomials to the fit of the map. The results of this new method are correlated with those of a previous analysis made on the same catalogue, using two parameters that combine either morphological or dynamical-state probes. We underline that instrumental angular resolution of the maps has an impact mainly when we extend this approach to high-redshift clusters. [ABSTRACT FROM AUTHOR]

We investigate the radiation fields around super-Eddington accretion flow, in which multiple inverse-Compton scattering plays a principal role, by using newly developed code describing Boltzmann radiation transfer in the Schwarzschild space-time. We apply this code to post-processing spectral calculations based on general relativistic, radiation magnetohydrodynamic simulation data to obtain X-ray spectra seen from various viewing angles. The radiation fields are distinctively separated into a funnel region with an opening angle of ∼30°, which is full with hot (gas temperature of T > 108 K), tenuous, and high-velocity plasmas, and surrounding cooler (T ∼ 107 K) and optically thick outflow regions. Accordingly, there is a clear tendency that the smaller the viewing angle, the harder the spectra. In particular, hard photons with several tens of keV are observable only by observers at viewing angles less than ∼30°, consistent with past spectral studies based on simulations. Further, we investigate how the spectra are varied by a flare occurring in the innermost region, finding that the variation amplitude grows as the photon energy increases and that the harder photons emerge more quickly than softer photons. The observational implications on long-term spectral variability of ultra-luminous X-ray sources are briefly discussed. [ABSTRACT FROM AUTHOR]

On 2019/07/30.86853 ut , IceCube detected a high-energy astrophysical neutrino candidate. The Flat Spectrum Radio Quasar PKS 1502+106 is located within the 50 per cent uncertainty region of the event. Our analysis of 15 GHz Very Long Baseline Array (VLBA) and astrometric 8 GHz VLBA data, in a time span prior and after the IceCube event, reveals evidence for a radio ring structure that develops with time. Several arc-structures evolve perpendicular to the jet ridge line. We find evidence for precession of a curved jet based on kinematic modelling and a periodicity analysis. An outflowing broad line region (BLR) based on the C  iv line emission (Sloan Digital Sky Survey) is found. We attribute the atypical ring to an interaction of the precessing jet with the outflowing material. We discuss our findings in the context of a spine-sheath scenario where the ring reveals the sheath and its interaction with the surroundings (narrow line region, NLR, clouds). We find that the radio emission is correlated with the γ-ray emission, with radio lagging the γ-rays. Based on the γ-ray variability time-scale, we constrain the γ-ray emission zone to the BLR (30–200  r g) and within the jet launching region. We discuss that the outflowing BLR provides the external radiation field for γ-ray production via external Compton scattering. The neutrino is most likely produced by proton–proton interaction in the blazar zone (beyond the BLR), enabled by episodic encounters of the jet with dense clouds, i.e. some molecular cloud in the NLR. [ABSTRACT FROM AUTHOR]

Blazars emit a highly variable non-thermal spectrum. It is usually assumed that the same non-thermal electrons are responsible for the IR-optical-UV emission (via synchrotron) and the gamma-ray emission (via inverse Compton). Hence, the light curves in the two bands should be correlated. Orphan gamma-ray flares (i.e. lacking a luminous low-frequency counterpart) challenge our theoretical understanding of blazars. By means of large-scale two-dimensional radiative particle-in-cell simulations, we show that orphan gamma-ray flares may be a self-consistent by-product of particle energization in turbulent magnetically dominated pair plasmas. The energized particles produce the gamma-ray flare by inverse Compton scattering an external radiation field, while the synchrotron luminosity is heavily suppressed since the particles are accelerated nearly along the direction of the local magnetic field. The ratio of inverse Compton to synchrotron luminosity is sensitive to the initial strength of turbulent fluctuations (a larger degree of turbulent fluctuations weakens the anisotropy of the energized particles, thus increasing the synchrotron luminosity). Our results show that the anisotropy of the non-thermal particle population is key to modelling the blazar emission. [ABSTRACT FROM AUTHOR]

We present the analysis of an optical data cube of the central region of NGC 1448, obtained with the Multi Unit Spectroscopic Explorer (MUSE). Chandra X-ray data indicate that the active galactic nucleus (AGN) is not located at the apparent stellar nucleus of the galaxy, but at a projected distance of |$1.75\, \pm \, 0.22$|  arcsec (139 ± 17 pc). This is probably caused by the high interstellar extinction in the surroundings of the AGN, which corresponds to the true nucleus of the galaxy, as also proposed by previous studies. The morphology and classification of the optical line-emitting regions indicate two ionization cones, around an axis with a position angle of PAcones = −50° ± 7°, with emission-line spectra characteristic of Seyfert galaxies. The stellar and gas kinematics are consistent with a stellar and gas rotating disc around the nucleus, with a velocity amplitude of 125 km s−1. Two probable outflows from the AGN were detected along the region of the two ionization cones. The AGN position does not coincide with the brightest line-emitting region at the centre of NGC 1448. That may be a consequence of the high obscuration from the AGN towards the observer (the AGN is actually Compton thick), mostly caused by a nearly edge-on torus. An additional hypothesis is that the AGN reduced its luminosity, during the last 440 yr, to nearly half of the value in the past. In this case, the brightest line-emitting region corresponds to a 'light echo' or a 'fossil' of the AGN in the past. [ABSTRACT FROM AUTHOR]

The GeV break in spectra of the blazar 3C 454.3 is a special observation feature that has been discovered by the Fermi -LAT. The origin of the GeV break in the spectra is still under debate. In order to explore the possible source of GeV spectral break in 3C 454.3, a one-zone homogeneous leptonic jet model and the McFit technique are utilized for fitting the quasi-simultaneous multiwaveband spectral energy distribution (SED) of 3C 454.3. The outside border of the broad-line region (BLR) and inner dust torus are chosen to contribute radiation in the model as external, seed photons to the external-Compton process, considering the observed γ-ray radiation. The combination of two components, namely the Compton-scattered BLR and dust torus radiation, assuming a broken power-law distribution of emitted particles, provides a proper fitting to the multiwaveband SED of 3C 454.3 detected 2008 August 3–September 2 and explains the GeV spectral break. We propose that the spectral break of 3C 454.3 may originate from an inherent break in the energy distribution of the emitted particles and the Klein–Nishina effect. A comparison is performed between the energy density of the 'external' photon field for the whole BLR U BLR achieved via model fitting and that constrained from the BLR data. The distance from the position of the γ-ray radiation area of 3C 454.3 to the central black hole could be constrained at ∼0.78 pc (∼4.00 R BLR, the size of the BLR). [ABSTRACT FROM AUTHOR]

We test two methods, including one that is newly proposed in this work, for correcting for the effects of chameleon f (R) gravity on the scaling relations between the galaxy cluster mass and four observable proxies. Using the first suite of cosmological simulations that simultaneously incorporate both full physics of galaxy formation and Hu-Sawicki f (R) gravity, we find that these rescaling methods work with a very high accuracy for the gas temperature, the Compton Y -parameter of the Sunyaev–Zel'dovich (SZ) effect and the X-ray analogue of the Y -parameter. This allows the scaling relations in f (R) gravity to be mapped to their Λ cold dark matter counterparts to within a few per cent. We confirm that a simple analytical tanh formula for the ratio between the dynamical and true masses of haloes in chameleon f (R) gravity, proposed and calibrated using dark-matter-only simulations in a previous work, works equally well for haloes identified in simulations with two very different – full-physics and non-radiative – baryonic models. The mappings of scaling relations can be computed using this tanh formula, which depends on the halo mass, redshift, and size of the background scalar field, also at a very good accuracy. Our results can be used for accurate determination of the cluster mass using SZ and X-ray observables, and will form part of a general framework for unbiased and self-consistent tests of gravity using data from present and upcoming galaxy cluster surveys. We also propose an alternative test of gravity, using the Y X–temperature relation, which does not involve mass calibration. [ABSTRACT FROM AUTHOR]

Utilizing cosmological hydrodynamic simulations, we quantify the distributions of the dispersion measure (DM) of fast radio bursts (FRBs). We examine the contributions of cold, warm-hot, and hot gas to the total DM. We find that the hot gas component (T > 107K), on average, makes a minor contribution (⁠|$\le 5{{\ \rm per\ cent}}$|⁠) to the overall DM. Cold (T < 105K) and warm-hot (T = 105 − 107K) gas components make comparable contributions to DM for FRBs at z = 1, with the former component making an increasingly larger contribution towards higher redshift. We provide a detailed DM distribution of FRBs at z = 0.25 to z = 2 that may be compared to observations. We also compute the relation between the Compton y parameter and DM, finding a strong correlation, y ∝ DM 4, providing an additional, independent constraint on the nature of the DM of FRBs. [ABSTRACT FROM AUTHOR]

We report on deep XMM–Newton and NuSTAR observations of the high redshift, z  = 2.94, extremely red quasar (ERQ), SDSS J165202.60+172852.4, with known galactic ionized outflows detected via spatially resolved [O  iii ] emission lines. X-ray observations allow us to directly probe the accretion disc luminosity and the geometry and scale of the circumnuclear obscuration. We fit the spectra from the XMM–Newton /EPIC and NuSTAR detectors with a physically motivated torus model and constrain the source to exhibit a near Compton-thick column density of N H = (1.02 |$^{+0.76}_{-0.41}$|⁠) × 1024 cm−2, a near edge-on geometry with the line-of-sight inclination angle of θi  = 85°, and a scattering fraction of f sc ∼ 3  per cent. The absorption-corrected, intrinsic 2–10 keV X-ray luminosity of L 2–10= (1.4 |$^{+1}_{-1}$|⁠) × 1045 erg s−1 reveals a powerful quasar that is not intrinsically X-ray weak, consistent with observed trends in other ERQs. We also estimate the physical properties of the obscuration, although highly uncertain: the warm ionized scattering density of n e ∼ 7.5 × (102–103) cm−3 and the obscuration mass of |$M_{\rm obsc} \sim 1.7\times (10^4\!-\!10^6)\,{\rm M}_{\odot}$|⁠. As previously suggested with shallower X-ray observations, optical and infrared selection of ERQ has proved effective in finding obscured quasars with powerful outflow signatures. Our observations provide an in-depth view into the X-ray properties of ERQs and support the conclusions of severely photon-limited studies of obscured quasar populations at high redshifts. [ABSTRACT FROM AUTHOR]

The triaxial and hexadecapole deformations of the |$K^\pi=0^+$| and |$K^\pi=2^+$| bands of |$^{24}$| Mg have been investigated by the inelastic scatterings of various probes, including electrons, protons, and alpha(⁠|$\alpha$|⁠) particles, for a prolonged time. However, it has been challenging to explain the unique properties of the scatterings observed for the |$4^+_1$| state through reaction calculations. This paper investigates the structure and transition properties of the |$K^\pi=0^+$| and |$K^\pi=2^+$| bands of |$^{24}$| Mg employing the microscopic structure and reaction calculations via inelastic proton and |$\alpha$| scattering. In particular, the |$E4$| transitions to the |$4^+_1$| and |$4^+_2$| states are reexamined. The structure of |$^{24}$| Mg was calculated employing the variation after the parity and total angular momentum projections in the framework of the antisymmetrized molecular dynamics (AMD). The inelastic proton and |$\alpha$| reactions were calculated by the microscopic coupled-channel (MCC) approach by folding the Melbourne |$g$| -matrix |$NN$| interaction with the AMD densities of |$^{24}$| Mg. Reasonable results were obtained on the properties of the structure, including the energy spectra and |$E2$| and |$E4$| transitions of the |$K^\pi=0^+$| and |$K^\pi=2^+$| bands owing to the enhanced collectivity of triaxial deformation. The MCC+AMD calculation successfully reproduced the angular distributions of the |$4^+_1$| and |$4^+_2$| cross sections of proton scattering at incident energies of |$E_p=40$| –100 MeV and |$\alpha$| scattering at |$E_\alpha=100$| –400 MeV. This is the first microscopic calculation to describe the unique properties of the |$0^+_1\to 4^+_1$| transition. In the inelastic scattering to the |$4^+_1$| state, the dominant two-step process of the |$0^+_1\to 2^+_1\to 4^+_1$| transitions and the deconstructive interference in the weak one-step process were essential. [ABSTRACT FROM AUTHOR]

The nature of the intense X-ray emission from powerful extragalactic jets at large (>1 kpc) scale is still debated. The scenario that invokes the inverse Compton scattering of the cosmic microwave background by electrons is challenged by the lack of gamma-ray emission in the GeV band. An alternative assumes synchrotron emission by a distinct population of ultra-high energy electrons. Here, we present a concrete attempt to apply this scenario, exploring the specific model in which the ultra-high energy electrons are accelerated in a shear layer surrounding the jet. We limit the study to non-relativistic flows and particle acceleration is treated by a Fokker–Planck equation. The observed relation between low energy (radio, optical) and X-ray emission prompts us to assume that the required population of pre-accelerated particles is provided by a shock responsible for the acceleration of the electrons emitting at low frequencies. We apply the model to the emission of the principal knots of the jets of PKS 0637–752 and PKS 1136–135, two of the best-studied objects. For the set of fiducial parameters adopted, the condition that the jet power does not exceeds a limiting value of 1048 erg s−1 constrains the magnetic field above |$10\, \mu$| G and indicates moderate beaming (δ ≃ 2) for PKS 0637–752. For both sources, the requirement that acceleration of the electrons proceeds faster than radiative cooling can be met if the magnetic turbulence in the shear layer follows a Kolmogorov spectrum, I (k) ∝  k − q with q  = 5/3, but cannot satisfied in the Bohm-like case (q  = 1). [ABSTRACT FROM AUTHOR]

Spectral-timing analysis of the fast variability observed in X-rays is a powerful tool to study the physical and geometrical properties of the accretion/ejection flows in black hole (BH) binaries. The origin of type-B quasi-periodic oscillations (QPO), predominantly observed in BH candidates in the soft-intermediate state, has been linked to emission arising from the relativistic jet. In this state, the X-ray spectrum is characterized by a soft-thermal blackbody-like emission due to the accretion disc, an iron emission line (in the 6–7 keV range), and a power-law-like hard component due to inverse-Compton scattering of the soft-photon source by hot electrons in a corona or the relativistic jet itself. The spectral-timing properties of MAXI J1348−630 have been recently studied using observations obtained with the NICER observatory. The data show a strong type-B QPO at ∼4.5 Hz with increasing fractional rms amplitude with energy and positive lags with respect to a reference band at 2–2.5 keV. We use a variable-Comptonization model that assumes a sinusoidal coherent oscillation of the Comptonized X-ray flux and the physical parameters of the corona at the QPO frequency, to fit simultaneously the energy-dependent fractional rms amplitude and phase lags of this QPO. We show that two physically connected Comptonization regions can successfully explain the radiative properties of the QPO in the full 0.8–10 keV energy range. [ABSTRACT FROM AUTHOR]

We investigate the absorption and emission features in observations of GX 301-2 detected with Insight -HXMT/LE in 2017–2019. At different orbital phases, we found prominent Fe Kα, Kβ, and Ni Kα lines, as well as Compton shoulders and Fe K-shell absorption edges. These features are due to the X-ray reprocessing caused by the interaction between the radiation from the source and surrounding accretion material. According to the ratio of iron lines (Kα and Kβ), we infer the accretion material is in a low ionization state. We find an orbital-dependent local absorption column density, which has a large value and strong variability around the periastron. We explain its variability as a result of inhomogeneities of the accretion environment and/or instabilities of accretion processes. In addition, the variable local column density is correlated with the equivalent width of the iron Kα lines throughout the orbit, which suggests that the accretion material near the neutron star is spherically distributed. [ABSTRACT FROM AUTHOR]