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Mature radio galaxies such as M87 belong to a specific subclass of active galaxies (AGN) whose evolution in time endows them with five distinguishing characteristics, including (1) low excitation emission, (2) low star formation rates, (3) high bulge stellar-velocity dispersion, (4) bright stellar nuclei, and (5) weak or nonexistent merger signatures. We show how to understand these seemingly disparate characteristics as originating from the time evolution of powerful radio quasars and describe a new model prediction that tilted accretion disks in AGN are expected to occur in bright quasars but not in other subclasses of AGN. The picture we present should be understood as the most compelling evidence for counter-rotation as a key element in feedback from accreting black holes., Comment: 11 pages, 6 Figures, Published in the Universe journal

For the first time, in March 2024, the transient Galactic black hole candidate Swift J151857.0-572147 experienced an outburst. Using publicly available archived {\it Insight}-HXMT data, we analyze the timing and spectral features of this source. Through model fitting of the power density spectrum, we were able to extract the properties of quasi-periodic oscillations, and based on those properties, we have determined that the QPOs are of type C. We also conclude that the shock instabilities in the transonic advective accretion processes surrounding black holes may be the source of the QPOs. This shock instability could produce variabilities of flux up to 48 keV, as we checked from the QPO energy dependence. High-frequency QPO is not observed during this period. In the broad energy band of $2-100$ keV, simultaneous data from the three on-board instruments of \textit{Insight}-HXMT were used to perform the spectral analysis. A combination of models, including broken power-law, multi-color disk-blackbody continuum, interstellar absorption, and reflection in both neutral and ionized medium were needed for spectral fitting to obtain the best fit. We discovered that at the beginning of the analysis period, the source was in an intermediate state and was transitioning toward the softer states based on the spectral features. It has a hydrogen column density of $(4.3-6.9) \times 10^{22}$ cm$^{-2}$., Comment: 23 pages (1 page Appendix), 14 figures, 7 tables

The transient Galactic black hole candidate Swift\,J1727.8-1613 went through an outburst for the very first time that started in August 2023 and lasted for almost 6 months. We study the timing and spectral properties of this source using publicly available archival {\it Insight-HXMT} data for the first 10 observation IDs that last from MJD 60181 to 60198 with a total of 92 exposures for all three energy bands. We extracted the quasi-periodic oscillation properties by model fitting the power density spectrum and from those properties we designate that the QPOs are type-C in nature. We also conclude that the origin of the QPOs could be the shock instabilities in the transonic advective accretion flows around black holes. The spectral analysis was performed using simultaneous data from the three on-board instruments LE, ME, and HE of \textit{Insight-HXMT} in the broad energy band of $2-150 $ keV. To achieve the best fit, spectral fitting required a combination of models e.g. interstellar absorption, power-law, multi-color disk-blackbody continuum, gaussian emission/absorption, and reflection by neutral material. From the spectral properties, we found that the source was in an intermediate state at the start of the analysis period and was making a transition toward the softer states. The inner edge of the accretion disk moved inward in progressive days following the spectral nature. We found that the source has a high inclination. The average hydrogen column density estimated from the model fitting is $0.27_{-0.17}^{+0.08}\times10^{22}$ cm$^{-2}$., Comment: Submitted to AAS (19 pages, 8 figures, 4 tables)

We study the spectro-polarimetric properties of a newly discovered black hole X-ray binary Swift\,J151857.0-572147 jointly using {\it IXPE} and {\it NuSTAR} observations during March 2024. The analysis of {\it IXPE} data reports the first detection of X-ray polarization with degree (PD) $1.34\pm0.27$ and polarization angle (PA) $-13.69^\circ\pm5.85^\circ$ using model-independent approach, while the model-dependent analysis gives PD $1.18\pm0.23$ and PA $-14.01^\circ\pm5.80^\circ$. The joint spectral analysis of the broadband data and {\it NuSTAR} analysis in isolation constrain the mass of the central black hole between $\sim 9.2\pm1.6-10.1\pm1.7 M_\odot$ and a moderate spin parameter of $\sim0.6\pm0.1-0.7\pm0.2$ with disk inclination $\sim 35^\circ\pm7^\circ-46^\circ\pm15^\circ$. The power-law photon index and cutoff energy are $2.19\pm0.03-2.47\pm0.06$ and $\sim 36\pm4-78\pm10$ keV, suggesting a transition to the soft spectral state (SS). Additionally, a relatively lower corona size of $6\pm1-9\pm2$ $r_S$, a low mass outflow rate ($<3$\% $\dot M_{\rm Edd}$), and the best-fitted halo accretion is less compared to the disk accretion rate further confirms the same state. The low PD detected in the SS can be due to repeated scattering inside the dense corona and the dominant emission from the disk, agrees with the low spin and low disk inclination. The hydrogen column density obtained from the fit is relatively high $\sim 4-5\times 10^{22}$ cm$^{-2}$., Comment: 10 pages, 5 figures, 3 tables, accepted for publication in ApJ, comments welcome. arXiv admin note: text overlap with arXiv:2403.14169

The counter-rotation between black holes and accretion disk configuration was introduced over a decade ago to elucidate the nature of the radio loud/radio-quiet dichotomy and the jet-disk connection, but has since been applied to a plethora of observations across space and time. We briefly review the paradigm in which counter-rotation is key for the triggering of radio galaxies and its observational support, then apply it to a series of observations concerning FR0 radio galaxies. FR0 radio galaxies appear to be radio galaxies in transition, with low-spinning black holes and thus weaker but tilted jets with respect to an earlier radio quasar phase. As a result, FR0 radio galaxies are prescribed to be in an earlier phase of star formation suppression in radio galaxies, compared to a later phase that is unlikely to be less than tens of millions of years in the future if they have enough accretion fuel to evolve into more powerful FRI radio galaxies. FR0 radio galaxies will have a greater or lesser star formation suppression feedback effect depending on how long they live. Tilted jets also enhance stellar velocities in the bulge. Because FR0 jet lengths are of the same order of magnitude as the radius of the stellar bulge, FR0 jets are prescribed to have begun, more or less recently depending on their age, to affect stellar velocity dispersions as well. As a result, they will be associated with dispersion values that tend to be larger than for characteristically non-jetted active galaxies, but smaller than giant radio galaxies such as M87 that have experienced a long-term tilted and more powerful FRI jet. With these ideas it is possible to make a coarse-grained prediction for the slope of the M-{\sigma} plane for FR0 radio galaxies with values between 4 and 8., Comment: 13 pages, 4 Figures, Accepted for publication in the Journal of High Energy Astrophysics

We present direct observations of acoustic waves in warm dense matter. We analyze wave-number- and energy-resolved x-ray spectra taken from warm dense methane created by laser heating a cryogenic liquid jet. X-ray diffraction and inelastic free-electron scattering yield sample conditions of 0.3$\pm$0.1 eV and 0.8$\pm$0.1 g/cm$^3$, corresponding to a pressure of $\sim$13 GPa. Inelastic x-ray scattering was used to observe the collective oscillations of the ions. With a highly improved energy resolution of $\sim$50 meV, we could clearly distinguish the Brillouin peaks from the quasielastic Rayleigh feature. Data at different wave numbers were utilized to derive a sound speed of 5.9$\pm$0.5 km/s, marking a high-temperature data point for methane and demonstrating consistency with Birch's law in this parameter regime., Comment: 7 pages, 4 figures

That jetted active galactic nuclei (AGN) are also hosted in spiral galaxies is now well established. Our understanding of how such objects might fit in the radio loud AGN subclass has been described by Foschini and others over the past decade in that jets in spirals are weaker than those of radio galaxies and quasars because the black holes in spirals tend to be less massive. Recent data, however, may be pointing to a different picture which we describe. Unlike powerful jetted AGN in ellipticals, we illustrate from model perspectives, features of jets in spirals responsible for limiting both their power as well as their effect on their host galaxies. AGN triggered by secular processes fail to generate jet re-orientation, a key ingredient in the jetted AGN feedback mechanism in merger-triggered ellipticals that leads to the red-and-dead radio galaxies at low redshift such as M87. As a result, jetted AGN in spirals tend to live in a separate part of the parameter space compared to radio galaxies and quasars. Because of the absence of jet reorientation and due to the relatively short-lived jet phases, jetted AGN in spirals are best compared to radio quiet or jetless AGN than any other jetted AGN subclass., Comment: 11 pages, 6 Figures, Accepted for publication in the Journal of High Energy Astrophysics

We examine the time delay between radio and X-ray and between narrow radio frequency flares in Sagittarius A* (Sgr A*), from analyses of the synchrotron, bremsstrahlung and monochromatic luminosity curves. Using the results of 2D relativistic radiation magnetohydrodynamic (MHD) simulations based on the shock oscillation model, we find three types of time delay between the synchrotron and bremsstrahlung emissions: Type A with a time delay of 2 -- 3 h on the shock descending branch, Type B with no time delay and Type C with an inverse time delay of 0.5 -- 1 h on the shock ascending branch. The time delays in Types A and C are interpreted as a transit time of Alfv\'{e}n and acoustic waves between both emission dominant regions, respectively. The delay times between 22 and 43 GHz flares and between 8 and 10 GHz flares are $\sim$ 13 -- 26 min and 13 min, respectively, while the inverse delay also occurs dependently on the shock location branch. These time delays between the narrow radio bands are interpreted as the transit time of the acoustic wave between the frequency-dependent effective radii $R_{\tau_{\rm \nu=1}}$, at which the optical depth $\tau_{\rm \nu}$ at the accretion disc surface becomes $\sim$ unity. The shock oscillation model explains well the observed delay times of 0.5 -- 5 h between radio and X-ray, 20 -- 30 min between 22 and 43 GHz and $\sim$ 18 min between 8 and 10 GHz in Sgr A*., Comment: 14 pages, 14 figures, (accepted for publication in MNRAS)

Jet re-orientation associated with the time evolution of radio quasars explains the formation of X-shaped radio galaxies and their preference for isolated environments. But since X-shaped radio galaxies are generally not found in dense environments (e.g. groups/clusters), the jet re-orientation phenomenon for radio galaxies in groups and clusters has been ignored. We take a closer look at the re-orientation of FRI jets with respect to FRII jets, and find that it may constitute the as-yet unidentified trigger for star formation suppression in radio galaxies. We show how the recently explored radio "red geyser" galaxies can be interpreted in this context and ultimately reveal a deeper understanding of why FRII radio galaxies are on one side of the star formation enhancement/suppression divide compared to FRI radio galaxies., Comment: 12 pages, 5 figures, Accepted for publication in Publications of the Astronomical Society of the Pacific (PASP) journal

The moderate spin estimate for the black hole at the center of the cool core cluster H1821+643 motivates the completion of a story about this object's origin and evolution that was in the making since the work by Blundell and Rawlings over two decades ago as the first example of a massive black hole accreting at near Eddington rates with an FRI jet. This elusive combination of properties was explained in our 2010 model where we showed it to be part of a small parameter space that includes X shaped radio galaxies. As an accreting black hole that never experienced a counterrotating phase, H1821+643 is constrained by theory to produce a jet for spin values between 0.1 and about 0.7 and an FRI jet for a slightly smaller range. The feedback from such a black hole is not subject to a tilted jet and is why star formation rates remain high in this cluster environment. The prediction is that H1821+643 is within millions of years of becoming jetless., Comment: in press

Low-frequency quasi-periodic oscillations (LFQPOs) have been routinely observed in black hole X-ray binaries (BHXRBs). These LFQPOs can be explained by axisymmetric shock oscillation in accretion flow around a rotating black hole. We address the physical origin of Type-C LFQPOs in BHXRBs observed by the Rossi X-ray Timing Explorer satellite considering a minimum number of free parameters, namely, specific energy and specific angular momentum of the infalling matter for a given set of BH mass and spin parameter. We apply the solution for a large number of BH candidates to further strengthen the scenario of an anti-correlation between the QPO frequency and the location of the shock. Our study also confirms that Compton cooling can be sufficient to explain the observed QPOs., Comment: 9 pages, 4 figures, 3 tables, accepted for publication in MNRAS

Recent work has called into question whether nature can extract the rotational energy of a black hole via electromagnetic fields by appealing to an alleged ability to absorb current. We describe the strategies needed to properly treat the astrophysics in curved spacetime near black holes, showing that while the Blandford-Znajek effect is sound, the deeper nature of the electric nature of black holes remains unresolved., Comment: 7 pages, Post-peer-review, pre-copyedit version of an article published in Nature Astronomy

Observations at low redshift have begun to tease out the star formation rate in active galaxies (AGN), which marks the beginning of the black hole-star formation connection over cosmic time. Star formation appears to depend on AGN type, cluster richness, and black hole accretion, but in ways that are not direct and have yet to be understood. Much of the confusion is that while some AGN appear to enhance star formation, others seem to suppress it. By implementing simplified, yet informed assumptions about AGN feedback on star formation, we show how AGN with jets might be dominated by two phases in which star formation is first enhanced, then suppressed. With this new element incorporated into our model, we make sense of radio and quasar mode behavior in the star formation rate-stellar mass (SFR-SM) plane for AGN. Due to jet feedback on star formation, jetted AGN tend to move upwards and rightward in the SFR-SM plane and then downward and to the right, past both the star-forming main sequence (SFMS) as well as the radio-quiet AGN. This picture allows us to predict the black hole connection to star formation as a function of the environment over the history of the universe., Comment: 15 pages, 5 figures, Accepted for publication in the PASP Journal

X-ray flux from the inner hot region around central compact object in a binary system illuminates the upper surface of an accretion disc and it behaves like a corona. This region can be photoionised by the illuminating radiation, thus can emit different emission lines. We study those line spectra in black hole X-ray binaries for different accretion flow parameters including its geometry. The varying range of model parameters captures maximum possible observational features. We also put light on the routinely observed Fe line emission properties based on different model parameters, ionization rate, and Fe abundances. We find that the Fe line equivalent width $W_{\rm E}$ decreases with increasing disc accretion rate and increases with the column density of the illuminated gas. Our estimated line properties are in agreement with observational signatures., Comment: 14 pages, 16 figures Accepted for publication in MNRAS (21/04/21)

The discovery of 3C 273 in 1963, and the emergence of the Kerr solution shortly thereafter, precipitated the current era in astrophysics focused on using black holes to explain active galactic nuclei (AGN). But while partial success was achieved in separately explaining the bright nuclei of some AGN via thin disks, as well as powerful jets with thick disks, the combination of both powerful jets in an AGN with a bright nucleus, such as in 3C 273, remained elusive. Although numerical simulations have taken center stage in the last 25 years, they have struggled to produce the conditions that explain them. This is because radiatively efficient disks have proved a challenge to simulate. Radio quasars have thus been the least understood objects in high energy astrophysics. But recent simulations have begun to change this. We explore this milestone in light of scale-invariance and show that transitory jets, possibly related to the jets seen in these recent simulations, as some have proposed, cannot explain radio quasars. We then provide a road map for a resolution., Comment: 9 pages

We examine radiative standing shocks in advective accretion flows around stellar-mass black holes by 2D radiation hydrodynamic simulations, focusing on the super-Eddington accreting flow. Under a set of input flow parameters responsible for the standing shock, the shock location on the equator decreases toward the event horizon with an increasing accretion rate. The optically thin and hot gas in the narrow funnel region along the rotational axis changes gradually into a dense and optically thick state with the increasingly dense gas transported from the base of the radiative shock near the equator. As a result, the luminosity becomes as high as ~ $10^{40}$ erg $s^{-1}$, and the radiation shows a strongly anisotropic distribution around the rotational axis and then very low edge-on luminosity as ~ $10^{36}$ erg $s^{-1}$. The mass outflow rate from the outer boundary is high as ~ $10^{-5}$ and $10^{-4}$ $M_{\odot} yr^{-1}$ but most of the outflow is originated through the radial outer boundary and may be observed over a wide wind region. The models show approximately black body spectra with a temperature of $5 \times 10^{6} - 3 \times 10^{7}$ K at the vertical outer boundary surface. The radiative shock models with the super-Eddington luminosities show a possible model for the superaccretor SS 433 and Ultraluminous X-ray sources with stellar-mass black holes., Comment: 9 pages, 8 figures, Accepted for publication in the MNRAS main journal

We study two dimensional low angular momentum flow around the black hole using the resistive magnetohydrodynamic module of PLUTO code. Simulations have been performed for the flows with parameters of specific angular momentum, specific energy, and magnetic field which may be expected for the flow around Sgr A*. For flows with lower resistivity $\eta=10^{-6}$ and $0.01$, the luminosity and the shock location on the equator vary quasi-periodically. The power density spectra of luminosity variation show the peak frequencies which correspond to the periods of $5 \times 10^5$, $1.4 \times 10^5$, and $5 \times 10^4$ seconds, respectively. These quasi-periodic oscillations (QPOs) occur due to the interaction between the outer oscillating standing shock and the inner weak shocks occurring at the innermost hot blob. While for cases with higher resistivity $\eta=0.1$ and 1.0, the high resistivity considerably suppresses the magnetic activity such as the MHD turbulence and the flows tend to be steady and symmetric to the equator. The steady standing shock is formed more outward compared with the hydrodynamical flow. The low angular momentum flow model with the above flow parameters and with low resistivity has a possibility for the explanation of the long-term flares with $\sim$ one per day and $\sim 5 - 10$ days of Sgr A* in the latest observations by Chandra, Swift, and XMM-Newton monitoring of Sgr A*., Comment: 14 pages, 9 figures, Accepted for publication in the Research in Astronomy and Astrophysics journal

The idea that mergers are more likely in dense groups or clusters coupled with the assumption that such events lead to cold gas flows onto black holes, suggests a direct relationship between the radiative efficiency of an active galactic nucleus and environmental richness. Observations, however, increasingly challenge this and other basic expectations. Mounting evidence, for example, shows an inverse trend between near-Eddington accreting objects and environmental richness. Broken down by radio galaxy subgroup, recent work has explored connections between low excitation radio galaxies with Fanaroff-Riley II jet morphology (FRII LERGs) and other radio galaxies. We make contact with that work by adding a discussion of the recently discovered FR0 radio galaxies and show how to fit them in a picture in which FRII LERGs are not initial nor final phases in the lifetime of a radio galaxy, but de facto transition states. We describe how to understand the observed X-ray luminosity/cluster richness relation as a fundamental correlation on the nature of the jet-disk connection.

Extreme states of matter exist throughout the universe e.g. inside planetary cores, stars or astrophysical jets. Such conditions are generated in the laboratory in the interaction of powerful lasers with solids, and their evolution can be probed with femtosecond precision using ultra-short X-ray pulses to study laboratory astrophysics, laser-fusion research or compact particle acceleration. X-ray scattering (SAXS) patterns and their asymmetries occurring at X-ray energies of atomic bound-bound transitions contain information on the volumetric nanoscopic distribution of density, ionization and temperature. Buried heavy ion structures in high intensity laser irradiated solids expand on the nanometer scale following heat diffusion, and are heated to more than 2 million Kelvin. These experiments demonstrate resonant SAXS with the aim to better characterize dynamic processes in extreme laboratory plasmas.