Cepheids are pulsating variable stars with a periodic chromospheric response at UV wavelengths close to their minimum radius phase. Recently, an X-ray variable signature was captured in observations ...during the maximum radius phase. This X-ray emission came as a surprise and is not understood. In this work, we use the modern astrophysical code PLUTO to investigate the effects of pulsations on Cepheid X-ray emission. We run a number of hydrodynamic numerical simulations with a variety of initial and boundary conditions in order to explore the capability of shocks to produce the observed phase-dependent X-ray behavior. Finally, we use the Simulated Observations of X-ray Sources (SOXS) package to create synthetic spectra for each simulation case and link our simulations to observables. We show that, for certain conditions, we can reproduce observed X-ray fluxes at phases 0.4-0.8 when the Cepheid is at maximum radius. Our results span a wide range of mass-loss rates, 2 × 10−13 M yr−1 to 3 × 10−8 M yr−1, and peak X-ray luminosities, 5 × 10−17 erg cm−2 s−1 to 1.4 × 10−12 erg cm−2 s−1. We conclude that Cepheids exhibit two-component emission with (a) shock waves being responsible for the phase-dependent variable emission (phases 0.2-0.6) and (b) a separate quiescent mechanism being the dominant emission mechanism for the remaining phases.
Abstract We investigate outflows and the physics of super‐Eddington versus sub‐Eddington regimes in black hole systems. Our focus is on prospective science using next‐generation high‐resolution soft ...x‐ray instruments. We highlight the properties of black hole ultraluminous x‐ray source (ULX) systems in particular. Owing to scale invariance in accreting black holes, ULX accretion properties, including their outflows, inform our understanding not only of the closely related population of (similar‐mass) x‐ray binary systems but also of tidal disruption events (TDEs) around supermassive black holes. A subsample of TDEs are likely to transcend super‐Eddington to sub‐Eddington regimes as they evolve, offering an important unifying analog to ULXs and sub‐Eddington x‐ray binaries. We demonstrate how next‐generation soft x‐ray observations with resolving power and collecting area can simultaneously identify ultrafast and more typical wind components, distinguish between different wind mechanisms, and constrain changing wind properties over characteristic variability timescales.
OLIMPO is a proposed Antarctic balloon-borne Sunyaev-Zel’dovich effect (SZE) imager to study gas dynamics associated with structure formation along with the properties of the warm-hot intergalactic ...medium (WHIM) residing in the connective filaments. During a 25 day flight OLIMPO will image a total of 10 z ∼0.05 galaxy clusters and 8 bridges at 145, 250, 365, and 460 GHz at an angular resolution of 1.0′–3.3′. The maps will be significantly deeper than those planned from CMB-S4 and CCAT-P, and will have excellent fidelity to the large angular scales of our low- z targets, which are difficult to probe from the ground. In combination with X-ray data from eROSITA and XRISM we will transform our current static view of galaxy clusters into a full dynamic picture by measuring the internal intra-cluster medium (ICM) velocity structure with the kinematic SZE, X-ray spectroscopy, and the power spectrum of ICM fluctuations. Radio observations from ASKAP and MeerKAT will be used to better understand the connection between ICM turbulence and shocks with the relativistic plasma. Beyond the cluster boundary, we will combine thermal SZE maps from OLIMPO with X-ray imaging from eROSITA to measure the thermodynamics of the WHIM residing in filaments, providing a better understanding of its properties and its contribution to the total baryon budget.
Several lines of evidence suggest that the galaxy cluster Cl0024+17, an apparently relaxed system, is actually a collision of two clusters, the interaction occurring along our line of sight. Recent ...lensing observations suggest the presence of a ringlike dark matter structure, which has been interpreted as the result of such a collision. In this paper, we present N-body simulations of cluster collisions along the line of sight to investigate the detectability of such features. We use realistic dark matter density profiles as determined from cosmological simulations. Our simulations show a 'shoulder' in the dark matter distribution after the collision, but no ring feature even when the initial particle velocity distribution is highly tangentially anisotropic ({sigma}{sub {theta}}/{sigma} {sub r} >> 1). Only when the initial particle velocity distribution is circular do our simulations show such a feature. Even modestly anisotropic velocity distributions are inconsistent with the halo velocity distributions seen in cosmological simulations and would require highly fine-tuned initial conditions. Our investigation leaves us without an explanation for the dark matter ringlike feature in Cl0024+17 suggested by lensing observations.
We report on the detection of diffuse radio emission with peculiar morphology in the central region of the galaxy cluster Abell 2657. The most striking feature identified in our 144 MHz LOFAR image ...is a bifurcated radio arc that extends for a projected size of 150-200 kpc. From the analysis of XMM-Newton data, we find clear evidence of gas sloshing in the cluster and a possible dip in X-ray surface brightness between the two radio arcs which deserves confirmation. Interestingly, the synchrotron emission of the bifurcated radio arc is stretched along the sloshing spiral. We compare our observational results with numerical simulations of non-thermal components interacting with gas motions. We suggest that the detected emission may trace a radio bubble shredded by gas sloshing, where relativistic electrons and magnetic fields are expected to be stretched and stirred as a consequence of tangential flows induced by the spiralling gas motion. Lastly, we report on the presence of two thin (6-7 kpc in width) and parallel strands of radio emission embedded in the outer arc that are morphologically similar to the emerging population of non-thermal filaments observed in galaxy clusters, radio galaxies, and the Galactic centre. While this work further demonstrates the complex interplay between thermal and non-thermal components in the intracluster medium, follow-up observations in radio and X-rays are required to firmly determine the origin of the features observed in Abell 2657.
We present results from a 140 ks Chandra/ACIS-S observation of the hot gas around the canonical FR I radio galaxy 3C 449. An earlier, shorter 30 ks Chandra observation of the group gas showed an ...unusual entropy distribution and a surface brightness edge in the gas that could be a strong shock around the inner radio lobes. In our deeper data we find no evidence for a temperature increase inside of the brightness edge, but a temperature decrease across part of the edge. This suggests that the edge is a "sloshing" cold front due to a merger within the last lap 1.3-1.6 Gyr. Both the northern and southern inner jets are bent slightly to the west in projection as they enter their respective lobes, suggesting that the sloshing core is moving to the east. The straight inner jet flares at approximately the position where it crosses the contact edge, suggesting that the jet is entraining and thermalizing some of the hot gas as it crosses the edge. We also detect filaments of X-ray emission around the southern inner radio jet and lobe which we attribute to low entropy entrained gas. The lobe flaring and gas entrainment were originally predicted in simulations of Loken et al. and are confirmed in our deep observation.
The hot, X-ray-emitting phase of the circumgalactic medium of massive galaxies is believed to be the reservoir of baryons from which gas flows onto the central galaxy and into which feedback from AGN ...and stars inject mass, momentum, energy, and metals. These effects shape the velocity fields of the hot gas, which can be observed via the Doppler shifting and broadening of emission lines by X-ray IFUs. In this work, we analyze the gas kinematics of the hot circumgalactic medium of Milky Way-mass disk galaxies from the TNG50 simulation with synthetic observations to determine how future instruments can probe this velocity structure. We find that the hot phase is often characterized by outflows from the disk driven by feedback processes, radial inflows near the galactic plane, and rotation, though in some systems the velocity field is more disorganized and turbulent. With a spectral resolution of \(\sim\)1 eV, fast and hot outflows (\(\sim\)200-500 km s\(^{-1}\)) can be measured, depending on the orientation of the galaxy on the sky. The rotation velocity of the hot phase (\(\sim\)100-200 km s\(^{-1}\)) can be measured using line shifts in edge-on galaxies, and is slower than that of colder gas phases but similar to stellar rotation velocities. By contrast, the slow inflows (\(\sim\)50-100 km s\(^{-1}\)) are difficult to measure in projection with these other components, but may be detected in multi-component spectral fits. We find that the velocity measured is sensitive to which emission lines are used. Measuring these flows will constrain theories of how the gas in these galaxies evolves.
The FLASH code has evolved into a modular and extensible scientific simulation software system over the decade of its existence. During this time it has been cumulatively used by over a thousand ...researchers to investigate problems in astrophysics, cosmology, and in some areas of basic physics, such as turbulence. Recently, many new capabilities have been added to the code to enable it to simulate problems in high-energy density physics. Enhancements to these capabilities continue, along with enhancements enabling simulations of problems in fluid-structure interactions. The code started its life as an amalgamation of already existing software packages and sections of codes developed independently by various participating members of the team for other purposes. The code has evolved through a mixture of incremental and deep infrastructural changes. In the process, it has undergone four major revisions, three of which involved a significant architectural advancement. Along the way, a software process evolved that addresses the issues of code verification, maintainability, and support for the expanding user base. The software process also resolves the conflicts arising out of being in development and production simultaneously with multiple research projects, and between performance and portability. This paper describes the process of code evolution with emphasis on the design decisions and software management policies that have been instrumental in the success of the code. The paper also makes the case for a symbiotic relationship between scientific research and good software engineering of the simulation software.
Several lines of evidence have suggested that the galaxy cluster Cl 0024+17, an apparently relaxed system, is actually a collision of two clusters, the interaction occurring along our line of sight. ...In this paper, we present a high-resolution N-body/hydrodynamics simulation of such a collision. We have created mock X-ray observations of our simulated system using MARX, a program that simulates the on-orbit performance of the Chandra X-ray Observatory. We analyze these simulated data to generate radial profiles of the surface brightness and temperature. At later times, t = 2.0-3.0 Gyr after the collision, the simulated surface brightness profiles are better fit by a superposition of two {beta}-model profiles than a single profile, in agreement with the observations of Cl 0024+17. In general, due to projection effects, much of the post-collision density and temperature structure of the clusters is not seen in the observations. In particular, the observed temperatures from spectral fitting are much lower than the temperature of the hottest gas. We determine from our fitted profiles that if the system is modeled as a single cluster, the hydrostatic mass estimate is a factor {approx}2-3 less than the actual mass, but if the system is modeled as two galaxy clusters in superposition, a hydrostatic mass estimation can be made which is accurate to within {approx}10%. We examine some implications of these results for galaxy cluster X-ray surveys.
Galaxy cluster mergers are representative of a wide range of physics, making them an excellent probe of the properties of dark matter and the ionized plasma of the intracluster medium. To date, most ...studies have focused on mergers occurring in the plane of the sky, where morphological features can be readily identified. To allow study of mergers with arbitrary orientation, we have assembled multi-probe data for the eight-cluster ICM-SHOX sample sensitive to both morphology and line of sight velocity. The first ICM-SHOX paper 1 provided an overview of our methodology applied to one member of the sample, MACS J0018.5+1626, in order to constrain its merger geometry. That work resulted in an exciting new discovery of a velocity space decoupling of its gas and dark matter distributions. In this work, we describe the availability and quality of multi-probe data for the full ICM-SHOX galaxy cluster sample. These datasets will form the observational basis of an upcoming full ICM-SHOX galaxy cluster sample analysis.
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