Peak Of X-ray Emission Research Articles

Simulated X-ray emission from a single-explosion model for a supernova remnant 3C 400.2

We present a single-explosion model study of the 3C 400.2 supernova remnant (SNR), made with two-dimensional axisymmetric simulations. The numerical simulations were made with the adaptive grid code YGUAZU-A. Several initial scenarios have been tested in order to reproduce the centrally peaked X-ray emission observed for this remnant. This study reveals that the explosion of the SN inside a pre-existing stellar wind bubble successfully generates the observed morphology, when thermal conduction is included in the model. The best morphological fit is obtained at an evolution time of 21 000 yr, when the total luminosity is 1.2 x 10 34 erg s -1 .

Study of X-ray and Neutron Emission in Experiments with Al Wires in an MA Plasma Focus

Results are presented from experimental studies of the correlation between X-ray and neutron emissions generated in the implosion of a deuteron plasma shell onto an Al wire. The experiments were carried out on the PF-1000 facility at currents of 1.5–1.8 MA. An Al wire 80 μm in diameter and 7–9 cm in length was placed at the end of the inner electrode. During the implosion of the plasma shell, Al K-shell X-rays were first emitted at the dip of the current derivative. After the X-ray pulse, a relatively stable corona with a diameter of 2–3 mm and lifetime of a few hundred nanoseconds formed around the wire. The presence of the wire did not considerably reduce the total neutron yield (at most 1011 neutrons per shot) in comparison to discharges without a wire. As a rule, the intensity of neutron emission was maximal a few tens of nanoseconds after the peak of X-ray emission. A detailed comparison of two shots with low and high neutron yields have shown that the neutron yield depends on the configuration and dynamics of the discharge. The possible influence of the self-generated axial component of the magnetic field on the development of the plasma focus and the acceleration of fast deuterons is discussed.

Mass-Profile and Instability-Growth Measurements for 300-WireZ-Pinch Implosions Driven by 14–18 MA

We present the first comprehensive study of high wire-number, wire-array Z-pinch dynamics at 14-18 MA using x-ray backlighting and optical shadowgraphy diagnostics. The cylindrical arrays retain slowly expanding, dense wire cores at the initial position up to 60% of the total implosion time. Azimuthally correlated instabilities at the array edge appear during this stage which continue to grow in amplitude and wavelength after the start of bulk motion, resulting in measurable trailing mass that does not arrive on axis before peak x-ray emission.

K‐band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light

We investigate the near-infrared K-band properties of the brightest cluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters and groups, using data from the Two Micron All Sky Survey. Our cluster sample spans a factor of 70 in mass, making it sensitive to any cluster mass-related trends. We derive the cumulative radial distribution for the BCGs in the ensemble and find that 70% of the BCGs are centered in the cluster to within 5% of the virial radius r200; this quantifies earlier findings that BCG position coincides with the cluster center as defined by the X-ray emission peak. We study the correlations between the luminosity of the BCGs (Lb) and the mass and the luminosity of the host clusters, finding that BCGs in more massive clusters are more luminous than their counterparts in less massive systems and that the BCGs become less important in the overall cluster light (L200) as cluster mass increases. By examining a large sample of optically selected groups, we find that these correlations hold for galactic systems less massive than our clusters (<3 × 1013 M☉). From the differences between luminosity functions in high- and low-mass clusters, we argue that BCGs grow in luminosity mainly by merging with other luminous galaxies as the host clusters grow hierarchically; the decreasing BCG luminosity fraction (Lb/L200) with cluster mass indicates that the rate of luminosity growth in BCGs is slow compared to the rate at which clusters acquire galaxy light from the field or other merging clusters. Utilizing the observed correlation between the cluster luminosity and mass and a merger tree model for cluster formation, we estimate that the amount of intracluster light (ICL) increases with cluster mass; our calculations suggest that in 1015 M☉ clusters more than 50% of total stellar mass is in ICL, making the role of ICL very important in the evolution and thermodynamic history of clusters. The cluster baryon fraction accounting for the ICL is in good agreement with the value derived from cosmic microwave background observations. The inclusion of ICL reduces the discrepancy between the observed cluster cold baryon fraction and that found in hydrodynamical simulations. Based on the observed abundance in the intracluster medium, we find that the ICL predicted by our model, together with the observed galaxy light, match the mass-to-light ratio expected from simple stellar population models, provided that the Salpeter initial mass function is adopted. The ICL also makes it easier to produce the iron excess found in the central regions of cool-core clusters.

X‐Raying A2125: A Large‐Scale Hierarchical Complex of Galaxies and Hot Gas

We present an 82 ks Chandra ACIS-I observation of a large-scale hierarchical complex, which consists of various clusters/groups of galaxies and low surface brightness X-ray emission at z = 0.247. This high-resolution Chandra observation allows us for the first time to separate unambiguously the X-ray contributions from discrete sources and large-scale diffuse hot gas. We detect 99 X-ray sources in a 17' × 17' field. Ten of these sources are identified as members of the complex and are mostly radio-bright. Whereas unresolved X-ray sources tend to be associated with galaxies in intermediate density environments, extended X-ray emission peak at bright radio galaxies in the central cluster. In particular, a distinct X-ray trail appears on one side of the fast-moving galaxy C153, clearly due to ram pressure stripping. The diffuse X-ray emission from the central cluster can be characterized by a thermal plasma with a characteristic temperature of 3.2 keV and a heavy element abundance of 0.24 solar (90% confidence uncertainties). In comparison, a patch of low surface brightness X-ray emission apparently originates in relatively low density intergalactic gas with a characteristic temperature of 0.98 keV and an abundance of 0.09 solar. The Chandra observation, together with extensive multiwavelength data, indicates that the complex represents a projection of several galaxy substructures, which may be undergoing major mergers. We discuss the dynamic states of the complex and its substructures, as well as properties of X-ray-emitting galaxies and the relationship to their environments.

ChandraObservations of NGC 4438: An Environmentally Damaged Galaxy in the Virgo Cluster

We present results from a 25 ksec CHANDRA ACIS-S observation of galaxies NGC4438 and NGC4435 in the Virgo Cluster. X-ray emission in NGC4438 is observed in a ~700 pc nuclear region, a 2.3 kpc spherical bulge, and a network of filaments extending 4-10 kpc to the W and SW of the galaxy. The X-ray emission in all 3 regions is highly correlated to similar features observed in Halpha. Spectra of the filaments and bulge are well represented by a 0.4 keV MEKAL model with combined 0.3-2 keV intrinsic luminosity of 1.24x10^{40}erg/s, electron densities ~ 0.02-0.04 cm^{-3}, cooling times of 400-700 Myr and X-ray gas mass <~ 3.7x10^8 Msolar. In the nuclear region of NGC4438 X-ray emission is seen from the nucleus and from two outflow bubbles extending 360(730) pc to the NW(SE) of the nucleus. The spectrum of the NW outflow bubble plus nucleus is well fitted by an absorbed (n_H=1.9x10^{21} cm^{-2}) 0.58 keV MEKAL plasma model plus a heavily absorbed (n_H = 2.9 x10^{22} cm^{-2}) Gamma = 2, power law component. The electron density, cooling time, and X-ray gas mass in the NW outflow are ~0.5 cm^{-3}, 30 Myr and 3.5x10^6 Msolar. Weak X-ray emission is observed in the central region of NGC4435 with the peak of the hard emission coincident with the galaxy's optical center; while the peak of the soft X-ray emission is displaced 316 pc to the NE. The spectrum of NGC 4435 is well fitted by a non-thermal power law plus a thermal component from 0.2-0.3 keV diffuse ISM gas. We argue that the X-ray properties of gas outside the nuclear region in NGC4438 and in NGC4435 favor a high velocity, off-center collision between these galaxies ~ 100 Myr ago; while the nuclear X-ray emitting outflow gas in NGC4438 has been heated only recently (within ~ 1-2 Myr) by shocks (v_s ~ 600 kms^{-1}) possibly powered by a central AGN.

Can Supermassive Black Holes Sufficiently Heat Cool Cores of Galaxy Clusters?

The activities of a supermassive black hole or active galactic nucleus in the central galaxy of a cluster of galaxies have been promising candidates for the heating sources of cool cluster cores. We estimate the masses of black holes using known correlations between the mass of a black hole and the velocity dispersion or the luminosity of the host galaxy. We find that the masses are ~108-109 M☉ and the central X-ray luminosities of the host clusters (the strength of the cooling flow) are well below the Eddington luminosities. However, we do not find a correlation between the mass and the central X-ray luminosity of the host cluster. If the heating is stable, this seems to contradict a simple expectation if a supermassive black hole is the main heating source of a cluster core. Moreover, if we assume a canonical energy conversion rate (10%), black holes alone would be unable to sufficiently heat the clusters with strong centrally peaked X-ray emission (massive cooling flows) over the lifetime of cluster cores. These results may indicate that massive cooling flows are a transient phenomenon, perhaps because the black holes are activated periodically. Alternatively, in the massive cooling flow clusters, the energy conversion rate may be larger than 10%, that is, the black holes may be Kerr black holes.

Multi-Wavelength Analysis of the 29 September 2002 M2.6/2N Flare

Using TRACE EUV 171 A line, Hα line, Zurich radio, RHESSI, and HXRS observations the 29 September 2002 flare (M2.6), which occurred in AR NOAA 0134, was analyzed. Flaring structures were compared with a potential magnetic field model (field lines and quasi-separatrix layers) made from SOHO/MDI full-disk magnetogram. Series of high-resolution SOHO/MDI magnetograms and TRACE white-light images were used to find changes in the active region at the photosphere during the flare. The flare began with a rising of a small dark loop followed by the flare brightening observed in 171 A with TRACE and Hα lines. In radio wavelengths, first type III bursts were observed 5 min prior to the start of hard X-ray emission, indicating a pre-flare coronal activity. The main hard X-ray emission peak (at 06:36 UT) was associated with the second type III burst activity and several slowly negatively drifting features, all starting from one point on the radio spectrum (probably a shock propagating through structures with different plasma parameters). After this time a huge loop formed and three minutes later it became visible in absorption both in Hα and 171 A EUV lines. The phase of huge dark loop formation was characterized by long-lasting, slowly negatively drifting pulsations and drifting continuum. Finally, considering this huge loop as a surge an evolution of the event under study is discussed.

LSI +61°303: A Pulsar Wind Nebula in a Binary?

LSI +61°303 outbursts are modeled as a pulsar wind nebula expanding inside the environment provided by the Be companion star's stellar wind and photon flux. A set of equations describing the system is developed and solved numerically for representative sets of parameters. Emission in X-rays through gamma-rays is due to inverse Compton emission from relativistic electrons around the pulsar. The radio emission is due to synchrotron emission of varying optical depth, which yields a varying spectral index. The peak of X-ray emission is near periastron and the peak of the radio emission is near apastron, due to reduced confining pressure on the relativistic electron cloud and its subsequent rapid expansion.

The Multicolored Hot Interstellar Medium of “the Antennae” Galaxies (NGC 4038/4039)

We report results of analysis of extended soft emission discovered in Chandra ACIS pointing at merging system NGC 4038/4039 (the Antennae). We present a multicolor X-ray image that suggests both extensive absorption by dust in this system, peaking in contact region, as well as variations in temperature of different emitting regions of hot interstellar medium (ISM). Spectral fits to multicomponent thermal emission models confirm this picture and give a first evaluation of parameters of hot plasma. We compare diffuse X-ray emission with radio continuum (6 cm), H I, CO, and Hα images to take a first look at multiphase ISM of the Antennae galaxies. We find that hot (X-ray) and cold (CO) gas have comparable thermal pressures in two nuclear regions. We also conclude that displacement between peak of diffuse X-ray emission in north of galaxy system, toward inner regions of northern spiral arm (as defined by Hα, radio continuum, and H I), could result from ram pressure of infalling H I clouds.

Signature of an Avalanche in Solar Flares as Measured by Photospheric Magnetic Fields

We analyzed time variations of turbulent parameters of the photospheric magnetic field of four active regions obtained during the course of major solar flares using longitudinal magnetograms from the Big Bear Solar Observatory and from SOHO/MDI full-disk measurements. Analysis of the data indicated that, before each flare, the degree of intermittency of the magnetic field had been increasing for 6-33 minutes and reached a maximum value approximately 3-14 minutes before the peak of the hard X-ray emission for each event. This result seems to suggest the existence in an active region of a turbulent phase prior to a solar flare. We also found that the maximum of the correlation length of the magnetic energy dissipation field tends to follow (or to occur nearly simultaneously) with the peak of the hard X-ray emission. The data suggest that the peak in the correlation length might be a trace of an avalanche of coronal reconnection events. We discuss the results in the framework of the concept of self-organized criticality.

X-ray spectroscopy of the cluster of galaxies PKS 0745-191 with XMM-Newton

We present the results from XMM-Newton observations of the cluster of galaxies PKS 0745-191. The spatially resolved spectra from the European Photon Imaging Cameras ( both EPN and EMOS) can be fitted with a single temperature thermal plasma model when the interstellar column density is closer to the lower limit of the range allowed by observations. Alternatively, a two-component model can be fitted to the spectra from the inner region for slightly higher values of N-H. The temperature profile shows a drop in the center of the cluster, from about 8 keV at radii larger than similar to350 kpc to about 4 keV at the center, indicating that the gas in the central region is cooling. The total cooling flow rate inferred from the spectral data is only 364(-94)(+97) M-circle dot yr(-1), however, much smaller than the previously obtained value. The metal abundance is found to decrease from 0.5 in solar units at the center to about 0.2 at a radius of similar to300 kpc. Deprojected spectra are also presented, which show a result similar to the projected spectra. The location of the X-ray emission peak is also the site of extended radio emission. Inspection of the higher resolution Chandra image of the cluster shows enhanced X-ray emission about 3 west of the center where also the radio emission is elongated. We explore possible implications on the interaction between the radio lobes and the intracluster plasma. Assuming that the gas is in hydrostatic equilibrium with the cluster potential, we find a total mass of about 1.18 +/- 0.04 x 10(13) M-circle dot within the critical radius of the observed gravitational arc, which is a factor similar to2 lower, however, than that from optical lensing. We also calculated the gas mass fraction profile up to 0.63 r(vir) and obtained a mean gas mass fraction f(gas) = 0.22 +/- 0.02.

ROSATHRI Investigation of the NGC 507 X‐Ray Halo

We present an X-ray investigation of the elliptical galaxy NGC 507. We make use of archival Rosat HRI, PSPC and Chandra data, to connect the large-scale structure of the halo to the core morphology. Our analysis shows that the halo core (r 3 r_e) are characterised by different dynamical properties and suggests a different origin of the two components. The halo core has a complex morphology with a main X-ray emission peak, coincident with the center of the optical galaxy, and several secondary peaks. The spatial and spectral analysis of the central peak shows that this feature is produced by denser hot gas in the galaxy core. Our data support the scenario where the gas is kinetically heated by stellar mass losses. Comparison with previously published studies suggest that the core of X-ray extended galaxies is associated to the stellar distribution and has similar properties to the X-ray halo of compact galaxies. The secondary peaks are due instead to interactions between the radio-emitting plasma and the surrounding ISM. We found that the energy input by the central radio source in the ISM may be large enough to prevent gas from cooling. The total mass profile shows the presence of a dark matter halo extending on cluster scales which is likely to be associated with the whole cluster rather than with NGC 507. This structure is typical of many X-ray bright Early-Type galaxies and may explain the spatial and spectral differences with X-ray compact galaxies largely debated in literature. Finally we discuss the nature of the point sources detected in the HRI FOV.

Angle-resolved soft X-ray emission and absorption spectroscopy of hexagonal boron nitride

Angle-resolved soft X-ray emission and absorption spectra in the BK and NK regions of hexagonal BN were measured using polarized synchrotron radiation. The take-off/incident-angle-dependence on the spectral features in both X-ray emission and absorption is clearly observed. The configuration of the σ and π orbitals, which were calculated using discrete variational (DV)-Xα molecular orbital calculations, explains the angle-resolved soft X-ray emission and absorption spectra. The relative peak intensity of the 394-eV peak in the NK X-ray emission provides useful information about the BN layer ordering.

Properties of the Brightest Cluster Galaxy and Its Host Cluster

We investigate the relation between the properties of brightest cluster galaxies (BCGs) and those of their host clusters. To quantify the properties of cluster hot gas, we employ the parameter Z of the fundamental plane of X-ray clusters. It is found that the offset of the BCG from the peak of cluster X-ray emission is larger for smaller Z clusters. The parameter Z (not the redshift z), which depends mainly on virial density ρvir, is considered to represent the formation epoch of a cluster. We thus consider that the offset of the BCG is correlated with the dynamical equilibrium state of its host cluster. On the contrary, no significant correlation is found between the absolute optical magnitude of the BCG and the parameter Z. If the extreme brightness of the BCG is acquired mainly in the course of cluster evolution by environmental effect, BCGs are expected to be brighter in large Z clusters. Our result is not consistent with this simplified view. On the contrary, it is possible that the extreme brightness of the BCG is likely to be determined in the early history of cluster collapse.

Surface X-ray emission from lanthanide metals

O 3 X-ray emission (XE) upon 5p 3/2 electron-impact ionization of La(0 0 0 1) and Sm(0 0 0 1) metal surfaces exhibits up to 30% spectral intensity from the topmost atomic surface layer. The energy separation of surface and bulk XE peaks is explained by the surface core-level shift of La and the surface valence transition of Sm. While the bulk XE spectra are in reasonable agreement with theoretical sd partial density of states (DOS), the experimental access to the partial surface-layer DOS opens new opportunities in studying surface phenomena in lanthanide metals and compounds.

ChandraObservations of Arp 220: The Nuclear Source

We present the first results from 60 ks of observations of Arp 220 using the ACIS-S instrument on Chandra. We report the detection of several sources near the galaxy's nucleus, including a point source with a hard spectrum that is coincident with the western radio nucleus B. This point source is mildly absorbed (NH ~ 3 × 1022 cm-2) and has an estimated luminosity of 4 × 1040 ergs s-1. In addition, a fainter source may coincide with the eastern nucleus A. Extended hard X-ray emission in the vicinity raises the total estimated nuclear 2-10 keV X-ray luminosity to 1.2 × 1041 ergs s-1, but we cannot rule out a hidden active galactic nucleus behind columns exceeding 5 × 1024 cm-2. We also detect a peak of soft X-ray emission to the west of the nucleus and a hard point source 2.5 kpc from the nucleus with a luminosity of 6 × 1039 ergs s-1.

ChandraX‐Ray Spectroscopy and Imaging of the Galaxy Cluster PKS 0745−191

We present a detailed spectral and spatial analysis of the galaxy cluster PKS 0745-191, using recent observations from the Chandra X-ray Observatory. The data provide information on the temperature and metallicity of the intracluster medium, the distribution of emission throughout the cluster, morphology of the cluster core, and an independent mass estimate which can be compared to that from gravitational lensing. X-ray spectra extracted from the central 300 kpc (~2 arcmin) are well described by a two-temperature plasma and the mean cluster temperature is consistent with previously determined values. The distribution of both temperature and metallicity within the inner 360 kpc (2.3 arcmin) of PKS 0745-191 is probed on scales of 8 arcsec (~20 kpc), yielding a relatively constant abundance throughout the region and a strong temperature gradient (down to ~4-5 keV) within the central 215 kpc. Beta-model fits to the surface brightness profile of PKS 0745-191 indicate that a second beta-model component is required to fit the inner ~10 kpc. Imaging analysis of the cluster core reveals an irregular morphology within the inner 50 kpc, and confirms that the X-ray emission peak lies within 0.5 arcsec (the spatial resolution of Chandra) of both the optical and radio central cD positions. The cluster mass, based on both two temperature and multiphase fits to the X-ray spectrum, is in close agreement with lensing mass estimates of PKS-0745-191.

Compact toroid injection as fueling in the JFT-2M tokamak

Compact toroid (CT) injection experiments have been carried out in JFT-2M for the understanding of the physics of CT injection as means of tokamak fueling. An increase in the line averaged electron density Δ n e ≈0.4×10 19 m −3 was obtained in the case of a CT velocity of 300 km/s and a toroidal magnetic field of 0.8 T. The fueling efficiency is roughly 40%. An asymmetric radial profile with a peripheral second peak in the soft X-ray emission was produced for ∼0.4 ms by this CT injection and resulting in a tokamak disruption.

On the peak radio and X-ray emission from neutron star and black hole candidate X-ray transients

We have compiled and analysed reports from the literature of (quasi-)simultaneous observations of X-ray transients at radio and X-ray wavelengths and compared them with each other and with more unusual radio-bright sources such as Cygnus X-3, GRS 1915+105 and Circinus X-1. There exists a significant (>97 per cent likelihood) positive (rank) correlation between the peak X-ray flux PX and radio flux density PR for the black hole candidate (BHC) systems, and a marginally significant positive (rank) correlation for the neutron star (NS) systems. This is further evidence for a coupling between accretion and outflows in X-ray binary systems, in this case implying a relation between peak disc-accretion rate and the number of synchrotron-emitting electrons ejected. However, we also show that the distribution of ‘radio loudness’, PR/PX, is significantly different for the two samples, in the sense that the BHCs generally have a higher PR/PX ratio. The origin of this discrepancy is uncertain, but probably reflects differences in the energetics and/or radiative efficiency of flows around the neutron stars and black holes; we briefly discuss some of these possibilities. Furthermore, the data for the two recently discovered ‘fast transients’ (FTs), XTE J0421+560/CI Cam and SAX J1819.3−2525/V4641 Sgr are entirely compatible with the distribution of BHCs. As at least three of the BHCs and both FTs have been directly resolved into mildly relativistic jets, it seems likely that such outflows are the origin of the radio emission in all BHC and FT transients, and probably also for the NS transients. We further note that the range of X-ray and radio fluxes observed from the unusual superluminal source GRS 1915+105 is also entirely compatible with the distribution for transients, implying that there is nothing special about the physics of jet formation in that system. We conclude that these data point to the formation of a mildly relativistic jet whose luminosity is a function of the accretion rate in the majority, if not all, X-ray transient outbursts, but whose relation to the observed X-ray emission is dependent on the nature of the accreting compact object.