arXiv subjects

A. R. King

Publications and source records attributed to A. R. King.

At least 73 records · Page 4Linked to original sources

arXiv2005

Chemical enrichment of the complex hot ISM of the Antennae Galaxies: II. Physical properties of the hot gas and supernova feedback

We investigate the physical properties of the interstellar medium (ISM) in the merging pair of galaxies known as The Antennae (NGC 4038/39), using the deep coadded ~411 ks Chandra ACIS-S data set. The method of analysis and some of the main results from the spectral analysis, such as metal abundances and their variations from ~0.2 to ~20-30 times solar, are described in Paper I (Baldi et al. submitted). In the present paper we investigate in detail the physics of the hot emitting gas, deriving measures for the hot-gas mass (~10^ M_sun), cooling times (10^7-10^8 yr), and pressure (3.5x10^-11-2.8x10^-10 dyne cm^-2). At least in one of the two nuclei (NGC 4038) the hot-gas pressure is significantly higher than the CO pressure, implying that shock waves may be driven into the CO clouds. Comparison of the metal abundances with the average stellar yields predicted by theoretical models of SN explosions points to SNe of Type II as the main contributors of metals to the hot ISM. There is no evidence of any correlation between radio-optical star-formation indicators and the measured metal abundances. Although due to uncertainties in the average gas density we cannot exclude that mixing may have played an important role, the short time required to produce the observed metal masses (<=2 Myr) suggests that the correlations are unlikely to have been destroyed by efficient mixing. More likely, a significant fraction of SN II ejecta may be in a cool phase, in grains, or escaping in hot winds. In each case, any such fraction of the ejecta would remain undetectable with soft X-ray observations.

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arXiv2005

Chemical enrichment of the complex hot ISM of the Antennae galaxies: I. Spatial and spectral analysis of the diffuse X-ray emission

We present an analysis of the properties of the hot interstellar medium (ISM) in the merging pair of galaxies known as The Antennae (NGC 4038/39), performed using the deep, coadded ~411 ks Chandra ACIS-S data set. These deep X-ray observations and Chandra's high angular resolution allow us to investigate the properties of the hot ISM with unprecedented spatial and spectral resolution. Through a spatially resolved spectral analysis, we find a variety of temperatures (from 0.2 to 0.7 keV) and Nh (from Galactic to 2x10^21 cm^-2). Metal abundances for Ne, Mg, Si, and Fe vary dramatically throughout the ISM from sub-solar values (~0.2) up to several times solar.

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arXiv2005

Wolf-Rayet and O Star Runaway Populations from Supernovae

We present numerical simulations of the runaway fractions expected amongst O and Wolf-Rayet star populations resulting from stars ejected from binaries by the supernova of the companion. Observationally the runaway fraction for both types of star is similar, prompting the explanation that close dynamical interactions are the main cause of these high-velocity stars. We show that, provided that the initial binary fraction is high, a scenario in which two-thirds of massive runaways are from supernovae is consistent with these observations. Our models also predict a low frequency of runaways with neutron star companions and a very low fraction of observable Wolf-Rayet--compact companion systems.

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arXiv2005

Aligning spinning black holes and accretion discs

We consider the alignment torque between a spinning black hole and an accretion disc whose angular momenta are misaligned. This situation must hold initially in almost all gas accretion events on to supermassive black holes, and may occur in binaries where the black hole receives a natal supernova kick. We show that the torque always acts to align the hole's spin with the total angular momentum without changing its magnitude. The torque acts dissipatively on the disc, reducing its angular momentum, and aligning it with the hole if and only if the angle theta between the angular momenta J_d of the disc and J_h of the hole satisfies the inequality cos theta > -J_d / 2 J_h. If this condition fails, which requires both theta > pi/2 and J_d < 2 J_h, the disc counteraligns.

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arXiv2005

Magnetic Fields, Accretion, and the Central Engine of Gamma-Ray Bursts

I briefly review magnetic effects in accretion physics, and then go on to discuss a possible central engine for gamma-ray bursts. A rotating black hole immersed in a non-axisymmetric magnetic field experiences a torque trying to align spin and field. I suggest that gamma-ray burst hosts may provide conditions where this effect allows rapid extraction of a significant fraction of the hole's rotational energy. I argue that much of the electromagnetic emission is in two narrow beams parallel and antiparallel to the asymptotic field direction. This picture suggests that only a mass 10^-5 Msun is expelled in a relativistic outflow, as required by the fireball picture.

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arXiv2005

The population of black widow pulsars

We consider the population of black widow pulsars (BWPs). The large majority of these are members of globular clusters. For minimum companion masses < 0.1 Msun, adiabatic evolution and consequent mass loss under gravitational radiation appear to provide a coherent explanation of all observable properties. We suggest that the group of BWPs with minimum companion masses > 0.1 Msun are systems relaxing to equilibrium after a relatively recent capture event. We point out that all binary millisecond pulsars (MSPs) with orbital periods P < 10 h are BWPs (our line of sight allows us to see the eclipses in 10 out of 16 cases). This implies that recycled MSPs emit either in a wide fan beam or a pencil beam close to the spin plane. Simple evolutionary ideas favour a fan beam.

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arXiv2004

The planet in M4: implications for planet formation in globular clusters

We consider the formation and evolution of the planetary system PSR B1620-26 in the globular cluster M4. We propose that as M4 is a very-low metallicity environment the standard model of planet formation around main-sequence stars through the accretion of gas onto metallic rocky cores should not be applied. Consequently the previously suggested methods for formation are unlikely. We propose that the planet formed through the interaction of a passing star with a circumbinary disc during the common-envelope phase of the inner binary's evolution. This formation route is favoured by dense stellar systems such as globular clusters.

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arXiv2004

A high velocity ionised outflow and XUV photosphere in the narrow emission line quasar PG1211+143

We report on the analysis of a ~60 ksec XMM observation of the bright, narrow emission line quasar PG 1211+143. Absorption lines are seen in both EPIC and RGS spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C. The observed line energies indicate an ionised outflow velocity of ~24000 km s^-1. The highest energy lines require a column density of N_H ~ 5 x 10^23 cm^-2, at an ionisation parameter of log(xi) ~ 3.4. If the origin of this high velocity outflow lies in matter being driven from the inner disc, then the flow is likely to be optically thick within a radius ~130 Schwarzschild radii, providing a natural explanation for the Big Blue Bump (and strong soft X-ray) emission in PG 1211+143.

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arXiv2004

How special is the Solar System?

Most mechanisms proposed for the formation of planets are modified versions of the mechanism proposed for the solar system. Here we argue that, in terms of those planetary systems which have been observed, the case for the solar system being a typical planetary system has yet to be established. We consider the possibility that most observed planetary systems have been formed in some quite different way. If so, it may be that none of the observed planetary systems is likely to harbour an earth-like planet.

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arXiv2004

GRS 1915+105: The first three months with INTEGRAL

GRS 1915+105 is being observed as part of an Open Time monitoring program with INTEGRAL. Three out of six observations from the monitoring program are presented here, in addition to data obtained through an exchange with other observers. We also present simultaneous RXTE observations of GRS 1915+105. During INTEGRAL Revolution 48 (2003 March 6) the source was observed to be in a highly variable state, characterized by 5-minute quasi-periodic oscillations. During these oscillations, the rise is faster than the decline, and is harder. This particular type of variability has never been observed before. During subsequent INTEGRAL revolutions (2003 March-May), the source was in a steady or ''plateau'' state (also known as class $χ$ according to Belloni et al. 2000). Here we discuss both the temporal and spectral characteristics of the source during the first three months of observations. The source was clearly detected with all three gamma-ray and X-ray instruments onboard INTEGRAL.

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arXiv2004

A Synoptic X-ray Study of M31 with the Chandra-HRC

We have obtained 17 epochs of Chandra High Resolution Camera (HRC) snapshot images, each covering most of the M31 disk. The data cover a total baseline of 2.5 years and contain a mean effective exposure of 17 ks. We have measured the mean fluxes and long-term lightcurves for 166 objects detected in these data. At least 25% of the sources show significant variability. The cumulative luminosity function (CLF) of the disk sources is well-fit by a power-law with a slope comparable to those observed in typical elliptical galaxies. The CLF of the bulge is a broken power law similar to measurements made by previous surveys. We note several sources in the southwestern disk with L_X > 10^{37} erg/s . We cross-correlate all of our sources with published optical and radio catalogs, as well as new optical data, finding counterpart candidates for 55 sources. In addition, 17 sources are likely X-ray transients. We analyze follow-up HST WFPC2 data of two X-ray transients, finding F336W (U-band equivalent) counterparts. In both cases, the counterparts are variable. In one case, the optical counterpart is transient with F336W = 22.3 +/- 0.1 mag. The X-ray and optical properties of this object are consistent with a ~10 solar mass black hole X-ray nova with an orbital period of ~20 days. In the other case, the optical counterpart varies between F336W = 20.82 +/- 0.06 mag and F336W = 21.11 +/- 0.02 mag. Ground-based and HST observations show this object is bright (V = 18.8 +/- 0.1) and slightly extended. Finally, the frequency of bright X-ray transients in the M31 bulge suggests that the ratio of neutron star to black hole primaries in low-mass X-ray binaries (NS/BH) is ~1.

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arXiv2004

An Observational Diagnostic for Ultraluminous X-Ray Sources

We consider observational tests for the nature of Ultraluminous X-ray sources (ULXs). These must distinguish between thermal-timescale mass transfer on to stellar-mass black holes leading to anisotropic X-ray emission, and accretion on to intermediate-mass black holes. We suggest that long-term transient behavior via the thermal-viscous disk instability could discriminate between these two possibilities for ULXs in regions of young stellar populations. Thermal-timescale mass transfer generally produces stable disks and persistent X-ray emission. In contrast, mass transfer from massive stars to black holes produces unstable disks and thus transient behavior, provided that the black hole mass exceeds some minimum value. This minimum mass depends primarily on the donor mass and evolutionary state. We show that it exceeds 50 solar masses for a large fraction (greater than 90%) of the mass-transfer lifetime for the most likely donors in young clusters. Thus if long-term monitoring reveals a large transient fraction among ULXs in a young stellar population, these systems would be good candidates for intermediate-mass black holes in a statistical sense; information about the donor star is needed to make this identification secure in any individual case. A transient ULX population would imply a much larger population of quiescent systems of the same type.

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arXiv2004

Exploring the complex X-ray spectrum of NGC 4051

Archival XMM-Newton data on the nearby Seyfert galaxy NGC 4051, taken in relatively high and low flux states, offer a unique opportunity to explore the complexity of its X-ray spectrum. We find the hard X-ray band to be significantly affected by reflection from cold matter, which can also explain a non-varying, narrow Fe K fluorescent line. We interpret major differences between the high and low flux hard X-ray spectra in terms of the varying ionisation (opacity) of a substantial column of outflowing gas. An emission line spectrum in the low flux state indicates an extended region of photoionised gas. A high velocity, highly ionised outflow seen in the high state spectrum can replenish the gas in the extended emission region over ~10^3 years, while having sufficient kinetic energy to contribute significantly to the hard X-ray continuum.

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arXiv2004

X-raying Chemical Evolution and Galaxy Formation in The Antennae

We present the integrated 411 ks {\it Chandra} ACIS-S exposure of the Antennae galaxies (NGC 4038/39). Besides a rich population of point-like sources, this spectacular image reveals a spatially and spectrally complex hot diffuse gaseous component. For the first time we detect intense line emission from Fe, Ne, Mg and Si in The Antennae, and obtain a detailed picture of spatially varied metal abundances in the hot interstellar medium (ISM) of a galaxy. In certain regions, the abundances of $α$-elements may be many times solar, while the Fe abundance is sub-solar or near-solar. The differences in the local metal enrichment of the hot ISM may be related to the local star formation rates and to the degree of confinement of the enriched hot ISM. We also report large-scale gaseous features, including two gigantic, $\sim$10-kpc-scale `loops' extending to the South of the merging disks, and a low-surface-brightness hot halo, extending out to $\sim$18 kpc. These features may be related to superwinds from the starburst in The Antennae or result from the merger hydrodynamics. Their long cooling times suggest that they may persist to form the hot X-ray halo of the emerging elliptical galaxy.

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arXiv2003

Variability in black hole accretion discs

Observations of accreting systems often show significant variability (10-20 percent of accretion luminosity) on timescales much longer than expected for the disc regions releasing most of the luminosity. We propose an explicit physical model for disc variability, consistent with Lyubarskii's (1997) general scheme for solving this problem. We suggest that local dynamo processes can affect the evolution of an accretion disc by driving angular momentum loss in the form of an outflow (a wind or jet). We model the dynamo as a small-scale stochastic phenomenon, operating on roughly the local dynamical timescale. We argue that large-scale outflow can only occur when the small-scale random processes in neighbouring disc annuli give rise by chance to a coherent large-scale magnetic field. This occurs on much longer timescales, and causes a bright large-amplitude flare as a wide range of disc radii evolve in a coherent fashion. Most of the time, dynamo action instead produces small-amplitude flickering. We reproduce power spectra similar to those observed, including a 1/f power spectrum below a break frequency given by the magnetic alignment timescale at the inner disc edge. However the relation between the black hole mass and the value of the break frequency is less straightforward than often assumed in the literature. The effect of an outer disc edge is to flatten the spectrum below the magnetic alignment frequency there. We also find a correlation between the variability amplitude and luminosity, similar to that found in some AGN.

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arXiv2003

Outflows from Quasars and Ultraluminous X-ray Sources

Mass outflows from Eddington-limited accreting compact objects appear to be a very widespread phenomenon. They may provide the soft excess observed in quasars and ULXs, and imply that such objects have a major effect on their surroundings. In particular they allow a simple parameter-free argument for the M_BH-sigma relation for galaxies, and offer a straightforward interpretation of the emission nebulae seen around ULXs.

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arXiv2003

Evidence of a high velocity ionised outflow in a second narrow line quasar PG0844+349

Following the discovery of X-ray absorption in a high velocity outflow from the bright quasar PG1211+143 we have searched for similar features in XMM archival data of a second (high accretion rate) quasar PG0844+349. Evidence is found for absorption lines in both the EPIC and RGS spectra, whose identification with resonance transitions in H-like Fe, S, and Ne implies an origin in highly ionised matter with an outflow velocity of order ~0.2c. The line equivalent widths require a line-of-sight column density of N_H ~ 4 x 10^23 cm^-2, at an ionisation parameter of log(xi) ~ 3.7. Assuming a radial outflow being driven by radiation pressure from the inner accretion disc, as suggested previously for PG1211+143, the flow is again likely to be optically thick, in this case within ~ 25 Schwarzschild radii. We suggest that a high velocity, highly ionised outflow is likely to be a significant component in the mass and energy budgets of many AGN accreting at or above the Eddington rate.

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arXiv2003

Black Hole Winds

We show that black holes accreting at or above the Eddington rate probably produce winds which are optically thick in the continuum, whether in quasars or X-ray binaries. The photospheric radius and outflow speed are proportional to \mo^2 and \mo^-1 respectively, where \mo is the mass outflow rate. The outflow momentum rate is always of order L_Edd/c. Blackbody emission from these winds may provide the big blue bump in some quasars and AGN, as well as ultrasoft X-ray components in ULXs.

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