David L. Meier

The Nuclear Spectroscopic Telescope Array (NuSTAR) High-Energy X-Ray Mission

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a National Aeronautics and Space Administration (NASA) Small Explorer mission that carried the first focusing hard X-ray (6-79 keV) telescope into orbit. It was launched on a Pegasus rocket into a low-inclination Earth orbit on June 13, 2012, from Reagan Test Site, Kwajalein Atoll. NuSTAR will carry out a two-year primary science mission. The NuSTAR observatory is composed of the X-ray instrument and the spacecraft. The NuSTAR spacecraft is three-axis stabilized with a single articulating solar array based on Orbital Sciences Corporations LEOStar-2 design. The NuSTAR science instrument consists of two co-aligned grazing incidence optics focusing on to two shielded solid state CdZnTe pixel detectors. The instrument was launched in a compact, stowed configuration, and after launch, a 10-meter mast was deployed to achieve a focal length of 10.15 m. The NuSTAR instrument provides sub-arcminute imaging with excellent spectral resolution over a 12-arcminute field of view. The NuSTAR observatory will be operated out of the Mission Operations Center (MOC) at UC Berkeley. Most science targets will be viewed for a week or more. The science data will be transferred from the UC Berkeley MOC to a Science Operations Center (SOC) located at the California Institute of Technology (Caltech). In this paper, we will describe the mission architecture, the technical challenges during the development phase, and the post-launch activities.

A Magnetically-Switched, Rotating Black Hole Model for the Production of Extragalactic Radio Jets and the Fanaroff and Riley Class Division

A model is presented in which both Fanaroff and Riley (FR) class I and II extragalactic jets are produced by magnetized accretion disk coronae in the ergospheres of rotating black holes. It employs a hybrid version of the Blandford-Payne and Blandford-Znajek magnetohydrodynamic mechanisms (similar to the Punsly-Coroniti model, with the addition of a metric shear-driven dynamo) and a generalized form of the magnetic switch, which is shown to be the MHD analog of the Eddington luminosity. While the jets are produced in the ergospheric accretion disk itself, the output power still is an increasing function of the black hole angular momentum. For high enough spin, the black hole triggers the magnetic switch, producing highly relativistic, kinetic energy-dominated jets instead of magnetic energy-dominated jets for lower spin. The coronal mass densities needed to trigger the switch at the observed FR break power are quite small (~10-15 g cm-3), implying that the source of the jet material may be either a pair plasma or very tenuous electron-proton corona, not the main accretion disk itself. The model explains the differences in morphology and Mach number between FR I and II sources and the observed trend for massive galaxies (which contain more massive black holes) to undergo the FR I/II transition at higher radio power. It also is consistent with the energy content of extended radio lobes and explains why, because of black hole spin-down, the space density of FR II sources should evolve more rapidly than that of FR I sources. A specific observational test is proposed to distinguish between models like this one, in which the FR I/II division arises from processes near the black hole, and models like Bicknells, in which the difference is produced by processes in the host galaxys interstellar medium. If the present model is correct, then the ensemble average speed of parsec-scale jets in sources distinguished by their FR I morphology (not luminosity) should be distinctly slower than that for sources with FR II morphology. The model also suggests the existence of a population of high-redshift, sub-mJy FR I and II radio sources associated with spiral or prespiral galaxies that flared once when their black holes were formed but were never again rekindled by mergers.

Numerical simulations of magnetized jets

The present axisymmetric numerical simulations of light hypersonic jets allow unmagnetized jets and jets carrying a dynamically important magnetic field to be contrasted. After decelerating a weakly magnetized jet through a series of weak, oblique shocks, a Mach disk and a strong annular shock are encountered near the outer edges of the contact discontinuity separating the shocked fluid from the shocked ambient gas. Upon passing the annular shock, the gas quickly expands and enters a backflowing cocoon surrounding the jet. The overall speed of advance of the jet is reduced; matter near the jet axis which passes through the terminal Mach disk accumulates in a plug, and gas is discharged into the cocoon by the intermittent shedding of vortices. When magnetic stresses dominate, however, the jet is rapidly decelerated via a Mach disk and strong annular shock. 28 refs.

Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources

We have measured mid-infrared radiation from an orientation-unbiased sample of 3CRR galaxies and quasars at redshifts 0.4 ≤ z ≤ 1.2 with the IRS and MIPS instruments on Spitzer. Powerful emission (L24 μm > 1022.4 W Hz-1 sr-1) was detected from all but one of the sources. We fit the Spitzer data and other measurements from the literature with synchrotron and dust components. The IRS data provide powerful constraints on the fits. At 15 μm, quasars are typically 4 times brighter than radio galaxies with the same isotropic radio power. Based on our fits, half of this difference can be attributed to the presence of nonthermal emission in the quasars but not the radio galaxies. The other half is consistent with dust absorption in the radio galaxies but not the quasars. Fitted optical depths are anticorrelated with core dominance, from which we infer an equatorial distribution of dust around the central engine. The median optical depth at 9.7 μm for objects with core dominance factor R > 10-2 is ≈0.4; for objects with R ≤ 10-2, it is ≈1.1. We have thus addressed a long-standing question in the unification of FR II quasars and galaxies: quasars are more luminous in the mid-infrared than galaxies because of a combination of Doppler-boosted synchrotron emission in quasars and extinction in galaxies, both orientation-dependent effects.

General Relativistic Simulations of Early Jet Formation in a Rapidly Rotating Black Hole Magnetosphere

To investigate the formation mechanism of relativistic jets in active galactic nuclei and microquasars, we have developed a new general relativistic magnetohydrodynamic code in Kerr geometry. Here we report on the —rst numerical simulations of jet formation in a rapidly rotating (a \ 0.95) Kerr black hole magnetosphere. We study cases in which the Keplerian accretion disk is both corotating and counter- rotating with respect to the black hole rotation, and investigate the —rst D50 light-crossing times. In the corotating disk case, our results are almost the same as those in Schwarzschild black hole cases: a gas pressuredriven jet is formed by a shock in the disk, and a weaker magnetically driven jet is also gener- ated outside the gas pressuredriven jet. On the other hand, in the counter-rotating disk case, a new powerful magnetically driven jet is formed inside the gas pressuredriven jet. The newly found magneti- cally driven jet in the latter case is accelerated by a strong magnetic —eld created by frame dragging in the ergosphere. Through this process, the magnetic —eld extracts the energy of the black hole rotation. Subject headings: accretion, accretion disksblack hole physicsgalaxies: jetsmagnetic —elds ¨ methods: numericalMHDrelativity

The Subparsec-Scale Structure and Evolution of Centaurus A: The Nearest Active Radio Galaxy

?????The subparsec-scale structure of Cen A is complex, consisting of a bright jet and a fainter counterjet. The bright jet contains components that have subluminal speeds of approximately 0.1c and undergo irregular episodes of rapid internal evolution. The rapid evolution sometimes observed could be interpreted as evidence for an underlying jet flow much faster (>0.45c) than observed from the proper motion of components (~0.1c). Considering the large-scale morphology of the source, the motions and temporal variations in the jet, and the detection of a counterjet, we conclude that the axis of the Cen A jet lies between ~50? and ~80? to our line of sight. We find that the estimated times of component ejection from the compact core are reasonably coincident with enhancements in hard X-ray intensity and 22 GHz flux density. In the context of the radio galaxy population, Cen A is a low-luminosity FR I?type source and in general has the properties observed in other FR I radio galaxies. Overall, the observations of Cen A presented here, and from other investigations, are consistent with the idea that sources with an FR I appearance are not aligned with our line of sight and have relativistic flow on the subparsec scale. The apparently subluminal subparsec-scale jet components are interpreted as being slow patterns on the relativistic flow.

The Nuclear Spectroscopic Telescope Array (NuSTAR)

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing hard X-ray (6 - 80 keV) telescope to orbit. NuSTAR will offer a factor 50 - 100 sensitivity improvement compared to previous collimated or coded mask imagers that have operated in this energy band. In addition, NuSTAR provides sub-arcminute imaging with good spectral resolution over a 12-arcminute eld of view. After launch, NuSTAR will carry out a two-year primary science mission that focuses on four key programs: studying the evolution of massive black holes through surveys carried out in fields with excellent multiwavelength coverage, understanding the population of compact objects and the nature of the massive black hole in the center of the Milky Way, constraining the explosion dynamics and nucleosynthesis in supernovae, and probing the nature of particle acceleration in relativistic jets in active galactic nuclei. A number of additional observations will be included in the primary mission, and a guest observer program will be proposed for an extended mission to expand the range of scientic targets. The payload consists of two co-aligned depth-graded multilayer coated grazing incidence optics focused onto a solid state CdZnTe pixel detectors. To be launched in early 2012 on a Pegasus rocket into a low-inclination Earth orbit, NuSTAR largely avoids SAA passage, and will therefore have low and stable detector backgrounds. The telescope achieves a 10.14-meter focal length through on-orbit deployment of an extendable mast. An aspect and alignment metrology system enable reconstruction of the absolute aspect and variations in the telescope alignment resulting from mast exure during ground data processing. Data will be publicly available at GSFCs High Energy Archive Research Center (HEASARC) following validation at the science operations center located at Caltech.

The theory and simulation of relativistic jet formation: towards a unified model for micro- and macroquasars

Abstract I review recent progress in the theory of relativistic jet production, with special emphasis on unifying black hole sources of stellar and supermassive size. Observations of both classes of objects, as well as theoretical considerations, indicate that such jets may be launched with a spine/sheath flow structure, having a much higher Lorentz factor (∼50) near the axis and a lower speed ( Γ ∼10 or so) away from the axis. It has become clear that one can no longer consider models of accretion flows without also considering the production of a jet by that flow. Furthermore, the rotation rate of the black hole also must be taken into account. It provides a third parameter that should break the mass/accretion rate degeneracy and perhaps explain why some sources are radio-loud and some radio-quiet. Slow jet acceleration and collimation is expected theoretically, and can explain some of the observed features of AGN jet sources. Finally, relativistic jets launched by MHD/ED processes are Poynting flux dominated by nature, and are potentially unstable if there is significant entrainment of thermal material.

A Magnetic Switch that Determines the Speed of Astrophysical Jets

The mechanism by which astrophysical jets form is an important factor in understanding the nature and evolution of phenomena such as active galactic nuclei and quasars, Galactic superluminal X-ray sources and young stellar objects. Of the many schemes proposed for jet production, only the magnetized accretion disk model of Blandford and Payne seems to be applicable to all of these systems, and also offers the potential for generating the highly relativistic flows observed in some quasars. But the source of variation in jet morphology observed for different sources remains unclear. Here we report time-dependent numerical simulations of jet formation which show that the character and speed of the jets produced depend dramatically on whether magnetic forces dominate over gravity in the accretion disk corona. This ‘magnetic switch’ is not predicted by steady-state, self-similar disk models, or by relativistic wind theory (which generally ignores the gravitational field). The effect provides a natural explanation for the existence of two known classes of extragalactic radio source and for the variation of their properties with radio luminosity. It also provides insight into protostellar and galactic microquasar systems.

Poynting Flux-dominated Jets in Decreasing-Density Atmospheres. I. The Nonrelativistic Current-driven Kink Instability and the Formation of “Wiggled” Structures

Nonrelativistic three-dimensional magnetohydrodynamic (MHD) simulations of Poynting flux-dominated (PFD) jets are presented. Our study focuses on the propagation of strongly magnetized hypersonic but sub-Alfvenic (C V 1). In the jet frame the mode grows locally and expands radially at each axial position where the jet is unstable: the instability, therefore, does not propagate as a wave along the jet length. CD instabilities have a number of features that make them an attractive explanation for the helical jet structure observed in active galactic nuclei and pulsars: (1) because the magnetic field remains strong, CD instabilities do not develop into full MHD turbulence; (2) the helical structures saturate and advect with the bulk flow; (3) they distort the body of the jet, not merely its interface with the ambient medium; (4) local plasma flow, then, follows a helical path along the kinked magnetic field backbone. A naturally occurring, external helically magnetized wind, which is (quasi-)axially current-free, surrounds the well-collimated current-carrying jet and reduces velocity shear between the jet and external medium. This stabilizes the growth of MHD Kelvin-Helmholtz surface modes in the inner jet flow.