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We have studied the newly-discovered microquasar in NGC 7793 in radio, optical and X-ray bands. This system comprises a large (250×120 pc) line-emitting optical nebula, detected in Ha and HeII λ4686. The optical nebula coincides with a synchrotron-emitting radio cocoon, with a radio luminosity about 3 times that of Cas A. The central BH appears as a hard X-ray source with a point-like, blue optical counterpart. Two prominent radio lobes are located at the extremities of the cocoon. Just ahead of the radio hot spots, we found two X-ray hot spots, which we interpret as a signature of the bow shock into the interstellar medium. The X-ray hot spots, radio hot spots, X-ray core and major axis of the cocoon are well aligned, proving that the system is powered by a jet. From both the X-ray and optical data, we estimate a jet power ∼a few×1040 erg s-1, active over a timescale ≈105 yrs. This extraordinary system is a long-sought analog of the Galactic microquasar SS433 and may represent a new class of non-nuclear BHs dominated by mechanical power even at very high accretion rates. [ABSTRACT FROM AUTHOR]

Black holes are the simplest objects in nature. All the matter enter into it with the speed of light at the horizon and thus the inner boundary condition is fixed, independent of whether we study stellar mass black holes (nano-quasars) or the massive (miliquasars) and super-massive black holes (Quasars). All types of flows are thus transonic. We compare the nature of the hydrodynamic solutions of the transonic flows and show that other solutions are special cases of this solution. Similarly, we describe the radiative properties of the accretion flows and compare the radiations emitted from other solutions. [ABSTRACT FROM AUTHOR]

The literature is full of a large number of accretion flow models, each of which claims to be the correct one. We present here the most general possible flow configuration around a black hole, different regions of which have characteristics of different models such as the Bondi flow, the Keplerian disk, the transonic flows, the thick disks, the disks with jets/outflows etc. We present recent observational results and use them to rationalize such a generalized solution. Our solution is likely to be applicable to all types of black hole candidates, from stellar mass (nano-quasars) to super-massive (quasars and active galaxies) variety. [ABSTRACT FROM AUTHOR]

The “torus” is a central component of Active Galactic Nuclei models that produces the observed mid-IR emission, and obscures a large fraction of accreting black holes from direct observation. We explore whether the torus is an outflowing dusty wind driven by both magnetocentrifugal forces and radiation pressure. We have developed a model that includes these driving mechanisms and utilizes 3D Monte Carlo simulations to produce SEDs and images of the wind. We find that, in initial tests, the model is able to approximately reproduce the luminosity of the IR composite Spectral Energy Distribution when the wind has a base column of NH∼1025 cm-2 and Mout∼1 M⊙yr-1. [ABSTRACT FROM AUTHOR]

We present an overview on how variability can be used to constrain the location of the ionized outflow in nearby Active Galactic Nuclei using high-resolution X-ray spectroscopy. Without these constraints on the location of the outflow, the kinetic luminosity and mass loss rate can not be determined. We focus on the Seyfert 1 galaxy NGC 5548, which is arguably the best studied AGN on a timescale of 10 years. Our results show that frequent observations combined with long term monitoring, such as with the Rossi X-ray Timing Explorer (RXTE) satellite, are crucial to investigate the effects of these outflows on their surroundings. [ABSTRACT FROM AUTHOR]

Bubbles are volumes of high temperature, low density gas surrounded by ionized and neutral shells. They form when hypersonic flows from massive stars interact with the interstellar medium. Other overpressured volumes of hot gas, such as supernova remnants and HII regions, can also be considered as bubbles. Simple analytical approximations exist to describe the expansion of these bubbles, however, meaningful comparisons with new observations can only be made if a more detailed, numerical approach is taken. In this paper, I describe some results of modeling these astrophysical objects. [ABSTRACT FROM AUTHOR]

High resolution observations in the region of the lines Hα and Hγ of the spectrum of the symbiotic binary Z And were performed during its small amplitude brightening at the end of 2002. The profiles of the two lines were double-peaked and the velocity of the dip between the two peaks was the same. This behavior was interpreted with emission mainly of an optically thin accretion disc. The Hα line had broad wings which were supposed to be due to high velocity stellar wind. The line Hγ had a broad emission component which was thought to be emitted by an optically thin accretion disc or a high velocity stellar wind. [ABSTRACT FROM AUTHOR]

We have conducted a spectro-astrometric (SA) analysis of high spectral resolution data of the near infrared HeI 10830Å and Paγ lines in the nearby classical T Tauri star TW Hya. We find clear position offsets associated to the blueshifted absorption part of the HeI 10830Å P Cygni profile. The derived spatial feature extend up to 50 mas (2.8 AU at TW Hya distance) in two opposite directions. By using simple exploratory models we show that this feature can not be produced by the same stellar wind which produces the P Cygni profile. Instead, we are able to reproduce the observed blueshifted SA profile with emission from a disk wind. The production of SA artifacts through instrumental effects was examined. Artifact models have difficulties in fitting both the PSF and the angular scale of the observed position spectra offsets, suggesting that the signal may be real. Based on originally published material in The Astrophysical Journal, Volume 670, Issue 2, pp. 1234–1239, 2007 [ABSTRACT FROM AUTHOR]

Using numerical simulations of magnetized stellar winds, we carry out a parameter study to find the dependence of the stellar wind torque on observable parameters. We find that the power-law dependencies of the torque on parameters is significantly different than what has been used in all spin evolution models to date. [ABSTRACT FROM AUTHOR]

Here we discuss our work to date on the topic of outflows driven by young brown dwarfs. Soon after the discovery of large numbers of young brown dwarfs in star forming regions it became apparent that many of these sub-stellar objects were accreting and had accretion disks, analogous to the T Tauri stars. As outflow activity in low mass protostars is strongly connected to accretion it was reasonable to expect these accreting brown dwarfs to also be driving outflows. In the last three years we have searched for brown dwarf outflows using high quality optical spectra obtained with UVES on the VLT and the technique of spectro-astrometry. To date we have uncovered 5 brown dwarf outflows. Here we discuss our method and outline our results to date. The long-term aim of this work is to make a comprehensive comparison between proto-stellar outflows and those driven by sub-stellar mass objects. [ABSTRACT FROM AUTHOR]

Mass loss of asymptotic giant branch (AGB) stars is commonly attributed to the combined effects of pulsation-induced shocks and radiation pressure on dust grains formed in the outer atmospheric layers. This paper discusses recent results of detailed radiation-hydrodynamical wind models, regarding the composition of silicate grains in M-type AGB stars, the influence of grain size dependent opacities, and basic differences in dust-driven outflows of C- and M-type AGB stars. [ABSTRACT FROM AUTHOR]

We present here continuing work, focussing on the Galactic globular clusters (GCs) ω Centauri (the most massive GC) and M15 (one of the most metal-poor). Spectral energy distribution fitting and dust envelope modelling using our recent Spitzer photometry in ω Centauri has allowed us to quantatively explore mass loss along the giant branch and yield a total mass-loss rate from the system. We also report on our recently-announced discovery of the most metal-poor Galactic AGB variable known, and investigate the link between long-secondary-period variability and outflow. [ABSTRACT FROM AUTHOR]

The spectroscopy of two carbon-rich mass-loosing variables—R Leporis and DY Persei -is presented. High-resolution echelle spectra of carbon Mira R Lep were observed for two seasons. The heliocentric photospheric radial velocity was found to be +32.6 and +38.4 km/s respectively. Strong emission in atomic resonance lines and C2 Swan system bandhead at 5165 Å was detected, which was apparently the result of dust formation and ejection. The spectroscopical features of the extremely cool R Coronae Borealis star DY Per indicate the presence of surrounding clouds of gas and dust ejected by this star. [ABSTRACT FROM AUTHOR]

With a self-similar magnetohydrodynamic (MHD) model of an exploding progenitor star and an outgoing rebound shock and with the thermal bremsstrahlung as the major radiation mechanism in X-ray bands, we reproduce the early X-ray light curve observed for the recent event of XRO 080109/SN 2008D association. The X-ray light curve consists of a fast rise, as the shock travels into the “visible layer” in the stellar envelope, and a subsequent power-law decay, as the plasma cools in a self-similar evolution. The observed spectral softening is naturally expected in our rebound MHD shock scenario. We propose to attribute the “non-thermal spectrum” observed to be a superposition of different thermal spectra produced at different layers of the stellar envelope. [ABSTRACT FROM AUTHOR]

Two relativistic X-ray jets have been detected with the Chandra X-ray observatory in the black hole X-ray transient XTE J1550-564. We report a full analysis of the evolution of the two jets with a gamma-ray burst external shock model. A plausible scenario suggests a cavity outside the central source and the jets first travelled with constant velocity and then are slowed down by the interactions between the jets and the interstellar medium (ISM). The best fitted radius of the cavity is ∼0.36 pc on the eastern side and ∼0.46 pc on the western side, and the densities also show asymmetry, of ∼0.015 cm-3 on the east to ∼0.21 cm-3 on the west. Large scale low density region is also found in another microquasar system, H 1743-322. These results are consistent with previous suggestions that the environment of microquasars should be rather vacuous, compared to the normal Galactic environment. A generic scenario for microquasar jets is proposed, classifying the observed jets into three main categories, with different jet morphologies (and sizes) corresponding to different scales of vacuous environments surrounding them. [ABSTRACT FROM AUTHOR]

I review aspects of the theory of long-duration gamma-ray burst (GRB) central engines. I focus on requirements of any model; these include the angular momentum of the progenitor, the power, Lorentz factor, asymmetry, and duration of the flow, and both the association and the non-association with bright supernovae. I compare and contrast the collapsar and millisecond proto-magnetar models in light of these requirements. The ability of the latter model to produce a flow with Lorentz factor ∼100 while simultaneously maintaining a kinetic luminosity of ∼1050 ergs s-1 for a timescale of ∼10–100 s is emphasized. [ABSTRACT FROM AUTHOR]

Rapidly-accreting black holes and young, rapidly-rotating magnetars (“proto-magnetars”) are two possible central engines for gamma-ray bursts (GRBs). The midplane of neutrino-cooled accretion disks and the surface of proto-magnetars are both neutron-rich, with a neutron-to-proton ratio n|p>1. If a large neutron fraction is preserved to large radii in relativistic, GRB-producing outflows, several observable consequences may result, including changes to the prompt and afterglow emission from the standard fireball model. We describe the results of detailed magnetohydrodynamic calculations of outflows from both proto-magnetars and hyper-accreting disks which predict the nucleonic content of the material at large radii. We summarize the prospects for neutron-rich GRB outflows from individual central engines, emphasizing a fundamental difference between neutino-heated mass-loading in proto-magnetar and accretion disk winds. [ABSTRACT FROM AUTHOR]

We model the interaction between the wind from a newly formed rapidly rotating magnetar and the surrounding progenitor. In the first few seconds after core collapse the magnetar inflates a bubble of plasma and magnetic fields behind the supernova shock, which expands asymmetrically because of the pinching effect of the toroidal magnetic field, as in PWNe, even if the host star is spherically symmetric. The degree of asymmetry depends on the ratio of the magnetic energy to the total energy in the bubble. We assume that the wind by newly formed magnetars inflating these bubbles is more magnetized than for PWNe. We show that for a magnetic to total power supplied by the central magnetar ∼0.1 the bubble expands relatively spherically while for values greater than 0.3, most of the pressure in the bubble is exerted close to the rotation axis, driving a collimated outflow out through the host star. This can account for the collimation inferred from observations of long-duration gamma-ray bursts (GRBs). Given that the wind magnetization increases in time, we thus suggest that the magnetar-driven bubble initially expands relatively spherically (enhancing the energy of the associated supernova) while at late times it becomes progressively more collimated (producing the GRB). Similar processes may operate in more modestly rotating neutron stars to produce asymmetric supernovae and lower energy transients such as X-ray flashes. [ABSTRACT FROM AUTHOR]

We study the structure of the circumstellar medium surrounding SN 1987A in the equatorial plane. Furthermore, we study the evolution of the SN shock within this medium during the first 25 years, and the resulting hard X-ray and radio emission from the remnant. [ABSTRACT FROM AUTHOR]

The role of magnetic fields in the formation and shaping of Planetary Nebulae has been debated for many years. In the last decade direct observational evidence, as well as a host of new theoretical arguments, has shown that magnetic fields may play a critical role the evolution of post-AGB, proto-PNe and PNe outflows. The growing emphasis on magneto-rotational processes in PNe is of particular importance as it allows the field of low and medium mass evolved stars to make contact with outflow studies in environments as diverse as YSOs and AGNs. In this article I review the arguments, both theoretical and observational, for the importance of MHD in PNe. Apologies must be made for studies I could not discuss in the contribution. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The solar atmosphere presents complexe magnetic structures, such as loops and coronal holes, which are intrinsically bounded to the solar wind acceleration and driven mechanism. UVCS/SOHO and ground observations gave a new insight on the problem. Using H I Lyman alpha and O VI line intensity distributions it is possible to identify the coronal holes boundaries, showing a super-radial geometry with diverging factor fmax ranging from 6.0 to 7.5. It is not clear yet if other stars present such structures. However, the diverging magnetic fields play an important role in the stellar winds. In this work we develop a method for determining the magnetic divergence based on its tension generated by an increase in gas pressure at the wind basis. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We test the possibility of winds blowing from hot H-He flrst stars, driven by either line or continuum processes. Because the material in the atmospheres of first stars is mostly ionized, the radiative force is too small to accelerate the wind. The radiative force due to the continuum transitions is also not able to drive a wind. We study the possibility of expulsion of individual heavier elements from the atmosphere, and the influence of the radiative force on the circumstellar environment of flrst stars. It is shown that some of these stars may have winds if their atmospheres are enriched by CNO elements. We also discuss the implications of our results in the evolution of Pop III stars and for models of the reionization of the Universe. [ABSTRACT FROM AUTHOR]

The archetypical wind-accreting X-ray pulsar Vela X-1 is known to be variable on a large range of timescales. Relatively tranquil phases exist as well as extended phases of high variability and flaring. We present results from a systematic study of variations with orbital phase and other timescales based on RXTE/ASM and Swift/BAT data. [ABSTRACT FROM AUTHOR]

We present results on the geometry and location of the X-ray narrow line region in NGC 5548 obtained by analyzing multiple high-resolution X-ray grating observation covering an almost 10 year period. Variability combined with the high spectral resolution of the gratings aboard Chandra and XMM-Newton are key for obtaining these results. The goal is to extend this method to other type 1 AGN as well. [ABSTRACT FROM AUTHOR]

Evidence for orbital modulation of the very high energy (VHE) γ-ray emission from the high-mass X-ray binary and microquasar LS 5039 has recently been reported by the HESS collaboration. The observed flux modulation was found to go in tandem with a change in the GeV – TeV spectral shape, which may partially be a result of γγ absorption in the intense radiation field of the massive companion star. In a recent paper [1], I have presented a parameter study of the γγ absorption effects in this system. For a range of plausible locations of the VHE γ-ray emission region and the allowable range of viewing angles, the de-absorbed, intrinsic VHE γ-ray spectra and total VHE photon fluxes and luminosities were calculated and compared to luminosity constraints based on Bondi-Hoyle limited wind accretion onto the compact object in LS 5039. It was found that (1) it is impossible to choose the viewing angle and location of the VHE emission region in a way that the intrinsic spectra in superior and inferior conjunction are identical; (2) if the VHE luminosity is limited by wind accretion from the companion star and the system is viewed at an inclination angle of i > 40°, the emission is most likely beamed by a larger Doppler factor than inferred from the dynamics of the large-scale radio outflows; (3) the still poorly constrained viewing angle between the line of sight and the jet axis is most likely substantially smaller than the maximum of ∼ 64° inferred from the lack of eclipses. (4) Consequently, the compact object is more likely to be a black hole rather than a neutron star. (5) There is a limited range of allowed configurations for which the expected VHE neutrino flux would actually anti-correlate with the observed VHE γ-ray emission. If hadronic models for the γ-ray production in LS 5039 apply, a solid detection of the expected VHE neutrino flux and its orbital modulation with km3 scale water-Cherenkov neutrino detectors might require the accumulation of data over more than 3 years. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]