From Multiwavelength to Mass Scaling: Accretion and Ejection in Microquasars and AGN

A solid theoretical understanding of how inflowing, accreting plasma around black holes and other compact objects gives rise to outflowing winds and jets is still lacking, despite decades of observations. The fact that similar processes and morphologies are observed in both X-ray binaries as well as active galactic nuclei has led to suggestions that the underlying physics could scale with black hole mass, which could provide a new handle on the problem. In the last decade, simultaneous broadband campaigns of the fast-varying X-ray binaries particularly in their microquasar state have driven the development of, and in some cases altered, our ideas about the inflow/outflow connection in accreting black holes. Specifically the discovery of correlations between the radio, infrared and X-ray bands has revealed a remarkable connectivity between the various emission regions, and argued for a more holistic approach to tackling questions about accretion. This article reviews the recent major observational and theoretical advances that focus specifically on the relation between the two "sides" of the accretion process in black holes, with an emphasis on how new tools can be derived for comparisons across the mass scale.Comment: 31 pages, 6 figures, To appear in Belloni, T. (ed.): The Jet Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009

Determining the optimal locations for shock acceleration in magnetohydrodynamical jets

Observations of relativistic jets from black holes systems suggest that particle acceleration often occurs at fixed locations within the flow. These sites could be associated with critical points that allow the formation of standing shock regions, such as the magnetosonic modified fast point. Using the self-similar formulation of special relativistic magnetohydrodynamics by Vlahakis & K\"onigl, we derive a new class of flow solutions that are both relativistic and cross the modified fast point at a finite height. Our solutions span a range of Lorentz factors up to at least 10, appropriate for most jets in X-ray binaries and active galactic nuclei, and a range in injected particle internal energy. A broad range of solutions exists, which will allow the eventual matching of these scale-free models to physical boundary conditions in the analysis of observed sources.Comment: 9 pages, 4 figures, accepted for publication in Ap

X-ray and Radio Monitoring of GX 339-4 and Cyg X-1

Previous work by Motch et al. (1985) suggested that in the low/hard state of GX339-4, the soft X-ray power-law extrapolated backward in energy agrees with the IR flux level. Corbel and Fender (2002) later showed that the typical hard state radio power-law extrapolated forward in energy meets the backward extrapolated X-ray power-law at an IR spectral break, which was explicitly observed twice in GX339-4. This has been cited as further evidence that jet synchrotron radiation might make a significant contribution to the observed X-rays in the hard state. We explore this hypothesis with a series of simultaneous radio/X-ray hard state observations of GX339-4. We fit these spectra with a simple, but remarkably successful, doubly broken power-law model that indeed requires a spectral break in the IR. For most of these observations, the break position as a function of X-ray flux agrees with the jet model predictions. We then examine the radio flux/X-ray flux correlation in Cyg X-1 through the use of 15 GHz radio data, obtained with the Ryle radio telescope, and Rossi X-ray Timing Explorer data, from the All Sky Monitor and pointed observations. We find evidence of `parallel tracks' in the radio/X-ray correlation which are associated with `failed transitions' to, or the beginning of a transition to, the soft state. We also find that for Cyg X-1 the radio flux is more fundamentally correlated with the hard, rather than the soft, X-ray flux.Comment: To Appear in the Proceedings of "From X-ray Binaries to Quasars: Black Hole Accretion on All Mass Scales" (Amsterdam, July 2004). Eds. T Maccarone, R. Fender, L. H

A Jet Model for the Broadband Spectrum of the Seyfert-1 Galaxy NGC 4051

Recent radio VLBI observations of the ~parsec-scale nuclear region of the narrow line Seyfert 1 galaxy NGC 4051 hint toward the presence of outflowing plasma. From available literature we have collected high-quality, high-resolution broadband spectral energy distribution data of the nuclear region of NGC 4051 spanning from radio through X-rays, to test whether the broadband SED can be explained within the framework of a relativistically outflowing jet model. We show that once the contribution from the host galaxy is taken into account, the broadband emission from the active galactic nucleus of NGC 4051 can be well described by the jet model. Contributions from dust and ongoing star-formation in the nuclear region tend to dominate the IR emission even at the highest resolutions. In the framework of the jet model, the correlated high variability of the extreme ultraviolet and X-rays compared to other wavelengths suggests that the emission at these wavelengths is optically thin synchrotron originating in the particle acceleration site(s) in the jet very close (few $r_g=GM_{BH}/c^2$) to the central supermassive black hole of mass M_{BH}. Our conclusions support the hypothesis that narrow line Seyfert 1 galaxies (which NGC 4051 is a member of) harbor a "jetted" outflow with properties similar to what has already been seen in low-luminosity AGNs and stellar mass black holes in hard X-ray state.Comment: Accepted for publication in ApJ. 24 pages, 2 figures, 2 tables (in aastex preprint format

Kinetic simulations of mildly relativistic shocks I: particle acceleration in high Mach number shocks

We use fully kinetic particle-in-cell simulations with unprecedentedly large transverse box sizes to study particle acceleration in weakly-magnetized mildly relativistic shocks traveling at a velocity $\approx 0.75c$ and a Mach number of 15. We examine both subluminal (quasi-parallel) and superluminal (quasi-perpendicular) magnetic field orientations. We find that quasi-parallel shocks are mediated by a filamentary non-resonant (Bell) instability driven by non-thermal ions, producing magnetic fluctuations on scales comparable to the ion gyro-radius. In quasi-parallel shocks, both electrons and ions are accelerated into non-thermal power-laws whose maximum energy grows linearly with time. The upstream heating of electrons is small, and the two species enter the shock front in rough thermal equilibrium. The shock's structure is complex; the current of reflected non-thermal ions evacuates cavities in the upstream which form filaments of amplified magnetic fields once advected downstream. At late times, $10\%$ of the shock's energy goes into non-thermal protons and $\gtrsim10\%$ into magnetic fields. We find that properly capturing the magnetic turbulence driven by the non-thermal ions is important for properly measuring the energy fraction of non-thermal electrons, $\epsilon_e$. We find $\epsilon_e\sim 5\times10^{-4}$ for quasi-parallel shocks with $v=0.75c$, slightly larger than what was measured in simulations of non-relativistic shocks. In quasi-perpendicular shocks, no non-thermal power-law develops in ions or electrons. The ion acceleration efficiency in quasi-parallel shocks suggests that astrophysical objects that could host mildly relativistic quasi-parallel shocks -- for example, the jets of active galactic nuclei or microquasars -- may be important sources of cosmic rays and their secondaries, such as gamma-rays and neutrinos.Comment: Submitted to MNRAS. 14 pages, 18 figure

The rise and fall of the compact jet in GRO J1655-40

In this work, we present some preliminary results on a multi-wavelength (radio/infrared/optical/X-ray) study of GRO J1655-40 during its 2005 outburst. We focus on the broadband spectral energy distribution during the different stages of the outburst. In particular, using this unprecedented coverage, and especially thanks to the new constraints given in the mid-IR by Spitzer, we can test the physical self-consistent disk-jet model during the hard state, where the source shows radio emission from a compact jet. The hard state broadband spectra of the observations during the decay of the outburst, are fairly well fit using the jet model with parameters overall similar to those found for Cyg X-1 and GX 339-4 in a previous work. However, we find that, compared to the other two BHs, GRO J1655-40 has a much higher jet power (at least a factor of 3), and that, most notably, the model seems to underestimate the radio emissio