A supermassive binary black hole with triple disks

Hierarchical structure formation inevitably leads to the formation of supermassive binary black holes (BBHs) with a sub-parsec separation in galactic nuclei. However, to date there has been no unambiguous detection of such systems. In an effort to search for potential observational signatures of supermassive BBHs, we performed high-resolution smoothed particle hydrodynamics (SPH) simulations of two black holes in a binary of moderate eccentricity surrounded by a circumbinary disk. Building on our previous work, which has shown that gas can periodically transfer from the circumbinary disk to the black holes when the binary is on an eccentric orbit, the current set of simulations focuses on the formation of the individual accretion disks, their evolution and mutual interaction, and the predicted radiative signature. The variation in mass transfer with orbital phase from the circumbinary disk induces periodic variations in the light curve of the two accretion disks at ultraviolet wavelengths, but not in the optical or near-infrared. Searches for this signal offer a promising method to detect supermassive BBHs.Comment: Accepted for publication in the Astrophysical Journal, 16 pages, 11 figures. High Resolution Version is Available at http://www2.yukawa.kyoto-u.ac.jp/~kimitake/bbhs.htm

Properties of Accretion Flows Around Coalescing Supermassive Black Holes

What are the properties of accretion flows in the vicinity of coalescing supermassive black holes (SBHs)? The answer to this question has direct implications for the feasibility of coincident detections of electromagnetic (EM) and gravitational wave (GW) signals from coalescences. Such detections are considered to be the next observational grand challenge that will enable testing general relativity in the strong, nonlinear regime and improve our understanding of evolution and growth of these massive compact objects. In this paper we review the properties of the environment of coalescing binaries in the context of the circumbinary disk and hot, radiatively inefficient accretion flow models and use them to mark the extent of the parameter space spanned by this problem. We report the results from an ongoing, general relativistic, hydrodynamical study of the inspiral and merger of black holes, motivated by the latter scenario. We find that correlated EM+GW oscillations can arise during the inspiral phase followed by the gradual rise and subsequent drop-off in the light curve at the time of coalescence. While there are indications that the latter EM signature is a more robust one, a detection of either signal coincidentally with GWs would be a convincing evidence for an impending SBH binary coalescence. The observability of an EM counterpart in the hot accretion flow scenario depends on the details of a model. In the case of the most massive binaries observable by the Laser Interferometer Space Antenna, upper limits on luminosity imply that they may be identified by EM searches out to z~0.1-1. However, given the radiatively inefficient nature of the gas flow, we speculate that a majority of massive binaries may appear as low luminosity AGN in the local universe.Comment: Revised version accepted to Class. Quantum Grav. for proceedings of 8th LISA Symposium. 15 pages, 3 figures, includes changes suggested in referee report

Observable Signatures of EMRI Black Hole Binaries Embedded in Thin Accretion Disks

We examine the electromagnetic (EM) and gravitational wave (GW) signatures of stellar-mass compact objects (COs) spiraling into a supermassive black hole (extreme mass-ratio inspirals or EMRIs), embedded in a thin, radiation-pressure dominated, accretion disk. At large separations, the tidal effect of the secondary CO clears a gap. We show that the gap refills during the late GW-driven phase of the inspiral, leading to a sudden EM brightening of the source. The accretion disk leaves an imprint on the GW through its angular momentum exchange with the binary, the mass increase of the binary members due to accretion, and its gravity. We compute the disk-modified GWs both in an analytical Newtonian approximation and in a numerical effective-one-body approach. We find that disk-induced migration provides the dominant perturbation to the inspiral, with weaker effects from the mass accretion onto the CO and hydrodynamic drag. Depending on whether a gap is present, the perturbation of the GW phase is between 10 and 1000 radians per year, detectable with the future Laser Interferometer Space Antenna (LISA) at high significance. The Fourier transform of the disk-modified GW in the stationary phase approximation is sensitive to disk parameters with a frequency trend different from post-Newtonian vacuum corrections. Our results suggest that observations of EMRIs may place new sensitive constraints on the physics of accretion disks.Comment: 42 pages, 8 figures, 3 tables, submitted to Phys. Rev.

The pre-outburst flare of the A 0535+26 August/September 2005 outburst

We study the spectral and temporal behavior of the High Mass X-ray Binary A 0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of a normal (type I) outburst in August/September 2005. We compare the studied behavior with that observed during the outburst. We analyse RXTE observations that monitored A 0535+26 during the outburst. We complete spectral and timing analyses of the data. We study the evolution of the pulse period, present energy-dependent pulse profiles both at the initial pre-outburst flare and close to outburst maximum, and measure how the cyclotron resonance-scattering feature (hereafter CRSF) evolves. We present three main results: a constant period P=103.3960(5)s is measured until periastron passage, followed by a spin-up with a decreasing period derivative of Pdot=(-1.69+/-0.04)x10^(-8)s/s at MJD 53618, and P remains constant again at the end of the main outburst. The spin-up provides evidence for the existence of an accretion disk during the normal outburst. We measure a CRSF energy of Ecyc~50kev during the pre-outburst flare, and Ecyc~46kev during the main outburst. The pulse shape, which varies significantly during both pre-outburst flare and main outburst, evolves strongly with photon energy.Comment: 4 pages, 4 figures, accepted for publication in A&A Letters. To be published in parallel to Postnov et al. 200

Quasi-periodic flares in EXO 2030+375 observed with INTEGRAL

Context: Episodic flaring activity is a common feature of X-ray pulsars in HMXBs. In some Be/X-ray binaries flares were observed in quiescence or prior to outbursts. EXO 2030+375 is a Be/X-ray binary showing "normal" outbursts almost every ~46 days, near periastron passage of the orbital revolution. Some of these outbursts were occasionally monitored with the INTEGRAL observatory. Aims: The INTEGRAL data revealed strong quasi-periodic flaring activity during the rising part of one of the system's outburst. Such activity has previously been observed in EXO 2030+375 only once, in 1985 with EXOSAT. (Some indications of single flares have also been observed with other satellites.) Methods: We present the analysis of the flaring behavior of the source based on INTEGRAL data and compare it with the flares observed in EXO 2030+375 in 1985. Results: Based on the observational properties of the flares, we argue that the instability at the inner edge of the accretion disk is the most probable cause of the flaring activity.Comment: Accepted for publication in A&A Lette

Joint H-alpha and X-Ray Observations of Massive X-Ray Binaries. II. The Be X-ray Binary and Microquasar LS I +61 303

We present the results of an H-alpha monitoring campaign on the BeXRB and microquasar system LS I +61 303. We use radial velocity measurements of HeI lines in our spectra to re-evaluate the orbital elements and to better establish the time of periastron. We list equivalent widths and other parameters for the H-alpha emission line and discuss the orbital phase related variations observed. We call attention to a dramatic episode of emission weakening that occurred in less than a day that probably resulted from exposure to a transient source of ionizing radiation. We argue that the increase in H-alpha and X-ray emission following periastron probably results from the creation of an extended density wave in the disk created by tidal forces. We also discuss estimates of the size of the disk from the H-alpha equivalent width measurements, and we suggest that the disk radius from the average equivalent width corresponds to a resonant truncation radius of the disk while the maximum equivalent width corresponds to a radius limited by the separation of the stars at periastron. We note that a nearby faint companion is probably an unrelated foreground object.Comment: 18 pages including 7 figures and 2 tables, accepted to Ap

Menus for Feeding Black Holes

Black holes are the ultimate prisons of the Universe, regions of spacetime where the enormous gravity prohibits matter or even light to escape to infinity. Yet, matter falling toward the black holes may shine spectacularly, generating the strongest source of radiation. These sources provide us with astrophysical laboratories of extreme physical conditions that cannot be realized on Earth. This chapter offers a review of the basic menus for feeding matter onto black holes and discusses their observational implications.Comment: 27 pages. Accepted for publication in Space Science Reviews. Also to appear in hard cover in the Space Sciences Series of ISSI "The Physics of Accretion onto Black Holes" (Springer Publisher

Tissue Microenvironments Define and Get Reinforced by Macrophage Phenotypes in Homeostasis or during Inflammation, Repair and Fibrosis

Current macrophage phenotype classifications are based on distinct in vitro culture conditions that do not adequately mirror complex tissue environments. In vivo monocyte progenitors populate all tissues for immune surveillance which supports the maintenance of homeostasis as well as regaining homeostasis after injury. Here we propose to classify macrophage phenotypes according to prototypical tissue environments, e.g. as they occur during homeostasis as well as during the different phases of (dermal) wound healing. In tissue necrosis and/or infection, damage- and/or pathogen-associated molecular patterns induce proinflammatory macrophages by Toll-like receptors or inflammasomes. Such classically activated macrophages contribute to further tissue inflammation and damage. Apoptotic cells and antiinflammatory cytokines dominate in postinflammatory tissues which induce macrophages to produce more antiinflammatory mediators. Similarly, tumor-associated macrophages also confer immunosuppression in tumor stroma. Insufficient parenchymal healing despite abundant growth factors pushes macrophages to gain a profibrotic phenotype and promote fibrocyte recruitment which both enforce tissue scarring. Ischemic scars are largely devoid of cytokines and growth factors so that fibrolytic macrophages that predominantly secrete proteases digest the excess extracellular matrix. Together, macrophages stabilize their surrounding tissue microenvironments by adapting different phenotypes as feed-forward mechanisms to maintain tissue homeostasis or regain it following injury. Furthermore, macrophage heterogeneity in healthy or injured tissues mirrors spatial and temporal differences in microenvironments during the various stages of tissue injury and repair. Copyright (C) 2012 S. Karger AG, Base