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Munoz, Diego Jose

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Munoz

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Diego Jose

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Munoz, Diego Jose
Author's Publications: search.filters.isAuthorOfPublication.c085998e-78b8-40fb-aa5c-06c0c4237438

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    An X‐Ray, Infrared, and Submillimeter Flare of Sagittarius A*
    (American Astronomical Society, 2008) Marrone, D. P.; Baganoff, F. K.; Morris, M. R.; Moran, James; Ghez, A. M.; Hornstein, S. D.; Dowell, C. D.; Munoz, Diego Jose; Bautz, M. W.; Ricker, G. R.; Brandt, W. N.; Garmire, G. P.; Lu, J. R.; Matthews, K.; Zhao, J.‐H.; Rao, R.; Bower, G. C.
    Energetic flares are observed in the Galactic supermassive black hole Sagittarius A* from radio to X-ray wavelengths. On a few occasions, simultaneous flares have been detected in IR and X-ray observations, but clear counterparts at longer wavelengths have not been seen. We present a flare observed over several hours on 2006 July 17 with the Chandra X-Ray Observatory, the Keck II telescope, the Caltech Submillimeter Observatory, and the Submillimeter Array. All telescopes observed strong flare events, but the submillimeter peak is found to occur nearly 100 minutes after the X-ray peak. Submillimeter polarization data show linear polarization in the excess flare emission, increasing from 9% to 17% as the flare passes through its peak, consistent with a transition from optically thick to thin synchrotron emission. The temporal and spectral behavior of the flare require that the energetic electrons responsible for the emission cool faster than expected from their radiative output. This is consistent with adiabatic cooling in an expanding emission region, with X-rays produced through self-Compton scattering, although not consistent with the simplest model of such expansion. We also present a submillimeter flare that followed a bright IR flare on 2005 July 31. Compared to 2006, this event had a larger peak IR flux and similar submillimeter flux, but it lacked measurable X-ray emission. It also showed a shorter delay between the IR and submillimeter peaks. Based on these events we propose a synchrotron and self-Compton model to relate the submillimeter lag and the variable IR/X-ray luminosity ratio.
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    Modeling and Simulation of Circumstellar Disks with the Next Generation of Hydrodynamic Solvers
    (2013-10-18) Munoz, Diego Jose; Hernquist, Lars Eric; Hernquist, Lars; Sasselov, Dimitar; Holman, Matthew; Murray-Clay, Ruth; Stone, James
    This thesis is a computational study of circumstellar gas disks, with a special focus on modeling techniques and on numerical methods not only as scientific tools but also as a target of study. In particular, in-depth discussions are included on the main numerical strategy used, namely the moving-mesh method for astrophysical hydrodynamics. In this work, the moving-mesh approach is used to simulate circumstellar disks for the first time.
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    Stellar orbit evolution in close circumstellar disc encounters
    (Oxford University Press (OUP), 2014) Munoz, Diego Jose; Kratter, K.; Vogelsberger, M.; Hernquist, Lars; Springel, V.
    The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code arepo, to circumstellar discs in 3D, focusing on disc–disc interactions that result from stellar flybys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericentre separation rp, disc orientation and disc–star mass ratio (Md/M*) on the orbital evolution of the host stars. Close encounters (2rp ≲ disc radius) can truncate discs on very short time-scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that for realistic primordial disc masses Md ≲ 0.1M*, non-colliding encounters induce minor orbital changes, which is consistent with analytic calculations of encounters in the linear regime. The same disc masses produce entirely different results for grazing/colliding encounters. In the latter case, rapidly cooling discs lose orbital energy by radiating away the energy excess of the shock-heated gas, thus causing capture of the host stars into a bound orbit. In rare cases, a tight binary with a circumbinary disc forms as a result of this encounter.