Explosions & Accretion Schedule

CASCA 2013 Schedule for Explosions & Accretion

Explosions & Accretion
Location: Hennings 202 Chair: Samar Safi-Harb
1400 Davis, Shane The Thermal Stability of Black Hole Accretion Flows
  Observations of radiation from accreting black holes remain one of our most powerful probes of strong gravity. However, our constraints are only as reliable as the accretion disk model that underlies them so considerable effort has been expended to understand the magnetohydrodynamic processes that determine these flows. I will briefly describe some new tools that we have developed to evolve the coupled equations of radiation transfer and magnetohydrodynamics without having to rely on ad hoc prescriptions that are usually employed. I will then address the question of whether black hole accretion flows are thermally stable -- the subject of a 40 year debate in the field.
1415 Gladstone, Jeanette Exploring ultraluminous X-ray sources using the optical regime
  Ultraluminous X-ray sources (ULXs) are extragalactic objects located outside the nucleus of their host galaxy, with luminosities >10^39 erg/s. Such high luminosities are in excess of the Eddington limit for a black hole that is about 10 times the mass of our Sun (M_Sun). ULXs have long been touted as evidence of intermediate mass black holes (M_BH = 10^2-10^5 M_Sun), which are thought to be the building blacks of super-massive black holes. The alternative is that ULXs could be stellar mass (< 100 M_Sun) black holes accreting at extreme rates, which could explain the rapid growth of super-massive black holes in the early universe. Either option has important cosmological implications, and as a result, mass measurements of these black holes have been a topic of intense interest. Here we present optical analysis of these exotic sources, designed to identify and constrain the companion stars to these black holes. We discuss results from the imaging analysis of 33 nearby ULXs using data from Chandra and the Hubble Space Telescope. We will also present findings from spectroscopic analysis of both pilot and multi-epoch data from 3 of these sources using the Gemini Observatory. By combing this information, we will summarize the implications this work has on both the nature of black holes and companion stars in these systems.
1430 Sivakoff, Gregory Multiwavelength Revelations of the Accretion Disc - Relativistic Jet Connection
  X-ray binaries are crucial laboratories for relativity and high energy astrophysics. Their rapid cycling through different accretion states allow studies that cannot be performed on supermassive black holes in galactic nuclei (AGN). The formation of compact relativistic jets in some accretion states provides for the potential of local feedback and acts an analogue for AGN feedback. Quasi-simultaneous multiwavelength observations are key to probe the connection between accretion discs and relativistic jets and maximize this useful tool for studying black holes of all sizes. I will review recent results, including how a dynamically changing SED across radio, sub-mm, far-IR, and optical wavelengths reveal an evolving compact jet in the black hole X-ray binary MAXI J1836–194.
1445 Graham, Melissa Supernovae with The Las Cumbres Observatory Global Telescope Network
  Supernovae are the spectacular endpoints of stellar evolution, brilliant explosions that release the heavy elements built up over millions to billions of years of fusion. The progenitor star scenario and explosion mechanisms are not well known for some types of supernovae, despite them being used as empirical standard candles for cosmology. Wide-area surveys are necessary to find supernovae because their rate is only about 1 per century in galaxies like the Milky Way, and it is most economical to survey in a single filter - but scientific understanding of supernovae require multi-band light curves and time series optical spectra, starting as soon after explosion as possible. I will present such data and analysis for the first several of supernovae (and one SN-like event) monitored with the new capabilities of The Las Cumbres Observatory Global Telescope Network. LCOGT.net has nearly completed a world-wide network of robotic 1.0m and 2.0m telescopes, with sites existing or in preparation in California, Texas, Hawaii, Chile, South Africa, and Australia. Observations are dynamically scheduled and automatically executed with no human intervention, providing round-the-clock imaging and spectroscopic capabilities with unprecedented time domain coverage. LCOGT.net is dedicated to time-domain astrophysics, specializing transient events such as exoplanets, NEOs, binary stars, AGN, and more.
1500 Zhu, Chenchong * White Dwarf Merger Lite: Can Small White Dwarf Mergers Explain Type Ia Supernovae?
  While there is ample evidence that type Ia supernovae result from the thermonuclear runaway of a carbon-oxygen (CO) white dwarf, there is much debate over how such an object, naturally inert, could be forced to explode. The traditional solution to this problem is to create an object close to the iconic Chandrasekhar mass, either via a merger of two CO white dwarfs or by mass accretion from a non-degenerate companion. Both methods suffer from an insufficient number of progenitors to explain the number of type Ia supernovae. There are, however, more than enough progenitors if carbon ignition were possible in objects far beneath the Chandrasekhar mass. We have explored this problem with two approaches: using a traditional smoothed-particle hydrodynamics code (Gasoline) and a novel grid code employing irregularly shaped grid cells that flow with the fluid (AREPO). In this talk, I will introduce the problems posed by sub-Chandrasekhar CO white dwarf mergers and will outline our simulation efforts. I will show preliminary comparisons of Gasoline and AREPO simulations, and explain why they are drastically different. I will conclude by discussing what regions of the merger parameter space could eventually see an explosive nuclear runaway.
1515 West, Jennifer * Modelling polarized radio emission from supernova remnants
  We present an overview and preliminary results of our project to model radio continuum and polarization emission from supernova remnants (SNRs) in the Galaxy with the goal of constraining the 3-D magnetic field in these objects. We produce physically-consistent models of the extended polarized emission and depolarization effects using the Hammurabi Galactic synchrotron emission simulation code adapted for SNRs studies. We discuss our model and present some initial attempts at comparisons with available data.